Version 2.3

When the file is opened in read-only mode, it will not be written and
the Cues do not have to be updated. Skipping the Cues will make the
reading of large Matroska files over network filesystems (SMB/NFS)
faster.

.github/workflows/build.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Set up Ubuntu
       run: sudo apt install -y libcppunit-dev libutfcpp-dev zlib1g-dev

CHANGELOG.md

@@ -1,3 +1,42 @@
+TagLib 2.3 (May 10, 2026)
+=========================
+
+ * MP4: Support for chapters (Nero and QuickTime).
+ * WAV: Support for BEXT and iXML chunks.
+ * FLAC: Support for BEXT and iXML application blocks.
+ * Opus: New audio property `outputGain()`.
+ * Speed up Matroska reading by using seek head for element lookup.
+ * Speed up Matroska writing by offering multiple write style modes.
+ * More tolerant handling of files with oversized RIFF chunks, zero size ID3v2
+   frames and Matroska chapters without edition.
+ * Avoid wrong content-based detection as MPEG files.
+ * Fix bitrate calculations for MPEG ADTS and MP4 ESDS.
+ * Fix data race with multi-threaded use of `MP4::ItemFactory`.
+ * Fix unbounded recursion in EBML/Matroska `MasterElement` and MP4 atoms.
+ * Limit number of MP4 atoms at top level.
+ * Fix writing too many offsets when updating MP4 stco/co64 atoms.
+ * Fix k bounds in Shorten Rice-Golomb coding.
+
+TagLib 2.2.1 (Mar 7, 2026)
+==========================
+
+ * Support edition, chapter and attachment UIDs in Matroska simple tags.
+ * Avoid duplicates in Matroska complex property keys.
+
+TagLib 2.2 (Feb 18, 2026)
+=========================
+
+ * Support for Matroska (MKA, MKV) and WebM files.
+ * Support for NI STEM in MP4 files.
+ * New method isDsd() in WavPack Properties.
+ * Stricter verification of ID3v2 frames.
+ * Fix setting the last header flag in Ogg FLAC files.
+ * Fix reading of the last page in Ogg streams.
+ * Avoid corrupting invalid Ogg FLAC files without Vorbis comment.
+ * Windows: Support MP4 files with 64-bit atoms.
+ * Fix use of property keys with non-ASCII characters in C bindings.
+ * Fix building with Android NDK 29.
+
 TagLib 2.1.1 (June 30, 2025)
 ============================
 

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5.0 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.10...3.31)
 
 project(taglib)
 
@@ -12,7 +12,7 @@ include(CMakePackageConfigHelpers)
 
 option(BUILD_SHARED_LIBS "Build shared libraries" OFF)
 if(APPLE)
-  option(BUILD_FRAMEWORK "Build an OS X framework" OFF)
+  option(BUILD_FRAMEWORK "Build a macOS framework" OFF)
   if(BUILD_FRAMEWORK)
     set(BUILD_SHARED_LIBS ON)
     #set(CMAKE_MACOSX_RPATH 1)
@@ -92,14 +92,15 @@ endif()
 # Minor version: increase it if you add ABI compatible features.
 # Patch version: increase it for bug fix releases.
 set(TAGLIB_SOVERSION_MAJOR 2)
-set(TAGLIB_SOVERSION_MINOR 1)
-set(TAGLIB_SOVERSION_PATCH 1)
+set(TAGLIB_SOVERSION_MINOR 3)
+set(TAGLIB_SOVERSION_PATCH 0)
 
 include(ConfigureChecks.cmake)
 
 option(WITH_APE "Build with APE, MPC, WavPack" ON)
 option(WITH_ASF "Build with ASF" ON)
 option(WITH_DSF "Build with DSF" ON)
+option(WITH_MATROSKA "Build with Matroska" ON)
 option(WITH_MOD "Build with Tracker modules" ON)
 option(WITH_MP4 "Build with MP4" ON)
 option(WITH_RIFF "Build with AIFF, RIFF, WAV" ON)
@@ -197,6 +198,9 @@ endif()
 if(WITH_DSF)
   set(TAGLIB_WITH_DSF TRUE)
 endif()
+if(WITH_MATROSKA)
+  set(TAGLIB_WITH_MATROSKA TRUE)
+endif()
 if(WITH_MOD)
   set(TAGLIB_WITH_MOD TRUE)
 endif()

INSTALL.md

@@ -63,12 +63,13 @@ and ID3 tags cannot be disabled. The following CMake options are available:
 | `WITH_APE`              | Build with APE, MPC, WavPack (default ON)          |
 | `WITH_ASF`              | Build with ASF (default ON)                        |
 | `WITH_DSF`              | Build with DSF (default ON)                        |
+| `WITH_MATROSKA`         | Build with Matroska, WebM (default ON)             |
 | `WITH_MOD`              | Build with Tracker modules (default ON)            |
 | `WITH_MP4`              | Build with MP4 (default ON)                        |
 | `WITH_RIFF`             | Build with AIFF, RIFF, WAV (default ON)            |
 | `WITH_SHORTEN`          | Build with Shorten (default ON)                    |
 | `WITH_TRUEAUDIO`        | Build with TrueAudio (default ON)                  |
-| `WITH_VORBIS`           | Build with Vorbis, FLAC, Ogg, Opus (default ON)    |
+| `WITH_VORBIS`           | Build with FLAC, Ogg, Opus, Speex (default ON)     |
 
 Note that disabling formats will remove exported symbols from the library and
 thus break binary compatibility. These options should therefore only be used

README.md

@@ -7,10 +7,11 @@
 https://taglib.org/
 
 TagLib is a library for reading and editing the metadata of several
-popular audio formats. Currently, it supports both ID3v1 and ID3v2
-for MP3 files, [Ogg Vorbis][] comments and ID3 tags
-in [FLAC][], MPC, Speex, WavPack, TrueAudio, WAV, AIFF, MP4, APE, ASF,
-DSF, DFF and AAC files.
+popular audio formats. Currently, it supports various metadata containers such
+as [ID3v1][], [ID3v2][] and [Vorbis][] comments for MP3, MP4, AAC,
+[Ogg][], [Opus][], [FLAC][], [Speex][], [APE][], [MPC][], [WavPack][],
+[WAV][], [AIFF][], [TrueAudio][], [Matroska][], [WebM][], ASF, WMA, DSF, DFF and
+tracker (MOD, XM, S3M, IT) files.
 
 TagLib is distributed under the [GNU Lesser General Public License][]
 (LGPL) and [Mozilla Public License][] (MPL). Essentially that means that
@@ -18,7 +19,20 @@ it may be used in proprietary applications, but if changes are made to
 TagLib they must be contributed back to the project. Please review the
 licenses if you are considering using TagLib in your project.
 
-  [Ogg Vorbis]: https://xiph.org/vorbis/
+  [ID3v1]: https://id3.org/ID3v1
+  [ID3v2]: https://id3.org/Home
+  [Vorbis]: https://xiph.org/vorbis/
+  [Ogg]: https://www.xiph.org/ogg/
+  [Opus]: https://opus-codec.org/
   [FLAC]: https://xiph.org/flac/
+  [Speex]: https://www.speex.org/
+  [APE]: https://www.monkeysaudio.com/
+  [MPC]: https://musepack.net/
+  [WavPack]: https://www.wavpack.com/
+  [WAV]: https://www.mmsp.ece.mcgill.ca/Documents/AudioFormats/WAVE/WAVE.html
+  [AIFF]: https://www.mmsp.ece.mcgill.ca/Documents/AudioFormats/AIFF/AIFF.html
+  [TrueAudio]: https://sourceforge.net/projects/tta/
+  [Matroska]: https://www.matroska.org/
+  [WebM]: https://www.webmproject.org/
   [GNU Lesser General Public License]: https://www.gnu.org/licenses/lgpl.html
   [Mozilla Public License]: https://www.mozilla.org/MPL/MPL-1.1.html

bindings/c/CMakeLists.txt

@@ -63,6 +63,12 @@ if(WITH_SHORTEN)
     ${CMAKE_CURRENT_SOURCE_DIR}/../../taglib/shorten
   )
 endif()
+if(WITH_MATROSKA)
+  set(tag_c_HDR_DIRS ${tag_c_HDR_DIRS}
+    ${CMAKE_CURRENT_SOURCE_DIR}/../../taglib/matroska
+    ${CMAKE_CURRENT_SOURCE_DIR}/../../taglib/matroska/ebml
+  )
+endif()
 include_directories(${tag_c_HDR_DIRS})
 
 set(tag_c_HDRS tag_c.h)

bindings/c/tag_c.cpp

@@ -80,6 +80,9 @@
 #ifdef TAGLIB_WITH_SHORTEN
 #include "shortenfile.h"
 #endif
+#ifdef TAGLIB_WITH_MATROSKA
+#include "matroskafile.h"
+#endif
 
 using namespace TagLib;
 
@@ -241,6 +244,11 @@ TagLib_File *taglib_file_new_type_any_char(const T *filename, TagLib_File_Type t
   case TagLib_File_SHORTEN:
     file = new Shorten::File(filename);
     break;
+#endif
+#ifdef TAGLIB_WITH_MATROSKA
+  case TagLib_File_MATROSKA:
+    file = new Matroska::File(filename);
+    break;
 #endif
   default:
     break;
@@ -469,12 +477,13 @@ void _taglib_property_set(TagLib_File *file, const char* prop, const char* value
     return;
 
   auto tfile = reinterpret_cast<FileRef *>(file);
+  auto propStr = charArrayToString(prop);
   PropertyMap map = tfile->tag()->properties();
 
   if(value) {
-    auto property = map.find(prop);
+    auto property = map.find(propStr);
     if(property == map.end()) {
-      map.insert(prop, StringList(charArrayToString(value)));
+      map.insert(propStr, StringList(charArrayToString(value)));
     }
     else {
       if(append) {
@@ -486,7 +495,7 @@ void _taglib_property_set(TagLib_File *file, const char* prop, const char* value
     }
   }
   else {
-    map.erase(prop);
+    map.erase(propStr);
   }
 
   tfile->setProperties(map);
@@ -531,7 +540,7 @@ char **taglib_property_get(const TagLib_File *file, const char *prop)
 
   const PropertyMap map = reinterpret_cast<const FileRef *>(file)->properties();
 
-  auto property = map.find(prop);
+  auto property = map.find(charArrayToString(prop));
   if(property == map.end())
     return NULL;
 
@@ -573,16 +582,17 @@ bool _taglib_complex_property_set(
     return false;
 
   auto tfile = reinterpret_cast<FileRef *>(file);
+  auto keyStr = charArrayToString(key);
 
   if(value == NULL) {
-    return tfile->setComplexProperties(key, {});
+    return tfile->setComplexProperties(keyStr, {});
   }
 
   VariantMap map;
   const TagLib_Complex_Property_Attribute** attrPtr = value;
   while(*attrPtr) {
     const TagLib_Complex_Property_Attribute *attr = *attrPtr;
-    String attrKey(attr->key);
+    auto attrKey = charArrayToString(attr->key);
     switch(attr->value.type) {
     case TagLib_Variant_Void:
       map.insert(attrKey, Variant());
@@ -627,8 +637,8 @@ bool _taglib_complex_property_set(
     ++attrPtr;
   }
 
-  return append ? tfile->setComplexProperties(key, tfile->complexProperties(key).append(map))
-                : tfile->setComplexProperties(key, {map});
+  return append ? tfile->setComplexProperties(keyStr, tfile->complexProperties(keyStr).append(map))
+                : tfile->setComplexProperties(keyStr, {map});
 }
 
 }  // namespace
@@ -676,7 +686,7 @@ TagLib_Complex_Property_Attribute*** taglib_complex_property_get(
     return NULL;
   }
 
-  const auto variantMaps = reinterpret_cast<const FileRef *>(file)->complexProperties(key);
+  const auto variantMaps = reinterpret_cast<const FileRef *>(file)->complexProperties(charArrayToString(key));
   if(variantMaps.isEmpty()) {
     return NULL;
   }

bindings/c/tag_c.h

@@ -132,7 +132,8 @@ typedef enum {
   TagLib_File_Opus,
   TagLib_File_DSF,
   TagLib_File_DSDIFF,
-  TagLib_File_SHORTEN
+  TagLib_File_SHORTEN,
+  TagLib_File_MATROSKA
 } TagLib_File_Type;
 
 /*!

examples/CMakeLists.txt

@@ -2,6 +2,7 @@ include_directories(
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/toolkit
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/ape
+  ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/matroska
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/mpeg
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/mpeg/id3v1
   ${CMAKE_CURRENT_SOURCE_DIR}/../taglib/mpeg/id3v2
@@ -38,6 +39,18 @@ target_link_libraries(framelist tag)
 add_executable(strip-id3v1 strip-id3v1.cpp)
 target_link_libraries(strip-id3v1 tag)
 
+if(WITH_MATROSKA)
+  ########### next target ###############
+
+  add_executable(matroskareader matroskareader.cpp)
+  target_link_libraries(matroskareader tag)
+
+  ########### next target ###############
+
+  add_executable(matroskawriter matroskawriter.cpp)
+  target_link_libraries(matroskawriter tag)
+endif()
+
 install(TARGETS tagreader tagreader_c tagwriter framelist strip-id3v1
   LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
   RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}

examples/matroskareader.cpp

@@ -0,0 +1,139 @@
+#include <cstdio>
+#include "matroskafile.h"
+#include "matroskatag.h"
+#include "matroskasimpletag.h"
+#include "matroskaattachments.h"
+#include "matroskaattachedfile.h"
+#include "matroskachapters.h"
+#include "matroskachapteredition.h"
+#include "tstring.h"
+#include "tutils.h"
+#include "tbytevector.h"
+#define GREEN_TEXT(s) "" s ""
+#define PRINT_PRETTY(label, value) printf("  " GREEN_TEXT(label) ": %s\n", value)
+
+int main(int argc, char *argv[])
+{
+  if(argc != 2) {
+    printf("Usage: matroskareader FILE\n");
+    return 1;
+  }
+  TagLib::Matroska::File file(argv[1]);
+  if(!file.isValid()) {
+    printf("File is not valid\n");
+    return 1;
+  }
+  auto tag = dynamic_cast<TagLib::Matroska::Tag*>(file.tag());
+  if(!tag) {
+    printf("File has no tag\n");
+    return 0;
+  }
+
+  const TagLib::Matroska::SimpleTagsList &list = tag->simpleTagsList();
+  printf("Found %u tag(s):\n", list.size());
+
+  for(const TagLib::Matroska::SimpleTag &t : list) {
+    PRINT_PRETTY("Tag Name", t.name().toCString(true));
+
+    if(t.type() == TagLib::Matroska::SimpleTag::StringType)
+      PRINT_PRETTY("Tag Value", t.toString().toCString(true));
+    else if(t.type() == TagLib::Matroska::SimpleTag::BinaryType)
+      PRINT_PRETTY("Tag Value",
+        TagLib::Utils::formatString("Binary with size %i", t.toByteVector().size()).toCString(false)
+      );
+
+    auto targetTypeValue = static_cast<unsigned int>(t.targetTypeValue());
+    PRINT_PRETTY("Target Type Value",
+      targetTypeValue == 0 ? "None" : TagLib::Utils::formatString("%i", targetTypeValue).toCString(false)
+    );
+    if(auto trackUid = t.trackUid()) {
+      PRINT_PRETTY("Track UID",
+        TagLib::Utils::formatString("%llu",trackUid).toCString(false)
+      );
+    }
+    if(auto editionUid = t.editionUid()) {
+      PRINT_PRETTY("Edition UID",
+        TagLib::Utils::formatString("%llu",editionUid).toCString(false)
+      );
+    }
+    if(auto chapterUid = t.chapterUid()) {
+      PRINT_PRETTY("Chapter UID",
+        TagLib::Utils::formatString("%llu",chapterUid).toCString(false)
+      );
+    }
+    if(auto attachmentUid = t.attachmentUid()) {
+      PRINT_PRETTY("Attachment UID",
+        TagLib::Utils::formatString("%llu",attachmentUid).toCString(false)
+      );
+    }
+    const TagLib::String &language = t.language();
+    PRINT_PRETTY("Language", !language.isEmpty() ? language.toCString(false) : "Not set");
+
+    printf("\n");
+  }
+
+  TagLib::Matroska::Attachments *attachments = file.attachments();
+  if(attachments) {
+    const TagLib::Matroska::Attachments::AttachedFileList &list = attachments->attachedFileList();
+    printf("Found %u attachment(s)\n", list.size());
+    for(const auto &attachedFile : list) {
+      PRINT_PRETTY("Filename", attachedFile.fileName().toCString(true));
+      const TagLib::String &description = attachedFile.description();
+      PRINT_PRETTY("Description", !description.isEmpty() ? description.toCString(true) : "None");
+      const TagLib::String &mediaType = attachedFile.mediaType();
+      PRINT_PRETTY("Media Type", !mediaType.isEmpty() ? mediaType.toCString(false) : "None");
+      PRINT_PRETTY("Data Size",
+        TagLib::Utils::formatString("%u byte(s)", attachedFile.data().size()).toCString(false)
+      );
+      PRINT_PRETTY("UID",
+        TagLib::Utils::formatString("%llu", attachedFile.uid()).toCString(false)
+      );
+    }
+  }
+  else
+    printf("File has no attachments\n");
+
+  TagLib::Matroska::Chapters *chapters = file.chapters();
+  if(chapters) {
+    printf("Chapters:\n");
+    const TagLib::Matroska::Chapters::ChapterEditionList &editions = chapters->chapterEditionList();
+    for(const auto &edition : editions) {
+      if(edition.uid()) {
+        PRINT_PRETTY("Edition UID", TagLib::Utils::formatString("%llu", edition.uid())
+          .toCString(false));
+      }
+      PRINT_PRETTY("Edition Flags", TagLib::Utils::formatString("default=%d, ordered=%d",
+        edition.isDefault(), edition.isOrdered())
+        .toCString(false));
+      printf("\n");
+      for(const auto &chapter : edition.chapterList()) {
+        PRINT_PRETTY("Chapter UID", TagLib::Utils::formatString("%llu", chapter.uid())
+          .toCString(false));
+        PRINT_PRETTY("Chapter flags", TagLib::Utils::formatString("hidden=%d", chapter.isHidden())
+          .toCString(false));
+        PRINT_PRETTY("Start-End", TagLib::Utils::formatString("%llu-%llu",
+          chapter.timeStart(), chapter.timeEnd()).toCString(false));
+        for(const auto &display : chapter.displayList()) {
+          PRINT_PRETTY("Display", display.string().toCString(false));
+          PRINT_PRETTY("Language", !display.language().isEmpty()
+            ? display.language().toCString(false) : "Not set");
+        }
+        printf("\n");
+      }
+    }
+  }
+  else
+    printf("File has no chapters\n");
+
+  if(auto properties = dynamic_cast<const TagLib::Matroska::Properties *>(file.audioProperties())) {
+    printf("Properties:\n");
+    PRINT_PRETTY("Doc Type", properties->docType().toCString(false));
+    PRINT_PRETTY("Doc Type Version", TagLib::String::number(properties->docTypeVersion()).toCString(false));
+    PRINT_PRETTY("Codec Name", properties->codecName().toCString(true));
+    PRINT_PRETTY("Bitrate", TagLib::String::number(properties->bitrate()).toCString(false));
+    PRINT_PRETTY("Sample Rate", TagLib::String::number(properties->sampleRate()).toCString(false));
+    PRINT_PRETTY("Channels", TagLib::String::number(properties->channels()).toCString(false));
+    PRINT_PRETTY("Length [ms]", TagLib::String::number(properties->lengthInMilliseconds()).toCString(false));
+  }
+  return 0;
+}

examples/matroskawriter.cpp

@@ -0,0 +1,45 @@
+#include <cstdio>
+#include "matroskafile.h"
+#include "matroskatag.h"
+#include "matroskasimpletag.h"
+#include "matroskaattachments.h"
+#include "matroskaattachedfile.h"
+#include "tfilestream.h"
+#include "tstring.h"
+#include "tutils.h"
+
+int main(int argc, char *argv[])
+{
+  if(argc != 3) {
+    printf("Usage: matroskawriter FILE ARTWORK\n");
+    return 1;
+  }
+  TagLib::Matroska::File file(argv[1]);
+  if(!file.isValid()) {
+    printf("File is not valid\n");
+    return 1;
+  }
+  auto tag = file.tag(true);
+  tag->clearSimpleTags();
+
+  tag->addSimpleTag(TagLib::Matroska::SimpleTag(
+    "Test Name 1", TagLib::String("Test Value 1"),
+    TagLib::Matroska::SimpleTag::TargetTypeValue::Track, "en"));
+
+  tag->addSimpleTag(TagLib::Matroska::SimpleTag(
+    "Test Name 2", TagLib::String("Test Value 2"),
+    TagLib::Matroska::SimpleTag::TargetTypeValue::Album));
+  tag->setTitle("Test title");
+  tag->setArtist("Test artist");
+  tag->setYear(1969);
+
+  TagLib::FileStream image(argv[2]);
+  auto data = image.readBlock(image.length());
+  auto attachments = file.attachments(true);
+  attachments->addAttachedFile(TagLib::Matroska::AttachedFile(
+    data, "cover.jpg", "image/jpeg"));
+
+  file.save();
+
+  return 0;
+}

examples/tagreader.cpp

@@ -117,4 +117,3 @@ int main(int argc, char *argv[])
   }
   return 0;
 }
-

examples/tagwriter.cpp

@@ -71,6 +71,7 @@ void usage()
   std::cout << "  -R <tagname> <tagvalue>"   << std::endl;
   std::cout << "  -I <tagname> <tagvalue>"   << std::endl;
   std::cout << "  -D <tagname>"   << std::endl;
+  std::cout << "  -C <complex-property-key> <key1=val1,key2=val2,...>" << std::endl;
   std::cout << "  -p <picturefile> <description> (\"\" \"\" to remove)" << std::endl;
   std::cout << std::endl;
 
@@ -95,6 +96,102 @@ void checkForRejectedProperties(const TagLib::PropertyMap &tags)
   }
 }
 
+/*!
+ * Create a list of variant maps from a string.
+ * The shorthand syntax in the string is kept simple, but should be sufficient
+ * for testing. Multiple maps are separated by ';', values within a map are
+ * assigned with key=value and separated by a ','. Types are detected, use
+ * double quotes to force a string. A ByteVector can be constructed from the
+ * contents of a file, the path is given after "file://". There is no escape
+ * character, use hex codes for ',' (\x2C) or ';' (\x3B).
+ */
+TagLib::List<TagLib::VariantMap> parseComplexPropertyValues(const TagLib::String &str)
+{
+  if(str.isEmpty() || str == "\"\"" || str == "''") {
+    return {};
+  }
+  TagLib::List<TagLib::VariantMap> values;
+  const auto valueStrs = str.split(";");
+  for(const auto &valueStr : valueStrs) {
+    TagLib::VariantMap value;
+    const auto keyValStrs = valueStr.split(",");
+    for(const auto &keyValStr : keyValStrs) {
+      if(int equalPos = keyValStr.find('='); equalPos != -1) {
+        TagLib::String key = keyValStr.substr(0, equalPos);
+        TagLib::String valStr = keyValStr.substr(equalPos + 1);
+        bool hasDot = false;
+        bool hasNonNumeric = false;
+        bool hasSign = false;
+        for(auto it = valStr.cbegin(); it != valStr.cend(); ++it) {
+          if(it == valStr.cbegin() && (*it == '-' || *it == '+')) {
+            hasSign = true;
+          }
+          else if(*it == '.') {
+            hasDot = true;
+          }
+          else if(*it < '0' || *it > '9') {
+            hasNonNumeric = true;
+          }
+        }
+        TagLib::Variant val;
+        if(valStr == "null") {
+          // keep empty variant
+        }
+        else if(valStr == "true" || valStr == "false") {
+          val = TagLib::Variant(valStr == "true");
+        }
+        else if(!hasNonNumeric && hasDot) {
+          val = TagLib::Variant(std::stod(valStr.to8Bit()));
+        }
+        else if(!hasNonNumeric && hasSign) {
+          val = valStr.toLongLong(nullptr);
+        }
+        else if(!hasNonNumeric) {
+          val = valStr.toULongLong(nullptr);
+        }
+        else if(valStr.startsWith("file://")) {
+          auto filePath = valStr.substr(7 );
+          if(isFile(filePath.toCString())) {
+            std::ifstream fs;
+            fs.open(filePath.toCString(), std::ios::in | std::ios::binary);
+            std::stringstream buffer;
+            buffer << fs.rdbuf();
+            fs.close();
+            TagLib::String buf(buffer.str());
+            val = TagLib::Variant(buf.data(TagLib::String::Latin1));
+          }
+          else {
+            std::cout << filePath.toCString() << " not found." << std::endl;
+            val = TagLib::Variant(TagLib::ByteVector());
+          }
+        }
+        else {
+          int len = valStr.size();
+          if(len >= 2 && valStr[0] == '"' && valStr[len - 1] == '"') {
+            valStr = valStr.substr(1, len - 2);
+          }
+          int hexPos = 0;
+          while((hexPos = valStr.find("\\x", hexPos)) != -1) {
+            char ch;
+            bool ok;
+            if(static_cast<int>(valStr.length()) < hexPos + 4 ||
+               (ch = static_cast<char>(
+                 valStr.substr(hexPos + 2, 2).toLongLong(&ok, 16)), !ok)) {
+              break;
+            }
+            valStr = valStr.substr(0, hexPos) + ch + valStr.substr(hexPos + 4);
+            ++hexPos;
+          }
+          val = TagLib::Variant(valStr);
+        }
+        value.insert(key, val);
+      }
+    }
+    values.append(value);
+  }
+  return values;
+}
+
 int main(int argc, char *argv[])
 {
   TagLib::List<TagLib::FileRef> fileList;
@@ -170,6 +267,19 @@ int main(int argc, char *argv[])
           checkForRejectedProperties(f.setProperties(map));
           break;
         }
+        case 'C': {
+          if(i + 2 < argc) {
+            numArgsConsumed = 3;
+            if(!value.isEmpty()) {
+              TagLib::List<TagLib::VariantMap> values = parseComplexPropertyValues(argv[i + 2]);
+              f.setComplexProperties(value, values);
+            }
+          }
+          else {
+            usage();
+          }
+          break;
+        }
         case 'p': {
           if(i + 2 < argc) {
             numArgsConsumed = 3;

taglib/CMakeLists.txt

@@ -64,8 +64,15 @@ if(WITH_SHORTEN)
     ${CMAKE_CURRENT_SOURCE_DIR}/shorten
   )
 endif()
+if(WITH_MATROSKA)
+  set(tag_HDR_DIRS ${tag_HDR_DIRS}
+    ${CMAKE_CURRENT_SOURCE_DIR}/matroska
+    ${CMAKE_CURRENT_SOURCE_DIR}/matroska/ebml
+  )
+endif()
 include_directories(${tag_HDR_DIRS})
 
+set(tag_PRIVATE_HDRS)
 set(tag_HDRS
   tag.h
   fileref.h
@@ -187,7 +194,12 @@ if(WITH_MP4)
     mp4/mp4item.h
     mp4/mp4properties.h
     mp4/mp4coverart.h
+    mp4/mp4stem.h
     mp4/mp4itemfactory.h
+    mp4/mp4chapter.h
+    mp4/mp4chapterholder.h
+    mp4/mp4nerochapterlist.h
+    mp4/mp4qtchapterlist.h
   )
 endif()
 if(WITH_MOD)
@@ -220,6 +232,42 @@ if(WITH_SHORTEN)
     shorten/shortentag.h
   )
 endif()
+if(WITH_MATROSKA)
+  set(tag_HDRS ${tag_HDRS}
+    matroska/matroskaattachedfile.h
+    matroska/matroskaattachments.h
+    matroska/matroskachapter.h
+    matroska/matroskachapteredition.h
+    matroska/matroskachapters.h
+    matroska/matroskaelement.h
+    matroska/matroskafile.h
+    matroska/matroskaproperties.h
+    matroska/matroskasimpletag.h
+    matroska/matroskatag.h
+    matroska/matroskawritestyle.h
+  )
+  set(tag_PRIVATE_HDRS ${tag_PRIVATE_HDRS}
+    matroska/ebml/ebmlbinaryelement.h
+    matroska/ebml/ebmlelement.h
+    matroska/ebml/ebmlmasterelement.h
+    matroska/ebml/ebmlmkattachments.h
+    matroska/ebml/ebmlmkchapters.h
+    matroska/ebml/ebmlmkcues.h
+    matroska/ebml/ebmlmkseekhead.h
+    matroska/ebml/ebmlmksegment.h
+    matroska/ebml/ebmlmkinfo.h
+    matroska/ebml/ebmlmktracks.h
+    matroska/ebml/ebmlmktags.h
+    matroska/ebml/ebmlstringelement.h
+    matroska/ebml/ebmluintelement.h
+    matroska/ebml/ebmlfloatelement.h
+    matroska/ebml/ebmlutils.h
+    matroska/ebml/ebmlvoidelement.h
+    matroska/matroskacues.h
+    matroska/matroskaseekhead.h
+    matroska/matroskasegment.h
+  )
+endif()
 
 set(mpeg_SRCS
   mpeg/mpegfile.cpp
@@ -327,7 +375,11 @@ if(WITH_MP4)
     mp4/mp4item.cpp
     mp4/mp4properties.cpp
     mp4/mp4coverart.cpp
+    mp4/mp4stem.cpp
     mp4/mp4itemfactory.cpp
+    mp4/mp4chapter.cpp
+    mp4/mp4nerochapterlist.cpp
+    mp4/mp4qtchapterlist.cpp
   )
 endif()
 
@@ -410,6 +462,43 @@ if(WITH_SHORTEN)
   )
 endif()
 
+if(WITH_MATROSKA)
+  set(matroska_SRCS
+    matroska/matroskaattachedfile.cpp
+    matroska/matroskaattachments.cpp
+    matroska/matroskachapter.cpp
+    matroska/matroskachapteredition.cpp
+    matroska/matroskachapters.cpp
+    matroska/matroskacues.cpp
+    matroska/matroskaelement.cpp
+    matroska/matroskafile.cpp
+    matroska/matroskaproperties.cpp
+    matroska/matroskaseekhead.cpp
+    matroska/matroskasegment.cpp
+    matroska/matroskasimpletag.cpp
+    matroska/matroskatag.cpp
+  )
+
+  set(ebml_SRCS
+    matroska/ebml/ebmlbinaryelement.cpp
+    matroska/ebml/ebmlelement.cpp
+    matroska/ebml/ebmlmasterelement.cpp
+    matroska/ebml/ebmlmkattachments.cpp
+    matroska/ebml/ebmlmkchapters.cpp
+    matroska/ebml/ebmlmkcues.cpp
+    matroska/ebml/ebmlmkseekhead.cpp
+    matroska/ebml/ebmlmksegment.cpp
+    matroska/ebml/ebmlmkinfo.cpp
+    matroska/ebml/ebmlmktracks.cpp
+    matroska/ebml/ebmlmktags.cpp
+    matroska/ebml/ebmlstringelement.cpp
+    matroska/ebml/ebmluintelement.cpp
+    matroska/ebml/ebmlfloatelement.cpp
+    matroska/ebml/ebmlutils.cpp
+    matroska/ebml/ebmlvoidelement.cpp
+  )
+endif()
+
 set(toolkit_SRCS
   toolkit/tstring.cpp
   toolkit/tstringlist.cpp
@@ -433,7 +522,7 @@ set(tag_LIB_SRCS
   ${vorbis_SRCS} ${oggflacs_SRCS} ${mpc_SRCS} ${ape_SRCS} ${toolkit_SRCS} ${flacs_SRCS}
   ${wavpack_SRCS} ${speex_SRCS} ${trueaudio_SRCS} ${riff_SRCS} ${aiff_SRCS} ${wav_SRCS}
   ${asf_SRCS} ${mp4_SRCS} ${mod_SRCS} ${s3m_SRCS} ${it_SRCS} ${xm_SRCS} ${opus_SRCS}
-  ${dsf_SRCS} ${dsdiff_SRCS} ${shorten_SRCS}
+  ${dsf_SRCS} ${dsdiff_SRCS} ${shorten_SRCS} ${matroska_SRCS} ${ebml_SRCS}
   tag.cpp
   tagunion.cpp
   fileref.cpp
@@ -441,7 +530,7 @@ set(tag_LIB_SRCS
   tagutils.cpp
 )
 
-add_library(tag ${tag_LIB_SRCS} ${tag_HDRS})
+add_library(tag ${tag_LIB_SRCS} ${tag_HDRS} ${tag_PRIVATE_HDRS})
 
 target_include_directories(tag INTERFACE
   $<INSTALL_INTERFACE:include>

taglib/ape/apeitem.h

@@ -172,7 +172,7 @@ namespace TagLib {
       void setReadOnly(bool readOnly);
 
       /*!
-       * Return \c true if the item is read-only.
+       * Returns \c true if the item is read-only.
        */
       bool isReadOnly() const;
 

taglib/dsdiff/dsdifffile.cpp

@@ -65,12 +65,8 @@ namespace
     if(name.size() != 4)
       return false;
 
-    for(int i = 0; i < 4; i++) {
-      if(name[i] < 32 || name[i] > 126)
-        return false;
-    }
-
-    return true;
+    return std::none_of(name.cbegin(), name.cend(),
+                        [](unsigned char c) { return c < 32 || c > 126; });
   }
 
   enum {
@@ -316,7 +312,7 @@ void DSDIFF::File::removeRootChunk(unsigned int i)
     unsigned long long chunkSize = d->chunks[i].size + d->chunks[i].padding + 12;
 
     d->size -= chunkSize;
-    insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+    insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
     removeBlock(d->chunks[i].offset - 12, chunkSize);
 
@@ -350,7 +346,7 @@ void DSDIFF::File::setRootChunkData(unsigned int i, const ByteVector &data)
   // First we update the global size
 
   d->size += ((data.size() + 1) & ~1) - (d->chunks[i].size + d->chunks[i].padding);
-  insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+  insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
   // Now update the specific chunk
 
@@ -387,7 +383,7 @@ void DSDIFF::File::setRootChunkData(const ByteVector &name, const ByteVector &da
 
   // First we update the global size
   d->size += (offset & 1) + ((data.size() + 1) & ~1) + 12;
-  insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+  insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
   // Now add the chunk to the file
   const unsigned long long fileLength = length();
@@ -414,12 +410,12 @@ void DSDIFF::File::removeChildChunk(unsigned int i, unsigned int childChunkNum)
 
     unsigned long long removedChunkTotalSize = childChunks[i].size + childChunks[i].padding + 12;
     d->size -= removedChunkTotalSize;
-    insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+    insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
     // Update child chunk size
 
     d->chunks[d->childChunkIndex[childChunkNum]].size -= removedChunkTotalSize;
-    insert(ByteVector::fromLongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
+    insert(ByteVector::fromULongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
                                     d->endianness == BigEndian),
            d->chunks[d->childChunkIndex[childChunkNum]].offset - 8, 8);
     // Remove the chunk
@@ -466,13 +462,13 @@ void DSDIFF::File::setChildChunkData(unsigned int i,
 
   d->size += ((data.size() + 1) & ~1) - (childChunks[i].size + childChunks[i].padding);
 
-  insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+  insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
   // And the PROP chunk size
 
   d->chunks[d->childChunkIndex[childChunkNum]].size +=
     ((data.size() + 1) & ~1) - (childChunks[i].size + childChunks[i].padding);
-  insert(ByteVector::fromLongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
+  insert(ByteVector::fromULongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
                                   d->endianness == BigEndian),
          d->chunks[d->childChunkIndex[childChunkNum]].offset - 8, 8);
 
@@ -542,13 +538,13 @@ void DSDIFF::File::setChildChunkData(const ByteVector &name,
   // First we update the global size
 
   d->size += (offset & 1) + ((data.size() + 1) & ~1) + 12;
-  insert(ByteVector::fromLongLong(d->size, d->endianness == BigEndian), 4, 8);
+  insert(ByteVector::fromULongLong(d->size, d->endianness == BigEndian), 4, 8);
 
   // And the child chunk size
 
   d->chunks[d->childChunkIndex[childChunkNum]].size += (offset & 1)
     + ((data.size() + 1) & ~1) + 12;
-  insert(ByteVector::fromLongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
+  insert(ByteVector::fromULongLong(d->chunks[d->childChunkIndex[childChunkNum]].size,
                                   d->endianness == BigEndian),
          d->chunks[d->childChunkIndex[childChunkNum]].offset - 8, 8);
 
@@ -610,14 +606,14 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
   bool bigEndian = d->endianness == BigEndian;
 
   d->type = readBlock(4);
-  d->size = readBlock(8).toLongLong(bigEndian);
+  d->size = readBlock(8).toULongLong(bigEndian);
   d->format = readBlock(4);
 
   // + 12: chunk header at least, fix for additional junk bytes
 
   while(tell() + 12 <= length()) {
     ByteVector chunkName = readBlock(4);
-    unsigned long long chunkSize = readBlock(8).toLongLong(bigEndian);
+    unsigned long long chunkSize = readBlock(8).toULongLong(bigEndian);
 
     if(!isValidChunkID(chunkName)) {
       debug("DSDIFF::File::read() -- Chunk '" + chunkName + "' has invalid ID");
@@ -670,14 +666,14 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
     }
     else if(d->chunks[i].name == "DST ") {
       // Now decode the chunks inside the DST chunk to read the DST Frame Information one
-      long long dstChunkEnd = d->chunks[i].offset + d->chunks[i].size;
+      unsigned long long dstChunkEnd = d->chunks[i].offset + d->chunks[i].size;
       seek(d->chunks[i].offset);
 
       audioDataSizeinBytes = d->chunks[i].size;
 
-      while(tell() + 12 <= dstChunkEnd) {
+      while(static_cast<unsigned long long>(tell()) + 12 <= dstChunkEnd) {
         ByteVector dstChunkName = readBlock(4);
-        long long dstChunkSize = readBlock(8).toLongLong(bigEndian);
+        unsigned long long dstChunkSize = readBlock(8).toULongLong(bigEndian);
 
         if(!isValidChunkID(dstChunkName)) {
           debug("DSDIFF::File::read() -- DST Chunk '" + dstChunkName + "' has invalid ID");
@@ -685,7 +681,7 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
           break;
         }
 
-        if(static_cast<long long>(tell()) + dstChunkSize > dstChunkEnd) {
+        if(tell() + dstChunkSize > dstChunkEnd) {
           debug("DSDIFF::File::read() -- DST Chunk '" + dstChunkName
                 + "' has invalid size (larger than the DST chunk)");
           setValid(false);
@@ -712,14 +708,14 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
       }
     }
     else if(d->chunks[i].name == "PROP") {
-      d->childChunkIndex[PROPChunk] = i;
+      d->childChunkIndex[PROPChunk] = static_cast<int>(i);
       // Now decodes the chunks inside the PROP chunk
-      long long propChunkEnd = d->chunks[i].offset + d->chunks[i].size;
+      unsigned long long propChunkEnd = d->chunks[i].offset + d->chunks[i].size;
       // +4 to remove the 'SND ' marker at beginning of 'PROP' chunk
       seek(d->chunks[i].offset + 4);
-      while(tell() + 12 <= propChunkEnd) {
+      while(static_cast<unsigned long long>(tell()) + 12 <= propChunkEnd) {
         ByteVector propChunkName = readBlock(4);
-        long long propChunkSize = readBlock(8).toLongLong(bigEndian);
+        unsigned long long propChunkSize = readBlock(8).toULongLong(bigEndian);
 
         if(!isValidChunkID(propChunkName)) {
           debug("DSDIFF::File::read() -- PROP Chunk '" + propChunkName + "' has invalid ID");
@@ -727,7 +723,7 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
           break;
         }
 
-        if(static_cast<long long>(tell()) + propChunkSize > propChunkEnd) {
+        if(tell() + propChunkSize > propChunkEnd) {
           debug("DSDIFF::File::read() -- PROP Chunk '" + propChunkName
                 + "' has invalid size (larger than the PROP chunk)");
           setValid(false);
@@ -755,17 +751,17 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
       }
     }
     else if(d->chunks[i].name == "DIIN") {
-      d->childChunkIndex[DIINChunk] = i;
+      d->childChunkIndex[DIINChunk] = static_cast<int>(i);
       d->hasDiin = true;
 
       // Now decode the chunks inside the DIIN chunk
 
-      long long diinChunkEnd = d->chunks[i].offset + d->chunks[i].size;
+      unsigned long long diinChunkEnd = d->chunks[i].offset + d->chunks[i].size;
       seek(d->chunks[i].offset);
 
-      while(tell() + 12 <= diinChunkEnd) {
+      while(static_cast<unsigned long long>(tell()) + 12 <= diinChunkEnd) {
         ByteVector diinChunkName = readBlock(4);
-        long long diinChunkSize = readBlock(8).toLongLong(bigEndian);
+        unsigned long long diinChunkSize = readBlock(8).toULongLong(bigEndian);
 
         if(!isValidChunkID(diinChunkName)) {
           debug("DSDIFF::File::read() -- DIIN Chunk '" + diinChunkName + "' has invalid ID");
@@ -773,7 +769,7 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
           break;
         }
 
-        if(static_cast<long long>(tell()) + diinChunkSize > diinChunkEnd) {
+        if(tell() + diinChunkSize > diinChunkEnd) {
           debug("DSDIFF::File::read() -- DIIN Chunk '" + diinChunkName
                 + "' has invalid size (larger than the DIIN chunk)");
           setValid(false);
@@ -829,7 +825,7 @@ void DSDIFF::File::read(bool readProperties, Properties::ReadStyle propertiesSty
     if(d->childChunks[PROPChunk][i].name == "ID3 " ||
        d->childChunks[PROPChunk][i].name == "id3 ") {
       if(d->hasID3v2) {
-        d->duplicateID3V2chunkIndex = i;
+        d->duplicateID3V2chunkIndex = static_cast<int>(i);
         // ID3V2 tag has already been found at root level
         continue;
       }
@@ -917,7 +913,7 @@ void DSDIFF::File::writeChunk(const ByteVector &name, const ByteVector &data,
     combined.append(ByteVector(leadingPadding, '\x00'));
 
   combined.append(name);
-  combined.append(ByteVector::fromLongLong(data.size(), d->endianness == BigEndian));
+  combined.append(ByteVector::fromULongLong(data.size(), d->endianness == BigEndian));
   combined.append(data);
   if((data.size() & 0x01) != 0)
     combined.append('\x00');

taglib/dsf/dsffile.cpp

@@ -46,8 +46,8 @@ public:
   FilePrivate &operator=(const FilePrivate &) = delete;
 
   const ID3v2::FrameFactory *ID3v2FrameFactory;
-  long long fileSize = 0;
-  long long metadataOffset = 0;
+  unsigned long long fileSize = 0;
+  unsigned long long metadataOffset = 0;
   std::unique_ptr<Properties> properties;
   std::unique_ptr<ID3v2::Tag> tag;
 };
@@ -116,17 +116,17 @@ bool DSF::File::save(ID3v2::Version version)
   // Three things must be updated: the file size, the tag data, and the metadata offset
 
   if(d->tag->isEmpty()) {
-    long long newFileSize = d->metadataOffset ? d->metadataOffset : d->fileSize;
+    unsigned long long newFileSize = d->metadataOffset ? d->metadataOffset : d->fileSize;
 
     // Update the file size
     if(d->fileSize != newFileSize) {
-      insert(ByteVector::fromLongLong(newFileSize, false), 12, 8);
+      insert(ByteVector::fromULongLong(newFileSize, false), 12, 8);
       d->fileSize = newFileSize;
     }
 
     // Update the metadata offset to 0 since there is no longer a tag
     if(d->metadataOffset) {
-      insert(ByteVector::fromLongLong(0ULL, false), 20, 8);
+      insert(ByteVector::fromULongLong(0ULL, false), 20, 8);
       d->metadataOffset = 0;
     }
 
@@ -136,19 +136,19 @@ bool DSF::File::save(ID3v2::Version version)
   else {
     ByteVector tagData = d->tag->render(version);
 
-    long long newMetadataOffset = d->metadataOffset ? d->metadataOffset : d->fileSize;
-    long long newFileSize = newMetadataOffset + tagData.size();
-    long long oldTagSize = d->fileSize - newMetadataOffset;
+    unsigned long long newMetadataOffset = d->metadataOffset ? d->metadataOffset : d->fileSize;
+    unsigned long long newFileSize = newMetadataOffset + tagData.size();
+    unsigned long long oldTagSize = d->fileSize - newMetadataOffset;
 
     // Update the file size
     if(d->fileSize != newFileSize) {
-      insert(ByteVector::fromLongLong(newFileSize, false), 12, 8);
+      insert(ByteVector::fromULongLong(newFileSize, false), 12, 8);
       d->fileSize = newFileSize;
     }
 
     // Update the metadata offset
     if(d->metadataOffset != newMetadataOffset) {
-      insert(ByteVector::fromLongLong(newMetadataOffset, false), 20, 8);
+      insert(ByteVector::fromULongLong(newMetadataOffset, false), 20, 8);
       d->metadataOffset = newMetadataOffset;
     }
 
@@ -175,7 +175,7 @@ void DSF::File::read(AudioProperties::ReadStyle propertiesStyle)
     return;
   }
 
-  long long dsdHeaderSize = readBlock(8).toLongLong(false);
+  unsigned long long dsdHeaderSize = readBlock(8).toULongLong(false);
 
   // Integrity check
   if(dsdHeaderSize != 28) {
@@ -184,16 +184,16 @@ void DSF::File::read(AudioProperties::ReadStyle propertiesStyle)
     return;
   }
 
-  d->fileSize = readBlock(8).toLongLong(false);
+  d->fileSize = readBlock(8).toULongLong(false);
 
   // File is malformed or corrupted, allow trailing garbage
-  if(d->fileSize > length()) {
+  if(d->fileSize > static_cast<unsigned long long>(length())) {
     debug("DSF::File::read() -- File is corrupted wrong length");
     setValid(false);
     return;
   }
 
-  d->metadataOffset = readBlock(8).toLongLong(false);
+  d->metadataOffset = readBlock(8).toULongLong(false);
 
   // File is malformed or corrupted
   if(d->metadataOffset > d->fileSize) {
@@ -210,7 +210,7 @@ void DSF::File::read(AudioProperties::ReadStyle propertiesStyle)
     return;
   }
 
-  long long fmtHeaderSize = readBlock(8).toLongLong(false);
+  unsigned long long fmtHeaderSize = readBlock(8).toULongLong(false);
   if(fmtHeaderSize != 52) {
     debug("DSF::File::read() -- File is corrupted, wrong FMT header size");
     setValid(false);

taglib/fileref.cpp

@@ -77,6 +77,9 @@
 #ifdef TAGLIB_WITH_SHORTEN
 #include "shortenfile.h"
 #endif
+#ifdef TAGLIB_WITH_MATROSKA
+#include "matroskafile.h"
+#endif
 
 using namespace TagLib;
 
@@ -220,6 +223,10 @@ namespace
     else if(ext == "SHN")
       file = new Shorten::File(stream, readAudioProperties, audioPropertiesStyle);
 #endif
+#ifdef TAGLIB_WITH_MATROSKA
+    else if(ext == "MKA" || ext == "MKV" || ext == "WEBM")
+      file = new Matroska::File(stream, readAudioProperties, audioPropertiesStyle);
+#endif
 
     // if file is not valid, leave it to content-based detection.
 
@@ -239,8 +246,7 @@ namespace
   {
     File *file = nullptr;
 
-    if(MPEG::File::isSupported(stream))
-      file = new MPEG::File(stream, readAudioProperties, audioPropertiesStyle);
+    if(false);
 #ifdef TAGLIB_WITH_VORBIS
     else if(Ogg::Vorbis::File::isSupported(stream))
       file = new Ogg::Vorbis::File(stream, readAudioProperties, audioPropertiesStyle);
@@ -289,6 +295,12 @@ namespace
     else if(Shorten::File::isSupported(stream))
       file = new Shorten::File(stream, readAudioProperties, audioPropertiesStyle);
 #endif
+#ifdef TAGLIB_WITH_MATROSKA
+    else if(Matroska::File::isSupported(stream))
+      file = new Matroska::File(stream, readAudioProperties, audioPropertiesStyle);
+#endif
+    else if(MPEG::File::isSupported(stream))
+      file = new MPEG::File(stream, readAudioProperties, audioPropertiesStyle);
 
     // isSupported() only does a quick check, so double check the file here.
 
@@ -513,6 +525,11 @@ StringList FileRef::defaultFileExtensions()
 #ifdef TAGLIB_WITH_SHORTEN
   l.append("shn");
 #endif
+#ifdef TAGLIB_WITH_MATROSKA
+  l.append("mkv");
+  l.append("mka");
+  l.append("webm");
+#endif
 
   return l;
 }

taglib/flac/flacfile.cpp

@@ -70,6 +70,8 @@ public:
 
   std::unique_ptr<Properties> properties;
   ByteVector xiphCommentData;
+  String iXMLData;
+  ByteVector bextData;
   List<FLAC::MetadataBlock *> blocks;
 
   offset_t flacStart { 0 };
@@ -241,6 +243,52 @@ bool FLAC::File::save()
 
   d->xiphCommentData = xiphComment()->render(false);
 
+  // Drop any APPLICATION blocks we recognize as iXML or bext from the block
+  // list.  Recognized blocks were normally extracted to d->iXMLData /
+  // d->bextData during scan() and never added here, but this also catches
+  // entries inserted after scan() (defensive).
+  for(auto it = d->blocks.begin(); it != d->blocks.end();) {
+    if((*it)->code() == MetadataBlock::Application) {
+      const ByteVector blockData = (*it)->render();
+      if(blockData.size() >= 4) {
+        const ByteVector appId = blockData.mid(0, 4);
+        ByteVector innerId;
+        if(appId == "riff" && blockData.size() >= 12)
+          innerId = blockData.mid(4, 4);
+        else if(appId == "iXML" || appId == "bext")
+          innerId = appId;
+
+        if(innerId == "iXML" || innerId == "bext") {
+          delete *it;
+          it = d->blocks.erase(it);
+          continue;
+        }
+      }
+    }
+    ++it;
+  }
+
+  // Append fresh APPLICATION/"riff" blocks for iXML and bext if non-empty.
+  // Per FLAC foreign-metadata convention the payload is a RIFF chunk:
+  // <4 byte FOURCC><4 byte LE size><data>.
+  if(!d->iXMLData.isEmpty()) {
+    const ByteVector xml = d->iXMLData.data(String::UTF8);
+    ByteVector payload;
+    payload.append("riff");
+    payload.append("iXML");
+    payload.append(ByteVector::fromUInt(xml.size(), false));
+    payload.append(xml);
+    d->blocks.append(new UnknownMetadataBlock(MetadataBlock::Application, payload));
+  }
+  if(!d->bextData.isEmpty()) {
+    ByteVector payload;
+    payload.append("riff");
+    payload.append("bext");
+    payload.append(ByteVector::fromUInt(d->bextData.size(), false));
+    payload.append(d->bextData);
+    d->blocks.append(new UnknownMetadataBlock(MetadataBlock::Application, payload));
+  }
+
   // Replace metadata blocks
 
   MetadataBlock *commentBlock =
@@ -433,6 +481,26 @@ void FLAC::File::removePictures()
   }
 }
 
+String FLAC::File::iXMLData() const
+{
+  return d->iXMLData;
+}
+
+void FLAC::File::setiXMLData(const String &data)
+{
+  d->iXMLData = data;
+}
+
+ByteVector FLAC::File::BEXTData() const
+{
+  return d->bextData;
+}
+
+void FLAC::File::setBEXTData(const ByteVector &data)
+{
+  d->bextData = data;
+}
+
 void FLAC::File::strip(int tags)
 {
   if(tags & ID3v1)
@@ -462,6 +530,16 @@ bool FLAC::File::hasID3v2Tag() const
   return d->ID3v2Location >= 0;
 }
 
+bool FLAC::File::hasiXMLData() const
+{
+  return !d->iXMLData.isEmpty();
+}
+
+bool FLAC::File::hasBEXTData() const
+{
+  return !d->bextData.isEmpty();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // private members
 ////////////////////////////////////////////////////////////////////////////////
@@ -613,6 +691,49 @@ void FLAC::File::scan()
     else if(blockType == MetadataBlock::Padding) {
       // Skip all padding blocks.
     }
+    else if(blockType == MetadataBlock::Application && data.size() >= 4) {
+      // APPLICATION block (RFC 9639 § 8.4):
+      //   <4 bytes>  big-endian application ID (ASCII FOURCC in practice)
+      //   <n bytes>  application-defined data
+      //
+      // We recognize two conventions for carrying RIFF iXML / bext metadata:
+      //   1. App ID "riff" — IANA-registered FLAC foreign-metadata wrapper.
+      //      Payload is a RIFF chunk: <4 byte FOURCC><4 byte LE size><data>.
+      //   2. App ID "iXML" or "bext" — direct, used by some third-party tools
+      //      (e.g. Sequoia). Payload is the chunk data verbatim.
+      //
+      // Other application IDs (and "riff" wrapping FOURCCs we don't recognize)
+      // fall through to UnknownMetadataBlock so they round-trip unchanged.
+      const ByteVector appId = data.mid(0, 4);
+      ByteVector innerId;
+      ByteVector innerData;
+
+      if(appId == "riff" && data.size() >= 12) {
+        innerId = data.mid(4, 4);
+        const unsigned int innerSize = data.toUInt(8U, false);
+        innerData = data.mid(12, innerSize);
+      }
+      else if(appId == "iXML" || appId == "bext") {
+        innerId = appId;
+        innerData = data.mid(4);
+      }
+
+      if(innerId == "iXML") {
+        if(d->iXMLData.isEmpty())
+          d->iXMLData = String(innerData, String::UTF8);
+        else
+          debug("FLAC::File::scan() -- multiple iXML blocks found, discarding");
+      }
+      else if(innerId == "bext") {
+        if(d->bextData.isEmpty())
+          d->bextData = innerData;
+        else
+          debug("FLAC::File::scan() -- multiple BEXT blocks found, discarding");
+      }
+      else {
+        block = new UnknownMetadataBlock(blockType, data);
+      }
+    }
     else {
       block = new UnknownMetadataBlock(blockType, data);
     }

taglib/flac/flacfile.h

@@ -296,6 +296,52 @@ namespace TagLib {
        */
       void addPicture(Picture *picture);
 
+      /*!
+       * Returns the raw iXML data as a String.  Empty if no iXML metadata
+       * is present.  Read from an APPLICATION metadata block (RFC 9639 § 8.4)
+       * carrying either the FLAC foreign-metadata application ID "riff"
+       * (with an iXML RIFF chunk as payload) or the direct application ID
+       * "iXML" used by some third-party tools.
+       *
+       * \see setiXMLData()
+       * \see hasiXMLData()
+       */
+      String iXMLData() const;
+
+      /*!
+       * Sets the iXML data.  Pass an empty string to remove the iXML
+       * APPLICATION block on save.  On save, the data is written using the
+       * FLAC foreign-metadata convention: an APPLICATION block with
+       * application ID "riff" wrapping an iXML RIFF chunk.
+       *
+       * \see iXMLData()
+       * \see hasiXMLData()
+       */
+      void setiXMLData(const String &data);
+
+      /*!
+       * Returns the raw BEXT (Broadcast Audio Extension) data as a
+       * ByteVector.  Empty if no BEXT metadata is present.  Read from an
+       * APPLICATION metadata block (RFC 9639 § 8.4) carrying either the FLAC
+       * foreign-metadata application ID "riff" (with a bext RIFF chunk as
+       * payload) or the direct application ID "bext".
+       *
+       * \see setBEXTData()
+       * \see hasBEXTData()
+       */
+      ByteVector BEXTData() const;
+
+      /*!
+       * Sets the BEXT data.  Pass an empty ByteVector to remove the BEXT
+       * APPLICATION block on save.  On save, the data is written using the
+       * FLAC foreign-metadata convention: an APPLICATION block with
+       * application ID "riff" wrapping a bext RIFF chunk.
+       *
+       * \see BEXTData()
+       * \see hasBEXTData()
+       */
+      void setBEXTData(const ByteVector &data);
+
       /*!
        * This will remove the tags that match the OR-ed together TagTypes from
        * the file.  By default it removes all tags.
@@ -332,6 +378,22 @@ namespace TagLib {
        */
       bool hasID3v2Tag() const;
 
+      /*!
+       * Returns whether or not the file on disk actually has iXML data
+       * stored in an APPLICATION metadata block.
+       *
+       * \see iXMLData()
+       */
+      bool hasiXMLData() const;
+
+      /*!
+       * Returns whether or not the file on disk actually has BEXT data
+       * stored in an APPLICATION metadata block.
+       *
+       * \see BEXTData()
+       */
+      bool hasBEXTData() const;
+
       /*!
        * Returns whether or not the given \a stream can be opened as a FLAC
        * file.

taglib/flac/flacproperties.h

@@ -87,7 +87,7 @@ namespace TagLib {
       int bitsPerSample() const;
 
       /*!
-       * Return the number of sample frames.
+       * Returns the number of sample frames.
        */
       unsigned long long sampleFrames() const;
 

taglib/matroska/ebml/ebmlbinaryelement.cpp

@@ -0,0 +1,70 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlbinaryelement.h"
+#include "ebmlutils.h"
+#include "tfile.h"
+#include "tdebug.h"
+
+using namespace TagLib;
+
+EBML::BinaryElement::BinaryElement(Id id, int sizeLength, offset_t dataSize):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::BinaryElement::BinaryElement(Id id, int sizeLength, offset_t dataSize, offset_t):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::BinaryElement::BinaryElement(Id id):
+  Element(id, 0, 0)
+{
+}
+
+const ByteVector& EBML::BinaryElement::getValue() const
+{
+  return value;
+}
+
+void EBML::BinaryElement::setValue(const ByteVector& val)
+{
+  value = val;
+}
+
+bool EBML::BinaryElement::read(File &file)
+{
+  value = file.readBlock(dataSize);
+  if(value.size() != dataSize) {
+    debug("Failed to read binary element");
+    return false;
+  }
+  return true;
+}
+
+ByteVector EBML::BinaryElement::render()
+{
+  ByteVector buffer = renderId();
+  dataSize = value.size();
+  buffer.append(renderVINT(dataSize, 0));
+  buffer.append(value);
+  return buffer;
+}

taglib/matroska/ebml/ebmlbinaryelement.h

@@ -0,0 +1,51 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLBINARYELEMENT_H
+#define TAGLIB_EBMLBINARYELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlelement.h"
+#include "tbytevector.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class BinaryElement : public Element
+    {
+    public:
+      BinaryElement(Id id, int sizeLength, offset_t dataSize);
+      BinaryElement(Id id, int sizeLength, offset_t dataSize, offset_t);
+      explicit BinaryElement(Id id);
+
+      const ByteVector &getValue() const;
+      void setValue(const ByteVector &val);
+      bool read(File &file) override;
+      ByteVector render() override;
+
+    private:
+      ByteVector value;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlelement.cpp

@@ -0,0 +1,216 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlelement.h"
+#include "ebmlvoidelement.h"
+#include "ebmlmasterelement.h"
+#include "ebmlbinaryelement.h"
+#include "ebmlfloatelement.h"
+#include "ebmlmkseekhead.h"
+#include "ebmlmksegment.h"
+#include "ebmlmktags.h"
+#include "ebmlmkattachments.h"
+#include "ebmlmkchapters.h"
+#include "ebmlmktracks.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "ebmlutils.h"
+#include "tfile.h"
+#include "tdebug.h"
+#include "tutils.h"
+
+using namespace TagLib;
+
+#define RETURN_ELEMENT_FOR_CASE(eid) \
+  case (eid): return make_unique_element<eid>(id, sizeLength, dataSize, offset)
+
+std::unique_ptr<EBML::Element> EBML::Element::factory(File &file)
+{
+  // Get the element ID
+  const offset_t offset = file.tell();
+  unsigned int uintId = readId(file);
+  if(!uintId) {
+    debug("Failed to parse EMBL ElementID");
+    return nullptr;
+  }
+
+  // Get the size length and data length
+  const auto &[sizeLength, dataSize] = readVINT(file);
+  if(!sizeLength)
+    return nullptr;
+
+  // Return the subclass
+  // The enum switch without default will give us a warning if an ID is missing
+  auto id = static_cast<Id>(uintId);
+  switch(id) {
+    RETURN_ELEMENT_FOR_CASE(Id::EBMLHeader);
+    RETURN_ELEMENT_FOR_CASE(Id::DocType);
+    RETURN_ELEMENT_FOR_CASE(Id::DocTypeVersion);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSegment);
+    RETURN_ELEMENT_FOR_CASE(Id::MkInfo);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTracks);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTags);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachments);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTag);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagTargets);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSimpleTag);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFile);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSeek);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTrackEntry);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAudio);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagName);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagString);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFileName);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFileDescription);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagLanguage);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFileMediaType);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCodecID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagTargetTypeValue);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagTrackUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagEditionUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagChapterUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagAttachmentUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagsLanguageDefault);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFileUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSeekPosition);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTimestampScale);
+    RETURN_ELEMENT_FOR_CASE(Id::MkBitDepth);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChannels);
+    RETURN_ELEMENT_FOR_CASE(Id::MkAttachedFileData);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSeekID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkDuration);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTitle);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSamplingFrequency);
+    RETURN_ELEMENT_FOR_CASE(Id::MkSeekHead);
+    RETURN_ELEMENT_FOR_CASE(Id::VoidElement);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCluster);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCodecState);
+    RETURN_ELEMENT_FOR_CASE(Id::MkTagBinary);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCues);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCuePoint);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueTime);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueTrackPositions);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueTrack);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueClusterPosition);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueRelativePosition);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueDuration);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueBlockNumber);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueCodecState);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueReference);
+    RETURN_ELEMENT_FOR_CASE(Id::MkCueRefTime);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapters);
+    RETURN_ELEMENT_FOR_CASE(Id::MkEditionEntry);
+    RETURN_ELEMENT_FOR_CASE(Id::MkEditionUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkEditionFlagDefault);
+    RETURN_ELEMENT_FOR_CASE(Id::MkEditionFlagOrdered);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterAtom);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterUID);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterTimeStart);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterTimeEnd);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterFlagHidden);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapterDisplay);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapString);
+    RETURN_ELEMENT_FOR_CASE(Id::MkChapLanguage);
+  }
+  return std::make_unique<Element>(id, sizeLength, dataSize);
+}
+
+unsigned int EBML::Element::readId(File &file)
+{
+  auto buffer = file.readBlock(1);
+  if(buffer.size() != 1) {
+    debug("Failed to read VINT size");
+    return 0;
+  }
+  const unsigned int numBytes = VINTSizeLength<4>(*buffer.begin());
+  if(!numBytes)
+    return 0;
+  if(numBytes > 1)
+    buffer.append(file.readBlock(numBytes - 1));
+  if(buffer.size() != numBytes) {
+    debug("Failed to read VINT data");
+    return 0;
+  }
+  return buffer.toUInt(true);
+}
+
+EBML::Element::Element(Id id, int sizeLength, offset_t dataSize):
+  id(id), sizeLength(sizeLength), dataSize(dataSize)
+{
+}
+
+EBML::Element::Element(Id id, int sizeLength, offset_t dataSize, offset_t):
+  id(id), sizeLength(sizeLength), dataSize(dataSize)
+{
+}
+
+EBML::Element::~Element() = default;
+
+bool EBML::Element::read(File& file)
+{
+  skipData(file);
+  return true;
+}
+
+void EBML::Element::skipData(File &file)
+{
+  file.seek(dataSize, File::Position::Current);
+}
+
+EBML::Element::Id EBML::Element::getId() const
+{
+  return id;
+}
+
+offset_t EBML::Element::headSize() const
+{
+  return idSize(id) + sizeLength;
+}
+
+offset_t EBML::Element::getSize() const
+{
+  return headSize() + dataSize;
+}
+
+int EBML::Element::getSizeLength() const
+{
+  return sizeLength;
+}
+
+int64_t EBML::Element::getDataSize() const
+{
+  return dataSize;
+}
+
+ByteVector EBML::Element::render()
+{
+  ByteVector buffer = renderId();
+  buffer.append(renderVINT(0, 0));
+  return buffer;
+}
+
+ByteVector EBML::Element::renderId() const
+{
+  const int numBytes = idSize(id);
+  static const auto byteOrder = Utils::systemByteOrder();
+  const auto uintId = static_cast<uint32_t>(id);
+  uint32_t data = byteOrder == Utils::LittleEndian ? Utils::byteSwap(uintId) : uintId;
+  return ByteVector(reinterpret_cast<char *>(&data) + (4 - numBytes), numBytes);
+}

taglib/matroska/ebml/ebmlelement.h

@@ -0,0 +1,255 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLELEMENT_H
+#define TAGLIB_EBMLELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <cstdint>
+#include <memory>
+#include "taglib.h"
+
+namespace TagLib
+{
+  class File;
+  class ByteVector;
+
+  namespace EBML {
+
+    class Element
+    {
+    public:
+      enum class Id : unsigned int
+      {
+        EBMLHeader                = 0x1A45DFA3,
+        DocType                   = 0x4282,
+        DocTypeVersion            = 0x4287,
+        VoidElement               = 0xEC,
+        MkSegment                 = 0x18538067,
+        MkTags                    = 0x1254C367,
+        MkTag                     = 0x7373,
+        MkTagTargets              = 0x63C0,
+        MkTagTargetTypeValue      = 0x68CA,
+        MkTagTrackUID             = 0x63C5,
+        MkTagEditionUID           = 0x63C9,
+        MkTagChapterUID           = 0x63C4,
+        MkTagAttachmentUID        = 0x63C6,
+        MkSimpleTag               = 0x67C8,
+        MkTagName                 = 0x45A3,
+        MkTagLanguage             = 0x447A,
+        MkTagBinary               = 0x4485,
+        MkTagString               = 0x4487,
+        MkTagsTagLanguage         = 0x447A,
+        MkTagsLanguageDefault     = 0x4484,
+        MkAttachments             = 0x1941A469,
+        MkAttachedFile            = 0x61A7,
+        MkAttachedFileDescription = 0x467E,
+        MkAttachedFileName        = 0x466E,
+        MkAttachedFileMediaType   = 0x4660,
+        MkAttachedFileData        = 0x465C,
+        MkAttachedFileUID         = 0x46AE,
+        MkSeekHead                = 0x114D9B74,
+        MkSeek                    = 0x4DBB,
+        MkSeekID                  = 0x53AB,
+        MkSeekPosition            = 0x53AC,
+        MkCluster                 = 0x1F43B675,
+        MkCodecState              = 0xA4,
+        MkCues                    = 0x1C53BB6B,
+        MkCuePoint                = 0xBB,
+        MkCueTime                 = 0xB3,
+        MkCueTrackPositions       = 0xB7,
+        MkCueTrack                = 0xF7,
+        MkCueClusterPosition      = 0xF1,
+        MkCueRelativePosition     = 0xF0,
+        MkCueDuration             = 0xB2,
+        MkCueBlockNumber          = 0x5378,
+        MkCueCodecState           = 0xEA,
+        MkCueReference            = 0xDB,
+        MkCueRefTime              = 0x96,
+        MkInfo                    = 0x1549A966,
+        MkTimestampScale          = 0x2AD7B1,
+        MkDuration                = 0x4489,
+        MkTitle                   = 0x7BA9,
+        MkTracks                  = 0x1654AE6B,
+        MkTrackEntry              = 0xAE,
+        MkCodecID                 = 0x86,
+        MkAudio                   = 0xE1,
+        MkSamplingFrequency       = 0xB5,
+        MkBitDepth                = 0x6264,
+        MkChannels                = 0x9F,
+        MkChapters                = 0x1043A770,
+        MkEditionEntry            = 0x45B9,
+        MkEditionUID              = 0x45BC,
+        MkEditionFlagDefault      = 0x45DB,
+        MkEditionFlagOrdered      = 0x45DD,
+        MkChapterAtom             = 0xB6,
+        MkChapterUID              = 0x73C4,
+        MkChapterTimeStart        = 0x91,
+        MkChapterTimeEnd          = 0x92,
+        MkChapterFlagHidden       = 0x98,
+        MkChapterDisplay          = 0x80,
+        MkChapString              = 0x85,
+        MkChapLanguage            = 0x437C,
+      };
+
+      Element(Id id, int sizeLength, offset_t dataSize);
+      Element(Id id, int sizeLength, offset_t dataSize, offset_t);
+      virtual ~Element();
+
+      virtual bool read(File &file);
+      void skipData(File &file);
+      Id getId() const;
+      offset_t headSize() const;
+      offset_t getSize() const;
+      int getSizeLength() const;
+      int64_t getDataSize() const;
+      ByteVector renderId() const;
+      virtual ByteVector render();
+      static std::unique_ptr<Element> factory(File &file);
+      static unsigned int readId(File &file);
+
+    protected:
+      Id id;
+      int sizeLength;
+      offset_t dataSize;
+    };
+
+    // Template specializations to ensure that elements for the different IDs
+    // are consistently created and cast. They provide a mapping between IDs
+    // and Element subclasses. The switch in factory() makes sure that the
+    // template for all IDs are instantiated, i.e. that every ID has its Element
+    // subclass mapped.
+    class MasterElement;
+    class UIntElement;
+    class BinaryElement;
+    class FloatElement;
+    class MkSegment;
+    class MkInfo;
+    class MkTracks;
+    class MkTags;
+    class MkAttachments;
+    class MkSeekHead;
+    class MkChapters;
+    class MkCues;
+    class VoidElement;
+    class UTF8StringElement;
+    class Latin1StringElement;
+
+    template <Element::Id ID>
+    struct GetElementTypeById;
+
+    template <> struct GetElementTypeById<Element::Id::EBMLHeader> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::DocType> { using type = Latin1StringElement; };
+    template <> struct GetElementTypeById<Element::Id::DocTypeVersion> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSegment> { using type = MkSegment; };
+    template <> struct GetElementTypeById<Element::Id::MkInfo> { using type = MkInfo; };
+    template <> struct GetElementTypeById<Element::Id::MkTracks> { using type = MkTracks; };
+    template <> struct GetElementTypeById<Element::Id::MkTags> { using type = MkTags; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachments> { using type = MkAttachments; };
+    template <> struct GetElementTypeById<Element::Id::MkTag> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagTargets> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSimpleTag> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFile> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSeek> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTrackEntry> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAudio> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCuePoint> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueTrackPositions> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueReference> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCluster> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCues> { using type = MkCues; };
+    template <> struct GetElementTypeById<Element::Id::MkTagName> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagString> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFileName> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFileDescription> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagLanguage> { using type = Latin1StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFileMediaType> { using type = Latin1StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCodecID> { using type = Latin1StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagTargetTypeValue> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagTrackUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagEditionUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagChapterUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagAttachmentUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFileUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSeekPosition> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTimestampScale> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkBitDepth> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChannels> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueTime> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueTrack> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueClusterPosition> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueRelativePosition> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueDuration> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueBlockNumber> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueCodecState> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCueRefTime> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagsLanguageDefault> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkAttachedFileData> { using type = BinaryElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSeekID> { using type = BinaryElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTagBinary> { using type = BinaryElement; };
+    template <> struct GetElementTypeById<Element::Id::MkCodecState> { using type = BinaryElement; };
+    template <> struct GetElementTypeById<Element::Id::MkDuration> { using type = FloatElement; };
+    template <> struct GetElementTypeById<Element::Id::MkTitle> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSamplingFrequency> { using type = FloatElement; };
+    template <> struct GetElementTypeById<Element::Id::MkSeekHead> { using type = MkSeekHead; };
+    template <> struct GetElementTypeById<Element::Id::MkChapters> { using type = MkChapters; };
+    template <> struct GetElementTypeById<Element::Id::MkEditionEntry> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkEditionUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkEditionFlagDefault> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkEditionFlagOrdered> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterAtom> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterUID> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterTimeStart> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterTimeEnd> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterFlagHidden> { using type = UIntElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapterDisplay> { using type = MasterElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapString> { using type = UTF8StringElement; };
+    template <> struct GetElementTypeById<Element::Id::MkChapLanguage> { using type = Latin1StringElement; };
+    template <> struct GetElementTypeById<Element::Id::VoidElement> { using type = VoidElement; };
+
+    template <Element::Id ID, typename T=typename GetElementTypeById<ID>::type>
+    const T *element_cast(const std::unique_ptr<Element> &ptr)
+    {
+      return static_cast<const T *>(ptr.get());
+    }
+
+    template <Element::Id ID, typename T=typename GetElementTypeById<ID>::type>
+    std::unique_ptr<T> element_cast(std::unique_ptr<Element> &&ptr)
+    {
+      return std::unique_ptr<T>(static_cast<T *>(ptr.release()));
+    }
+
+    template <Element::Id ID, typename T=typename GetElementTypeById<ID>::type>
+    std::unique_ptr<T> make_unique_element(Element::Id id, int sizeLength, offset_t dataSize, offset_t offset)
+    {
+      return std::make_unique<T>(id, sizeLength, dataSize, offset);
+    }
+
+    template <Element::Id ID, typename T=typename GetElementTypeById<ID>::type>
+    std::unique_ptr<T> make_unique_element()
+    {
+      return std::make_unique<T>(ID, 0, 0, 0);
+    }
+
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlfloatelement.cpp

@@ -0,0 +1,109 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlfloatelement.h"
+#include "ebmlutils.h"
+#include "tbytevector.h"
+#include "tfile.h"
+#include "tdebug.h"
+
+using namespace TagLib;
+
+EBML::FloatElement::FloatElement(Id id, int sizeLength, offset_t dataSize):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::FloatElement::FloatElement(Id id, int sizeLength, offset_t dataSize, offset_t):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::FloatElement::FloatElement(Id id):
+  FloatElement(id, 0, 0)
+{
+}
+
+EBML::FloatElement::FloatVariantType EBML::FloatElement::getValue() const
+{ return value; }
+
+double EBML::FloatElement::getValueAsDouble(double defaultValue) const
+{
+  if(std::holds_alternative<double>(value)) {
+    // get_if() used instead of get() to support restricted compilers
+    return *std::get_if<double>(&value);
+  }
+  if(std::holds_alternative<float>(value)) {
+    // get_if() used instead of get() to support restricted compilers
+    return *std::get_if<float>(&value);
+  }
+  return defaultValue;
+}
+
+void EBML::FloatElement::setValue(FloatVariantType val)
+{
+  value = val;
+}
+
+bool EBML::FloatElement::read(File &file)
+{
+  const ByteVector buffer = file.readBlock(dataSize);
+  if(buffer.size() != dataSize) {
+    debug("Failed to read EBML Float element");
+    return false;
+  }
+
+  if(dataSize == 0) {
+    value = std::monostate();
+  }
+  else if(dataSize == 4) {
+    value = buffer.toFloat32BE(0);
+  }
+  else if(dataSize == 8) {
+    value = buffer.toFloat64BE(0);
+  }
+  else {
+    debug("Invalid size for EBML Float element");
+    return false;
+  }
+  return true;
+}
+
+ByteVector EBML::FloatElement::render()
+{
+  ByteVector data;
+  if(std::holds_alternative<double>(value)) {
+    // get_if() used instead of get() to support restricted compilers
+    data = ByteVector::fromFloat64BE(*std::get_if<double>(&value));
+  }
+  else if(std::holds_alternative<float>(value)) {
+    // get_if() used instead of get() to support restricted compilers
+    data = ByteVector::fromFloat32BE(*std::get_if<float>(&value));
+  }
+  ByteVector buffer = renderId();
+  buffer.append(renderVINT(data.size(), 0));
+  buffer.append(data);
+  return buffer;
+}

taglib/matroska/ebml/ebmlfloatelement.h

@@ -0,0 +1,59 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLFLOATELEMENT_H
+#define TAGLIB_EBMLFLOATELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <variant>
+#include "ebmlelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class FloatElement : public Element
+    {
+    public:
+      using FloatVariantType = std::variant<std::monostate, float, double>;
+
+      FloatElement(Id id, int sizeLength, offset_t dataSize);
+      FloatElement(Id id, int sizeLength, offset_t dataSize, offset_t);
+      explicit FloatElement(Id id);
+
+      FloatVariantType getValue() const;
+      double getValueAsDouble(double defaultValue = 0.0) const;
+      void setValue(FloatVariantType val);
+      bool read(File &file) override;
+      ByteVector render() override;
+
+    private:
+      FloatVariantType value;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmasterelement.cpp

@@ -0,0 +1,144 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmasterelement.h"
+#include "ebmlvoidelement.h"
+#include "ebmlutils.h"
+#include "tdebug.h"
+#include "tfile.h"
+
+using namespace TagLib;
+
+EBML::MasterElement::MasterElement(Id id, int sizeLength, offset_t dataSize, offset_t offset):
+  Element(id, sizeLength, dataSize), offset(offset)
+{
+}
+
+EBML::MasterElement::MasterElement(Id id):
+  Element(id, 0, 0), offset(0)
+{
+}
+
+EBML::MasterElement::~MasterElement() = default;
+
+offset_t EBML::MasterElement::getOffset() const
+{
+  return offset;
+}
+
+void EBML::MasterElement::appendElement(std::unique_ptr<Element> &&element)
+{
+  elements.push_back(std::move(element));
+}
+
+std::list<std::unique_ptr<EBML::Element>>::iterator EBML::MasterElement::begin()
+{
+  return elements.begin();
+}
+
+std::list<std::unique_ptr<EBML::Element>>::iterator EBML::MasterElement::end()
+{
+  return elements.end();
+}
+
+std::list<std::unique_ptr<EBML::Element>>::const_iterator EBML::MasterElement::begin() const
+{
+  return elements.begin();
+}
+
+std::list<std::unique_ptr<EBML::Element>>::const_iterator EBML::MasterElement::end() const
+{
+  return elements.end();
+}
+
+std::list<std::unique_ptr<EBML::Element>>::const_iterator EBML::MasterElement::cbegin() const
+{
+  return elements.cbegin();
+}
+
+std::list<std::unique_ptr<EBML::Element>>::const_iterator EBML::MasterElement::cend() const
+{
+  return elements.cend();
+}
+
+offset_t EBML::MasterElement::getPadding() const
+{
+  return padding;
+}
+
+void EBML::MasterElement::setPadding(offset_t numBytes)
+{
+  padding = numBytes;
+}
+
+offset_t EBML::MasterElement::getMinRenderSize() const
+{
+  return minRenderSize;
+}
+
+void EBML::MasterElement::setMinRenderSize(offset_t minimumSize)
+{
+  minRenderSize = minimumSize;
+}
+
+bool EBML::MasterElement::read(File &file, int depth)
+{
+  static constexpr int MAX_EBML_DEPTH = 64;
+  if(depth > MAX_EBML_DEPTH) {
+    debug("EBML: Maximum nesting depth exceeded");
+    return false;
+  }
+  const offset_t maxOffset = file.tell() + dataSize;
+  std::unique_ptr<Element> element;
+  while((element = findNextElement(file, maxOffset))) {
+    if(auto master = dynamic_cast<MasterElement *>(element.get())) {
+      if(!master->read(file, depth + 1))
+        return false;
+    }
+    else {
+      if(!element->read(file))
+        return false;
+    }
+    elements.push_back(std::move(element));
+  }
+  return file.tell() == maxOffset;
+}
+
+bool EBML::MasterElement::read(File &file)
+{
+  return read(file, 0);
+}
+
+ByteVector EBML::MasterElement::render()
+{
+  ByteVector buffer = renderId();
+  ByteVector data;
+  for(const auto &element : elements)
+    data.append(element->render());
+  dataSize = data.size();
+  buffer.append(renderVINT(dataSize, 0));
+  buffer.append(data);
+  if(minRenderSize) {
+    if(const auto bufferSize = buffer.size();
+       minRenderSize >= bufferSize + MIN_VOID_ELEMENT_SIZE)
+      buffer.append(VoidElement::renderSize(minRenderSize - bufferSize));
+  }
+  return buffer;
+}

taglib/matroska/ebml/ebmlmasterelement.h

@@ -0,0 +1,70 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMASTERELEMENT_H
+#define TAGLIB_EBMLMASTERELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <list>
+
+#include "ebmlelement.h"
+#include "taglib.h"
+
+namespace TagLib
+{
+  class ByteVector;
+
+  namespace EBML {
+    class MasterElement : public Element
+    {
+    public:
+      MasterElement(Id id, int sizeLength, offset_t dataSize, offset_t offset);
+      explicit MasterElement(Id id);
+      ~MasterElement() override;
+
+      offset_t getOffset() const;
+      bool read(File &file) override;
+      ByteVector render() override;
+      void appendElement(std::unique_ptr<Element> &&element);
+      std::list<std::unique_ptr<Element>>::iterator begin();
+      std::list<std::unique_ptr<Element>>::iterator end();
+      std::list<std::unique_ptr<Element>>::const_iterator begin() const;
+      std::list<std::unique_ptr<Element>>::const_iterator end() const;
+      std::list<std::unique_ptr<Element>>::const_iterator cbegin() const;
+      std::list<std::unique_ptr<Element>>::const_iterator cend() const;
+      offset_t getPadding() const;
+      void setPadding(offset_t numBytes);
+      offset_t getMinRenderSize() const;
+      void setMinRenderSize(offset_t minimumSize);
+
+    protected:
+      bool read(File &file, int depth);
+
+      offset_t offset;
+      offset_t padding = 0;
+      offset_t minRenderSize = 0;
+      std::list<std::unique_ptr<Element>> elements;
+    };
+
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmkattachments.cpp

@@ -0,0 +1,81 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmkattachments.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "ebmlbinaryelement.h"
+#include "matroskaattachments.h"
+#include "matroskaattachedfile.h"
+
+using namespace TagLib;
+
+EBML::MkAttachments::MkAttachments(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkAttachments, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkAttachments::MkAttachments(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkAttachments, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkAttachments::MkAttachments():
+  MasterElement(Id::MkAttachments, 0, 0, 0)
+{
+}
+
+std::unique_ptr<Matroska::Attachments> EBML::MkAttachments::parse() const
+{
+  auto attachments = std::make_unique<Matroska::Attachments>();
+  attachments->setOffset(offset);
+  attachments->setSize(getSize() + padding);
+
+  for(const auto &element : elements) {
+    if(element->getId() != Id::MkAttachedFile)
+      continue;
+
+    const String *filename = nullptr;
+    const String *description = nullptr;
+    const String *mediaType = nullptr;
+    const ByteVector *data = nullptr;
+    Matroska::AttachedFile::UID uid = 0;
+    const auto attachedFile = element_cast<Id::MkAttachedFile>(element);
+    for(const auto &attachedFileChild : *attachedFile) {
+      if(const Id id = attachedFileChild->getId(); id == Id::MkAttachedFileName)
+        filename = &element_cast<Id::MkAttachedFileName>(attachedFileChild)->getValue();
+      else if(id == Id::MkAttachedFileData)
+        data = &element_cast<Id::MkAttachedFileData>(attachedFileChild)->getValue();
+      else if(id == Id::MkAttachedFileDescription)
+        description = &element_cast<Id::MkAttachedFileDescription>(attachedFileChild)->getValue();
+      else if(id == Id::MkAttachedFileMediaType)
+        mediaType = &element_cast<Id::MkAttachedFileMediaType>(attachedFileChild)->getValue();
+      else if(id == Id::MkAttachedFileUID)
+        uid = element_cast<Id::MkAttachedFileUID>(attachedFileChild)->getValue();
+    }
+    if(!(filename && data))
+      continue;
+
+    attachments->addAttachedFile(Matroska::AttachedFile(
+      *data, *filename, mediaType ? *mediaType : String(),
+      uid, description ? *description : String()));
+  }
+  return attachments;
+}

taglib/matroska/ebml/ebmlmkattachments.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKATTACHMENTS_H
+#define TAGLIB_EBMLMKATTACHMENTS_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Attachments;
+  }
+
+  namespace EBML {
+    class MkAttachments : public MasterElement
+    {
+    public:
+      MkAttachments(int sizeLength, offset_t dataSize, offset_t offset);
+      MkAttachments(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkAttachments();
+
+      std::unique_ptr<Matroska::Attachments> parse() const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmkchapters.cpp

@@ -0,0 +1,146 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmkchapters.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "matroskachapters.h"
+#include "matroskachapteredition.h"
+
+using namespace TagLib;
+
+namespace {
+
+Matroska::Chapter parseChapterAtom(
+  const std::unique_ptr<EBML::Element> &atomElement)
+{
+  Matroska::Chapter::UID chapterUid = 0;
+  Matroska::Chapter::Time chapterTimeStart = 0;
+  Matroska::Chapter::Time chapterTimeEnd = 0;
+  List<Matroska::Chapter::Display> chapterDisplays;
+  bool chapterHidden = false;
+
+  const auto chapterAtom = EBML::element_cast<EBML::Element::Id::MkChapterAtom>(atomElement);
+  for(const auto &chapterChild : *chapterAtom) {
+    if(const EBML::Element::Id cid = chapterChild->getId(); cid == EBML::Element::Id::MkChapterUID)
+      chapterUid = EBML::element_cast<EBML::Element::Id::MkChapterUID>(chapterChild)->getValue();
+    else if(cid == EBML::Element::Id::MkChapterTimeStart)
+      chapterTimeStart = EBML::element_cast<EBML::Element::Id::MkChapterTimeStart>(chapterChild)->getValue();
+    else if(cid == EBML::Element::Id::MkChapterTimeEnd)
+      chapterTimeEnd = EBML::element_cast<EBML::Element::Id::MkChapterTimeEnd>(chapterChild)->getValue();
+    else if(cid == EBML::Element::Id::MkChapterFlagHidden)
+      chapterHidden = EBML::element_cast<EBML::Element::Id::MkChapterFlagHidden>(chapterChild)->getValue() != 0;
+    else if (cid == EBML::Element::Id::MkChapterDisplay) {
+      const auto display = EBML::element_cast<EBML::Element::Id::MkChapterDisplay>(chapterChild);
+      String displayString;
+      String displayLanguage;
+      for(const auto &displayChild : *display) {
+        if (const EBML::Element::Id did = displayChild->getId(); did == EBML::Element::Id::MkChapString)
+          displayString = EBML::element_cast<EBML::Element::Id::MkChapString>(displayChild)->getValue();
+        else if(did == EBML::Element::Id::MkChapLanguage)
+          displayLanguage = EBML::element_cast<EBML::Element::Id::MkChapLanguage>(displayChild)->getValue();
+      }
+      if(!displayString.isEmpty()) {
+        chapterDisplays.append(Matroska::Chapter::Display(displayString, displayLanguage));
+      }
+    }
+  }
+  return Matroska::Chapter(chapterTimeStart, chapterTimeEnd, chapterDisplays,
+    chapterUid, chapterHidden);
+}
+
+} // namespae
+
+EBML::MkChapters::MkChapters(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkChapters, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkChapters::MkChapters(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkChapters, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkChapters::MkChapters() :
+  MasterElement(Id::MkChapters, 0, 0, 0)
+{
+}
+
+std::unique_ptr<Matroska::Chapters> EBML::MkChapters::parse() const
+{
+  auto chapters = std::make_unique<Matroska::Chapters>();
+  chapters->setOffset(offset);
+  chapters->setSize(getSize() + padding);
+
+  // Collect any orphan ChapterAtom elements not wrapped in an EditionEntry.
+  // The Matroska spec requires ChapterAtom to be inside an EditionEntry, but
+  // some muxers produce files with ChapterAtom directly under Chapters.
+  // MKVToolNix and FFmpeg handle this case by treating the orphan atoms as
+  // belonging to an implicit default edition.
+  List<Matroska::Chapter> orphanChapters;
+
+  for(const auto &element : elements) {
+    if(element->getId() == Id::MkChapterAtom) {
+      if(auto chapter = parseChapterAtom(element); chapter.uid()) {
+        orphanChapters.append(chapter);
+      }
+      continue;
+    }
+    if(element->getId() != Id::MkEditionEntry)
+      continue;
+
+    List<Matroska::Chapter> editionChapters;
+    Matroska::ChapterEdition::UID editionUid = 0;
+    bool editionIsDefault = false;
+    bool editionIsOrdered = false;
+    const auto edition = element_cast<Id::MkEditionEntry>(element);
+    for(const auto &editionChild : *edition) {
+      if(const Id id = editionChild->getId(); id == Id::MkEditionUID)
+        editionUid = element_cast<Id::MkEditionUID>(editionChild)->getValue();
+      else if(id == Id::MkEditionFlagDefault)
+        editionIsDefault = element_cast<Id::MkEditionFlagDefault>(editionChild)->getValue() != 0;
+      else if(id == Id::MkEditionFlagOrdered)
+        editionIsOrdered = element_cast<Id::MkEditionFlagOrdered>(editionChild)->getValue() != 0;
+      else if(id == Id::MkChapterAtom) {
+        if(auto chapter = parseChapterAtom(editionChild); chapter.uid()) {
+          editionChapters.append(chapter);
+        }
+      }
+    }
+    if(!editionChapters.isEmpty()) {
+      chapters->addChapterEdition(Matroska::ChapterEdition(
+        editionChapters, editionIsDefault, editionIsOrdered, editionUid));
+    }
+  }
+
+  // If orphan chapters were found, wrap them in an implicit default edition
+  // so they are not silently lost.
+  if (!orphanChapters.isEmpty()) {
+    chapters->addChapterEdition(Matroska::ChapterEdition(
+      orphanChapters, true, false, 0));
+  }
+
+  return chapters;
+}

taglib/matroska/ebml/ebmlmkchapters.h

@@ -0,0 +1,52 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKCHAPTERS_H
+#define TAGLIB_EBMLMKCHAPTERS_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Chapters;
+  }
+
+  namespace EBML {
+    class MkChapters : public MasterElement
+    {
+    public:
+      MkChapters(int sizeLength, offset_t dataSize, offset_t offset);
+      MkChapters(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkChapters();
+
+      std::unique_ptr<Matroska::Chapters> parse() const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmkcues.cpp

@@ -0,0 +1,89 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmkcues.h"
+#include "ebmluintelement.h"
+#include "matroskacues.h"
+
+using namespace TagLib;
+
+EBML::MkCues::MkCues(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkCues, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkCues::MkCues(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkCues, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkCues::MkCues():
+  MasterElement(Id::MkCues, 0, 0, 0)
+{
+}
+
+std::unique_ptr<Matroska::Cues> EBML::MkCues::parse(offset_t segmentDataOffset) const
+{
+  auto cues = std::make_unique<Matroska::Cues>(segmentDataOffset);
+  cues->setOffset(offset);
+  cues->setSize(getSize());
+  cues->setID(static_cast<Matroska::Element::ID>(id));
+
+  for(const auto &cuesChild : elements) {
+    if(cuesChild->getId() != Id::MkCuePoint)
+      continue;
+    const auto cuePointElement = element_cast<Id::MkCuePoint>(cuesChild);
+    auto cuePoint = std::make_unique<Matroska::CuePoint>();
+
+    for(const auto &cuePointChild : *cuePointElement) {
+      if(const Id id = cuePointChild->getId(); id == Id::MkCueTime)
+        cuePoint->setTime(element_cast<Id::MkCueTime>(cuePointChild)->getValue());
+      else if(id == Id::MkCueTrackPositions) {
+        auto cueTrack = std::make_unique<Matroska::CueTrack>();
+        const auto cueTrackElement = element_cast<Id::MkCueTrackPositions>(cuePointChild);
+        for(const auto &cueTrackChild : *cueTrackElement) {
+          if(const Id trackId = cueTrackChild->getId(); trackId == Id::MkCueTrack)
+            cueTrack->setTrackNumber(element_cast<Id::MkCueTrack>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueClusterPosition)
+            cueTrack->setClusterPosition(element_cast<Id::MkCueClusterPosition>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueRelativePosition)
+            cueTrack->setRelativePosition(element_cast<Id::MkCueRelativePosition>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueDuration)
+            cueTrack->setDuration(element_cast<Id::MkCueDuration>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueBlockNumber)
+            cueTrack->setBlockNumber(element_cast<Id::MkCueBlockNumber>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueCodecState)
+            cueTrack->setCodecState(element_cast<Id::MkCueCodecState>(cueTrackChild)->getValue());
+          else if(trackId == Id::MkCueReference) {
+            const auto cueReference = element_cast<Id::MkCueReference>(cueTrackChild);
+            for(const auto &cueReferenceChild : *cueReference) {
+              if(cueReferenceChild->getId() != Id::MkCueRefTime)
+                continue;
+              cueTrack->addReferenceTime(element_cast<Id::MkCueRefTime>(cueReferenceChild)->getValue());
+            }
+          }
+        }
+        cuePoint->addCueTrack(std::move(cueTrack));
+      }
+    }
+    cues->addCuePoint(std::move(cuePoint));
+  }
+  return cues;
+}

taglib/matroska/ebml/ebmlmkcues.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKCUES_H
+#define TAGLIB_EBMLMKCUES_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Cues;
+  }
+
+  namespace EBML {
+    class MkCues : public MasterElement
+    {
+    public:
+      MkCues(int sizeLength, offset_t dataSize, offset_t offset);
+      MkCues(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkCues();
+
+      std::unique_ptr<Matroska::Cues> parse(offset_t segmentDataOffset) const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmkinfo.cpp

@@ -0,0 +1,72 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmkinfo.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "ebmlfloatelement.h"
+#include "matroskaproperties.h"
+
+using namespace TagLib;
+
+EBML::MkInfo::MkInfo(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkInfo, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkInfo::MkInfo(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkInfo, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkInfo::MkInfo():
+  MasterElement(Id::MkInfo, 0, 0, 0)
+{
+}
+
+void EBML::MkInfo::parse(Matroska::Properties *properties) const
+{
+  if(!properties)
+    return;
+
+  unsigned long long timestampScale = 1000000;
+  double duration = 0.0;
+  String title;
+  for(const auto &element : elements) {
+    if(const Id id = element->getId(); id == Id::MkTimestampScale) {
+      timestampScale = element_cast<Id::MkTimestampScale>(element)->getValue();
+    }
+    else if(id == Id::MkDuration) {
+      duration = element_cast<Id::MkDuration>(element)->getValueAsDouble();
+    }
+    else if(id == Id::MkTitle) {
+      title = element_cast<Id::MkTitle>(element)->getValue();
+    }
+  }
+
+  properties->setLengthInMilliseconds(
+    static_cast<int>(duration * static_cast<double>(timestampScale) / 1000000.0));
+  properties->setTitle(title);
+}

taglib/matroska/ebml/ebmlmkinfo.h

@@ -0,0 +1,52 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKINFO_H
+#define TAGLIB_EBMLMKINFO_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Properties;
+  }
+
+  namespace EBML {
+    class MkInfo : public MasterElement
+    {
+    public:
+      MkInfo(int sizeLength, offset_t dataSize, offset_t offset);
+      MkInfo(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkInfo();
+
+      void parse(Matroska::Properties * properties) const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmkseekhead.cpp

@@ -0,0 +1,73 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmkseekhead.h"
+#include "matroskaseekhead.h"
+#include "ebmluintelement.h"
+#include "ebmlbinaryelement.h"
+
+using namespace TagLib;
+
+EBML::MkSeekHead::MkSeekHead(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkSeekHead, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkSeekHead::MkSeekHead(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkSeekHead, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkSeekHead::MkSeekHead():
+  MasterElement(Id::MkSeekHead, 0, 0, 0)
+{
+}
+
+std::unique_ptr<Matroska::SeekHead> EBML::MkSeekHead::parse(offset_t segmentDataOffset) const
+{
+  auto seekHead = std::make_unique<Matroska::SeekHead>(segmentDataOffset);
+  seekHead->setOffset(offset);
+  seekHead->setSize(getSize() + padding);
+
+  for(const auto &element : elements) {
+    if(element->getId() != Id::MkSeek)
+      continue;
+    const auto seekElement = element_cast<Id::MkSeek>(element);
+    Matroska::Element::ID entryId = 0;
+    offset_t offset = 0;
+    for(const auto &seekElementChild : *seekElement) {
+      if(const Id id = seekElementChild->getId(); id == Id::MkSeekID && !entryId) {
+        if(auto data = element_cast<Id::MkSeekID>(seekElementChild)->getValue();
+           data.size() == 4)
+          entryId = data.toUInt(true);
+      }
+      else if(id == Id::MkSeekPosition && !offset)
+        offset = element_cast<Id::MkSeekPosition>(seekElementChild)->getValue();
+    }
+    if(entryId && offset)
+      seekHead->addEntry(entryId, offset);
+    else {
+      seekHead.reset();
+      return nullptr;
+    }
+  }
+
+  return seekHead;
+}

taglib/matroska/ebml/ebmlmkseekhead.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKSEEKHEAD_H
+#define TAGLIB_EBMLMKSEEKHEAD_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class SeekHead;
+  }
+
+  namespace EBML {
+    class MkSeekHead : public MasterElement
+    {
+    public:
+      MkSeekHead(int sizeLength, offset_t dataSize, offset_t offset);
+      MkSeekHead(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkSeekHead();
+
+      std::unique_ptr<Matroska::SeekHead> parse(offset_t segmentDataOffset) const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmksegment.cpp

@@ -0,0 +1,296 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmksegment.h"
+#include "ebmlutils.h"
+#include "matroskafile.h"
+#include "matroskatag.h"
+#include "matroskaattachments.h"
+#include "matroskachapters.h"
+#include "matroskacues.h"
+#include "matroskaseekhead.h"
+#include "matroskasegment.h"
+
+using namespace TagLib;
+
+namespace {
+
+template <EBML::Element::Id Id, typename ElementType>
+std::unique_ptr<ElementType> readElementAt(File &file,
+                                           offset_t offset,
+                                           offset_t maxOffset)
+{
+  if(offset < 0 || offset >= maxOffset) {
+    return nullptr;
+  }
+
+  file.seek(offset);
+  auto element = EBML::Element::factory(file);
+  if(!element || element->getId() != Id) {
+    return nullptr;
+  }
+
+  auto typed = EBML::element_cast<Id>(std::move(element));
+  if(!typed || !typed->read(file)) {
+    return nullptr;
+  }
+  return typed;
+}
+
+} // namespace
+
+EBML::MkSegment::MkSegment(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkSegment, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkSegment::MkSegment(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkSegment, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkSegment::~MkSegment() = default;
+
+offset_t EBML::MkSegment::segmentDataOffset() const
+{
+  return offset + idSize(id) + sizeLength;
+}
+
+bool EBML::MkSegment::read(File &file)
+{
+  return readLimited(file, dataSize);
+}
+
+bool EBML::MkSegment::readLimited(File &file, offset_t scanLimit)
+{
+  const offset_t filePos = file.tell();
+  const offset_t maxOffset = filePos + dataSize;
+  const offset_t maxScanOffset = filePos + std::min(scanLimit, dataSize);
+  // When scanLimit is less than dataSize, the caller has requested a
+  // fast/limited scan (e.g. AudioProperties::Fast).  In that case and if the
+  // file has been opened in read-only mode, we skip parsing the Cues element,
+  // which can be tens of MB on large files, causing severe slowdowns over
+  // network filesystems, and do not have to be updated in read-only mode.
+  const bool skipCues = file.readOnly() && scanLimit < dataSize;
+  MasterElement *pendingPaddingTarget = nullptr;
+  offset_t accumulatedPadding = 0;
+  std::unique_ptr<Element> element;
+  while((element = findNextElement(file, maxScanOffset))) {
+    if(const Id id = element->getId(); id == Id::MkSeekHead) {
+      seekHead = element_cast<Id::MkSeekHead>(std::move(element));
+      if(!seekHead->read(file))
+        return false;
+      // We have a seek head, let's use it for faster access to the other elements
+      if(const auto elementAfterSeekHead = findNextElement(file, maxScanOffset);
+         elementAfterSeekHead && elementAfterSeekHead->getId() == Id::VoidElement)
+        seekHead->setPadding(elementAfterSeekHead->getSize());
+      const offset_t segDataOffset = segmentDataOffset();
+      const auto matroskaSeekHead = parseSeekHead();
+      const auto accumulateVoidPadding = [&](MasterElement *target) {
+        offset_t accPadding = 0;
+        while(const auto next = findNextElement(file, maxOffset)) {
+          if(next->getId() != Id::VoidElement)
+            break;
+          accPadding += next->getSize();
+          next->skipData(file);
+        }
+        if(accPadding > 0)
+          target->setPadding(accPadding);
+      };
+
+      // Build a work list of seek entries.  Some muxers (e.g. MakeMKV,
+      // mkvmerge) write a small primary SeekHead at the start of the segment
+      // that only references a secondary SeekHead at the end of the file,
+      // which in turn lists Info / Tracks / Tags / Chapters / Attachments.
+      // Follow such MkSeekHead -> MkSeekHead chains so the real entries are
+      // not silently dropped.
+      List<std::pair<unsigned int, offset_t>> entries =
+        matroskaSeekHead->entryList();
+      // Guard against pathological / circular chains.
+      int chainedSeekHeadsFollowed = 0;
+      constexpr int MAX_CHAINED_SEEKHEADS = 8;
+
+      for(unsigned int i = 0; i < entries.size(); ++i) {
+        const auto &[idValue, relativeOffset] = entries[i];
+        const offset_t absoluteOffset = segDataOffset + relativeOffset;
+        switch(static_cast<Id>(idValue)) {
+        case Id::MkSeekHead: {
+          if(chainedSeekHeadsFollowed++ >= MAX_CHAINED_SEEKHEADS)
+            break;
+          auto chained = readElementAt<Id::MkSeekHead, MkSeekHead>(
+            file, absoluteOffset, maxOffset);
+          if(!chained)
+            break;
+          if(const auto parsed = chained->parse(segDataOffset)) {
+            for(const auto &entry : parsed->entryList())
+              entries.append(entry);
+          }
+          break;
+        }
+        case Id::MkCues:
+          if(!skipCues) {
+            if(!((cues = readElementAt<Id::MkCues, MkCues>(
+              file, absoluteOffset, maxOffset))))
+              return false;
+          }
+          break;
+        case Id::MkInfo:
+          if(!((info = readElementAt<Id::MkInfo, MkInfo>(
+            file, absoluteOffset, maxOffset))))
+            return false;
+          break;
+        case Id::MkTracks:
+          if(!((tracks = readElementAt<Id::MkTracks, MkTracks>(
+            file, absoluteOffset, maxOffset))))
+            return false;
+          break;
+        case Id::MkTags:
+          if(!((tags = readElementAt<Id::MkTags, MkTags>(
+            file, absoluteOffset, maxOffset))))
+            return false;
+          accumulateVoidPadding(tags.get());
+          break;
+        case Id::MkAttachments:
+          if(!((attachments = readElementAt<Id::MkAttachments, MkAttachments>(
+            file, absoluteOffset, maxOffset))))
+            return false;
+          accumulateVoidPadding(attachments.get());
+          break;
+        case Id::MkChapters:
+          if(!((chapters = readElementAt<Id::MkChapters, MkChapters>(
+            file, absoluteOffset, maxOffset))))
+            return false;
+          accumulateVoidPadding(chapters.get());
+          break;
+        default:
+          break;
+        }
+      }
+      return true;
+    }
+    else if(id == Id::VoidElement) {
+      if(pendingPaddingTarget) {
+        accumulatedPadding += element->getSize();
+        pendingPaddingTarget->setPadding(accumulatedPadding);
+      }
+      element->skipData(file);
+    }
+    else if(id == Id::MkCues) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      if(!skipCues) {
+        cues = element_cast<Id::MkCues>(std::move(element));
+        if(!cues->read(file))
+          return false;
+      }
+      else {
+        element->skipData(file);
+      }
+    }
+    else if(id == Id::MkInfo) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      info = element_cast<Id::MkInfo>(std::move(element));
+      if(!info->read(file))
+        return false;
+    }
+    else if(id == Id::MkTracks) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      tracks = element_cast<Id::MkTracks>(std::move(element));
+      if(!tracks->read(file))
+        return false;
+    }
+    else if(id == Id::MkTags) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      tags = element_cast<Id::MkTags>(std::move(element));
+      if(!tags->read(file))
+        return false;
+      pendingPaddingTarget = tags.get();
+    }
+    else if(id == Id::MkAttachments) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      attachments = element_cast<Id::MkAttachments>(std::move(element));
+      if(!attachments->read(file))
+        return false;
+      pendingPaddingTarget = attachments.get();
+    }
+    else if(id == Id::MkChapters) {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      chapters = element_cast<Id::MkChapters>(std::move(element));
+      if(!chapters->read(file))
+        return false;
+      pendingPaddingTarget = chapters.get();
+    }
+    else {
+      pendingPaddingTarget = nullptr;
+      accumulatedPadding = 0;
+      element->skipData(file);
+    }
+  }
+  return true;
+}
+
+std::unique_ptr<Matroska::Tag> EBML::MkSegment::parseTag() const
+{
+  return tags ? tags->parse() : nullptr;
+}
+
+std::unique_ptr<Matroska::Attachments> EBML::MkSegment::parseAttachments() const
+{
+  return attachments ? attachments->parse() : nullptr;
+}
+
+std::unique_ptr<Matroska::Chapters> EBML::MkSegment::parseChapters() const
+{
+  return chapters ? chapters->parse() : nullptr;
+}
+
+std::unique_ptr<Matroska::SeekHead> EBML::MkSegment::parseSeekHead() const
+{
+  return seekHead ? seekHead->parse(segmentDataOffset()) : nullptr;
+}
+
+std::unique_ptr<Matroska::Cues> EBML::MkSegment::parseCues() const
+{
+  return cues ? cues->parse(segmentDataOffset()) : nullptr;
+}
+
+std::unique_ptr<Matroska::Segment> EBML::MkSegment::parseSegment() const
+{
+  return std::make_unique<Matroska::Segment>(sizeLength, dataSize, offset + idSize(id));
+}
+
+void EBML::MkSegment::parseInfo(Matroska::Properties *properties) const
+{
+  if(info) {
+    info->parse(properties);
+  }
+}
+
+void EBML::MkSegment::parseTracks(Matroska::Properties *properties) const
+{
+  if(tracks) {
+    tracks->parse(properties);
+  }
+}

taglib/matroska/ebml/ebmlmksegment.h

@@ -0,0 +1,77 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKSEGMENT_H
+#define TAGLIB_EBMLMKSEGMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "ebmlmktags.h"
+#include "ebmlmkattachments.h"
+#include "ebmlmkchapters.h"
+#include "ebmlmkseekhead.h"
+#include "ebmlmkcues.h"
+#include "ebmlmkinfo.h"
+#include "ebmlmktracks.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Tag;
+    class Attachments;
+    class Chapters;
+    class SeekHead;
+    class Segment;
+  }
+
+  namespace EBML {
+    class MkSegment : public MasterElement
+    {
+    public:
+      MkSegment(int sizeLength, offset_t dataSize, offset_t offset);
+      MkSegment(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      ~MkSegment() override;
+
+      offset_t segmentDataOffset() const;
+      bool read(File &file) override;
+      bool readLimited(File &file, offset_t scanLimit);
+      std::unique_ptr<Matroska::Tag> parseTag() const;
+      std::unique_ptr<Matroska::Attachments> parseAttachments() const;
+      std::unique_ptr<Matroska::Chapters> parseChapters() const;
+      std::unique_ptr<Matroska::SeekHead> parseSeekHead() const;
+      std::unique_ptr<Matroska::Cues> parseCues() const;
+      std::unique_ptr<Matroska::Segment> parseSegment() const;
+      void parseInfo(Matroska::Properties *properties) const;
+      void parseTracks(Matroska::Properties *properties) const;
+
+    private:
+      std::unique_ptr<MkTags> tags;
+      std::unique_ptr<MkAttachments> attachments;
+      std::unique_ptr<MkChapters> chapters;
+      std::unique_ptr<MkSeekHead> seekHead;
+      std::unique_ptr<MkCues> cues;
+      std::unique_ptr<MkInfo> info;
+      std::unique_ptr<MkTracks> tracks;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmktags.cpp

@@ -0,0 +1,131 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmktags.h"
+#include "ebmlbinaryelement.h"
+#include "ebmluintelement.h"
+#include "ebmlstringelement.h"
+#include "matroskatag.h"
+#include "matroskasimpletag.h"
+#include "tlist.h"
+
+using namespace TagLib;
+
+EBML::MkTags::MkTags(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkTags, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkTags::MkTags(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkTags, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkTags::MkTags():
+  MasterElement(Id::MkTags, 0, 0, 0)
+{
+}
+
+std::unique_ptr<Matroska::Tag> EBML::MkTags::parse() const
+{
+  auto mTag = std::make_unique<Matroska::Tag>();
+  mTag->setOffset(offset);
+  mTag->setSize(getSize() + padding);
+  mTag->setID(static_cast<Matroska::Element::ID>(id));
+
+  // Loop through each <Tag> element
+  for(const auto &tagsChild : elements) {
+    if(tagsChild->getId() != Id::MkTag)
+      continue;
+    const auto tag = element_cast<Id::MkTag>(tagsChild);
+    List<const MasterElement *> simpleTags;
+    const MasterElement *targets = nullptr;
+
+    // Identify the <Targets> element and the <SimpleTag> elements
+    for(const auto &tagChild : *tag) {
+      if(const Id tagChildId = tagChild->getId(); !targets && tagChildId == Id::MkTagTargets)
+        targets = element_cast<Id::MkTagTargets>(tagChild);
+      else if(tagChildId == Id::MkSimpleTag)
+        simpleTags.append(element_cast<Id::MkSimpleTag>(tagChild));
+    }
+
+    // Parse the <Targets> element
+    Matroska::SimpleTag::TargetTypeValue targetTypeValue = Matroska::SimpleTag::TargetTypeValue::None;
+    unsigned long long trackUid = 0;
+    unsigned long long edtionUid = 0;
+    unsigned long long chapterUid = 0;
+    unsigned long long attachmentUid = 0;
+    if(targets) {
+      for(const auto &targetsChild : *targets) {
+        if(const Id id = targetsChild->getId(); id == Id::MkTagTargetTypeValue
+            && targetTypeValue == Matroska::SimpleTag::TargetTypeValue::None) {
+          targetTypeValue = static_cast<Matroska::SimpleTag::TargetTypeValue>(
+            element_cast<Id::MkTagTargetTypeValue>(targetsChild)->getValue()
+          );
+        }
+        else if(id == Id::MkTagTrackUID) {
+          trackUid = element_cast<Id::MkTagTrackUID>(targetsChild)->getValue();
+        }
+        else if(id == Id::MkTagEditionUID) {
+          edtionUid = element_cast<Id::MkTagEditionUID>(targetsChild)->getValue();
+        }
+        else if(id == Id::MkTagChapterUID) {
+          chapterUid = element_cast<Id::MkTagChapterUID>(targetsChild)->getValue();
+        }
+        else if(id == Id::MkTagAttachmentUID) {
+          attachmentUid = element_cast<Id::MkTagAttachmentUID>(targetsChild)->getValue();
+        }
+      }
+    }
+
+    // Parse each <SimpleTag>
+    for(const auto simpleTag : simpleTags) {
+      const String *tagValueString = nullptr;
+      const ByteVector *tagValueBinary = nullptr;
+      String tagName;
+      String language;
+      bool defaultLanguageFlag = true;
+
+      for(const auto &simpleTagChild : *simpleTag) {
+        if(const Id id = simpleTagChild->getId(); id == Id::MkTagName && tagName.isEmpty())
+          tagName = element_cast<Id::MkTagName>(simpleTagChild)->getValue();
+        else if(id == Id::MkTagString && !tagValueString)
+          tagValueString = &element_cast<Id::MkTagString>(simpleTagChild)->getValue();
+        else if(id == Id::MkTagBinary && !tagValueBinary)
+          tagValueBinary = &element_cast<Id::MkTagBinary>(simpleTagChild)->getValue();
+        else if(id == Id::MkTagsTagLanguage && language.isEmpty())
+          language = element_cast<Id::MkTagsTagLanguage>(simpleTagChild)->getValue();
+        else if(id == Id::MkTagsLanguageDefault)
+          defaultLanguageFlag = element_cast<Id::MkTagsLanguageDefault>(simpleTagChild)->getValue() ? true : false;
+      }
+      if(tagName.isEmpty() || (tagValueString && tagValueBinary) || (!tagValueString && !tagValueBinary))
+        continue;
+
+      mTag->addSimpleTag(tagValueString
+        ? Matroska::SimpleTag(tagName, *tagValueString,
+                             targetTypeValue, language, defaultLanguageFlag,
+                             trackUid, edtionUid, chapterUid, attachmentUid)
+        : Matroska::SimpleTag(tagName, *tagValueBinary,
+                             targetTypeValue, language, defaultLanguageFlag,
+                             trackUid, edtionUid, chapterUid, attachmentUid));
+    }
+  }
+  return mTag;
+}

taglib/matroska/ebml/ebmlmktags.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKTAGS_H
+#define TAGLIB_EBMLMKTAGS_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Tag;
+  }
+
+  namespace EBML {
+    class MkTags : public MasterElement
+    {
+    public:
+      MkTags(int sizeLength, offset_t dataSize, offset_t offset);
+      MkTags(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkTags();
+
+      std::unique_ptr<Matroska::Tag> parse() const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlmktracks.cpp

@@ -0,0 +1,86 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlmktracks.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "ebmlfloatelement.h"
+#include "matroskaproperties.h"
+
+using namespace TagLib;
+
+EBML::MkTracks::MkTracks(int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkTracks, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkTracks::MkTracks(Id, int sizeLength, offset_t dataSize, offset_t offset):
+  MasterElement(Id::MkTracks, sizeLength, dataSize, offset)
+{
+}
+
+EBML::MkTracks::MkTracks():
+  MasterElement(Id::MkTracks, 0, 0, 0)
+{
+}
+
+void EBML::MkTracks::parse(Matroska::Properties *properties) const
+{
+  if(!properties)
+    return;
+
+  for(const auto &element : elements) {
+    if(element->getId() != Id::MkTrackEntry)
+      continue;
+
+    String codecId;
+    double samplingFrequency = 0.0;
+    unsigned long long bitDepth = 0;
+    unsigned long long channels = 0;
+    const auto trackEntry = element_cast<Id::MkTrackEntry>(element);
+    for(const auto &trackEntryChild : *trackEntry) {
+      if(const Id trackEntryChildId = trackEntryChild->getId(); trackEntryChildId == Id::MkCodecID)
+        codecId = element_cast<Id::MkCodecID>(trackEntryChild)->getValue();
+      else if(trackEntryChildId == Id::MkAudio) {
+        const auto audio = element_cast<Id::MkAudio>(trackEntryChild);
+        for(const auto &audioChild : *audio) {
+          if(const Id audioChildId = audioChild->getId(); audioChildId == Id::MkSamplingFrequency)
+            samplingFrequency = element_cast<Id::MkSamplingFrequency>(audioChild)->getValueAsDouble();
+          else if(audioChildId == Id::MkBitDepth)
+            bitDepth = element_cast<Id::MkBitDepth>(audioChild)->getValue();
+          else if(audioChildId == Id::MkChannels)
+            channels = element_cast<Id::MkChannels>(audioChild)->getValue();
+        }
+      }
+    }
+    if(bitDepth || channels) {
+      properties->setSampleRate(static_cast<int>(samplingFrequency));
+      properties->setBitsPerSample(static_cast<int>(bitDepth));
+      properties->setChannels(static_cast<int>(channels));
+      properties->setCodecName(codecId);
+      return;
+    }
+  }
+}

taglib/matroska/ebml/ebmlmktracks.h

@@ -0,0 +1,52 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLMKTRACKS_H
+#define TAGLIB_EBMLMKTRACKS_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlmasterelement.h"
+#include "taglib.h"
+
+namespace TagLib {
+  namespace Matroska {
+    class Properties;
+  }
+
+  namespace EBML {
+    class MkTracks : public MasterElement
+    {
+    public:
+      MkTracks(int sizeLength, offset_t dataSize, offset_t offset);
+      MkTracks(Id, int sizeLength, offset_t dataSize, offset_t offset);
+      MkTracks();
+
+      void parse(Matroska::Properties *properties) const;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlstringelement.cpp

@@ -0,0 +1,100 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlstringelement.h"
+#include <string>
+#include "tfile.h"
+#include "tbytevector.h"
+#include "tdebug.h"
+#include "ebmlutils.h"
+
+using namespace TagLib;
+
+EBML::StringElement::StringElement(
+  String::Type stringEncoding, Id id, int sizeLength, offset_t dataSize):
+  Element(id, sizeLength, dataSize), encoding(stringEncoding)
+{
+}
+
+const String& EBML::StringElement::getValue() const
+{
+  return value;
+}
+
+void EBML::StringElement::setValue(const String& val)
+{
+  value = val;
+}
+
+bool EBML::StringElement::read(File &file)
+{
+  ByteVector buffer = file.readBlock(dataSize);
+  if(buffer.size() != dataSize) {
+    debug("Failed to read string");
+    return false;
+  }
+
+  // The EBML strings aren't supposed to be null-terminated,
+  // but we'll check for it and strip the null terminator if found
+  if(const int nullByte = buffer.find('\0'); nullByte >= 0)
+    buffer = ByteVector(buffer.data(), nullByte);
+  value = String(buffer, encoding);
+  return true;
+}
+
+ByteVector EBML::StringElement::render()
+{
+  ByteVector buffer = renderId();
+  const std::string string = value.to8Bit(encoding == String::UTF8);
+  dataSize = string.size();
+  buffer.append(renderVINT(dataSize, 0));
+  buffer.append(ByteVector(string.data(), static_cast<unsigned int>(dataSize)));
+  return buffer;
+}
+
+EBML::UTF8StringElement::UTF8StringElement(Id id, int sizeLength, offset_t dataSize):
+  StringElement(String::UTF8, id, sizeLength, dataSize)
+{
+}
+
+EBML::UTF8StringElement::UTF8StringElement(Id id, int sizeLength, offset_t dataSize, offset_t):
+  UTF8StringElement(id, sizeLength, dataSize)
+{
+}
+
+EBML::UTF8StringElement::UTF8StringElement(Id id):
+  UTF8StringElement(id, 0, 0)
+{
+}
+
+EBML::Latin1StringElement::Latin1StringElement(Id id, int sizeLength, offset_t dataSize):
+  StringElement(String::Latin1, id, sizeLength, dataSize)
+{
+}
+
+EBML::Latin1StringElement::Latin1StringElement(Id id, int sizeLength, offset_t dataSize, offset_t):
+  Latin1StringElement(id, sizeLength, dataSize)
+{
+}
+
+EBML::Latin1StringElement::Latin1StringElement(Id id):
+  Latin1StringElement(id, 0, 0)
+{
+}

taglib/matroska/ebml/ebmlstringelement.h

@@ -0,0 +1,65 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLSTRINGELEMENT_H
+#define TAGLIB_EBMLSTRINGELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlelement.h"
+#include "tstring.h"
+
+namespace TagLib {
+  class File;
+  class ByteVector;
+
+  namespace EBML {
+    class StringElement : public Element
+    {
+    public:
+      StringElement(String::Type stringEncoding, Id id, int sizeLength, offset_t dataSize);
+
+      const String &getValue() const;
+      void setValue(const String &val);
+      bool read(File &file) override;
+      ByteVector render() override;
+
+    private:
+      String value;
+      String::Type encoding;
+    };
+
+    class UTF8StringElement : public StringElement {
+    public:
+      UTF8StringElement(Id id, int sizeLength, offset_t dataSize);
+      UTF8StringElement(Id id, int sizeLength, offset_t dataSize, offset_t);
+      explicit UTF8StringElement(Id id);
+    };
+
+    class Latin1StringElement : public StringElement {
+    public:
+      Latin1StringElement(Id id, int sizeLength, offset_t dataSize);
+      Latin1StringElement(Id id, int sizeLength, offset_t dataSize, offset_t);
+      explicit Latin1StringElement(Id id);
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmluintelement.cpp

@@ -0,0 +1,95 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmluintelement.h"
+#include "ebmlutils.h"
+#include "tbytevector.h"
+#include "tfile.h"
+#include "tutils.h"
+#include "tdebug.h"
+
+using namespace TagLib;
+
+EBML::UIntElement::UIntElement(Id id, int sizeLength, offset_t dataSize):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::UIntElement::UIntElement(Id id, int sizeLength, offset_t dataSize, offset_t):
+  Element(id, sizeLength, dataSize)
+{
+}
+
+EBML::UIntElement::UIntElement(Id id):
+  UIntElement(id, 0, 0)
+{
+}
+
+unsigned long long EBML::UIntElement::getValue() const
+{
+  return value;
+}
+
+void EBML::UIntElement::setValue(unsigned long long val)
+{
+  value = val;
+}
+
+bool EBML::UIntElement::read(File &file)
+{
+  const ByteVector buffer = file.readBlock(dataSize);
+  if(buffer.size() != dataSize) {
+    debug("Failed to read EBML Uint element");
+    return false;
+  }
+  value = buffer.toULongLong(true);
+  return true;
+}
+
+ByteVector EBML::UIntElement::render()
+{
+  int dataSize = 0;
+  if(value <= 0xFFull)
+    dataSize = 1;
+  else if(value <= 0xFFFFull)
+    dataSize = 2;
+  else if(value <= 0xFFFFFFull)
+    dataSize = 3;
+  else if(value <= 0xFFFFFFFFull)
+    dataSize = 4;
+  else if(value <= 0xFFFFFFFFFFull)
+    dataSize = 5;
+  else if(value <= 0xFFFFFFFFFFFFull)
+    dataSize = 6;
+  else if(value <= 0xFFFFFFFFFFFFFFull)
+    dataSize = 7;
+  else if(value <= 0xFFFFFFFFFFFFFFFFull)
+    dataSize = 8;
+
+  ByteVector buffer = renderId();
+  buffer.append(renderVINT(dataSize, 0));
+  uint64_t val = value;
+  static const auto byteOrder = Utils::systemByteOrder();
+  if(byteOrder == Utils::LittleEndian)
+    val = Utils::byteSwap(val);
+
+  buffer.append(ByteVector(reinterpret_cast<char *>(&val) + (sizeof(val) - dataSize), dataSize));
+  return buffer;
+}

taglib/matroska/ebml/ebmluintelement.h

@@ -0,0 +1,50 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLUINTELEMENT_H
+#define TAGLIB_EBMLUINTELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class UIntElement : public Element
+    {
+    public:
+      UIntElement(Id id, int sizeLength, offset_t dataSize);
+      UIntElement(Id id, int sizeLength, offset_t dataSize, offset_t);
+      explicit UIntElement(Id id);
+
+      unsigned long long getValue() const;
+      void setValue(unsigned long long val);
+      bool read(File &file) override;
+      ByteVector render() override;
+
+    private:
+      unsigned long long value = 0;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlutils.cpp

@@ -0,0 +1,122 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlutils.h"
+#include <random>
+#include "tbytevector.h"
+#include "matroskafile.h"
+#include "tutils.h"
+#include "tdebug.h"
+
+using namespace TagLib;
+
+std::unique_ptr<EBML::Element> EBML::findElement(File &file, Element::Id id, offset_t maxOffset)
+{
+  std::unique_ptr<Element> element;
+  while(file.tell() < maxOffset) {
+    element = Element::factory(file);
+    if(!element || element->getId() == id)
+      return element;
+    element->skipData(file);
+    element.reset();
+  }
+  return element;
+}
+
+std::unique_ptr<EBML::Element> EBML::findNextElement(File &file, offset_t maxOffset)
+{
+  return file.tell() < maxOffset ? Element::factory(file) : nullptr;
+}
+
+template <int maxSizeLength>
+unsigned int EBML::VINTSizeLength(uint8_t firstByte)
+{
+  static_assert(maxSizeLength >= 1 && maxSizeLength <= 8);
+  if(!firstByte) {
+    debug("VINT with greater than 8 bytes not allowed");
+    return 0;
+  }
+  uint8_t mask = 0b10000000;
+  unsigned int numBytes = 1;
+  while(!(mask & firstByte)) {
+    numBytes++;
+    mask >>= 1;
+  }
+  if(numBytes > maxSizeLength) {
+    debug(Utils::formatString("VINT size length exceeds %i bytes", maxSizeLength));
+    return 0;
+  }
+  return numBytes;
+}
+
+namespace TagLib::EBML {
+  template unsigned int VINTSizeLength<4>(uint8_t firstByte);
+  template unsigned int VINTSizeLength<8>(uint8_t firstByte);
+}
+
+std::pair<unsigned int, uint64_t> EBML::readVINT(File &file)
+{
+  auto buffer = file.readBlock(1);
+  if(buffer.size() != 1) {
+    debug("Failed to read VINT size");
+    return {0, 0};
+  }
+  unsigned int numBytes = VINTSizeLength<8>(*buffer.begin());
+  if(!numBytes)
+    return {0, 0};
+
+  if(numBytes > 1)
+    buffer.append(file.readBlock(numBytes - 1));
+  const int bitsToShift = static_cast<int>(sizeof(uint64_t) * 8) - 7 * numBytes;
+  const uint64_t mask = 0xFFFFFFFFFFFFFFFF >> bitsToShift;
+  return { numBytes, buffer.toULongLong(true) & mask };
+}
+
+std::pair<unsigned int, uint64_t> EBML::parseVINT(const ByteVector &buffer)
+{
+  if(buffer.isEmpty())
+    return {0, 0};
+
+  unsigned int numBytes = VINTSizeLength<8>(*buffer.begin());
+  if(!numBytes)
+    return {0, 0};
+
+  const int bitsToShift = static_cast<int>(sizeof(uint64_t) * 8) - 7 * numBytes;
+  const uint64_t mask = 0xFFFFFFFFFFFFFFFF >> bitsToShift;
+  return { numBytes, buffer.toULongLong(true) & mask };
+}
+
+ByteVector EBML::renderVINT(uint64_t number, int minSizeLength)
+{
+  const int numBytes = std::max(minSizeLength, minSize(number));
+  number |= 1ULL << (numBytes * 7);
+  static const auto byteOrder = Utils::systemByteOrder();
+  if(byteOrder == Utils::LittleEndian)
+    number = Utils::byteSwap(number);
+  return ByteVector(reinterpret_cast<char *>(&number) + (sizeof(number) - numBytes), numBytes);
+}
+
+unsigned long long EBML::randomUID()
+{
+  static std::random_device device;
+  static std::mt19937 generator(device());
+  static std::uniform_int_distribution<unsigned long long> distribution;
+  return distribution(generator);
+}

taglib/matroska/ebml/ebmlutils.h

@@ -0,0 +1,78 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLUTILS_H
+#define TAGLIB_EBMLUTILS_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <utility>
+#include "taglib.h"
+#include "ebmlelement.h"
+
+namespace TagLib {
+  class File;
+  class ByteVector;
+
+  namespace EBML {
+    std::unique_ptr<Element> findElement(File &file, Element::Id id, offset_t maxOffset);
+    std::unique_ptr<Element> findNextElement(File &file, offset_t maxOffset);
+
+    template <int maxSizeLength>
+    unsigned int VINTSizeLength(uint8_t firstByte);
+
+    std::pair<unsigned int, uint64_t> readVINT(File &file);
+
+    std::pair<unsigned int, uint64_t> parseVINT(const ByteVector &buffer);
+
+    ByteVector renderVINT(uint64_t number, int minSizeLength);
+
+    unsigned long long randomUID();
+
+    constexpr int minSize(uint64_t data)
+    {
+      if(data <= 0x7Fu)
+        return 1;
+      if(data <= 0x3FFFu)
+        return 2;
+      if(data <= 0x1FFFFFu)
+        return 3;
+      if(data <= 0xFFFFFFFu)
+        return 4;
+      if(data <= 0x7FFFFFFFFu)
+        return 5;
+      return 0;
+    }
+
+    constexpr int idSize(Element::Id id)
+    {
+      const auto uintId = static_cast<unsigned int>(id);
+      if(uintId <= 0xFF)
+        return 1;
+      if(uintId <= 0xFFFF)
+        return 2;
+      if(uintId <= 0xFFFFFF)
+        return 3;
+      return 4;
+    }
+  }
+}
+
+#endif
+#endif

taglib/matroska/ebml/ebmlvoidelement.cpp

@@ -0,0 +1,73 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "ebmlvoidelement.h"
+#include <algorithm>
+#include "ebmlutils.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+EBML::VoidElement::VoidElement(int sizeLength, offset_t dataSize):
+  Element(Id::VoidElement, sizeLength, dataSize)
+{
+}
+
+EBML::VoidElement::VoidElement(Id, int sizeLength, offset_t dataSize, offset_t):
+  Element(Id::VoidElement, sizeLength, dataSize)
+{
+}
+
+EBML::VoidElement::VoidElement():
+  Element(Id::VoidElement, 0, 0)
+{
+}
+
+ByteVector EBML::VoidElement::render()
+{
+  offset_t bytesNeeded = targetSize;
+  ByteVector buffer = renderId();
+  bytesNeeded -= buffer.size();
+  sizeLength = static_cast<int>(std::min(bytesNeeded, static_cast<offset_t>(8)));
+  bytesNeeded -= sizeLength;
+  dataSize = bytesNeeded;
+  buffer.append(renderVINT(dataSize, sizeLength));
+  if(dataSize)
+    buffer.append(ByteVector(static_cast<unsigned int>(dataSize), 0));
+
+  return buffer;
+}
+
+offset_t EBML::VoidElement::getTargetSize() const
+{
+  return targetSize;
+}
+
+void EBML::VoidElement::setTargetSize(offset_t size)
+{
+  this->targetSize = std::max(size, MIN_VOID_ELEMENT_SIZE);
+}
+
+ByteVector EBML::VoidElement::renderSize(offset_t targetSize)
+{
+  VoidElement element;
+  element.setTargetSize(targetSize);
+  return element.render();
+}

taglib/matroska/ebml/ebmlvoidelement.h

@@ -0,0 +1,51 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_EBMLVOIDELEMENT_H
+#define TAGLIB_EBMLVOIDELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "ebmlelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    inline constexpr offset_t MIN_VOID_ELEMENT_SIZE = 2;
+    class VoidElement : public Element
+    {
+    public:
+      VoidElement(int sizeLength, offset_t dataSize);
+      VoidElement(Id, int sizeLength, offset_t dataSize, offset_t);
+      VoidElement();
+
+      ByteVector render() override;
+      offset_t getTargetSize() const;
+      void setTargetSize(offset_t size);
+      static ByteVector renderSize(offset_t targetSize);
+
+    private:
+      offset_t targetSize = MIN_VOID_ELEMENT_SIZE;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/matroskaattachedfile.cpp

@@ -0,0 +1,99 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskaattachedfile.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+class Matroska::AttachedFile::AttachedFilePrivate
+{
+public:
+  AttachedFilePrivate(const ByteVector &data, const String &fileName,
+    const String &mediaType, UID uid, const String &description) :
+    fileName(fileName), description(description), mediaType(mediaType),
+    data(data), uid(uid) {}
+  ~AttachedFilePrivate() = default;
+  String fileName;
+  String description;
+  String mediaType;
+  ByteVector data;
+  UID uid = 0;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::AttachedFile::AttachedFile(const ByteVector &data,
+  const String &fileName, const String &mediaType, UID uid,
+  const String &description) :
+  d(std::make_unique<AttachedFilePrivate>(data, fileName, mediaType, uid, description))
+{
+}
+
+Matroska::AttachedFile::AttachedFile(const AttachedFile &other) :
+  d(std::make_unique<AttachedFilePrivate>(*other.d))
+{
+}
+
+Matroska::AttachedFile::AttachedFile(AttachedFile &&other) noexcept = default;
+
+Matroska::AttachedFile::~AttachedFile() = default;
+
+Matroska::AttachedFile &Matroska::AttachedFile::operator=(AttachedFile &&other) noexcept = default;
+
+Matroska::AttachedFile &Matroska::AttachedFile::operator=(const AttachedFile &other)
+{
+  AttachedFile(other).swap(*this);
+  return *this;
+}
+
+void Matroska::AttachedFile::swap(AttachedFile &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+const String &Matroska::AttachedFile::fileName() const
+{
+  return d->fileName;
+}
+
+const String &Matroska::AttachedFile::description() const
+{
+  return d->description;
+}
+
+const String &Matroska::AttachedFile::mediaType() const
+{
+  return d->mediaType;
+}
+
+const ByteVector &Matroska::AttachedFile::data() const
+{
+  return d->data;
+}
+
+Matroska::AttachedFile::UID Matroska::AttachedFile::uid() const
+{
+  return d->uid;
+}

taglib/matroska/matroskaattachedfile.h

@@ -0,0 +1,110 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAATTACHEDFILE_H
+#define TAGLIB_MATROSKAATTACHEDFILE_H
+
+#include <memory>
+#include "tstring.h"
+#include "taglib_export.h"
+
+namespace TagLib {
+  class String;
+  class ByteVector;
+
+  namespace Matroska {
+    //! Attached file embedded into a Matroska file.
+    class TAGLIB_EXPORT AttachedFile
+    {
+    public:
+      //! Unique identifier.
+      using UID = unsigned long long;
+
+      /*!
+       * Construct an attached file.
+       */
+      AttachedFile(const ByteVector &data, const String &fileName,
+                   const String &mediaType, UID uid = 0,
+                   const String &description = String());
+
+      /*!
+       * Construct an attached file as a copy of \a other.
+       */
+      AttachedFile(const AttachedFile &other);
+
+      /*!
+       * Construct an attached file moving from \a other.
+       */
+      AttachedFile(AttachedFile &&other) noexcept;
+
+      /*!
+       * Destroys this attached file.
+       */
+      ~AttachedFile();
+
+      /*!
+       * Copies the contents of \a other into this object.
+       */
+      AttachedFile &operator=(const AttachedFile &other);
+
+      /*!
+       * Moves the contents of \a other into this object.
+       */
+      AttachedFile &operator=(AttachedFile &&other) noexcept;
+
+      /*!
+       * Exchanges the content of the object with the content of \a other.
+       */
+      void swap(AttachedFile &other) noexcept;
+
+      /*!
+       * Returns the filename of the attached file.
+       */
+      const String &fileName() const;
+
+      /*!
+       * Returns the human-friendly description for the attached file.
+       */
+      const String &description() const;
+
+      /*!
+       * Returns the media type of the attached file.
+       */
+      const String &mediaType() const;
+
+      /*!
+       * Returns the data of the attached file.
+       */
+      const ByteVector &data() const;
+
+      /*!
+       * Returns the UID of the attached file.
+       */
+      UID uid() const;
+
+    private:
+      class AttachedFilePrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<AttachedFilePrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskaattachments.cpp

@@ -0,0 +1,150 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskaattachments.h"
+#include "matroskaattachedfile.h"
+#include "ebmlmkattachments.h"
+#include "ebmlmasterelement.h"
+#include "ebmlstringelement.h"
+#include "ebmlbinaryelement.h"
+#include "ebmluintelement.h"
+#include "ebmlutils.h"
+#include "tlist.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+class Matroska::Attachments::AttachmentsPrivate
+{
+public:
+  AttachmentsPrivate() = default;
+  ~AttachmentsPrivate() = default;
+  AttachmentsPrivate(const AttachmentsPrivate &) = delete;
+  AttachmentsPrivate &operator=(const AttachmentsPrivate &) = delete;
+  AttachedFileList files;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::Attachments::Attachments() :
+  Element(static_cast<ID>(EBML::Element::Id::MkAttachments)),
+  d(std::make_unique<AttachmentsPrivate>())
+{
+}
+
+Matroska::Attachments::~Attachments() = default;
+
+void Matroska::Attachments::addAttachedFile(const AttachedFile &file)
+{
+  d->files.append(file);
+  setNeedsRender(true);
+}
+
+void Matroska::Attachments::removeAttachedFile(unsigned long long uid)
+{
+  const auto it = std::find_if(d->files.begin(), d->files.end(),
+    [uid](const AttachedFile &file) {
+      return file.uid() == uid;
+    });
+  if(it != d->files.end()) {
+    d->files.erase(it);
+    setNeedsRender(true);
+  }
+}
+
+void Matroska::Attachments::clear()
+{
+  d->files.clear();
+  setNeedsRender(true);
+}
+
+const Matroska::Attachments::AttachedFileList &Matroska::Attachments::attachedFileList() const
+{
+  return d->files;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// private members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::Attachments::AttachedFileList &Matroska::Attachments::attachedFiles()
+{
+  setNeedsRender(true);
+  return d->files;
+}
+
+ByteVector Matroska::Attachments::renderInternal()
+{
+  if(d->files.isEmpty()) {
+    // Avoid writing an Attachments element without AttachedFile element.
+    return {};
+  }
+
+  EBML::MkAttachments attachments;
+  for(const auto &attachedFile : std::as_const(d->files)) {
+    auto attachedFileElement = EBML::make_unique_element<EBML::Element::Id::MkAttachedFile>();
+
+    // Filename
+    auto fileNameElement = EBML::make_unique_element<EBML::Element::Id::MkAttachedFileName>();
+    fileNameElement->setValue(attachedFile.fileName());
+    attachedFileElement->appendElement(std::move(fileNameElement));
+
+    // Media/MIME type
+    auto mediaTypeElement =
+      EBML::make_unique_element<EBML::Element::Id::MkAttachedFileMediaType>();
+    mediaTypeElement->setValue(attachedFile.mediaType());
+    attachedFileElement->appendElement(std::move(mediaTypeElement));
+
+    // Description
+    if(const String &description = attachedFile.description(); !description.isEmpty()) {
+      auto descriptionElement =
+        EBML::make_unique_element<EBML::Element::Id::MkAttachedFileDescription>();
+      descriptionElement->setValue(description);
+      attachedFileElement->appendElement(std::move(descriptionElement));
+    }
+
+    // Data
+    auto dataElement = EBML::make_unique_element<EBML::Element::Id::MkAttachedFileData>();
+    dataElement->setValue(attachedFile.data());
+    attachedFileElement->appendElement(std::move(dataElement));
+
+    // UID
+    auto uidElement = EBML::make_unique_element<EBML::Element::Id::MkAttachedFileUID>();
+    AttachedFile::UID uid = attachedFile.uid();
+    if(!uid)
+      uid = EBML::randomUID();
+    uidElement->setValue(uid);
+    attachedFileElement->appendElement(std::move(uidElement));
+
+    attachments.appendElement(std::move(attachedFileElement));
+  }
+  // Pad to the previous size so the element keeps its slot in the file,
+  // unless this element is the trailing element of the segment in
+  // AvoidInsert mode -- shrinking from the end never inserts anything.
+  if(writeStyle() != WriteStyle::Compact &&
+     !(writeStyle() == WriteStyle::AvoidInsert && isTrailingInSegment())) {
+    const auto beforeSize = sizeRenderedOrWritten();
+    if(beforeSize > 0)
+      attachments.setMinRenderSize(beforeSize);
+  }
+  return attachments.render();
+}

taglib/matroska/matroskaattachments.h

@@ -0,0 +1,83 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAATTACHMENTS_H
+#define TAGLIB_MATROSKAATTACHMENTS_H
+
+#include <memory>
+#include "taglib_export.h"
+#include "tlist.h"
+#include "matroskaelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class MkAttachments;
+  }
+
+  namespace Matroska {
+    class AttachedFile;
+    class File;
+
+    //! Collection of attached files.
+    class TAGLIB_EXPORT Attachments
+#ifndef DO_NOT_DOCUMENT
+      : private Element
+#endif
+    {
+    public:
+      //! List of attached files.
+      using AttachedFileList = List<AttachedFile>;
+
+      //! Construct attachments.
+      Attachments();
+
+      //! Destroy attachments.
+      virtual ~Attachments();
+
+      //! Add an attached file.
+      void addAttachedFile(const AttachedFile &file);
+
+      //! Remove an attached file.
+      void removeAttachedFile(unsigned long long uid);
+
+      //! Remove all attached files.
+      void clear();
+
+      //! Get list of all attached files.
+      const AttachedFileList &attachedFileList() const;
+
+    private:
+      friend class EBML::MkAttachments;
+      friend class File;
+      class AttachmentsPrivate;
+
+      // private Element implementation
+      ByteVector renderInternal() override;
+      AttachedFileList &attachedFiles();
+
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<AttachmentsPrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskachapter.cpp

@@ -0,0 +1,157 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskachapter.h"
+#include "tstring.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+class Matroska::Chapter::Display::DisplayPrivate
+{
+public:
+  DisplayPrivate() = default;
+  ~DisplayPrivate() = default;
+  String string;
+  String language;
+};
+
+class Matroska::Chapter::ChapterPrivate
+{
+public:
+  ChapterPrivate() = default;
+  ~ChapterPrivate() = default;
+  UID uid = 0;
+  Time timeStart = 0;
+  Time timeEnd = 0;
+  List<Display> displayList;
+  bool hidden = false;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::Chapter::Chapter(Time timeStart, Time timeEnd,
+  const List<Display> &displayList, UID uid, bool hidden) :
+  d(std::make_unique<ChapterPrivate>())
+{
+  d->uid = uid;
+  d->timeStart = timeStart;
+  d->timeEnd = timeEnd;
+  d->displayList = displayList;
+  d->hidden = hidden;
+}
+
+Matroska::Chapter::Chapter(const Chapter &other) :
+  d(std::make_unique<ChapterPrivate>(*other.d))
+{
+}
+
+Matroska::Chapter::Chapter(Chapter &&other) noexcept = default;
+
+Matroska::Chapter::~Chapter() = default;
+
+Matroska::Chapter &Matroska::Chapter::operator=(Chapter &&other) noexcept = default;
+
+Matroska::Chapter &Matroska::Chapter::operator=(const Chapter &other)
+{
+  Chapter(other).swap(*this);
+  return *this;
+}
+
+void Matroska::Chapter::swap(Chapter &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+Matroska::Chapter::UID Matroska::Chapter::uid() const
+{
+  return d->uid;
+}
+
+Matroska::Chapter::Time Matroska::Chapter::timeStart() const
+{
+  return d->timeStart;
+}
+
+Matroska::Chapter::Time Matroska::Chapter::timeEnd() const
+{
+  return d->timeEnd;
+}
+
+bool Matroska::Chapter::isHidden() const
+{
+  return d->hidden;
+}
+
+const List<Matroska::Chapter::Display> &Matroska::Chapter::displayList() const
+{
+  return d->displayList;
+}
+
+Matroska::Chapter::Display::Display(const String &string, const String &language) :
+  d(std::make_unique<DisplayPrivate>())
+{
+  d->string = string;
+  d->language = language;
+}
+
+Matroska::Chapter::Display::Display(const Display &other) :
+  d(std::make_unique<DisplayPrivate>(*other.d))
+{
+}
+
+Matroska::Chapter::Display::Display(Display &&other) noexcept = default;
+
+Matroska::Chapter::Display::~Display() = default;
+
+Matroska::Chapter::Display &Matroska::Chapter::Display::operator=(const Display &other)
+{
+  Display(other).swap(*this);
+  return *this;
+}
+
+Matroska::Chapter::Display &Matroska::Chapter::Display::operator=(
+  Display &&other) noexcept = default;
+
+void Matroska::Chapter::Display::swap(Display &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+const String &Matroska::Chapter::Display::string() const
+{
+  return d->string;
+}
+
+const String &Matroska::Chapter::Display::language() const
+{
+  return d->language;
+}

taglib/matroska/matroskachapter.h

@@ -0,0 +1,178 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKACHAPTER_H
+#define TAGLIB_MATROSKACHAPTER_H
+
+#include <memory>
+#include "taglib_export.h"
+#include "tlist.h"
+
+namespace TagLib {
+  class String;
+  class ByteVector;
+
+  namespace EBML {
+    class MkChapters;
+  }
+
+  namespace Matroska {
+    //! Matroska chapter.
+    class TAGLIB_EXPORT Chapter
+    {
+    public:
+      //! Unique identifier.
+      using UID = unsigned long long;
+
+      //! Timestamp in nanoseconds.
+      using Time = unsigned long long;
+
+      /*!
+       * Contains all possible strings to use for the chapter display.
+       */
+      class TAGLIB_EXPORT Display
+      {
+      public:
+        /*!
+         * Construct a chapter display.
+         */
+        Display(const String &string, const String &language);
+
+        /*!
+         * Construct a chapter display as a copy of \a other.
+         */
+        Display(const Display &other);
+
+        /*!
+         * Construct a chapter display moving from \a other.
+         */
+        Display(Display &&other) noexcept;
+
+        /*!
+         * Destroys this chapter display.
+         */
+        ~Display();
+
+        /*!
+         * Copies the contents of \a other into this object.
+         */
+        Display &operator=(const Display &other);
+
+        /*!
+         * Moves the contents of \a other into this object.
+         */
+        Display &operator=(Display &&other) noexcept;
+
+        /*!
+         * Exchanges the content of the object with the content of \a other.
+         */
+        void swap(Display &other) noexcept;
+
+        /*!
+         * Returns string representing the chapter.
+         */
+        const String &string() const;
+
+        /*!
+         * Returns language corresponding to the string.
+         */
+        const String &language() const;
+
+      private:
+        class DisplayPrivate;
+        TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+        std::unique_ptr<DisplayPrivate> d;
+      };
+
+      /*!
+       * Construct a chapter.
+       */
+      Chapter(Time timeStart, Time timeEnd, const List<Display> &displayList,
+        UID uid, bool hidden = false);
+
+      /*!
+       * Construct a chapter as a copy of \a other.
+       */
+      Chapter(const Chapter &other);
+
+      /*!
+       * Construct a chapter moving from \a other.
+       */
+      Chapter(Chapter &&other) noexcept;
+
+      /*!
+       * Destroys this chapter.
+       */
+      ~Chapter();
+
+      /*!
+       * Copies the contents of \a other into this object.
+       */
+      Chapter &operator=(const Chapter &other);
+
+      /*!
+       * Moves the contents of \a other into this object.
+       */
+      Chapter &operator=(Chapter &&other) noexcept;
+
+      /*!
+       * Exchanges the content of the object with the content of \a other.
+       */
+      void swap(Chapter &other) noexcept;
+
+      /*!
+       * Returns the UID of the chapter.
+       */
+      UID uid() const;
+
+      /*!
+       * Returns the timestamp of the start of the chapter in nanoseconds.
+       */
+      Time timeStart() const;
+
+      /*!
+       * Returns the timestamp of the start of the chapter in nanoseconds.
+       */
+      Time timeEnd() const;
+
+      /*!
+       * Check if chapter is hidden.
+       */
+      bool isHidden() const;
+
+      /*!
+       * Returns strings with language.
+       */
+      const List<Display> &displayList() const;
+
+    private:
+      class ChapterPrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<ChapterPrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskachapteredition.cpp

@@ -0,0 +1,102 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskachapter.h"
+#include "matroskachapteredition.h"
+#include "tstring.h"
+#include "tbytevector.h"
+#include "tlist.h"
+
+using namespace TagLib;
+
+class Matroska::ChapterEdition::ChapterEditionPrivate
+{
+public:
+  ChapterEditionPrivate() = default;
+  ~ChapterEditionPrivate() = default;
+  List<Chapter> chapters;
+  UID uid = 0;
+  bool flagDefault = false;
+  bool flagOrdered = false;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::ChapterEdition::ChapterEdition(const List<Chapter> &chapterList,
+        bool isDefault, bool isOrdered, UID uid) :
+  d(std::make_unique<ChapterEditionPrivate>())
+{
+  d->chapters = chapterList;
+  d->uid = uid;
+  d->flagDefault = isDefault;
+  d->flagOrdered = isOrdered;
+}
+
+Matroska::ChapterEdition::ChapterEdition(const ChapterEdition &other) :
+  d(std::make_unique<ChapterEditionPrivate>(*other.d))
+{
+}
+
+Matroska::ChapterEdition::ChapterEdition(ChapterEdition &&other) noexcept = default;
+
+Matroska::ChapterEdition::~ChapterEdition() = default;
+
+Matroska::ChapterEdition &Matroska::ChapterEdition::operator=(
+  ChapterEdition &&other) noexcept = default;
+
+Matroska::ChapterEdition &Matroska::ChapterEdition::operator=(const ChapterEdition &other)
+{
+  ChapterEdition(other).swap(*this);
+  return *this;
+}
+
+void Matroska::ChapterEdition::swap(ChapterEdition &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+Matroska::ChapterEdition::UID Matroska::ChapterEdition::uid() const
+{
+  return d->uid;
+}
+
+bool Matroska::ChapterEdition::isDefault() const
+{
+  return d->flagDefault;
+}
+
+bool Matroska::ChapterEdition::isOrdered() const
+{
+  return d->flagOrdered;
+}
+
+const List<Matroska::Chapter> &Matroska::ChapterEdition::chapterList() const
+{
+  return d->chapters;
+}

taglib/matroska/matroskachapteredition.h

@@ -0,0 +1,108 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKACHAPTEREDITION_H
+#define TAGLIB_MATROSKACHAPTEREDITION_H
+
+#include "matroskachapter.h"
+
+namespace TagLib {
+  class String;
+  class ByteVector;
+
+  namespace Matroska {
+    //! Edition of chapters.
+    class TAGLIB_EXPORT ChapterEdition
+    {
+    public:
+      //! Unique identifier.
+      using UID = unsigned long long;
+
+      /*!
+       * Construct an edition.
+       */
+      ChapterEdition(const List<Chapter> &chapterList,
+        bool isDefault, bool isOrdered = false, UID uid = 0);
+
+      /*!
+       * Construct an edition as a copy of \a other.
+       */
+      ChapterEdition(const ChapterEdition &other);
+
+      /*!
+       * Construct an edition moving from \a other.
+       */
+      ChapterEdition(ChapterEdition &&other) noexcept;
+
+      /*!
+       * Destroys this edition.
+       */
+      ~ChapterEdition();
+
+      /*!
+       * Copies the contents of \a other into this object.
+       */
+      ChapterEdition &operator=(const ChapterEdition &other);
+
+      /*!
+       * Moves the contents of \a other into this object.
+       */
+      ChapterEdition &operator=(ChapterEdition &&other) noexcept;
+
+      /*!
+       * Exchanges the content of the object with the content of \a other.
+       */
+      void swap(ChapterEdition &other) noexcept;
+
+      /*!
+       * Returns the UID of the edition.
+       */
+      UID uid() const;
+
+      /*!
+       * Check if this edition should be used as the default one.
+       */
+      bool isDefault() const;
+
+      /*!
+       * Check if the chapters can be defined multiple times and the order to
+       * play them is enforced.
+       */
+      bool isOrdered() const;
+
+      /*!
+       * Get the list of all chapters.
+       */
+      const List<Chapter> &chapterList() const;
+
+    private:
+      class ChapterEditionPrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<ChapterEditionPrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskachapters.cpp

@@ -0,0 +1,160 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskachapters.h"
+#include "matroskachapteredition.h"
+#include "ebmlstringelement.h"
+#include "ebmlbinaryelement.h"
+#include "ebmlmkchapters.h"
+#include "ebmluintelement.h"
+#include "ebmlutils.h"
+#include "tlist.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+class Matroska::Chapters::ChaptersPrivate
+{
+public:
+  ChaptersPrivate() = default;
+  ~ChaptersPrivate() = default;
+  ChaptersPrivate(const ChaptersPrivate &) = delete;
+  ChaptersPrivate &operator=(const ChaptersPrivate &) = delete;
+  ChapterEditionList editions;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::Chapters::Chapters() :
+  Element(static_cast<ID>(EBML::Element::Id::MkChapters)),
+  d(std::make_unique<ChaptersPrivate>())
+{
+}
+
+Matroska::Chapters::~Chapters() = default;
+
+void Matroska::Chapters::addChapterEdition(const ChapterEdition &edition)
+{
+  d->editions.append(edition);
+  setNeedsRender(true);
+}
+
+void Matroska::Chapters::removeChapterEdition(unsigned long long uid)
+{
+  const auto it = std::find_if(d->editions.begin(), d->editions.end(),
+    [uid](const ChapterEdition &file) {
+      return file.uid() == uid;
+    });
+  if(it != d->editions.end()) {
+    d->editions.erase(it);
+    setNeedsRender(true);
+  }
+}
+
+void Matroska::Chapters::clear()
+{
+  d->editions.clear();
+  setNeedsRender(true);
+}
+
+const Matroska::Chapters::ChapterEditionList &Matroska::Chapters::chapterEditionList() const
+{
+  return d->editions;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// private members
+////////////////////////////////////////////////////////////////////////////////
+ByteVector Matroska::Chapters::renderInternal()
+{
+  if(d->editions.isEmpty()) {
+    // Avoid writing a Chapters element without ChapterEdition element.
+    return {};
+  }
+
+  EBML::MkChapters chapters;
+  for(const auto &chapterEdition : std::as_const(d->editions)) {
+    auto chapterEditionElement = EBML::make_unique_element<EBML::Element::Id::MkEditionEntry>();
+
+    if(const auto uid = chapterEdition.uid()) {
+      auto uidElement = EBML::make_unique_element<EBML::Element::Id::MkEditionUID>();
+      uidElement->setValue(uid);
+      chapterEditionElement->appendElement(std::move(uidElement));
+    }
+    auto defaultElement = EBML::make_unique_element<EBML::Element::Id::MkEditionFlagDefault>();
+    defaultElement->setValue(chapterEdition.isDefault());
+    chapterEditionElement->appendElement(std::move(defaultElement));
+    auto orderedElement = EBML::make_unique_element<EBML::Element::Id::MkEditionFlagOrdered>();
+    orderedElement->setValue(chapterEdition.isOrdered());
+    chapterEditionElement->appendElement(std::move(orderedElement));
+
+    for(const auto &chapter : chapterEdition.chapterList()) {
+      auto chapterElement = EBML::make_unique_element<EBML::Element::Id::MkChapterAtom>();
+
+      auto cuidElement = EBML::make_unique_element<EBML::Element::Id::MkChapterUID>();
+      const auto cuid = chapter.uid();
+      cuidElement->setValue(cuid ? cuid : EBML::randomUID());
+      chapterElement->appendElement(std::move(cuidElement));
+      auto timeStartElement = EBML::make_unique_element<EBML::Element::Id::MkChapterTimeStart>();
+      timeStartElement->setValue(chapter.timeStart());
+      chapterElement->appendElement(std::move(timeStartElement));
+      auto timeEndElement = EBML::make_unique_element<EBML::Element::Id::MkChapterTimeEnd>();
+      timeEndElement->setValue(chapter.timeEnd());
+      chapterElement->appendElement(std::move(timeEndElement));
+      auto hiddenElement = EBML::make_unique_element<EBML::Element::Id::MkChapterFlagHidden>();
+      hiddenElement->setValue(chapter.isHidden());
+      chapterElement->appendElement(std::move(hiddenElement));
+
+      for(const auto &display : chapter.displayList()) {
+        auto displayElement = EBML::make_unique_element<EBML::Element::Id::MkChapterDisplay>();
+
+        auto stringElement = EBML::make_unique_element<EBML::Element::Id::MkChapString>();
+        stringElement->setValue(display.string());
+        displayElement->appendElement(std::move(stringElement));
+        auto languageElement = EBML::make_unique_element<EBML::Element::Id::MkChapLanguage>();
+        languageElement->setValue(display.language());
+        displayElement->appendElement(std::move(languageElement));
+
+        chapterElement->appendElement(std::move(displayElement));
+      }
+
+      chapterEditionElement->appendElement(std::move(chapterElement));
+    }
+
+    chapters.appendElement(std::move(chapterEditionElement));
+  }
+  // Pad to the previous size so the element keeps its slot in the file,
+  // unless this element is the trailing element of the segment in
+  // AvoidInsert mode -- shrinking from the end never inserts anything.
+  if(writeStyle() != WriteStyle::Compact &&
+     !(writeStyle() == WriteStyle::AvoidInsert && isTrailingInSegment())) {
+    const auto beforeSize = sizeRenderedOrWritten();
+    if(beforeSize > 0)
+      chapters.setMinRenderSize(beforeSize);
+  }
+  return chapters.render();
+}

taglib/matroska/matroskachapters.h

@@ -0,0 +1,87 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKACHAPTERS_H
+#define TAGLIB_MATROSKACHAPTERS_H
+
+#include <memory>
+#include "taglib_export.h"
+#include "tlist.h"
+#include "matroskaelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class MkChapters;
+  }
+
+  namespace Matroska {
+    class ChapterEdition;
+    class File;
+
+    //! Collection of chapter editions.
+    class TAGLIB_EXPORT Chapters
+#ifndef DO_NOT_DOCUMENT
+      : private Element
+#endif
+    {
+    public:
+      //! List of chapter editions.
+      using ChapterEditionList = List<ChapterEdition>;
+
+      //! Construct chapters.
+      Chapters();
+
+      //! Destroy chapters.
+      virtual ~Chapters();
+
+      //! Add a chapter edition.
+      void addChapterEdition(const ChapterEdition &edition);
+
+      //! Remove a chapter edition.
+      void removeChapterEdition(unsigned long long uid);
+
+      //! Remove all chapter editions.
+      void clear();
+
+      //! Get list of all chapter editions.
+      const ChapterEditionList &chapterEditionList() const;
+
+    private:
+      friend class EBML::MkChapters;
+      friend class File;
+      class ChaptersPrivate;
+
+      // private Element implementation
+      ByteVector renderInternal() override;
+
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<ChaptersPrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskacues.cpp

@@ -0,0 +1,312 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskacues.h"
+#include "ebmlelement.h"
+#include "ebmlmkcues.h"
+#include "ebmlmasterelement.h"
+#include "ebmluintelement.h"
+#include "tlist.h"
+#include "tdebug.h"
+#include "tfile.h"
+
+using namespace TagLib;
+
+Matroska::Cues::Cues(offset_t segmentDataOffset) :
+  Element(static_cast<ID>(EBML::Element::Id::MkCues)),
+  segmentDataOffset(segmentDataOffset)
+{
+  setNeedsRender(false);
+}
+
+Matroska::Cues::~Cues() = default;
+
+ByteVector Matroska::Cues::renderInternal()
+{
+  const auto beforeSize = sizeRenderedOrWritten();
+  EBML::MkCues cues;
+  cues.setMinRenderSize(beforeSize);
+  for(const auto &cuePoint : cuePoints) {
+    auto cuePointElement = EBML::make_unique_element<EBML::Element::Id::MkCuePoint>();
+    auto timestamp = EBML::make_unique_element<EBML::Element::Id::MkCueTime>();
+    timestamp->setValue(cuePoint->getTime());
+    cuePointElement->appendElement(std::move(timestamp));
+
+    const auto &trackList = cuePoint->cueTrackList();
+    for(const auto &cueTrack : trackList) {
+      auto cueTrackElement = EBML::make_unique_element<EBML::Element::Id::MkCueTrackPositions>();
+
+      // Track number
+      auto trackNumber = EBML::make_unique_element<EBML::Element::Id::MkCueTrack>();
+      trackNumber->setValue(cueTrack->getTrackNumber());
+      cueTrackElement->appendElement(std::move(trackNumber));
+
+      // Cluster position
+      auto clusterPosition = EBML::make_unique_element<EBML::Element::Id::MkCueClusterPosition>();
+      clusterPosition->setValue(cueTrack->getClusterPosition());
+      cueTrackElement->appendElement(std::move(clusterPosition));
+
+      // Relative position, optional
+      if(cueTrack->getRelativePosition().has_value()) {
+        auto relativePosition = EBML::make_unique_element<EBML::Element::Id::MkCueRelativePosition>();
+        // operator*() used instead of value() to support restricted compilers
+        relativePosition->setValue(*cueTrack->getRelativePosition());
+        cueTrackElement->appendElement(std::move(relativePosition));
+      }
+
+      // Duration, optional
+      if(cueTrack->getDuration().has_value()) {
+        auto duration = EBML::make_unique_element<EBML::Element::Id::MkCueDuration>();
+        // operator*() used instead of value() to support restricted compilers
+        duration->setValue(*cueTrack->getDuration());
+        cueTrackElement->appendElement(std::move(duration));
+      }
+
+      // Block number, optional
+      if(cueTrack->getBlockNumber().has_value()) {
+        auto blockNumber = EBML::make_unique_element<EBML::Element::Id::MkCueBlockNumber>();
+        // operator*() used instead of value() to support restricted compilers
+        blockNumber->setValue(*cueTrack->getBlockNumber());
+        cueTrackElement->appendElement(std::move(blockNumber));
+      }
+
+      // Codec state, not in version 1
+      if(cueTrack->getCodecState().has_value()) {
+        auto codecState = EBML::make_unique_element<EBML::Element::Id::MkCueCodecState>();
+        // operator*() used instead of value() to support restricted compilers
+        codecState->setValue(*cueTrack->getCodecState());
+        cueTrackElement->appendElement(std::move(codecState));
+      }
+
+      // Reference times
+      if(auto referenceTimes = cueTrack->referenceTimes(); !referenceTimes.isEmpty()) {
+        auto cueReference = EBML::make_unique_element<EBML::Element::Id::MkCueReference>();
+        for(const auto reference : referenceTimes) {
+          auto refTime = EBML::make_unique_element<EBML::Element::Id::MkCueRefTime>();
+          refTime->setValue(reference);
+          cueReference->appendElement(std::move(refTime));
+        }
+        cueTrackElement->appendElement(std::move(cueReference));
+      }
+      cuePointElement->appendElement(std::move(cueTrackElement));
+    }
+    cues.appendElement(std::move(cuePointElement));
+  }
+  return cues.render();
+}
+
+void Matroska::Cues::write(TagLib::File &file)
+{
+  if(!data().isEmpty())
+    Element::write(file);
+}
+
+bool Matroska::Cues::sizeChanged(Element &caller, offset_t delta)
+{
+  // Adjust own offset
+  if(!Element::sizeChanged(caller, delta))
+    return false;
+
+  const offset_t offset = caller.offset() - segmentDataOffset;
+  for(const auto &cuePoint : cuePoints) {
+    if(cuePoint->adjustOffset(offset, delta)) {
+      setNeedsRender(true);
+    }
+  }
+  return true;
+}
+
+bool Matroska::Cues::isValid(TagLib::File &file) const
+{
+  for(const auto &cuePoint : cuePoints) {
+    if(!cuePoint->isValid(file, segmentDataOffset))
+      return false;
+  }
+  return true;
+}
+
+void Matroska::Cues::addCuePoint(std::unique_ptr<CuePoint> &&cuePoint)
+{
+  cuePoints.push_back(std::move(cuePoint));
+}
+
+const Matroska::Cues::CuePointList &Matroska::Cues::cuePointList()
+{
+  return cuePoints;
+}
+
+Matroska::CuePoint::CuePoint() = default;
+
+Matroska::CuePoint::~CuePoint() = default;
+
+bool Matroska::CuePoint::isValid(TagLib::File &file, offset_t segmentDataOffset) const
+{
+  for(const auto &track : cueTracks) {
+    if(!track->isValid(file, segmentDataOffset))
+      return false;
+  }
+  return true;
+}
+
+void Matroska::CuePoint::addCueTrack(std::unique_ptr<CueTrack> &&cueTrack)
+{
+  cueTracks.push_back(std::move(cueTrack));
+}
+
+const Matroska::CuePoint::CueTrackList &Matroska::CuePoint::cueTrackList() const
+{
+  return cueTracks;
+}
+
+void Matroska::CuePoint::setTime(Time timestamp)
+{
+  time = timestamp;
+}
+
+Matroska::CuePoint::Time Matroska::CuePoint::getTime() const
+{
+  return time;
+}
+
+bool Matroska::CuePoint::adjustOffset(offset_t offset, offset_t delta)
+{
+  bool ret = false;
+  for(const auto &cueTrack : cueTracks)
+    ret |= cueTrack->adjustOffset(offset, delta);
+
+  return ret;
+}
+
+Matroska::CueTrack::CueTrack() = default;
+
+Matroska::CueTrack::~CueTrack() = default;
+
+bool Matroska::CueTrack::isValid(TagLib::File &file, offset_t segmentDataOffset) const
+{
+  if(!trackNumber) {
+    debug("Cue track number not set");
+    return false;
+  }
+  if(!clusterPosition) {
+    debug("Cue track cluster position not set");
+    return false;
+  }
+  file.seek(segmentDataOffset + clusterPosition);
+  if(EBML::Element::readId(file) != static_cast<unsigned int>(EBML::Element::Id::MkCluster)) {
+    debug("No cluster found at position");
+    return false;
+  }
+  if(codecState.has_value() && *codecState != 0) {
+    // operator*() used instead of value() to support restricted compilers
+    file.seek(segmentDataOffset + *codecState);
+    if(EBML::Element::readId(file) != static_cast<unsigned int>(EBML::Element::Id::MkCodecState)) {
+      debug("No codec state found at position");
+      return false;
+    }
+  }
+  return true;
+}
+
+void Matroska::CueTrack::setTrackNumber(unsigned long long trackNr)
+{
+  trackNumber = trackNr;
+}
+
+unsigned long long Matroska::CueTrack::getTrackNumber() const
+{
+  return trackNumber;
+}
+
+void Matroska::CueTrack::setClusterPosition(offset_t clusterPos)
+{
+  clusterPosition = clusterPos;
+}
+
+offset_t Matroska::CueTrack::getClusterPosition() const
+{
+  return clusterPosition;
+}
+
+void Matroska::CueTrack::setRelativePosition(std::optional<offset_t> relativePos)
+{
+  relativePosition = relativePos;
+}
+
+std::optional<offset_t> Matroska::CueTrack::getRelativePosition() const
+{
+  return relativePosition;
+}
+
+void Matroska::CueTrack::setCodecState(std::optional<offset_t> codecStatePos)
+{
+  codecState = codecStatePos;
+}
+
+std::optional<offset_t> Matroska::CueTrack::getCodecState() const
+{
+  return codecState;
+}
+
+void Matroska::CueTrack::setBlockNumber(std::optional<unsigned long long> blockNr)
+{
+  blockNumber = blockNr;
+}
+
+std::optional<unsigned long long> Matroska::CueTrack::getBlockNumber() const
+{
+  return blockNumber;
+}
+
+void Matroska::CueTrack::setDuration(std::optional<unsigned long long> segmentTicks)
+{
+  duration = segmentTicks;
+}
+
+std::optional<unsigned long long> Matroska::CueTrack::getDuration() const
+{
+  return duration;
+}
+
+void Matroska::CueTrack::addReferenceTime(unsigned long long refTime)
+{
+  refTimes.append(refTime);
+}
+
+const Matroska::CueTrack::ReferenceTimeList &Matroska::CueTrack::referenceTimes() const
+{
+  return refTimes;
+}
+
+bool Matroska::CueTrack::adjustOffset(offset_t offset, offset_t delta)
+{
+  bool ret = false;
+  if(clusterPosition > offset) {
+    clusterPosition += delta;
+    ret = true;
+  }
+  // operator*() used instead of value() to support restricted compilers
+  if(offset_t codecStateValue;
+     codecState.has_value() && (codecStateValue = *codecState) != 0 &&
+     codecStateValue > offset) {
+    codecState = codecStateValue + delta;
+    ret = true;
+  }
+  return ret;
+}

taglib/matroska/matroskacues.h

@@ -0,0 +1,116 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKACUES_H
+#define TAGLIB_MATROSKACUES_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <optional>
+
+#include "tlist.h"
+#include "matroskaelement.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class MkCues;
+  }
+
+  namespace Matroska {
+    class CuePoint;
+    class CueTrack;
+
+    class Cues : public Element
+    {
+    public:
+      using CuePointList = std::list<std::unique_ptr<CuePoint>>;
+      explicit Cues(offset_t segmentDataOffset);
+      ~Cues() override;
+      bool isValid(TagLib::File &file) const;
+      void addCuePoint(std::unique_ptr<CuePoint> &&cuePoint);
+      const CuePointList &cuePointList();
+      bool sizeChanged(Element &caller, offset_t delta) override;
+      void write(TagLib::File &file) override;
+
+    private:
+      friend class EBML::MkCues;
+      ByteVector renderInternal() override;
+
+      CuePointList cuePoints;
+      const offset_t segmentDataOffset;
+    };
+
+    class CuePoint
+    {
+    public:
+      using CueTrackList = std::list<std::unique_ptr<CueTrack>>;
+      using Time = unsigned long long;
+      CuePoint();
+      ~CuePoint();
+      bool isValid(TagLib::File &file, offset_t segmentDataOffset) const;
+      void addCueTrack(std::unique_ptr<CueTrack> &&cueTrack);
+      const CueTrackList &cueTrackList() const;
+      void setTime(Time timestamp);
+      Time getTime() const;
+      bool adjustOffset(offset_t offset, offset_t delta);
+
+    private:
+      CueTrackList cueTracks;
+      Time time = 0;
+    };
+
+    class CueTrack
+    {
+    public:
+      using ReferenceTimeList = List<unsigned long long>;
+      CueTrack();
+      ~CueTrack();
+      bool isValid(TagLib::File &file, offset_t segmentDataOffset) const;
+      void setTrackNumber(unsigned long long trackNr);
+      unsigned long long getTrackNumber() const;
+      void setClusterPosition(offset_t clusterPos);
+      offset_t getClusterPosition() const;
+      void setRelativePosition(std::optional<offset_t> relativePos);
+      std::optional<offset_t> getRelativePosition() const;
+      void setCodecState(std::optional<offset_t> codecStatePos);
+      std::optional<offset_t> getCodecState() const;
+      void setBlockNumber(std::optional<unsigned long long> blockNr);
+      std::optional<unsigned long long> getBlockNumber() const;
+      void setDuration(std::optional<unsigned long long> segmentTicks);
+      std::optional<unsigned long long> getDuration() const;
+      void addReferenceTime(unsigned long long refTime);
+      const ReferenceTimeList &referenceTimes() const;
+      bool adjustOffset(offset_t offset, offset_t delta);
+
+    private:
+      unsigned long long trackNumber = 0;
+      offset_t clusterPosition = 0;
+      std::optional<offset_t> relativePosition;
+      std::optional<unsigned long long> blockNumber;
+      std::optional<unsigned long long> duration;
+      std::optional<offset_t> codecState;
+      ReferenceTimeList refTimes;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/matroskaelement.cpp

@@ -0,0 +1,240 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskaelement.h"
+#include <memory>
+#include "tlist.h"
+#include "tfile.h"
+#include "tbytevector.h"
+#include "ebmlvoidelement.h"
+
+using namespace TagLib;
+
+class Matroska::Element::ElementPrivate
+{
+public:
+  ElementPrivate() = default;
+  ~ElementPrivate() = default;
+  ElementPrivate(const ElementPrivate &) = delete;
+  ElementPrivate &operator=(const ElementPrivate &) = delete;
+  offset_t size = 0;
+  offset_t offset = 0;
+  ID id = 0;
+  ByteVector data;
+  List<Element *> sizeListeners;
+  // The default write() implementation will delete an unrendered element,
+  // therefore rendering is required by default and needs to be explicitly set
+  // using setNeedsRender(false) together with overriding the write() method.
+  bool needsRender = true;
+  WriteStyle writeStyle = WriteStyle::Compact;
+  bool isLastElement = true;
+  bool isTrailingInSegment = false;
+  offset_t appendOffset = 0;
+  // Populated during render() for AvoidInsert+grow+non-last: the offset and
+  // original size of the slot that should be overwritten with a Void element.
+  offset_t voidAtOffset = 0;
+  offset_t voidAtSize = 0;
+};
+
+Matroska::Element::Element(ID id) :
+  e(std::make_unique<ElementPrivate>())
+{
+  e->id = id;
+}
+
+Matroska::Element::~Element() = default;
+
+offset_t Matroska::Element::size() const
+{
+  return e->size;
+}
+
+offset_t Matroska::Element::offset() const
+{
+  return e->offset;
+}
+
+void Matroska::Element::setData(const ByteVector &data)
+{
+  e->data = data;
+}
+
+const ByteVector &Matroska::Element::data() const
+{
+  return e->data;
+}
+
+void Matroska::Element::setOffset(offset_t offset)
+{
+  e->offset = offset;
+}
+
+void Matroska::Element::adjustOffset(offset_t delta)
+{
+  e->offset += delta;
+}
+
+void Matroska::Element::setSize(offset_t size)
+{
+  e->size = size;
+}
+
+Matroska::Element::ID Matroska::Element::id() const
+{
+  return e->id;
+}
+
+void Matroska::Element::addSizeListener(Element *element)
+{
+  e->sizeListeners.append(element);
+}
+
+void Matroska::Element::addSizeListeners(const List<Element *> &elements)
+{
+  e->sizeListeners.append(elements);
+}
+
+void Matroska::Element::setID(ID id)
+{
+  e->id = id;
+}
+
+bool Matroska::Element::render()
+{
+  if(!needsRender())
+    return true;
+
+  const auto beforeSize = sizeRenderedOrWritten();
+  const auto data = renderInternal();
+  setNeedsRender(false);
+  if(const auto afterSize = data.size(); afterSize != beforeSize) {
+    if(e->writeStyle == WriteStyle::AvoidInsert && !e->isLastElement
+       && afterSize > beforeSize && beforeSize > 0) {
+      // Record old slot for void-overwrite, move element to end of segment.
+      e->voidAtOffset = e->offset;
+      e->voidAtSize = beforeSize;
+      e->offset = e->appendOffset;
+      // Notify listeners that a new element of afterSize bytes appeared at
+      // appendOffset (which is past all other elements, so no offset shifts).
+      if(!emitSizeChanged(static_cast<offset_t>(afterSize))) {
+        return false;
+      }
+      // Update appendOffset for any subsequent AvoidInsert-grow in this round.
+      e->appendOffset += static_cast<offset_t>(afterSize);
+    }
+    else {
+      if(!emitSizeChanged(afterSize - beforeSize)) {
+        return false;
+      }
+    }
+  }
+
+  setData(data);
+  return true;
+}
+
+void Matroska::Element::setNeedsRender(bool needsRender)
+{
+  e->needsRender = needsRender;
+}
+
+bool Matroska::Element::needsRender() const
+{
+  return e->needsRender;
+}
+
+bool Matroska::Element::emitSizeChanged(offset_t delta)
+{
+  for(const auto element : e->sizeListeners) {
+    if(!element->sizeChanged(*this, delta))
+      return false;
+  }
+  return true;
+}
+
+bool Matroska::Element::sizeChanged(Element &caller, offset_t delta)
+{
+  // The equal case is needed when multiple new elements are added
+  // (e.g. Attachments and Tags), they will start with the same offset
+  // are updated via size change handling.
+  if(caller.offset() <= e->offset && caller.id() != e->id) {
+    e->offset += delta;
+  }
+  return true;
+}
+
+offset_t Matroska::Element::sizeRenderedOrWritten() const
+{
+  const offset_t dataSize = e->data.size();
+  return dataSize != 0 ? dataSize : e->size;
+}
+
+void Matroska::Element::setWriteStyle(WriteStyle style)
+{
+  e->writeStyle = style;
+}
+
+Matroska::WriteStyle Matroska::Element::writeStyle() const
+{
+  return e->writeStyle;
+}
+
+void Matroska::Element::setIsLastElement(bool isLast)
+{
+  e->isLastElement = isLast;
+}
+
+void Matroska::Element::setAppendOffset(offset_t appendOffset)
+{
+  e->appendOffset = appendOffset;
+}
+
+void Matroska::Element::setIsTrailingInSegment(bool isTrailing)
+{
+  e->isTrailingInSegment = isTrailing;
+}
+
+bool Matroska::Element::isTrailingInSegment() const
+{
+  return e->isTrailingInSegment;
+}
+
+bool Matroska::Element::wasMoved() const
+{
+  // voidAtSize is set when the element was moved during render().
+  // After write() it is cleared, but the caller checks before write().
+  return e->voidAtOffset != 0 || e->voidAtSize != 0;
+}
+
+void Matroska::Element::write(File &file)
+{
+  if(e->voidAtSize > 0) {
+    // AvoidInsert: overwrite the old slot with a Void element.
+    const auto voidData = EBML::VoidElement::renderSize(e->voidAtSize);
+    file.insert(voidData, e->voidAtOffset, e->voidAtSize);
+    e->voidAtOffset = 0;
+    // The element was moved to a new position (end of segment),
+    // so there are no existing bytes to replace at the new offset.
+    e->size = 0;
+    e->voidAtSize = 0;
+  }
+  file.insert(e->data, e->offset, e->size);
+  e->size = e->data.size();
+}

taglib/matroska/matroskaelement.h

@@ -0,0 +1,86 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAELEMENT_H
+#define TAGLIB_MATROSKAELEMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include <memory>
+#include "taglib_export.h"
+#include "taglib.h"
+#include "tlist.h"
+#include "matroskawritestyle.h"
+
+namespace TagLib {
+  class File;
+  class ByteVector;
+
+  namespace Matroska {
+    class TAGLIB_EXPORT Element
+    {
+    public:
+      using ID = unsigned int;
+      explicit Element(ID id);
+      virtual ~Element();
+
+      offset_t size() const;
+      offset_t offset() const;
+      ID id() const;
+      void setOffset(offset_t offset);
+      void adjustOffset(offset_t delta);
+      void setSize(offset_t size);
+      void setID(ID id);
+      virtual bool render();
+      void setNeedsRender(bool needsRender);
+      bool needsRender() const;
+      void setData(const ByteVector &data);
+      const ByteVector &data() const;
+      virtual void write(TagLib::File &file);
+      void addSizeListener(Element *element);
+      void addSizeListeners(const List<Element *> &elements);
+      bool emitSizeChanged(offset_t delta);
+      virtual bool sizeChanged(Element &caller, offset_t delta);
+
+      void setWriteStyle(WriteStyle style);
+      WriteStyle writeStyle() const;
+      void setIsLastElement(bool isLast);
+      void setAppendOffset(offset_t appendOffset);
+      bool wasMoved() const;
+      //! Mark this element as the trailing element of the segment (no other
+      //! element follows it in the file). Trailing elements may shrink even
+      //! in non-Compact write styles because no offsets need to be preserved.
+      void setIsTrailingInSegment(bool isTrailing);
+      bool isTrailingInSegment() const;
+
+    protected:
+      offset_t sizeRenderedOrWritten() const;
+
+    private:
+      virtual ByteVector renderInternal() = 0;
+
+      class ElementPrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<ElementPrivate> e;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/matroskafile.cpp

@@ -0,0 +1,695 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskafile.h"
+#include <memory>
+#include "matroskatag.h"
+#include "matroskaattachments.h"
+#include "matroskaattachedfile.h"
+#include "matroskachapter.h"
+#include "matroskachapteredition.h"
+#include "matroskachapters.h"
+#include "matroskaseekhead.h"
+#include "matroskacues.h"
+#include "matroskasegment.h"
+#include "ebmlutils.h"
+#include "ebmlelement.h"
+#include "ebmlstringelement.h"
+#include "ebmluintelement.h"
+#include "ebmlmksegment.h"
+#include "tlist.h"
+#include "tdebug.h"
+#include "tagutils.h"
+#include "tpropertymap.h"
+
+using namespace TagLib;
+
+class Matroska::File::FilePrivate
+{
+public:
+  FilePrivate() = default;
+  ~FilePrivate() = default;
+
+  FilePrivate(const FilePrivate &) = delete;
+  FilePrivate &operator=(const FilePrivate &) = delete;
+
+  std::unique_ptr<Tag> tag;
+  std::unique_ptr<Attachments> attachments;
+  std::unique_ptr<Chapters> chapters;
+  std::unique_ptr<SeekHead> seekHead;
+  std::unique_ptr<Cues> cues;
+  std::unique_ptr<Segment> segment;
+  std::unique_ptr<Properties> properties;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// static members
+////////////////////////////////////////////////////////////////////////////////
+
+bool Matroska::File::isSupported(IOStream *stream)
+{
+  const ByteVector id = Utils::readHeader(stream, 4, false);
+  return id.startsWith("\x1A\x45\xDF\xA3");
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::File::File(FileName file, bool readProperties,
+                     Properties::ReadStyle readStyle) :
+  TagLib::File(file),
+  d(std::make_unique<FilePrivate>())
+{
+  if(!isOpen()) {
+    debug("Failed to open matroska file");
+    setValid(false);
+    return;
+  }
+  read(readProperties, readStyle);
+}
+
+Matroska::File::File(IOStream *stream, bool readProperties,
+                     Properties::ReadStyle readStyle) :
+  TagLib::File(stream),
+  d(std::make_unique<FilePrivate>())
+{
+  if(!isOpen()) {
+    debug("Failed to open matroska file");
+    setValid(false);
+    return;
+  }
+  read(readProperties, readStyle);
+}
+
+Matroska::File::~File() = default;
+
+Matroska::Properties *Matroska::File::audioProperties() const
+{
+  return d->properties.get();
+}
+
+Tag *Matroska::File::tag() const
+{
+  return tag(true);
+}
+
+Matroska::Tag *Matroska::File::tag(bool create) const
+{
+  if(!d->tag && create) {
+    d->tag = std::make_unique<Tag>();
+    if(d->properties) {
+      d->tag->setSegmentTitle(d->properties->title());
+    }
+  }
+  return d->tag.get();
+}
+
+PropertyMap Matroska::File::properties() const
+{
+  return d->tag ? d->tag->properties() : PropertyMap();
+}
+
+void Matroska::File::removeUnsupportedProperties(const StringList &properties)
+{
+  if(d->tag) {
+    d->tag->removeUnsupportedProperties(properties);
+  }
+}
+
+PropertyMap Matroska::File::setProperties(const PropertyMap &properties)
+{
+  if(!d->tag) {
+    d->tag = std::make_unique<Tag>();
+  }
+  return d->tag->setProperties(properties);
+}
+
+namespace {
+
+  constexpr offset_t FAST_SCAN_LIMIT = static_cast<offset_t>(512 * 1024);
+
+  String keyForAttachedFile(const Matroska::AttachedFile &attachedFile)
+  {
+    if(attachedFile.mediaType().startsWith("image/")) {
+      return "PICTURE";
+    }
+    if(!attachedFile.fileName().isEmpty()) {
+      return attachedFile.fileName();
+    }
+    if(!attachedFile.mediaType().isEmpty()) {
+      return attachedFile.mediaType();
+    }
+    return String::fromULongLong(attachedFile.uid());
+  }
+
+  bool keyMatchesAttachedFile(const String &key, const Matroska::AttachedFile &attachedFile)
+  {
+    return !key.isEmpty() && (
+      (key == "PICTURE" && attachedFile.mediaType().startsWith("image/")) ||
+      key == attachedFile.fileName() ||
+      key == attachedFile.mediaType() ||
+      key == String::fromULongLong(attachedFile.uid())
+    );
+  }
+
+}
+
+StringList Matroska::File::complexPropertyKeys() const
+{
+  StringList keys = TagLib::File::complexPropertyKeys();
+  if(d->attachments) {
+    const auto &attachedFiles = d->attachments->attachedFileList();
+    for(const auto &attachedFile : attachedFiles) {
+      if(String key = keyForAttachedFile(attachedFile);
+         !key.isEmpty() && !keys.contains(key)) {
+        keys.append(key);
+      }
+    }
+  }
+  if(d->chapters && !d->chapters->chapterEditionList().isEmpty()) {
+    keys.append("CHAPTERS");
+  }
+  return keys;
+}
+
+List<VariantMap> Matroska::File::complexProperties(const String &key) const
+{
+  List<VariantMap> props = TagLib::File::complexProperties(key);
+  if(key.upper() == "CHAPTERS") {
+    if(d->chapters) {
+      for(const auto &edition : d->chapters->chapterEditionList()) {
+        VariantMap property;
+        if(const auto uid = edition.uid()) {
+          property.insert("uid", uid);
+        }
+        if(const auto isDefault = edition.isDefault()) {
+          property.insert("isDefault", isDefault);
+        }
+        if(const auto isOrdered = edition.isOrdered()) {
+          property.insert("isOrdered", isOrdered);
+        }
+        if(auto chapters = edition.chapterList(); !chapters.isEmpty()) {
+          VariantList chaps;
+          for(const auto &chapter : chapters) {
+            VariantMap chap;
+            if(const auto uid = chapter.uid()) {
+              chap.insert("uid", uid);
+            }
+            if(const auto isHidden = chapter.isHidden()) {
+              chap.insert("isHidden", isHidden);
+            }
+            chap.insert("timeStart", chapter.timeStart());
+            if(const auto timeEnd = chapter.timeEnd()) {
+              chap.insert("timeEnd", timeEnd);
+            }
+            if(auto displays = chapter.displayList(); !displays.isEmpty()) {
+              VariantList disps;
+              for(const auto &display : displays) {
+                VariantMap disp;
+                if(auto str = display.string(); !str.isEmpty()) {
+                  disp.insert("string", str);
+                }
+                if(auto language = display.language(); !language.isEmpty()) {
+                  disp.insert("language", language);
+                }
+                disps.append(disp);
+              }
+              chap.insert("displays", disps);
+            }
+            chaps.append(chap);
+          }
+          property.insert("chapters", chaps);
+        }
+        props.append(property);
+      }
+    }
+  }
+  if(d->attachments) {
+    const auto &attachedFiles = d->attachments->attachedFileList();
+    for(const auto &attachedFile : attachedFiles) {
+      if(keyMatchesAttachedFile(key, attachedFile)) {
+        VariantMap property;
+        property.insert("data", attachedFile.data());
+        property.insert("mimeType", attachedFile.mediaType());
+        property.insert("description", attachedFile.description());
+        property.insert("fileName", attachedFile.fileName());
+        property.insert("uid", attachedFile.uid());
+        props.append(property);
+      }
+    }
+  }
+  return props;
+}
+
+bool Matroska::File::setComplexProperties(const String &key, const List<VariantMap> &value)
+{
+  if(TagLib::File::setComplexProperties(key, value)) {
+    return true;
+  }
+
+  if(key.upper() == "CHAPTERS") {
+    chapters(true)->clear();
+    for(const auto &ed : value) {
+      List<Chapter> editionChapters;
+      const auto chaps = ed.value("chapters").toList();
+      for(const auto &chapVar : chaps) {
+        auto chap = chapVar.toMap();
+        const auto disps = chap.value("displays").toList();
+        List<Chapter::Display> chapterDisplays;
+        for(const auto &dispVar : disps) {
+          auto disp = dispVar.toMap();
+          chapterDisplays.append(Chapter::Display(
+            disp.value("string").toString(),
+            disp.value("language").toString()));
+        }
+        editionChapters.append(Chapter(
+          chap.value("timeStart").toULongLong(),
+          chap.value("timeEnd").toULongLong(),
+          chapterDisplays,
+          chap.value("uid", 0ULL).toULongLong(),
+          chap.value("isHidden", false).toBool()));
+      }
+      d->chapters->addChapterEdition(ChapterEdition(
+        editionChapters,
+        ed.value("isDefault", false).toBool(),
+        ed.value("isOrdered", false).toBool(),
+        ed.value("uid", 0ULL).toULongLong()));
+    }
+    return true;
+  }
+
+  List<AttachedFile> &files = attachments(true)->attachedFiles();
+  for(auto it = files.begin(); it != files.end();) {
+    if(keyMatchesAttachedFile(key, *it)) {
+      it = files.erase(it);
+    }
+    else {
+      ++it;
+    }
+  }
+
+  for(const auto &property : value) {
+    if(property.isEmpty())
+      continue;
+    auto mimeType = property.value("mimeType").value<String>();
+    auto data = property.value("data").value<ByteVector>();
+    auto fileName = property.value("fileName").value<String>();
+    auto uid = property.value("uid").value<unsigned long long>();
+    bool ok;
+    if(key.upper() == "PICTURE" && !mimeType.startsWith("image/")) {
+      mimeType = data.startsWith("\x89PNG\x0d\x0a\x1a\x0a")
+                ? "image/png" : "image/jpeg";
+    }
+    else if(mimeType.isEmpty() && key.find("/") != -1) {
+      mimeType = key;
+    }
+    else if(fileName.isEmpty() && key.find(".") != -1) {
+      fileName = key;
+    }
+    else if(unsigned long long uidKey;
+            !uid && ((uidKey = key.toULongLong(&ok))) && ok) {
+      uid = uidKey;
+    }
+    if(fileName.isEmpty() && !mimeType.isEmpty()) {
+      const int slashPos = mimeType.rfind('/');
+      String ext = mimeType.substr(slashPos + 1);
+      if(ext == "jpeg") {
+        ext = "jpg";
+      }
+      fileName = "attachment." + ext;
+    }
+    if(!mimeType.isEmpty() && !fileName.isEmpty()) {
+      d->attachments->addAttachedFile(AttachedFile(
+        data, fileName, mimeType, uid,
+        property.value("description").value<String>()));
+    }
+  }
+  return true;
+}
+
+Matroska::Attachments *Matroska::File::attachments(bool create) const
+{
+  if(!d->attachments && create)
+    d->attachments = std::make_unique<Attachments>();
+  return d->attachments.get();
+}
+
+Matroska::Chapters *Matroska::File::chapters(bool create) const
+{
+  if(!d->chapters && create)
+    d->chapters = std::make_unique<Chapters>();
+  return d->chapters.get();
+}
+
+void Matroska::File::read(bool readProperties, Properties::ReadStyle readStyle)
+{
+  const offset_t fileLength = length();
+
+  // Find the EBML Header
+  const auto head = EBML::element_cast<EBML::Element::Id::EBMLHeader>(
+    EBML::Element::factory(*this));
+  if(!head || head->getId() != EBML::Element::Id::EBMLHeader) {
+    debug("Failed to find EBML head");
+    setValid(false);
+    return;
+  }
+  if(readProperties) {
+    head->read(*this);
+  }
+  else {
+    head->skipData(*this);
+  }
+
+  offset_t maxOffset = fileLength - tell();
+  if (readStyle == Properties::ReadStyle::Fast && maxOffset > FAST_SCAN_LIMIT) {
+    maxOffset = FAST_SCAN_LIMIT;
+  }
+
+  // Find the Matroska segment in the file
+  const std::unique_ptr<EBML::MkSegment> segment(
+    EBML::element_cast<EBML::Element::Id::MkSegment>(
+      EBML::findElement(*this, EBML::Element::Id::MkSegment, maxOffset)
+    )
+  );
+  if(!segment) {
+    debug("Failed to find Matroska segment");
+    setValid(false);
+    return;
+  }
+
+  // Read the segment into memory from file
+  d->segment = segment->parseSegment();
+  maxOffset = segment->getDataSize();
+  if (readStyle == Properties::ReadStyle::Fast && maxOffset > FAST_SCAN_LIMIT) {
+    maxOffset = FAST_SCAN_LIMIT;
+  }
+  if(!segment->readLimited(*this, maxOffset)) {
+    debug("Failed to read segment");
+    setValid(false);
+    return;
+  }
+
+  // Parse the elements
+  d->seekHead = segment->parseSeekHead();
+  d->cues = segment->parseCues();
+  d->tag = segment->parseTag();
+  d->attachments = segment->parseAttachments();
+  d->chapters = segment->parseChapters();
+
+  if(readProperties) {
+    d->properties = std::make_unique<Properties>(this);
+
+    for(const auto &element : *head) {
+      if(const auto id = element->getId(); id == EBML::Element::Id::DocType) {
+        d->properties->setDocType(
+          EBML::element_cast<EBML::Element::Id::DocType>(element)->getValue());
+      }
+      else if(id == EBML::Element::Id::DocTypeVersion) {
+        d->properties->setDocTypeVersion(static_cast<int>(
+          EBML::element_cast<EBML::Element::Id::DocTypeVersion>(element)->getValue()));
+      }
+    }
+
+    segment->parseInfo(d->properties.get());
+    segment->parseTracks(d->properties.get());
+    if(d->tag) {
+      d->tag->setSegmentTitle(d->properties->title());
+    }
+  }
+
+  if(readStyle == AudioProperties::Accurate &&
+     ((d->seekHead && !d->seekHead->isValid(*this)) ||
+      (d->cues && !d->cues->isValid(*this)))) {
+    setValid(false);
+    return;
+  }
+  setValid(true);
+}
+
+bool Matroska::File::save()
+{
+  return save(WriteStyle::Compact);
+}
+
+bool Matroska::File::save(WriteStyle writeStyle)
+{
+  if(readOnly()) {
+    debug("Matroska::File::save() -- File is read only.");
+    return false;
+  }
+  if(!isValid()) {
+    debug("Matroska::File::save() -- File is not valid.");
+    return false;
+  }
+
+  // Do not create new attachments, chapters or tags and corresponding
+  // seek head entries if only empty objects were created.
+  if(d->chapters && d->chapters->chapterEditionList().isEmpty() &&
+     d->chapters->size() == 0 && d->chapters->offset() == 0 &&
+     d->chapters->data().isEmpty()) {
+    d->chapters.reset();
+  }
+  if(d->attachments && d->attachments->attachedFileList().isEmpty() &&
+     d->attachments->size() == 0 && d->attachments->offset() == 0 &&
+     d->attachments->data().isEmpty()) {
+    d->attachments.reset();
+  }
+  if(d->tag && d->tag->isEmpty() &&
+     d->tag->size() == 0 && d->tag->offset() == 0 &&
+     d->tag->data().isEmpty()) {
+    d->tag.reset();
+  }
+
+  List<Element *> renderList;
+  List<Element *> newElements;
+
+  // List of all possible elements we can write
+  List<Element *> elements {
+    d->chapters.get(),
+    d->attachments.get(),
+    d->tag.get()
+  };
+
+  /* Build render list. New elements will be added
+   * to the end of the file. For new elements,
+   * the order is from least likely to change,
+   * to most likely to change:
+   *   1. Chapters
+   *   2. Attachments
+   *   3. Tags
+   */
+  for(auto element : elements) {
+    if(!element)
+      continue;
+    if(element->size())
+      renderList.append(element);
+    else {
+      element->setOffset(length());
+      newElements.append(element);
+    }
+  }
+  if(renderList.isEmpty() && newElements.isEmpty())
+    return true;
+
+  auto sortAscending = [](const auto a, const auto b) { return a->offset() < b->offset(); };
+  renderList.sort(sortAscending);
+  renderList.append(newElements);
+
+  // Configure write style on each data element. Determines whether elements
+  // may be padded (DoNotShrink/AvoidInsert) or moved to the end (AvoidInsert).
+  // New elements (no prior size) are always written compactly.
+  if(writeStyle != WriteStyle::Compact) {
+    // Determine which existing data element has the highest file offset
+    // (i.e., is "last" among the data elements, before cues/seekHead/segment).
+    // New elements always go after existing ones and are treated as compact.
+    const Element *lastDataElement = nullptr;
+    for(const auto element : renderList) {
+      if(element->size() > 0)
+        lastDataElement = element;
+    }
+
+    // For AvoidInsert: an existing data element (Tags, Chapters, Attachments)
+    // located before the LAST Cluster must not be grown in-place. Doing so
+    // would shift later clusters and invalidate their cue positions. Such
+    // elements are voided at their original position and appended at the
+    // end of the segment instead. The boundary is the maximum cluster offset
+    // (derived from cue-point cluster positions). If no cue points are
+    // available, the Cues element offset is used as a safe upper bound
+    // (Cues are always after the last Cluster). A value of 0 means
+    // "no boundary" – any offset compares >= 0, so the boundary check is
+    // a no-op in non-AvoidInsert modes.
+    offset_t audioBoundary = 0;
+    if(writeStyle == WriteStyle::AvoidInsert && d->cues) {
+      const offset_t segDataOffset = d->segment->dataOffset();
+      for(const auto &cp : d->cues->cuePointList()) {
+        for(const auto &ct : cp->cueTrackList()) {
+          audioBoundary = std::max(audioBoundary,
+            segDataOffset + ct->getClusterPosition());
+        }
+      }
+      if(audioBoundary == 0)
+        audioBoundary = d->cues->offset();
+    }
+
+    for(const auto element : renderList) {
+      if(element->size() > 0) {
+        element->setWriteStyle(writeStyle);
+        // An element is "last" only if it has the highest data-element
+        // offset AND sits past the last cluster. The latter is always true
+        // when audioBoundary == 0 (DoNotShrink, or AvoidInsert without cues).
+        element->setIsLastElement(element == lastDataElement
+                                  && element->offset() >= audioBoundary);
+      }
+    }
+
+    // For AvoidInsert: identify the segment-trailing element (highest offset
+    // among data elements, Cues, SeekHead). The trailing element may shrink
+    // without padding -- there is nothing after it whose offset would shift,
+    // so a trailing void would be wasted space.
+    if(writeStyle == WriteStyle::AvoidInsert) {
+      Element *trailing = nullptr;
+      offset_t maxOffset = 0;
+      const auto consider = [&](Element *e) {
+        if(e && e->size() > 0 && e->offset() > maxOffset) {
+          maxOffset = e->offset();
+          trailing = e;
+        }
+      };
+      for(const auto element : renderList)
+        consider(element);
+      consider(d->cues.get());
+      consider(d->seekHead.get());
+      if(trailing)
+        trailing->setIsTrailingInSegment(true);
+    }
+  }
+
+  // Add our new elements to the Seek Head (if the file has one)
+  if(d->seekHead) {
+    const auto segmentDataOffset = d->segment->dataOffset();
+    for(const auto element : newElements)
+      d->seekHead->addEntry(element->id(), element->offset() - segmentDataOffset);
+    d->seekHead->sort();
+  }
+
+  // Set up listeners, add seek head and segment length to the end
+  for(auto it = renderList.begin(); it != renderList.end(); ++it) {
+    for(auto it2 = std::next(it); it2 != renderList.end(); ++it2)
+      (*it)->addSizeListener(*it2);
+    if(d->cues)
+      (*it)->addSizeListener(d->cues.get());
+    if(d->seekHead)
+      (*it)->addSizeListener(d->seekHead.get());
+    (*it)->addSizeListener(d->segment.get());
+  }
+  if(d->cues) {
+    renderList.append(d->cues.get());
+    d->cues->addSizeListeners(renderList);
+    if(d->seekHead) {
+      d->cues->addSizeListener(d->seekHead.get());
+    }
+    d->cues->addSizeListener(d->segment.get());
+  }
+  if(d->seekHead) {
+    renderList.append(d->seekHead.get());
+    d->seekHead->addSizeListeners(renderList);
+    d->seekHead->addSizeListener(d->segment.get());
+  }
+  d->segment->addSizeListeners(renderList);
+  renderList.append(d->segment.get());
+
+  // Render the elements.
+  // Because size changes of elements can cause segment offset updates and
+  // size changes in other elements, we might need multiple rounds until no more
+  // element needs rendering.
+  int renderRound = 0;
+  bool rendering = true;
+  while(rendering && renderRound < 5) {
+    rendering = false;
+    // Initialize appendOffset for AvoidInsert elements at the start of each round.
+    if(writeStyle == WriteStyle::AvoidInsert) {
+      const offset_t appendOffset = d->segment->endOffset();
+      for(const auto element : renderList)
+        element->setAppendOffset(appendOffset);
+    }
+    for(const auto element : renderList) {
+      if(element->needsRender()) {
+        rendering = true;
+        if(!element->render()) {
+          return false;
+        }
+      }
+    }
+    ++renderRound;
+  }
+
+  // For AvoidInsert: elements that were moved during rendering may have
+  // stale offsets if in-place elements grew after the move was computed.
+  // Re-assign their offsets sequentially from the correct position.
+  if(writeStyle == WriteStyle::AvoidInsert) {
+    // Collect moved elements in render order (= ascending original-offset order
+    // = order they appear in renderList before any re-sort).
+    List<Element *> movedElements;
+    offset_t totalMovedSize = 0;
+    for(const auto element : renderList) {
+      if(element->wasMoved()) {
+        movedElements.append(element);
+        totalMovedSize += static_cast<offset_t>(element->data().size());
+      }
+    }
+    if(!movedElements.isEmpty()) {
+      // The segment end includes in-place growths AND all moved element sizes.
+      // The moved elements start right after all in-place content.
+      offset_t appendAt = d->segment->endOffset() - totalMovedSize;
+      for(const auto element : movedElements) {
+        element->setOffset(appendAt);
+        appendAt += static_cast<offset_t>(element->data().size());
+      }
+    }
+  }
+
+  // For elements that were moved to the end by AvoidInsert, update their
+  // seek head entry to reflect the new file position.
+  if(writeStyle == WriteStyle::AvoidInsert && d->seekHead) {
+    const offset_t segDataOffset = d->segment->dataOffset();
+    for(const auto element : renderList) {
+      if(element->wasMoved()) {
+        d->seekHead->updateEntry(element->id(), element->offset() - segDataOffset);
+      }
+    }
+    // Re-render the seekHead (and anything it affects) after updating entries.
+    // The seekHead slot was pre-padded, so this should not cause size changes.
+    d->seekHead->setNeedsRender(true);
+    for(const auto element : renderList) {
+      if(element->needsRender()) {
+        if(!element->render())
+          return false;
+      }
+    }
+  }
+
+  // Write out to file
+  renderList.sort(sortAscending);
+  for(const auto element : renderList)
+    element->write(*this);
+
+  return true;
+}

taglib/matroska/matroskafile.h

@@ -0,0 +1,194 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAFILE_H
+#define TAGLIB_MATROSKAFILE_H
+
+#include "taglib_export.h"
+#include "tfile.h"
+#include "matroskaproperties.h"
+#include "matroskawritestyle.h"
+
+//! An implementation of Matroska metadata
+namespace TagLib::Matroska {
+  class Tag;
+  class Attachments;
+  class Chapters;
+
+  //! An implementation of TagLib::File with Matroska specific methods
+
+  /*!
+   * Implementation of TagLib::File for Matroska.
+   */
+  class TAGLIB_EXPORT File : public TagLib::File
+  {
+  public:
+    /*!
+     * Constructs a Matroska file from \a file.  If \a readProperties is \c true the
+     * file's audio properties will also be read.
+     *
+     * If \a readStyle is \c Accurate all seek head and cues segment positions
+     * are verified for the isValid() state of the file.
+     */
+    explicit File(FileName file, bool readProperties = true,
+                  Properties::ReadStyle readStyle = Properties::Average);
+
+    /*!
+     * Constructs a Matroska file from \a stream.  If \a readProperties is \c true the
+     * file's audio properties will also be read.
+     *
+     * If \a readStyle is \c Accurate all seek head and cues segment positions
+     * are verified for the isValid() state of the file.
+     */
+    explicit File(IOStream *stream, bool readProperties = true,
+                  Properties::ReadStyle readStyle = Properties::Average);
+
+    /*!
+     * Destroys this instance of the File.
+     */
+    ~File() override;
+
+    File(const File &) = delete;
+    File &operator=(const File &) = delete;
+
+    /*!
+     * Returns a pointer to the tag of the file.
+     *
+     * It will create a tag if one does not exist and returns a valid pointer.
+     *
+     * \note The tag <b>is still</b> owned by the Matroska::File and should not
+     * be deleted by the user.  It will be deleted when the file (object) is
+     * destroyed.
+     */
+    TagLib::Tag *tag() const override;
+
+    /*!
+     * Returns a pointer to the Matroska tag of the file.
+     *
+     * If \a create is \c false this may return a null pointer if there is no tag.
+     * If \a create is \c true it will create a tag if one does not exist and
+     * returns a valid pointer.
+     *
+     * \note The tag <b>is still</b> owned by the Matroska::File and should not
+     * be deleted by the user.  It will be deleted when the file (object)
+     * destroyed.
+     */
+    Tag *tag(bool create) const;
+
+    /*!
+     * Implements the reading part of the unified property interface.
+     */
+    PropertyMap properties() const override;
+
+    void removeUnsupportedProperties(const StringList &properties) override;
+
+    /*!
+     * Implements the writing part of the unified tag dictionary interface.
+     */
+    PropertyMap setProperties(const PropertyMap &) override;
+
+    /*!
+     * Returns the keys for attached files, "PICTURE" for images, the media
+     * type, file name or UID for other attached files.
+     * The names of the binary simple tags are included too.
+     */
+    StringList complexPropertyKeys() const override;
+
+    /*!
+     * Get the pictures stored in the attachments as complex properties
+     * for \a key "PICTURE". Other attached files can be retrieved, by
+     * media type, file name or UID.
+     * The attached files are returned as maps with keys "data", "mimeType",
+     * "description", "fileName, "uid".
+     * Binary simple tags can be retrieved as maps with keys "data", "name",
+     * "targetTypeValue", "language", "defaultLanguage".
+     */
+    List<VariantMap> complexProperties(const String &key) const override;
+
+    /*!
+     * Set attached files as complex properties \a value, e.g. pictures for
+     * \a key "PICTURE" with the maps in \a value having keys "data", "mimeType",
+     * "description", "fileName, "uid". For other attached files, the mime type,
+     * file name or UID can be used as the \a key.
+     * Maps with keys "name" (with the same value as \a key) and "data" are
+     * stored as binary simple tags with additional keys "targetTypeValue",
+     * "language", "defaultLanguage".
+     */
+    bool setComplexProperties(const String &key, const List<VariantMap> &value) override;
+
+    /*!
+     * Returns the Matroska::Properties for this file.  If no audio properties
+     * were read then this will return a null pointer.
+     */
+    Properties *audioProperties() const override;
+
+    /*!
+     * Save the file.
+     *
+     * This returns \c true if the save was successful.
+     */
+    bool save() override;
+
+    /*!
+     * Save the file with the specified write style.
+     *
+     * This returns \c true if the save was successful.
+     */
+    bool save(WriteStyle style);
+
+    /*!
+     * Returns a pointer to the attachments of the file.
+     *
+     * If \a create is \c false this may return a null pointer if there are no
+     * attachments.
+     * If \a create is \c true it will create attachments if none exist and
+     * returns a valid pointer.
+     */
+    Attachments *attachments(bool create = false) const;
+
+    /*!
+     * Returns a pointer to the chapters of the file.
+     *
+     * If \a create is \c false this may return a null pointer if there are no
+     * chapters.
+     * If \a create is \c true it will create chapters if none exist and
+     * returns a valid pointer.
+     */
+    Chapters *chapters(bool create = false) const;
+
+    /*!
+     * Returns whether or not the given \a stream can be opened as a Matroska
+     * file.
+     *
+     * \note This method is designed to do a quick check.  The result may
+     * not necessarily be correct.
+     */
+    static bool isSupported(IOStream *stream);
+
+  private:
+    void read(bool readProperties, Properties::ReadStyle readStyle);
+    class FilePrivate;
+    friend class Properties;
+    TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+    std::unique_ptr<FilePrivate> d;
+  };
+}
+
+#endif

taglib/matroska/matroskaproperties.cpp

@@ -0,0 +1,155 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskaproperties.h"
+
+#include "matroskafile.h"
+
+using namespace TagLib;
+
+class Matroska::Properties::PropertiesPrivate
+{
+public:
+  explicit PropertiesPrivate(File *file) : file(file) {}
+  ~PropertiesPrivate() = default;
+
+  PropertiesPrivate(const PropertiesPrivate &) = delete;
+  PropertiesPrivate &operator=(const PropertiesPrivate &) = delete;
+
+  File *file;
+  String codecName;
+  String title;
+  String docType;
+  int docTypeVersion { 0 };
+  int length { 0 };
+  int bitrate { -1 };
+  int sampleRate { 0 };
+  int channels { 0 };
+  int bitsPerSample { 0 };
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::Properties::Properties(File *file, ReadStyle style) :
+  AudioProperties(style),
+  d(std::make_unique<PropertiesPrivate>(file))
+{
+}
+
+Matroska::Properties::~Properties() = default;
+
+int Matroska::Properties::lengthInMilliseconds() const
+{
+  return d->length;
+}
+
+int Matroska::Properties::bitrate() const
+{
+  if(d->bitrate == -1) {
+    d->bitrate = d->length != 0 ? static_cast<int>(d->file->length() * 8 / d->length) : 0;
+  }
+  return d->bitrate;
+}
+
+int Matroska::Properties::sampleRate() const
+{
+  return d->sampleRate;
+}
+
+int Matroska::Properties::channels() const
+{
+  return d->channels;
+}
+
+int Matroska::Properties::bitsPerSample() const
+{
+  return d->bitsPerSample;
+}
+
+String Matroska::Properties::docType() const
+{
+  return d->docType;
+}
+
+int Matroska::Properties::docTypeVersion() const
+{
+  return d->docTypeVersion;
+}
+
+String Matroska::Properties::codecName() const
+{
+  return d->codecName;
+}
+
+String Matroska::Properties::title() const
+{
+  return d->title;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// private members
+////////////////////////////////////////////////////////////////////////////////
+
+void Matroska::Properties::setLengthInMilliseconds(int length)
+{
+  d->length = length;
+}
+
+void Matroska::Properties::setSampleRate(int sampleRate)
+{
+  d->sampleRate = sampleRate;
+}
+
+void Matroska::Properties::setChannels(int channels)
+{
+  d->channels = channels;
+}
+
+void Matroska::Properties::setBitsPerSample(int bitsPerSample)
+{
+  d->bitsPerSample = bitsPerSample;
+}
+
+void Matroska::Properties::setDocType(const String &docType)
+{
+  d->docType = docType;
+}
+
+void Matroska::Properties::setDocTypeVersion(int docTypeVersion)
+{
+  d->docTypeVersion = docTypeVersion;
+}
+
+void Matroska::Properties::setCodecName(const String &codecName)
+{
+  d->codecName = codecName;
+}
+
+void Matroska::Properties::setTitle(const String &title)
+{
+  d->title = title;
+}

taglib/matroska/matroskaproperties.h

@@ -0,0 +1,127 @@
+/***************************************************************************
+    copyright            : (C) 2025 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAPROPERTIES_H
+#define TAGLIB_MATROSKAPROPERTIES_H
+
+#include "taglib_export.h"
+#include "audioproperties.h"
+
+namespace TagLib::EBML {
+  class MkTracks;
+  class MkInfo;
+}
+
+namespace TagLib::Matroska {
+  class File;
+
+  //! An implementation of Matroska audio properties
+  class TAGLIB_EXPORT Properties : public AudioProperties
+  {
+  public:
+    /*!
+     * Creates an instance of Matroska::Properties.
+     */
+    explicit Properties(File *file, ReadStyle style = Average);
+
+    /*!
+     * Destroys this Matroska::Properties instance.
+     */
+    ~Properties() override;
+
+    Properties(const Properties &) = delete;
+    Properties &operator=(const Properties &) = delete;
+
+    /*!
+     * Returns the length of the file in milliseconds.
+     *
+     * \see lengthInSeconds()
+     */
+    int lengthInMilliseconds() const override;
+
+    /*!
+     * Returns the average bit rate of the file in kb/s.
+     */
+    int bitrate() const override;
+
+    /*!
+     * Returns the sample rate in Hz.
+     */
+    int sampleRate() const override;
+
+    /*!
+     * Returns the number of audio channels.
+     */
+    int channels() const override;
+
+    /*!
+     * Returns the number of bits per audio sample.
+     */
+    int bitsPerSample() const;
+
+    /*!
+     * Returns the EBML doc type, "matroska" or "webm".
+     */
+    String docType() const;
+
+    /*!
+     * Returns the EBML doc type version, typical values are 2 or 4.
+     */
+    int docTypeVersion() const;
+
+    /*!
+     * Returns the concrete codec name, for example "A_MPEG/L3"
+     * used in the file if available, otherwise an empty string.
+     */
+    String codecName() const;
+
+    /*!
+     * Returns the general name of the segment.
+     * Some applications store the title of the file here, but players should
+     * prioritize the tag title over the segment title.
+     */
+    String title() const;
+
+  private:
+    class PropertiesPrivate;
+    friend class EBML::MkInfo;
+    friend class EBML::MkTracks;
+    friend class File;
+
+    void setLengthInMilliseconds(int length);
+    void setSampleRate(int sampleRate);
+    void setChannels(int channels);
+    void setBitsPerSample(int bitsPerSample);
+    void setDocType(const String &docType);
+    void setDocTypeVersion(int docTypeVersion);
+    void setCodecName(const String &codecName);
+    void setTitle(const String &title);
+
+    TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+    std::unique_ptr<PropertiesPrivate> d;
+  };
+}
+
+#endif

taglib/matroska/matroskaseekhead.cpp

@@ -0,0 +1,148 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskaseekhead.h"
+#include "ebmlmkseekhead.h"
+#include "ebmlbinaryelement.h"
+#include "ebmluintelement.h"
+#include "ebmlmasterelement.h"
+#include "tfile.h"
+#include "tutils.h"
+#include "tdebug.h"
+
+using namespace TagLib;
+
+Matroska::SeekHead::SeekHead(offset_t segmentDataOffset) :
+  Element(static_cast<ID>(EBML::Element::Id::MkSeekHead)),
+  segmentDataOffset(segmentDataOffset)
+{
+  setNeedsRender(false);
+}
+
+Matroska::SeekHead::~SeekHead() = default;
+
+bool Matroska::SeekHead::isValid(TagLib::File &file) const
+{
+  bool result = true;
+  for(const auto &[id, offset] : entries) {
+    file.seek(segmentDataOffset + offset);
+    if(EBML::Element::readId(file) != id) {
+      debug(Utils::formatString("No ID %x found at seek position", id));
+      result = false;
+    }
+  }
+  return result;
+}
+
+void Matroska::SeekHead::addEntry(const Element &element)
+{
+  entries.append({element.id(), element.offset()});
+  setNeedsRender(true);
+}
+
+void Matroska::SeekHead::addEntry(ID id, offset_t offset)
+{
+  entries.append({id, offset});
+  setNeedsRender(true);
+}
+
+void Matroska::SeekHead::updateEntry(ID id, offset_t newOffset)
+{
+  for(auto &entry : entries) {
+    if(entry.first == id) {
+      entry.second = newOffset;
+      setNeedsRender(true);
+      return;
+    }
+  }
+}
+
+const List<std::pair<unsigned int, offset_t>> &Matroska::SeekHead::entryList() const
+{
+  return entries;
+}
+
+ByteVector Matroska::SeekHead::renderInternal()
+{
+  const auto beforeSize = sizeRenderedOrWritten();
+  EBML::MkSeekHead seekHead;
+  seekHead.setMinRenderSize(beforeSize);
+  for(const auto &[id, position] : entries) {
+    auto seekElement = EBML::make_unique_element<EBML::Element::Id::MkSeek>();
+    auto idElement = EBML::make_unique_element<EBML::Element::Id::MkSeekID>();
+    idElement->setValue(ByteVector::fromUInt(id, true));
+    seekElement->appendElement(std::move(idElement));
+
+    auto positionElement = EBML::make_unique_element<EBML::Element::Id::MkSeekPosition>();
+    positionElement->setValue(static_cast<unsigned long long>(position));
+    seekElement->appendElement(std::move(positionElement));
+
+    seekHead.appendElement(std::move(seekElement));
+  }
+  return seekHead.render();
+}
+
+void Matroska::SeekHead::write(File &file)
+{
+  if(!data().isEmpty())
+    Element::write(file);
+}
+
+void Matroska::SeekHead::sort()
+{
+  entries.sort([](const auto &a, const auto &b) { return a.second < b.second; });
+}
+
+bool Matroska::SeekHead::sizeChanged(Element &caller, offset_t delta)
+{
+  ID callerID = caller.id();
+  if(callerID == static_cast<ID>(EBML::Element::Id::MkSegment)) {
+    adjustOffset(delta);
+    return true;
+  }
+  // The equal case is needed when multiple new elements are added
+  // (e.g. Attachments and Tags), they will start with the same offset
+  // and are updated via size change handling.
+  offset_t offset = caller.offset() - segmentDataOffset;
+  auto it = entries.begin();
+  while(it != entries.end()) {
+    it = std::find_if(it,
+      entries.end(),
+      [offset, callerID](const auto &a) {
+        return a.second >= offset && a.first != callerID;
+      }
+    );
+    if(it != entries.end()) {
+      it->second += delta;
+      setNeedsRender(true);
+      ++it;
+    }
+  }
+
+  if(caller.data().isEmpty() && caller.size() + delta == 0) {
+    // The caller element is removed, remove it from the seek head.
+    it = std::find_if(entries.begin(), entries.end(),
+      [callerID](const auto &a){ return a.first == callerID; });
+    if(it != entries.end()) {
+      entries.erase(it);
+    }
+  }
+  return true;
+}

taglib/matroska/matroskaseekhead.h

@@ -0,0 +1,57 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKASEEKHEAD_H
+#define TAGLIB_MATROSKASEEKHEAD_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "matroskaelement.h"
+#include "tlist.h"
+
+namespace TagLib {
+  class File;
+  class ByteVector;
+
+  namespace Matroska {
+    class SeekHead : public Element
+    {
+    public:
+      explicit SeekHead(offset_t segmentDataOffset);
+      ~SeekHead() override;
+
+      bool isValid(TagLib::File &file) const;
+      void addEntry(const Element &element);
+      void addEntry(ID id, offset_t offset);
+      void updateEntry(ID id, offset_t offset);
+      const List<std::pair<unsigned int, offset_t>> &entryList() const;
+      void write(TagLib::File &file) override;
+      void sort();
+      bool sizeChanged(Element &caller, offset_t delta) override;
+
+    private:
+      ByteVector renderInternal() override;
+      List<std::pair<unsigned int, offset_t>> entries;
+      const offset_t segmentDataOffset;
+    };
+  }
+}
+
+#endif
+#endif

taglib/matroska/matroskasegment.cpp

@@ -0,0 +1,76 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskasegment.h"
+#include "ebmlutils.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+Matroska::Segment::Segment(offset_t sizeLength, offset_t dataSize, offset_t lengthOffset) :
+  Element(static_cast<ID>(EBML::Element::Id::MkSegment)),
+  sizeLength(sizeLength), dataSize(dataSize)
+{
+  setOffset(lengthOffset);
+  setSize(sizeLength);
+}
+
+Matroska::Segment::~Segment() = default;
+
+ByteVector Matroska::Segment::renderInternal()
+{
+  return EBML::renderVINT(dataSize, static_cast<int>(sizeLength));
+}
+
+bool Matroska::Segment::render()
+{
+  const auto beforeSize = sizeLength;
+  auto data = renderInternal();
+  setNeedsRender(false);
+  if(auto afterSize = data.size(); afterSize != beforeSize) {
+    sizeLength = 8;
+    data = renderInternal();
+    setNeedsRender(false);
+    afterSize = data.size();
+    if(!emitSizeChanged(afterSize - beforeSize)) {
+      return false;
+    }
+  }
+
+  setData(data);
+  return true;
+}
+
+bool Matroska::Segment::sizeChanged(Element &, offset_t delta)
+{
+  dataSize += delta;
+  setNeedsRender(true);
+  return true;
+}
+
+offset_t Matroska::Segment::dataOffset() const
+{
+  return offset() + sizeLength;
+}
+
+offset_t Matroska::Segment::endOffset() const
+{
+  return dataOffset() + dataSize;
+}

taglib/matroska/matroskasegment.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKASEGMENT_H
+#define TAGLIB_MATROSKASEGMENT_H
+#ifndef DO_NOT_DOCUMENT
+
+#include "matroskaelement.h"
+
+namespace TagLib::Matroska {
+  class Segment : public Element
+  {
+  public:
+    Segment(offset_t sizeLength, offset_t dataSize, offset_t lengthOffset);
+    ~Segment() override;
+    bool render() override;
+    bool sizeChanged(Element &caller, offset_t delta) override;
+    offset_t dataOffset() const;
+    offset_t endOffset() const;
+
+  private:
+    ByteVector renderInternal() override;
+
+    offset_t sizeLength;
+    offset_t dataSize;
+  };
+}
+
+#endif
+#endif

taglib/matroska/matroskasimpletag.cpp

@@ -0,0 +1,188 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskasimpletag.h"
+#include <variant>
+#include "matroskatag.h"
+#include "tbytevector.h"
+
+using namespace TagLib;
+
+class Matroska::SimpleTag::SimpleTagPrivate
+{
+public:
+  SimpleTagPrivate(const String &name, const String &value,
+    TargetTypeValue targetTypeValue, const String &language, bool defaultLanguage,
+    unsigned long long trackUid, unsigned long long editionUid,
+    unsigned long long chapterUid, unsigned long long attachmentUid) :
+    value(value), name(name), language(language), trackUid(trackUid),
+    editionUid(editionUid), chapterUid(chapterUid), attachmentUid(attachmentUid),
+    targetTypeValue(targetTypeValue), defaultLanguageFlag(defaultLanguage) {}
+  SimpleTagPrivate(const String &name, const ByteVector &value,
+    TargetTypeValue targetTypeValue, const String &language, bool defaultLanguage,
+    unsigned long long trackUid, unsigned long long editionUid,
+    unsigned long long chapterUid, unsigned long long attachmentUid) :
+    value(value), name(name), language(language), trackUid(trackUid),
+    editionUid(editionUid), chapterUid(chapterUid), attachmentUid(attachmentUid),
+    targetTypeValue(targetTypeValue), defaultLanguageFlag(defaultLanguage) {}
+
+  const std::variant<String, ByteVector> value;
+  const String name;
+  const String language;
+  const unsigned long long trackUid;
+  const unsigned long long editionUid;
+  const unsigned long long chapterUid;
+  const unsigned long long attachmentUid;
+  const TargetTypeValue targetTypeValue;
+  const bool defaultLanguageFlag;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+Matroska::SimpleTag::SimpleTag(const String &name, const String &value,
+                               TargetTypeValue targetTypeValue,
+                               const String &language, bool defaultLanguage,
+                               unsigned long long trackUid) :
+  d(std::make_unique<SimpleTagPrivate>(name, value, targetTypeValue,
+    language, defaultLanguage, trackUid, 0, 0, 0))
+{
+}
+
+Matroska::SimpleTag::SimpleTag(const String &name, const String &value,
+                               TargetTypeValue targetTypeValue,
+                               const String &language, bool defaultLanguage,
+                               unsigned long long trackUid,
+                               unsigned long long editionUid,
+                               unsigned long long chapterUid,
+                               unsigned long long attachmentUid) :
+  d(std::make_unique<SimpleTagPrivate>(name, value, targetTypeValue,
+    language, defaultLanguage, trackUid, editionUid, chapterUid, attachmentUid))
+{
+}
+
+Matroska::SimpleTag::SimpleTag(const String &name, const ByteVector &value,
+                               TargetTypeValue targetTypeValue,
+                               const String &language, bool defaultLanguage,
+                               unsigned long long trackUid) :
+  d(std::make_unique<SimpleTagPrivate>(name, value, targetTypeValue,
+    language, defaultLanguage, trackUid, 0, 0, 0))
+{
+}
+
+Matroska::SimpleTag::SimpleTag(const String &name, const ByteVector &value,
+                               TargetTypeValue targetTypeValue,
+                               const String &language, bool defaultLanguage,
+                               unsigned long long trackUid,
+                               unsigned long long editionUid,
+                               unsigned long long chapterUid,
+                               unsigned long long attachmentUid) :
+  d(std::make_unique<SimpleTagPrivate>(name, value, targetTypeValue,
+    language, defaultLanguage, trackUid, editionUid, chapterUid, attachmentUid))
+{
+}
+
+Matroska::SimpleTag::SimpleTag(const SimpleTag &other) :
+  d(std::make_unique<SimpleTagPrivate>(*other.d))
+{
+}
+
+Matroska::SimpleTag::SimpleTag(SimpleTag &&other) noexcept = default;
+
+Matroska::SimpleTag::~SimpleTag() = default;
+
+Matroska::SimpleTag &Matroska::SimpleTag::operator=(SimpleTag &&other) noexcept = default;
+
+Matroska::SimpleTag &Matroska::SimpleTag::operator=(const SimpleTag &other)
+{
+  SimpleTag(other).swap(*this);
+  return *this;
+}
+
+void Matroska::SimpleTag::swap(SimpleTag &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+Matroska::SimpleTag::TargetTypeValue Matroska::SimpleTag::targetTypeValue() const
+{
+  return d->targetTypeValue;
+}
+
+const String &Matroska::SimpleTag::name() const
+{
+  return d->name;
+}
+
+const String &Matroska::SimpleTag::language() const
+{
+  return d->language;
+}
+
+bool Matroska::SimpleTag::defaultLanguageFlag() const
+{
+  return d->defaultLanguageFlag;
+}
+
+unsigned long long Matroska::SimpleTag::trackUid() const
+{
+  return d->trackUid;
+}
+
+unsigned long long Matroska::SimpleTag::editionUid() const
+{
+  return d->editionUid;
+}
+
+unsigned long long Matroska::SimpleTag::chapterUid() const
+{
+  return d->chapterUid;
+}
+
+unsigned long long Matroska::SimpleTag::attachmentUid() const
+{
+  return d->attachmentUid;
+}
+
+Matroska::SimpleTag::ValueType Matroska::SimpleTag::type() const
+{
+  return std::holds_alternative<ByteVector>(d->value) ? BinaryType : StringType;
+}
+
+String Matroska::SimpleTag::toString() const
+{
+  if(std::holds_alternative<String>(d->value)) {
+    // get_if() used instead of get() to support restricted compilers
+    return *std::get_if<String>(&d->value);
+  }
+  return {};
+}
+
+ByteVector Matroska::SimpleTag::toByteVector() const
+{
+  if(std::holds_alternative<ByteVector>(d->value)) {
+    // get_if() used instead of get() to support restricted compilers
+    return *std::get_if<ByteVector>(&d->value);
+  }
+  return {};
+}

taglib/matroska/matroskasimpletag.h

@@ -0,0 +1,185 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKASIMPLETAG_H
+#define TAGLIB_MATROSKASIMPLETAG_H
+
+#include <memory>
+
+#include "tstring.h"
+
+namespace TagLib {
+  class String;
+  class ByteVector;
+
+  namespace Matroska {
+    //! Attribute of Matroska metadata.
+    class TAGLIB_EXPORT SimpleTag
+    {
+    public:
+      //! Specifies the level of other elements the tag value applies to.
+      enum TargetTypeValue {
+        None = 0,       //!< Empty or omitted, everything in the segment
+        Shot = 10,      //!< Shot
+        Subtrack = 20,  //!< Subtrack / movement / scene
+        Track = 30,     //!< Track / song / chapter
+        Part = 40,      //!< Part / session
+        Album = 50,     //!< Album / opera / concert / movie / episode
+        Edition = 60,   //!< Edition / issue / volume / opus / season / sequel
+        Collection = 70 //!< Collection
+      };
+
+      //! The types the value can have.
+      enum ValueType {
+        StringType = 0, //!< Item contains text information coded in UTF-8
+        BinaryType = 1  //!< Item contains binary information
+      };
+
+      /*!
+       * Construct a string simple tag.
+       */
+      SimpleTag(const String &name, const String &value,
+                TargetTypeValue targetTypeValue = None,
+                const String &language = String(), bool defaultLanguage = true,
+                unsigned long long trackUid = 0);
+
+      /*!
+       * Construct a string simple tag.
+       */
+      // BIC: merge with constructor above
+      SimpleTag(const String& name, const String& value, TargetTypeValue targetTypeValue, const String& language,
+                bool defaultLanguage, unsigned long long trackUid, unsigned long long editionUid,
+                unsigned long long chapterUid = 0, unsigned long long attachmentUid = 0);
+
+      /*!
+       * Construct a binary simple tag.
+       */
+      SimpleTag(const String &name, const ByteVector &value,
+        TargetTypeValue targetTypeValue = None,
+        const String &language = String(), bool defaultLanguage = true,
+        unsigned long long trackUid = 0);
+
+      /*!
+       * Construct a binary simple tag.
+       */
+      // BIC: merge with constructor above
+      SimpleTag(const String& name, const ByteVector& value, TargetTypeValue targetTypeValue, const String& language,
+                bool defaultLanguage, unsigned long long trackUid, unsigned long long editionUid,
+                unsigned long long chapterUid = 0, unsigned long long attachmentUid = 0);
+
+      /*!
+       * Construct a simple tag as a copy of \a other.
+       */
+      SimpleTag(const SimpleTag &other);
+
+      /*!
+       * Construct a simple tag moving from \a other.
+       */
+      SimpleTag(SimpleTag &&other) noexcept;
+
+      /*!
+       * Destroys this simple tag.
+       */
+      ~SimpleTag();
+
+      /*!
+       * Copies the contents of \a other into this item.
+       */
+      SimpleTag &operator=(const SimpleTag &other);
+
+      /*!
+       * Moves the contents of \a other into this item.
+       */
+      SimpleTag &operator=(SimpleTag &&other) noexcept;
+
+      /*!
+       * Exchanges the content of the simple tag with the content of \a other.
+       */
+      void swap(SimpleTag &other) noexcept;
+
+      /*!
+       * Returns the name of the simple tag.
+       */
+      const String &name() const;
+
+      /*!
+       * Returns the logical level of the target.
+       */
+      TargetTypeValue targetTypeValue() const;
+
+      /*!
+       * Returns the language of the tag.
+       */
+      const String &language() const;
+
+      /*!
+       * Returns if this is the default/original language to use for the tag.
+       */
+      bool defaultLanguageFlag() const;
+
+      /*!
+       * Returns the UID that identifies the track that the tags belong to,
+       * zero if not defined, the tag applies to all tracks
+       */
+      unsigned long long trackUid() const;
+
+      /*!
+       * Returns the UID that identifies the edition that the tags belong to,
+       * zero if not defined, the tag applies to all editions
+       */
+      unsigned long long editionUid() const;
+
+      /*!
+       * Returns the UID that identifies the chapter that the tags belong to,
+       * zero if not defined, the tag applies to all chapters
+       */
+      unsigned long long chapterUid() const;
+
+      /*!
+       * Returns the UID that identifies the attachment that the tags belong to,
+       * zero if not defined, the tag applies to all attachments
+       */
+      unsigned long long attachmentUid() const;
+
+      /*!
+       * Returns the type of the value.
+       */
+      ValueType type() const;
+
+      /*!
+       * Returns the StringType value.
+       */
+      String toString() const;
+
+      /*!
+       * Returns the BinaryType value.
+       */
+      ByteVector toByteVector() const;
+
+    private:
+      class SimpleTagPrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<SimpleTagPrivate> d;
+    };
+
+  }
+}
+
+#endif

taglib/matroska/matroskatag.cpp

@@ -0,0 +1,670 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "matroskatag.h"
+#include <algorithm>
+#include <array>
+#include <tuple>
+#include "ebmlmasterelement.h"
+#include "ebmlstringelement.h"
+#include "ebmlbinaryelement.h"
+#include "ebmlmktags.h"
+#include "ebmluintelement.h"
+#include "ebmlutils.h"
+#include "tpropertymap.h"
+
+using namespace TagLib;
+
+class Matroska::Tag::TagPrivate
+{
+public:
+  TagPrivate() = default;
+  ~TagPrivate() = default;
+
+  bool setTag(const String &key, const String &value);
+  String getTag(const String &key) const;
+
+  template <typename T>
+  int removeSimpleTags(T &&p)
+  {
+    auto &list = tags;
+    int numRemoved = 0;
+    for(auto it = list.begin(); it != list.end();) {
+      it = std::find_if(it, list.end(), std::forward<T>(p));
+      if(it != list.end()) {
+        it = list.erase(it);
+        numRemoved++;
+      }
+    }
+    return numRemoved;
+  }
+
+  template <typename T>
+  SimpleTagsList findSimpleTags(T &&p)
+  {
+    auto &list = tags;
+    for(auto it = list.begin(); it != list.end();) {
+      it = std::find_if(it, list.end(), std::forward<T>(p));
+      if(it != list.end()) {
+        list.append(*it);
+        ++it;
+      }
+    }
+    return list;
+  }
+
+  SimpleTagsList tags;
+  ByteVector data;
+  String segmentTitle;
+};
+
+Matroska::Tag::Tag() :
+  Element(static_cast<ID>(EBML::Element::Id::MkTags)),
+  d(std::make_unique<TagPrivate>())
+{
+}
+
+Matroska::Tag::~Tag() = default;
+
+void Matroska::Tag::addSimpleTag(const SimpleTag &tag)
+{
+  d->tags.append(tag);
+  setNeedsRender(true);
+}
+
+void Matroska::Tag::addSimpleTags(const SimpleTagsList& simpleTags)
+{
+  d->tags.append(simpleTags);
+  setNeedsRender(true);
+}
+
+void Matroska::Tag::insertSimpleTag(unsigned int index, const SimpleTag &tag)
+{
+  if(index < d->tags.size()) {
+    auto it = d->tags.begin();
+    std::advance(it, index);
+    d->tags.insert(it, tag);
+  }
+  else {
+    d->tags.append(tag);
+  }
+  setNeedsRender(true);
+}
+
+void Matroska::Tag::removeSimpleTag(unsigned int index)
+{
+  if(index < d->tags.size()) {
+    auto it = d->tags.begin();
+    std::advance(it, index);
+    d->tags.erase(it);
+    setNeedsRender(true);
+  }
+}
+
+void Matroska::Tag::removeSimpleTag(const String &name,
+  SimpleTag::TargetTypeValue targetTypeValue,
+  unsigned long long trackUid)
+{
+  removeSimpleTag(name, targetTypeValue, trackUid, 0, 0, 0);
+}
+
+void Matroska::Tag::removeSimpleTag(const String& name,
+  SimpleTag::TargetTypeValue targetTypeValue,
+  unsigned long long trackUid, unsigned long long editionUid,
+  unsigned long long chapterUid, unsigned long long attachmentUid)
+{
+  const auto it = std::find_if(d->tags.begin(), d->tags.end(),
+    [&name, targetTypeValue, trackUid, editionUid, chapterUid, attachmentUid](
+      const SimpleTag &t) {
+        return t.name() == name && t.targetTypeValue() == targetTypeValue &&
+               t.trackUid() == trackUid && t.editionUid() == editionUid &&
+               t.chapterUid() == chapterUid && t.attachmentUid() == attachmentUid;
+    }
+  );
+  if(it != d->tags.end()) {
+    d->tags.erase(it);
+    setNeedsRender(true);
+  }
+}
+
+void Matroska::Tag::clearSimpleTags()
+{
+  d->tags.clear();
+  setNeedsRender(true);
+}
+
+const Matroska::SimpleTagsList &Matroska::Tag::simpleTagsList() const
+{
+  return d->tags;
+}
+
+void Matroska::Tag::setSegmentTitle(const String &title)
+{
+  d->segmentTitle = title;
+}
+
+bool Matroska::Tag::setTag(const String &key, const String &value)
+{
+  const bool found = d->setTag(key, value);
+  if(found) {
+    setNeedsRender(true);
+  }
+  return found;
+}
+
+void Matroska::Tag::setTitle(const String &s)
+{
+  setTag("TITLE", s);
+}
+
+void Matroska::Tag::setArtist(const String &s)
+{
+  setTag("ARTIST", s);
+}
+
+void Matroska::Tag::setAlbum(const String &s)
+{
+  setTag("ALBUM", s);
+}
+
+void Matroska::Tag::setComment(const String &s)
+{
+  setTag("COMMENT", s);
+}
+
+void Matroska::Tag::setGenre(const String &s)
+{
+  setTag("GENRE", s);
+}
+
+void Matroska::Tag::setYear(unsigned int i)
+{
+  setTag("DATE", i != 0 ? String::number(i) : String());
+}
+
+void Matroska::Tag::setTrack(unsigned int i)
+{
+  setTag("TRACKNUMBER", i != 0 ? String::number(i) : String());
+}
+
+String Matroska::Tag::title() const
+{
+  String s = d->getTag("TITLE");
+  if(s.isEmpty()) {
+    return d->segmentTitle;
+  }
+  return s;
+}
+
+String Matroska::Tag::artist() const
+{
+  return d->getTag("ARTIST");
+}
+
+String Matroska::Tag::album() const
+{
+  return d->getTag("ALBUM");
+}
+
+String Matroska::Tag::comment() const
+{
+  return d->getTag("COMMENT");
+}
+
+String Matroska::Tag::genre() const
+{
+  return d->getTag("GENRE");
+}
+
+unsigned int Matroska::Tag::year() const
+{
+  const auto value = d->getTag("DATE");
+  if(value.isEmpty())
+    return 0;
+  auto list = value.split("-");
+  return static_cast<unsigned int>(list.front().toInt());
+}
+
+unsigned int Matroska::Tag::track() const
+{
+  const auto value = d->getTag("TRACKNUMBER");
+  if(value.isEmpty())
+    return 0;
+  auto list = value.split("-");
+  return static_cast<unsigned int>(list.front().toInt());
+}
+
+bool Matroska::Tag::isEmpty() const
+{
+  return d->tags.isEmpty();
+}
+
+ByteVector Matroska::Tag::renderInternal()
+{
+  if(d->tags.isEmpty()) {
+    // Avoid writing a Tags element without Tag element.
+    return {};
+  }
+
+  EBML::MkTags tags;
+  List<SimpleTagsList> targetList;
+
+  // Build target-based list
+  for(const auto &tag : std::as_const(d->tags)) {
+    auto targetTypeValue = tag.targetTypeValue();
+    auto trackUid = tag.trackUid();
+    auto editionUid = tag.editionUid();
+    auto chapterUid = tag.chapterUid();
+    auto attachmentUid = tag.attachmentUid();
+    auto it = std::find_if(targetList.begin(),
+      targetList.end(),
+      [&](const auto &list) {
+        const auto &simpleTag = list.front();
+        return simpleTag.targetTypeValue() == targetTypeValue &&
+               simpleTag.trackUid() == trackUid &&
+               simpleTag.editionUid() == editionUid &&
+               simpleTag.chapterUid() == chapterUid &&
+               simpleTag.attachmentUid() == attachmentUid;
+      }
+    );
+    if(it == targetList.end()) {
+      SimpleTagsList list;
+      list.append(tag);
+      targetList.append(list);
+    }
+    else
+      it->append(tag);
+  }
+  for(const auto &list : targetList) {
+    const auto &frontTag = list.front();
+    const auto targetTypeValue = frontTag.targetTypeValue();
+    const auto trackUid = frontTag.trackUid();
+    const auto editionUid = frontTag.editionUid();
+    const auto chapterUid = frontTag.chapterUid();
+    const auto attachmentUid = frontTag.attachmentUid();
+    auto tag = EBML::make_unique_element<EBML::Element::Id::MkTag>();
+
+    // Build <Tag Targets> element
+    auto targets = EBML::make_unique_element<EBML::Element::Id::MkTagTargets>();
+    if(targetTypeValue != SimpleTag::TargetTypeValue::None) {
+      auto element = EBML::make_unique_element<EBML::Element::Id::MkTagTargetTypeValue>();
+      element->setValue(static_cast<unsigned int>(targetTypeValue));
+      targets->appendElement(std::move(element));
+    }
+    if(trackUid != 0) {
+      auto element = EBML::make_unique_element<EBML::Element::Id::MkTagTrackUID>();
+      element->setValue(trackUid);
+      targets->appendElement(std::move(element));
+    }
+    if(editionUid != 0) {
+      auto element = EBML::make_unique_element<EBML::Element::Id::MkTagEditionUID>();
+      element->setValue(editionUid);
+      targets->appendElement(std::move(element));
+    }
+    if(chapterUid != 0) {
+      auto element = EBML::make_unique_element<EBML::Element::Id::MkTagChapterUID>();
+      element->setValue(chapterUid);
+      targets->appendElement(std::move(element));
+    }
+    if(attachmentUid != 0) {
+      auto element = EBML::make_unique_element<EBML::Element::Id::MkTagAttachmentUID>();
+      element->setValue(attachmentUid);
+      targets->appendElement(std::move(element));
+    }
+    tag->appendElement(std::move(targets));
+
+    // Build <Simple Tag> element
+    for(const auto &simpleTag : list) {
+      auto t = EBML::make_unique_element<EBML::Element::Id::MkSimpleTag>();
+      auto tagName = EBML::make_unique_element<EBML::Element::Id::MkTagName>();
+      tagName->setValue(simpleTag.name());
+      t->appendElement(std::move(tagName));
+
+      // Tag Value
+      if(simpleTag.type() == SimpleTag::StringType) {
+        auto tagValue = EBML::make_unique_element<EBML::Element::Id::MkTagString>();
+        tagValue->setValue(simpleTag.toString());
+        t->appendElement(std::move(tagValue));
+      }
+      else if(simpleTag.type() == SimpleTag::BinaryType) {
+        auto tagValue = EBML::make_unique_element<EBML::Element::Id::MkTagBinary>();
+        tagValue->setValue(simpleTag.toByteVector());
+        t->appendElement(std::move(tagValue));
+      }
+
+      // Language
+      auto language = EBML::make_unique_element<EBML::Element::Id::MkTagsTagLanguage>();
+      const String &lang = simpleTag.language();
+      language->setValue(!lang.isEmpty() ? lang : "und");
+      t->appendElement(std::move(language));
+
+      // Default language flag
+      auto dlf = EBML::make_unique_element<EBML::Element::Id::MkTagsLanguageDefault>();
+      dlf->setValue(simpleTag.defaultLanguageFlag() ? 1 : 0);
+      t->appendElement(std::move(dlf));
+
+      tag->appendElement(std::move(t));
+    }
+    tags.appendElement(std::move(tag));
+  }
+  // Pad to the previous size so the element keeps its slot in the file,
+  // unless this element is the trailing element of the segment in
+  // AvoidInsert mode -- shrinking from the end never inserts anything,
+  // so the trailing void would be wasted space.
+  if(writeStyle() != WriteStyle::Compact &&
+     !(writeStyle() == WriteStyle::AvoidInsert && isTrailingInSegment())) {
+    const auto beforeSize = sizeRenderedOrWritten();
+    if(beforeSize > 0)
+      tags.setMinRenderSize(beforeSize);
+  }
+  return tags.render();
+}
+
+namespace
+{
+  // PropertyMap key, Tag name, Target type value, strict
+  // If the key is the same as the name and the target type value is Track,
+  // no translation is needed because this is the default mapping.
+  // Therefore, keys like TITLE, ARTIST, GENRE, COMMENT, etc. are omitted
+  // unless they shall have priority over higher level tags with the same name
+  // when no target type value is given. The strict boolean marks
+  // entries which shall not be mapped without correct target type value.
+  // For offical tags, see https://www.matroska.org/technical/tagging.html
+  constexpr std::array simpleTagsTranslation {
+    std::tuple("TITLE", "TITLE", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ALBUM", "TITLE", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("ARTIST", "ARTIST", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ALBUMARTIST", "ARTIST", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("TRACKNUMBER", "PART_NUMBER", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("DISCNUMBER", "PART_NUMBER", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("TRACKTOTAL", "TOTAL_PARTS", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("DISCTOTAL", "TOTAL_PARTS", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("DATE", "DATE_RECORDED", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("TITLESORT", "TITLESORT", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ALBUMSORT", "TITLESORT", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("ARTISTSORT", "ARTISTSORT", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ALBUMARTISTSORT", "ARTISTSORT", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("MEDIA", "ORIGINAL_MEDIA_TYPE", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("LABEL", "LABEL_CODE", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("CATALOGNUMBER", "CATALOG_NUMBER", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("DJMIXER", "MIXED_BY", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("REMIXER", "REMIXED_BY", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("INITIALKEY", "INITIAL_KEY", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("RELEASEDATE", "DATE_RELEASED", Matroska::SimpleTag::TargetTypeValue::Album, false),
+    std::tuple("ENCODINGTIME", "DATE_ENCODED", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("TAGGINGDATE", "DATE_TAGGED", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ENCODEDBY", "ENCODER", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("ENCODING", "ENCODER_SETTINGS", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("OWNER", "PURCHASE_OWNER", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("REPLAYGAIN_TRACK_GAIN", "REPLAYGAIN_GAIN", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("REPLAYGAIN_ALBUM_GAIN", "REPLAYGAIN_GAIN", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("REPLAYGAIN_TRACK_PEAK", "REPLAYGAIN_PEAK", Matroska::SimpleTag::TargetTypeValue::Track, false),
+    std::tuple("REPLAYGAIN_ALBUM_PEAK", "REPLAYGAIN_PEAK", Matroska::SimpleTag::TargetTypeValue::Album, true),
+    std::tuple("MUSICBRAINZ_ALBUMARTISTID", "MUSICBRAINZ_ALBUMARTISTID", Matroska::SimpleTag::TargetTypeValue::Album, false),
+    std::tuple("MUSICBRAINZ_ALBUMID", "MUSICBRAINZ_ALBUMID", Matroska::SimpleTag::TargetTypeValue::Album, false),
+    std::tuple("MUSICBRAINZ_RELEASEGROUPID", "MUSICBRAINZ_RELEASEGROUPID", Matroska::SimpleTag::TargetTypeValue::Album, false),
+  };
+
+  std::tuple<String, Matroska::SimpleTag::TargetTypeValue, bool> translateKey(const String &key)
+  {
+    auto it = std::find_if(simpleTagsTranslation.cbegin(),
+      simpleTagsTranslation.cend(),
+      [&key](const auto &t) { return key == std::get<0>(t); }
+    );
+    if(it != simpleTagsTranslation.end())
+      return { std::get<1>(*it), std::get<2>(*it), std::get<3>(*it) };
+    if(!key.isEmpty())
+      return { key, Matroska::SimpleTag::TargetTypeValue::Track, false };
+    return { String(), Matroska::SimpleTag::TargetTypeValue::None, false };
+  }
+
+  String translateTag(const String &name, Matroska::SimpleTag::TargetTypeValue targetTypeValue)
+  {
+    const auto it = std::find_if(simpleTagsTranslation.cbegin(),
+      simpleTagsTranslation.cend(),
+      [&name, targetTypeValue](const auto &t) {
+        return name == std::get<1>(t)
+               && (targetTypeValue == std::get<2>(t) ||
+                   (targetTypeValue == Matroska::SimpleTag::TargetTypeValue::None
+                     && !std::get<3>(t)));
+      }
+    );
+    return it != simpleTagsTranslation.end()
+      ? String(std::get<0>(*it), String::UTF8)
+      : targetTypeValue == Matroska::SimpleTag::TargetTypeValue::Track ||
+        targetTypeValue == Matroska::SimpleTag::TargetTypeValue::None
+      ? name
+        : String();
+  }
+}
+
+bool Matroska::Tag::TagPrivate::setTag(const String &key, const String &value)
+{
+  const auto tpl = translateKey(key);
+  // Workaround Clang issue - no lambda capture of structured bindings
+  const String &name = std::get<0>(tpl);
+  auto targetTypeValue = std::get<1>(tpl);
+  if(name.isEmpty())
+    return false;
+  removeSimpleTags(
+    [&name, targetTypeValue] (const auto &t) {
+      return t.name() == name
+             && t.targetTypeValue() == targetTypeValue;
+    }
+  );
+  if(!value.isEmpty()) {
+    tags.append(SimpleTag(name, value, targetTypeValue));
+  }
+  return true;
+}
+
+String Matroska::Tag::TagPrivate::getTag(const String &key) const
+{
+  const auto tpl = translateKey(key);
+  // Workaround Clang issue - no lambda capture of structured bindings
+  const String &name = std::get<0>(tpl);
+  auto targetTypeValue = std::get<1>(tpl);
+  bool strict = std::get<2>(tpl);
+  if(name.isEmpty())
+    return {};
+  const auto it = std::find_if(tags.begin(), tags.end(),
+    [&name, targetTypeValue, strict] (const SimpleTag &t) {
+      return t.name() == name
+        && t.type() == SimpleTag::StringType
+        && (t.targetTypeValue() == targetTypeValue ||
+            (t.targetTypeValue() == SimpleTag::TargetTypeValue::None && !strict))
+        && t.trackUid() == 0 && t.editionUid() == 0 && t.chapterUid() == 0
+        && t.attachmentUid() == 0;
+    }
+  );
+  return it != tags.end() ? it->toString() : String();
+}
+
+PropertyMap Matroska::Tag::properties() const
+{
+  PropertyMap properties;
+  for(const auto &simpleTag : std::as_const(d->tags)) {
+    if(simpleTag.type() == SimpleTag::StringType && simpleTag.trackUid() == 0 &&
+       simpleTag.editionUid() == 0 && simpleTag.chapterUid() == 0 &&
+       simpleTag.attachmentUid() == 0) {
+      if(String key = translateTag(simpleTag.name(), simpleTag.targetTypeValue());
+         !key.isEmpty())
+        properties[key].append(simpleTag.toString());
+      else
+        properties.addUnsupportedData(simpleTag.name());
+    }
+  }
+  return properties;
+}
+
+PropertyMap Matroska::Tag::setProperties(const PropertyMap &propertyMap)
+{
+  // Remove all simple tags which would be returned in properties()
+  for(auto it = d->tags.begin(); it != d->tags.end();) {
+    if(it->type() == SimpleTag::StringType &&
+       it->trackUid() == 0 && it->editionUid() == 0 &&
+       it->chapterUid() == 0 && it->attachmentUid() == 0 &&
+       !translateTag(it->name(), it->targetTypeValue()).isEmpty()) {
+      it = d->tags.erase(it);
+      setNeedsRender(true);
+    }
+    else {
+      ++it;
+    }
+  }
+
+  // Add the new properties
+  PropertyMap unsupportedProperties;
+  for(const auto &[key, values] : propertyMap) {
+    for(const auto &value : values) {
+      if(auto [name, targetTypeValue, _] = translateKey(key);
+         !name.isEmpty()) {
+        d->tags.append(SimpleTag(name, value, targetTypeValue));
+        setNeedsRender(true);
+      }
+      else {
+        unsupportedProperties[key] = values;
+      }
+    }
+  }
+  return unsupportedProperties;
+}
+
+void Matroska::Tag::removeUnsupportedProperties(const StringList &properties)
+{
+  if(d->removeSimpleTags(
+     [&properties](const SimpleTag &t) {
+         return properties.contains(t.name());
+       }) > 0) {
+    setNeedsRender(true);
+  }
+}
+
+StringList Matroska::Tag::complexPropertyKeys() const
+{
+  StringList keys;
+  for(const SimpleTag &t : std::as_const(d->tags)) {
+    if((t.type() != SimpleTag::StringType ||
+        t.trackUid() != 0 || t.editionUid() != 0 ||
+        t.chapterUid() != 0 || t.attachmentUid() != 0 ||
+        translateTag(t.name(), t.targetTypeValue()).isEmpty()) &&
+       !keys.contains(t.name())) {
+      keys.append(t.name());
+    }
+  }
+  return keys;
+}
+
+List<VariantMap> Matroska::Tag::complexProperties(const String &key) const
+{
+  List<VariantMap> props;
+  if(key.upper() != "PICTURE") { // Pictures are handled at the file level
+    for(const SimpleTag &t : std::as_const(d->tags)) {
+      if(t.name() == key &&
+         (t.type() != SimpleTag::StringType ||
+          t.trackUid() != 0 || t.editionUid() != 0 ||
+          t.chapterUid() != 0 || t.attachmentUid() != 0 ||
+          translateTag(t.name(), t.targetTypeValue()).isEmpty())) {
+        VariantMap property;
+        if(t.type() != SimpleTag::StringType) {
+          property.insert("data", t.toByteVector());
+        }
+        else {
+          property.insert("value", t.toString());
+        }
+        property.insert("name", t.name());
+        if(t.targetTypeValue() != SimpleTag::TargetTypeValue::None) {
+          property.insert("targetTypeValue", t.targetTypeValue());
+        }
+        if(t.trackUid()) {
+          property.insert("trackUid", t.trackUid());
+        }
+        if(t.editionUid()) {
+          property.insert("editionUid", t.editionUid());
+        }
+        if(t.chapterUid()) {
+          property.insert("chapterUid", t.chapterUid());
+        }
+        if(t.attachmentUid()) {
+          property.insert("attachmentUid", t.attachmentUid());
+        }
+        property.insert("language", t.language());
+        property.insert("defaultLanguage", t.defaultLanguageFlag());
+        props.append(property);
+      }
+    }
+  }
+  return props;
+}
+
+bool Matroska::Tag::setComplexProperties(const String &key, const List<VariantMap> &value)
+{
+  if(key.upper() == "PICTURE") {
+    // Pictures are handled at the file level
+    return false;
+  }
+  if(d->removeSimpleTags(
+       [&key](const SimpleTag &t) {
+         return t.name() == key &&
+           (t.type() != SimpleTag::StringType ||
+            t.trackUid() != 0 || t.editionUid() != 0 ||
+            t.chapterUid() != 0 || t.attachmentUid() != 0 ||
+            translateTag(t.name(), t.targetTypeValue()).isEmpty());
+       }) > 0) {
+    setNeedsRender(true);
+  }
+  bool result = false;
+  for(const auto &property : value) {
+    if(property.value("name").value<String>() == key &&
+       (property.contains("data") || property.contains("value") )) {
+      SimpleTag::TargetTypeValue targetTypeValue;
+      switch(Variant targetTypeValueVar = property.value("targetTypeValue", 0);
+             targetTypeValueVar.type()) {
+      case Variant::UInt:
+        targetTypeValue = static_cast<SimpleTag::TargetTypeValue>(targetTypeValueVar.value<unsigned int>());
+        break;
+      case Variant::LongLong:
+        targetTypeValue = static_cast<SimpleTag::TargetTypeValue>(targetTypeValueVar.value<long long>());
+        break;
+      case Variant::ULongLong:
+        targetTypeValue = static_cast<SimpleTag::TargetTypeValue>(targetTypeValueVar.value<unsigned long long>());
+        break;
+      default:
+        targetTypeValue = static_cast<SimpleTag::TargetTypeValue>(targetTypeValueVar.value<int>());
+      }
+      auto language = property.value("language").value<String>();
+      const bool defaultLanguage = property.value("defaultLanguage", true).value<bool>();
+      const auto trackUid = property.value("trackUid", 0ULL).value<unsigned long long>();
+      const auto editionUid = property.value("editionUid", 0ULL).value<unsigned long long>();
+      const auto chapterUid = property.value("chapterUid", 0ULL).value<unsigned long long>();
+      const auto attachmentUid = property.value("attachmentUid", 0ULL).value<unsigned long long>();
+      d->tags.append(property.contains("data")
+        ? SimpleTag(key, property.value("data").value<ByteVector>(),
+                    targetTypeValue, language, defaultLanguage, trackUid,
+                    editionUid, chapterUid, attachmentUid)
+        : SimpleTag(key, property.value("value").value<String>(),
+                    targetTypeValue, language, defaultLanguage, trackUid,
+                    editionUid, chapterUid, attachmentUid));
+      setNeedsRender(true);
+      result = true;
+    }
+  }
+  return result;
+}

taglib/matroska/matroskatag.h

@@ -0,0 +1,158 @@
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKATAG_H
+#define TAGLIB_MATROSKATAG_H
+
+#include <memory>
+
+#include "tag.h"
+#include "tlist.h"
+#include "matroskaelement.h"
+#include "matroskasimpletag.h"
+
+namespace TagLib {
+  class File;
+
+  namespace EBML {
+    class MkTags;
+  }
+
+  namespace Matroska {
+    //! List of tag attributes.
+    using SimpleTagsList = List<SimpleTag>;
+
+    //! Matroska tag implementation.
+    class TAGLIB_EXPORT Tag : public TagLib::Tag
+#ifndef DO_NOT_DOCUMENT
+    , private Element
+#endif
+    {
+    public:
+      /*!
+       * Constructs a Matroska tag.
+       */
+      Tag();
+
+      ~Tag() override;
+      String title() const override;
+      String artist() const override;
+      String album() const override;
+      String comment() const override;
+      String genre() const override;
+      unsigned int year() const override;
+      unsigned int track() const override;
+      void setTitle(const String &s) override;
+      void setArtist(const String &s) override;
+      void setAlbum(const String &s) override;
+      void setComment(const String &s) override;
+      void setGenre(const String &s) override;
+      void setYear(unsigned int i) override;
+      void setTrack(unsigned int i) override;
+      bool isEmpty() const override;
+      PropertyMap properties() const override;
+      PropertyMap setProperties(const PropertyMap &propertyMap) override;
+      void removeUnsupportedProperties(const StringList &properties) override;
+
+      /*!
+       * Returns the names of the binary simple tags.
+       */
+      StringList complexPropertyKeys() const override;
+
+      /*!
+       * Get the binary simple tags as maps with keys "data", "name",
+       * "targetTypeValue", "language", "defaultLanguage".
+       * The attached files such as pictures with key "PICTURE" are available
+       * with Matroska::File::complexProperties().
+       */
+      List<VariantMap> complexProperties(const String &key) const override;
+
+      /*!
+       * Set the binary simple tags as maps with keys "data", "name",
+       * "targetTypeValue", "language", "defaultLanguage".
+       * The attached files such as pictures with key "PICTURE" can be set
+       * with Matroska::File::setComplexProperties().
+       *
+       * Returns \c true if \c key can be stored as binary simple tags.
+       */
+      bool setComplexProperties(const String &key, const List<VariantMap> &value) override;
+
+      /*!
+       * Add a tag attribute.
+       */
+      void addSimpleTag(const SimpleTag &tag);
+
+      /*!
+       * Add multiple tag attributes.
+       */
+      void addSimpleTags(const SimpleTagsList &simpleTags);
+
+      /*!
+       * Insert a tag attribute at position \a index.
+       */
+      void insertSimpleTag(unsigned int index, const SimpleTag &tag);
+
+      /*!
+       * Remove a tag attribute at position \a index.
+       */
+      void removeSimpleTag(unsigned int index);
+
+      /*!
+       * Remove a tag attribute.
+       */
+      void removeSimpleTag(const String &name, SimpleTag::TargetTypeValue targetTypeValue,
+                           unsigned long long trackUid = 0);
+
+      /*!
+       * Remove a tag attribute.
+       */
+      // BIC: Merge with the method above
+      void removeSimpleTag(const String &name, SimpleTag::TargetTypeValue targetTypeValue,
+                           unsigned long long trackUid, unsigned long long editionUid,
+                           unsigned long long chapterUid = 0, unsigned long long attachmentUid = 0);
+
+      /*!
+       * Remove all tag attributes.
+       */
+      void clearSimpleTags();
+
+      /*!
+       * Get list of all tag attributes.
+       */
+      const SimpleTagsList &simpleTagsList() const;
+
+    private:
+      friend class File;
+      friend class EBML::MkTags;
+      class TagPrivate;
+
+      bool setTag(const String &key, const String &value);
+      void setSegmentTitle(const String &title);
+
+      // private Element implementation
+      ByteVector renderInternal() override;
+
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<TagPrivate> d;
+    };
+  }
+}
+
+#endif

taglib/matroska/matroskawritestyle.h

@@ -0,0 +1,49 @@
+/***************************************************************************
+    copyright            : (C) 2026 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ ***************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MATROSKAWRITESTYLE_H
+#define TAGLIB_MATROSKAWRITESTYLE_H
+
+namespace TagLib::Matroska {
+  /*!
+   * Controls the trade-off between file size and write speed when saving.
+   * Mode of writing tags, attachments and chapters to the file.
+   * For very large files and/or slow (network) filesystems, using
+   * \c AvoidInsert will reduce write time significantly.
+   */
+  enum class WriteStyle {
+    //! Write tags, attachments and chapters as compact as possible (default).
+    Compact,
+    //! Do not shrink elements; add void padding when content gets smaller.
+    //! Allow inserts when content gets larger.
+    DoNotShrink,
+    //! Like \c DoNotShrink but also avoid inserts for non-last elements:
+    //! replace a growing non-last element with a void of the old size and
+    //! append the new element at the end of the segment.
+    AvoidInsert
+  };
+}
+
+#endif //TAGLIB_MATROSKAWRITESTYLE_H

taglib/mp4/mp4atom.cpp

@@ -37,7 +37,7 @@ namespace {
   constexpr std::array containers {
     "moov", "udta", "mdia", "meta", "ilst",
     "stbl", "minf", "moof", "traf", "trak",
-    "stsd"
+    "stsd", "stem"
   };
 } // namespace
 
@@ -51,7 +51,7 @@ public:
   AtomList children;
 };
 
-MP4::Atom::Atom(File *file)
+MP4::Atom::Atom(File *file, int depth)
   : d(std::make_unique<AtomPrivate>(file->tell()))
 {
   d->children.setAutoDelete(true);
@@ -74,17 +74,7 @@ MP4::Atom::Atom(File *file)
   }
   else if(d->length == 1) {
     // The atom has a 64-bit length.
-    if(const long long longLength = file->readBlock(8).toLongLong();
-       longLength <= LONG_MAX) {
-      // The actual length fits in long. That's always the case if long is 64-bit.
-      d->length = static_cast<long>(longLength);
-    }
-    else {
-      debug("MP4: 64-bit atoms are not supported");
-      d->length = 0;
-      file->seek(0, File::End);
-      return;
-    }
+    d->length = file->readBlock(8).toLongLong();
   }
 
   if(d->length < 8 || d->length > file->length() - d->offset) {
@@ -96,6 +86,11 @@ MP4::Atom::Atom(File *file)
 
   d->name = header.mid(4, 4);
 
+  if(d->name == "stem") {
+    file->seek(d->length - 8, File::Current);
+    return;
+  }
+
   for(auto c : containers) {
     if(d->name == c) {
       if(d->name == "meta") {
@@ -114,8 +109,13 @@ MP4::Atom::Atom(File *file)
       else if(d->name == "stsd") {
         file->seek(8, File::Current);
       }
+      static constexpr int MAX_MP4_ATOM_DEPTH = 64;
+      if(depth > MAX_MP4_ATOM_DEPTH) {
+        debug("MP4: Maximum nesting depth exceeded");
+        return;
+      }
       while(file->tell() < d->offset + d->length) {
-        auto child = new MP4::Atom(file);
+        auto child = new MP4::Atom(file, depth + 1);
         d->children.append(child);
         if(child->d->length == 0)
           return;
@@ -127,6 +127,11 @@ MP4::Atom::Atom(File *file)
   file->seek(d->offset + d->length);
 }
 
+MP4::Atom::Atom(File *file)
+  : Atom(file, 0)
+{
+}
+
 MP4::Atom::~Atom() = default;
 
 MP4::Atom *
@@ -217,6 +222,8 @@ public:
 MP4::Atoms::Atoms(File *file) :
   d(std::make_unique<AtomsPrivate>())
 {
+  static constexpr int MAX_MP4_ATOM_COUNT_PER_LEVEL = 5000;
+
   d->atoms.setAutoDelete(true);
 
   file->seek(0, File::End);
@@ -227,6 +234,13 @@ MP4::Atoms::Atoms(File *file) :
     d->atoms.append(atom);
     if (atom->length() == 0)
       break;
+
+    if(d->atoms.size() > MAX_MP4_ATOM_COUNT_PER_LEVEL) {
+      debug("MP4: Maximum atom count exceeded");
+      // Make sure the file is detected as invalid.
+      d->atoms.clear();
+      break;
+    }
   }
 }
 

taglib/mp4/mp4atom.h

@@ -35,27 +35,48 @@ namespace TagLib {
   namespace MP4 {
 
     enum AtomDataType {
-      TypeImplicit  = 0,  // for use with tags for which no type needs to be indicated because only one type is allowed
-      TypeUTF8      = 1,  // without any count or null terminator
-      TypeUTF16     = 2,  // also known as UTF-16BE
-      TypeSJIS      = 3,  // deprecated unless it is needed for special Japanese characters
-      TypeHTML      = 6,  // the HTML file header specifies which HTML version
-      TypeXML       = 7,  // the XML header must identify the DTD or schemas
-      TypeUUID      = 8,  // also known as GUID; stored as 16 bytes in binary (valid as an ID)
-      TypeISRC      = 9,  // stored as UTF-8 text (valid as an ID)
-      TypeMI3P      = 10, // stored as UTF-8 text (valid as an ID)
-      TypeGIF       = 12, // (deprecated) a GIF image
-      TypeJPEG      = 13, // a JPEG image
-      TypePNG       = 14, // a PNG image
-      TypeURL       = 15, // absolute, in UTF-8 characters
-      TypeDuration  = 16, // in milliseconds, 32-bit integer
-      TypeDateTime  = 17, // in UTC, counting seconds since midnight, January 1, 1904; 32 or 64-bits
-      TypeGenred    = 18, // a list of enumerated values
-      TypeInteger   = 21, // a signed big-endian integer with length one of { 1,2,3,4,8 } bytes
-      TypeRIAAPA    = 24, // RIAA parental advisory; { -1=no, 1=yes, 0=unspecified }, 8-bit integer
-      TypeUPC       = 25, // Universal Product Code, in text UTF-8 format (valid as an ID)
-      TypeBMP       = 27, // Windows bitmap image
-      TypeUndefined = 255 // undefined
+      //! For use with tags for which no type needs to be indicated because only one type is allowed
+      TypeImplicit  = 0,
+      //! Without any count or null terminator
+      TypeUTF8      = 1,
+      //! Also known as UTF-16BE
+      TypeUTF16     = 2,
+      //! Deprecated unless it is needed for special Japanese characters
+      TypeSJIS      = 3,
+      //! The HTML file header specifies which HTML version
+      TypeHTML      = 6,
+      //! The XML header must identify the DTD or schemas
+      TypeXML       = 7,
+      //! Also known as GUID; stored as 16 bytes in binary (valid as an ID)
+      TypeUUID      = 8,
+      //! Stored as UTF-8 text (valid as an ID)
+      TypeISRC      = 9,
+      //! Stored as UTF-8 text (valid as an ID)
+      TypeMI3P      = 10,
+      //! (Deprecated) A GIF image
+      TypeGIF       = 12,
+      //! A JPEG image
+      TypeJPEG      = 13,
+      //! A PNG image
+      TypePNG       = 14,
+      //! Absolute, in UTF-8 characters
+      TypeURL       = 15,
+      //! In milliseconds, 32-bit integer
+      TypeDuration  = 16,
+      //! In UTC, counting seconds since midnight, January 1, 1904; 32 or 64-bits
+      TypeDateTime  = 17,
+      //! A list of enumerated values
+      TypeGenred    = 18,
+      //! A signed big-endian integer with length one of { 1,2,3,4,8 } bytes
+      TypeInteger   = 21,
+      //! RIAA parental advisory; { -1=no, 1=yes, 0=unspecified }, 8-bit integer
+      TypeRIAAPA    = 24,
+      //! Universal Product Code, in text UTF-8 format (valid as an ID)
+      TypeUPC       = 25,
+      //! Windows bitmap image
+      TypeBMP       = 27,
+      //! Undefined
+      TypeUndefined = 255
     };
 
 #ifndef DO_NOT_DOCUMENT
@@ -89,6 +110,9 @@ namespace TagLib {
       const ByteVector &name() const;
       const AtomList &children() const;
 
+    protected:
+      Atom(File *file, int depth);
+
     private:
       class AtomPrivate;
       TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE

taglib/mp4/mp4chapter.cpp

@@ -0,0 +1,89 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Ryan Francesconi
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "mp4chapter.h"
+#include "tstring.h"
+
+using namespace TagLib;
+
+class MP4::Chapter::ChapterPrivate
+{
+public:
+  ChapterPrivate() = default;
+  ~ChapterPrivate() = default;
+  String title;
+  long long startTime {0};
+};
+
+MP4::Chapter::Chapter(const String &title, long long startTime) :
+  d(std::make_unique<ChapterPrivate>())
+{
+  d->title = title;
+  d->startTime = startTime;
+}
+
+MP4::Chapter::Chapter(const Chapter &other) :
+  d(std::make_unique<ChapterPrivate>(*other.d))
+{
+}
+
+MP4::Chapter::Chapter(Chapter &&other) noexcept = default;
+
+MP4::Chapter::Chapter::~Chapter() = default;
+
+MP4::Chapter &MP4::Chapter::Chapter::operator=(const Chapter &other)
+{
+  Chapter(other).swap(*this);
+  return *this;
+}
+
+MP4::Chapter &MP4::Chapter::Chapter::operator=(
+  Chapter &&other) noexcept = default;
+
+bool MP4::Chapter::operator==(const Chapter &other) const
+{
+  return title() == other.title() && startTime() == other.startTime();
+}
+
+bool MP4::Chapter::operator!=(const Chapter &other) const
+{
+  return !(*this == other);
+}
+
+void MP4::Chapter::swap(Chapter &other) noexcept
+{
+  using std::swap;
+
+  swap(d, other.d);
+}
+
+const String &MP4::Chapter::title() const
+{
+  return d->title;
+}
+
+long long MP4::Chapter::startTime() const
+{
+  return d->startTime;
+}

taglib/mp4/mp4chapter.h

@@ -0,0 +1,108 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Ryan Francesconi
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MP4CHAPTER_H
+#define TAGLIB_MP4CHAPTER_H
+
+#include <memory>
+#include "taglib_export.h"
+#include "tlist.h"
+
+namespace TagLib {
+  class String;
+  namespace MP4 {
+
+    /*!
+     * A single Nero-style chapter marker.
+     */
+    class TAGLIB_EXPORT Chapter {
+    public:
+      /*!
+       * Construct a chapter.
+       */
+      Chapter(const String &title, long long startTime);
+
+      /*!
+       * Construct a chapter as a copy of \a other.
+       */
+      Chapter(const Chapter &other);
+
+      /*!
+       * Construct a chapter moving from \a other.
+       */
+      Chapter(Chapter &&other) noexcept;
+
+      /*!
+       * Destroys this chapter.
+       */
+      ~Chapter();
+
+      /*!
+       * Copies the contents of \a other into this object.
+       */
+      Chapter &operator=(const Chapter &other);
+
+      /*!
+       * Moves the contents of \a other into this object.
+       */
+      Chapter &operator=(Chapter &&other) noexcept;
+
+      /*!
+       * Returns \c true if the chapter and \a other contain the same data.
+       */
+      bool operator==(const Chapter &other) const;
+
+      /*!
+       * Returns \c true if the chapter and \a other differ in data.
+       */
+      bool operator!=(const Chapter &other) const;
+
+      /*!
+       * Exchanges the content of the object with the content of \a other.
+       */
+      void swap(Chapter &other) noexcept;
+
+      /*!
+       * Returns the title representing the chapter.
+       */
+      const String &title() const;
+
+      /*!
+       * Returns the start time in milliseconds.
+       */
+      long long startTime() const;
+
+    private:
+      class ChapterPrivate;
+      TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+      std::unique_ptr<ChapterPrivate> d;
+    };
+
+    //! List of chapters.
+    using ChapterList = List<Chapter>;
+
+  }  // namespace MP4
+}  // namespace TagLib
+
+#endif

taglib/mp4/mp4chapterholder.h

@@ -0,0 +1,126 @@
+/**************************************************************************
+    copyright            : (C) 2006 by Urs Fleisch
+    email                : ufleisch@users.sourceforge.net
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MP4CHAPTERHOLDER_H
+#define TAGLIB_MP4CHAPTERHOLDER_H
+
+#include "mp4chapter.h"
+
+namespace TagLib {
+  class File;
+  namespace MP4 {
+    /*!
+     * Base class to hold chapters and store modified state.
+     */
+    class ChapterHolder {
+    public:
+      /*!
+       * Get list of chapters.
+       */
+      ChapterList chapters() const { return chapterList; }
+
+      /*!
+       * Set list of chapters.
+       */
+      void setChapters(const ChapterList &chapters) { chapterList = chapters; }
+
+      /*!
+       * Returns \c true if the list of chapters has been modified.
+       */
+      bool isModified() const { return modified; }
+
+      /*!
+       * Set if the contained chapters are modified.
+       */
+      void setModified(bool chaptersModified) { modified = chaptersModified; }
+
+    protected:
+      ChapterList chapterList;
+      bool modified = false;
+    };
+
+    /*!
+     * Lazily fetch list of chapters.
+     * @tparam T class derived from ChapterHolder and implementing read(File *)
+     * @param holder unique pointer to holder, initially null
+     * @param file file with chapters
+     * @return list of chapters, empty if no chapters found.
+     */
+    template <typename T>
+    ChapterList getChaptersLazy(std::unique_ptr<T> &holder, TagLib::File *file)
+    {
+      if (!holder) {
+        holder = std::make_unique<T>();
+        holder->read(file);
+      }
+      return holder->chapters();
+    }
+
+    /*!
+     * Lazily set a list of chapters.
+     * @tparam T class derived from ChapterHolder
+     * @param holder unique pointer to holder, initially null
+     * @param chapters list of chapters to set
+     */
+    template <typename T>
+    void setChaptersLazy(std::unique_ptr<T> &holder, const ChapterList& chapters)
+    {
+      if (!holder) {
+        holder = std::make_unique<T>();
+        // The chapters have not been read before, so we do not know their
+        // current state and mark them as modified. Otherwise, the check below
+        // would not set the chapters if they are empty.
+        holder->setModified(true);
+      }
+      if(holder->isModified() || holder->chapters() != chapters) {
+        holder->setChapters(chapters);
+        holder->setModified(true);
+      }
+    }
+
+    /*!
+     * Save a list of chapters if it has been modified.
+     * @tparam T class derived from ChapterHolder and implementing write(File *)
+     * @param holder unique pointer to holder, initially null
+     * @param file file with chapters
+     * @return true if write successful or not modified.
+     */
+    template <typename T>
+    bool saveChaptersIfModified(std::unique_ptr<T> &holder, TagLib::File *file)
+    {
+      if(holder && holder->isModified()) {
+        if(holder->write(file)) {
+          holder->setModified(false);
+          return true;
+        }
+        return false;
+      }
+      return true;
+    }
+
+  }  // namespace MP4
+}  // namespace TagLib
+
+#endif

taglib/mp4/mp4file.cpp

@@ -30,6 +30,8 @@
 #include "tagutils.h"
 
 #include "mp4itemfactory.h"
+#include "mp4nerochapterlist.h"
+#include "mp4qtchapterlist.h"
 
 using namespace TagLib;
 
@@ -48,6 +50,8 @@ public:
   std::unique_ptr<MP4::Tag> tag;
   std::unique_ptr<MP4::Atoms> atoms;
   std::unique_ptr<MP4::Properties> properties;
+  std::unique_ptr<MP4::NeroChapterList> neroChapterList;
+  std::unique_ptr<MP4::QtChapterList> qtChapterList;
 };
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -111,6 +115,26 @@ MP4::Properties *MP4::File::audioProperties() const
   return d->properties.get();
 }
 
+MP4::ChapterList MP4::File::neroChapters()
+{
+  return getChaptersLazy(d->neroChapterList, this);
+}
+
+void MP4::File::setNeroChapters(const ChapterList& chapters)
+{
+  setChaptersLazy(d->neroChapterList, chapters);
+}
+
+MP4::ChapterList MP4::File::qtChapters()
+{
+  return getChaptersLazy(d->qtChapterList, this);
+}
+
+void MP4::File::setQtChapters(const ChapterList& chapters)
+{
+  setChaptersLazy(d->qtChapterList, chapters);
+}
+
 void
 MP4::File::read(bool readProperties)
 {
@@ -148,7 +172,9 @@ MP4::File::save()
     return false;
   }
 
-  return d->tag->save();
+  return d->tag->save() &&
+    saveChaptersIfModified(d->neroChapterList, this) &&
+    saveChaptersIfModified(d->qtChapterList, this);
 }
 
 bool

taglib/mp4/mp4file.h

@@ -31,6 +31,7 @@
 #include "mp4tag.h"
 #include "tag.h"
 #include "mp4properties.h"
+#include "mp4chapter.h"
 
 namespace TagLib {
   //! An implementation of MP4 (AAC, ALAC, ...) metadata
@@ -130,6 +131,26 @@ namespace TagLib {
        */
       Properties *audioProperties() const override;
 
+      /*!
+       * Returns the Nero style chapters for this file.
+       */
+      ChapterList neroChapters();
+
+      /*!
+       * Sets the Nero style chapters for this file.
+       */
+      void setNeroChapters(const ChapterList &chapters);
+
+      /*!
+       * Returns the QuickTime chapters for this file.
+       */
+      ChapterList qtChapters();
+
+      /*!
+       * Sets the QuickTime style chapters for this file.
+       */
+      void setQtChapters(const ChapterList &chapters);
+
       /*!
        * Save the file.
        *

taglib/mp4/mp4item.cpp

@@ -44,6 +44,7 @@ public:
   StringList m_stringList;
   ByteVectorList m_byteVectorList;
   MP4::CoverArtList m_coverArtList;
+  MP4::Stem m_stem;
 };
 
 MP4::Item::Item() :
@@ -130,6 +131,13 @@ MP4::Item::Item(const MP4::CoverArtList &value) :
   d->m_coverArtList = value;
 }
 
+MP4::Item::Item(const MP4::Stem &value) :
+  d(std::make_shared<ItemPrivate>())
+{
+  d->type = Type::Stem;
+  d->m_stem = value;
+}
+
 void MP4::Item::setAtomDataType(MP4::AtomDataType type)
 {
   d->atomDataType = type;
@@ -194,6 +202,12 @@ MP4::Item::toCoverArtList() const
   return d->m_coverArtList;
 }
 
+MP4::Stem
+MP4::Item::toStem() const
+{
+  return d->m_stem;
+}
+
 bool
 MP4::Item::isValid() const
 {
@@ -234,6 +248,8 @@ bool MP4::Item::operator==(const Item &other) const
       return toByteVectorList() == other.toByteVectorList();
     case Type::CoverArtList:
       return toCoverArtList() == other.toCoverArtList();
+    case Type::Stem:
+      return toStem() == other.toStem();
     }
   }
   return false;

taglib/mp4/mp4item.h

@@ -29,6 +29,7 @@
 #include "tstringlist.h"
 #include "taglib_export.h"
 #include "mp4coverart.h"
+#include "mp4stem.h"
 
 namespace TagLib {
   namespace MP4 {
@@ -49,7 +50,8 @@ namespace TagLib {
         LongLong,
         StringList,
         ByteVectorList,
-        CoverArtList
+        CoverArtList,
+        Stem,
       };
 
       struct IntPair {
@@ -80,6 +82,7 @@ namespace TagLib {
       Item(const StringList &value);
       Item(const ByteVectorList &value);
       Item(const CoverArtList &value);
+      Item(const Stem &value);
 
       void setAtomDataType(AtomDataType type);
       AtomDataType atomDataType() const;
@@ -93,6 +96,7 @@ namespace TagLib {
       StringList toStringList() const;
       ByteVectorList toByteVectorList() const;
       CoverArtList toCoverArtList() const;
+      Stem toStem() const;
 
       bool isValid() const;
 

taglib/mp4/mp4itemfactory.cpp

@@ -25,6 +25,7 @@
 
 #include "mp4itemfactory.h"
 
+#include <mutex>
 #include <utility>
 
 #include "tbytevector.h"
@@ -47,6 +48,8 @@ public:
   NameHandlerMap handlerTypeForName;
   Map<ByteVector, String> propertyKeyForName;
   Map<String, ByteVector> nameForPropertyKey;
+  mutable std::once_flag handlerMapOnce;
+  mutable std::once_flag propertyMapsOnce;
 };
 
 ItemFactory ItemFactory::factory;
@@ -87,6 +90,8 @@ std::pair<String, Item> ItemFactory::parseItem(
     return parseGnre(atom, data);
   case ItemHandlerType::Covr:
     return parseCovr(atom, data);
+  case ItemHandlerType::Stem:
+    return parseStem(atom, data);
   case ItemHandlerType::TextImplicit:
     return parseText(atom, data, -1);
   case ItemHandlerType::Text:
@@ -128,6 +133,8 @@ ByteVector ItemFactory::renderItem(
     return renderInt(name, item);
   case ItemHandlerType::Covr:
     return renderCovr(name, item);
+  case ItemHandlerType::Stem:
+    return renderStem(name, item);
   case ItemHandlerType::TextImplicit:
     return renderText(name, item, TypeImplicit);
   case ItemHandlerType::Text:
@@ -175,8 +182,8 @@ std::pair<ByteVector, Item> ItemFactory::itemFromProperty(
     case ItemHandlerType::TextImplicit:
     case ItemHandlerType::Text:
       return {name, values};
-
     case ItemHandlerType::Covr:
+    case ItemHandlerType::Stem:
       debug("MP4: Invalid item \"" + name + "\" for property");
       break;
     case ItemHandlerType::Unknown:
@@ -222,6 +229,7 @@ std::pair<String, StringList> ItemFactory::itemToProperty(
       return {key, item.toStringList()};
 
     case ItemHandlerType::Covr:
+    case ItemHandlerType::Stem:
       debug("MP4: Invalid item \"" + itemName + "\" for property");
       break;
     case ItemHandlerType::Unknown:
@@ -234,9 +242,11 @@ std::pair<String, StringList> ItemFactory::itemToProperty(
 
 String ItemFactory::propertyKeyForName(const ByteVector &name) const
 {
-  if(d->propertyKeyForName.isEmpty()) {
+  std::call_once(d->propertyMapsOnce, [this] {
     d->propertyKeyForName = namePropertyMap();
-  }
+    for(const auto &[k, t] : std::as_const(d->propertyKeyForName))
+      d->nameForPropertyKey[t] = k;
+  });
   String key = d->propertyKeyForName.value(name);
   if(key.isEmpty() && name.startsWith(freeFormPrefix)) {
     key = name.mid(std::size(freeFormPrefix) - 1);
@@ -246,14 +256,11 @@ String ItemFactory::propertyKeyForName(const ByteVector &name) const
 
 ByteVector ItemFactory::nameForPropertyKey(const String &key) const
 {
-  if(d->nameForPropertyKey.isEmpty()) {
-    if(d->propertyKeyForName.isEmpty()) {
-      d->propertyKeyForName = namePropertyMap();
-    }
-    for(const auto &[k, t] : std::as_const(d->propertyKeyForName)) {
+  std::call_once(d->propertyMapsOnce, [this] {
+    d->propertyKeyForName = namePropertyMap();
+    for(const auto &[k, t] : std::as_const(d->propertyKeyForName))
       d->nameForPropertyKey[t] = k;
-    }
-  }
+  });
   ByteVector name = d->nameForPropertyKey.value(key);
   if(name.isEmpty() && !key.isEmpty()) {
     const auto &firstChar = key[0];
@@ -303,6 +310,7 @@ ItemFactory::NameHandlerMap ItemFactory::nameHandlerMap() const
     {"akID", ItemHandlerType::Byte},
     {"gnre", ItemHandlerType::Gnre},
     {"covr", ItemHandlerType::Covr},
+    {"stem", ItemHandlerType::Stem},
     {"purl", ItemHandlerType::TextImplicit},
     {"egid", ItemHandlerType::TextImplicit},
   };
@@ -311,9 +319,9 @@ ItemFactory::NameHandlerMap ItemFactory::nameHandlerMap() const
 ItemFactory::ItemHandlerType ItemFactory::handlerTypeForName(
   const ByteVector &name) const
 {
-  if(d->handlerTypeForName.isEmpty()) {
+  std::call_once(d->handlerMapOnce, [this] {
     d->handlerTypeForName = nameHandlerMap();
-  }
+  });
   auto type = d->handlerTypeForName.value(name, ItemHandlerType::Unknown);
   if (type == ItemHandlerType::Unknown && name.size() == 4) {
     type = ItemHandlerType::Text;
@@ -633,6 +641,12 @@ std::pair<String, Item> ItemFactory::parseCovr(
   };
 }
 
+std::pair<String, Item> ItemFactory::parseStem(
+  const MP4::Atom *atom, const ByteVector &data)
+{
+  return {atom->name(), Item(Stem(data))};
+}
+
 
 ByteVector ItemFactory::renderAtom(
   const ByteVector &name, const ByteVector &data)
@@ -742,6 +756,13 @@ ByteVector ItemFactory::renderCovr(
   return renderAtom(name, data);
 }
 
+ByteVector ItemFactory::renderStem(
+  const ByteVector &name, const MP4::Item &item)
+{
+  auto data = item.toStem().data();
+  return renderAtom(name, data);
+}
+
 ByteVector ItemFactory::renderFreeForm(
   const String &name, const MP4::Item &item)
 {

taglib/mp4/mp4itemfactory.h

@@ -142,6 +142,7 @@ namespace TagLib {
         Byte,
         Gnre,
         Covr,
+        Stem,
         TextImplicit,
         Text
       };
@@ -214,6 +215,8 @@ namespace TagLib {
         const MP4::Atom *atom, const ByteVector &bytes);
       static std::pair<String, Item> parseCovr(
         const MP4::Atom *atom, const ByteVector &data);
+      static std::pair<String, Item> parseStem(
+        const MP4::Atom *atom, const ByteVector &data);
 
       // Functions used by renderItem() to render atom data for items.
       static ByteVector renderAtom(
@@ -242,6 +245,8 @@ namespace TagLib {
         const ByteVector &name, const MP4::Item &item);
       static ByteVector renderCovr(
         const ByteVector &name, const MP4::Item &item);
+      static ByteVector renderStem(
+        const ByteVector &name, const MP4::Item &item);
 
     private:
       static ItemFactory factory;

taglib/mp4/mp4nerochapterlist.cpp

@@ -0,0 +1,320 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Ryan Francesconi
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "mp4nerochapterlist.h"
+
+#include <algorithm>
+
+#include "tdebug.h"
+#include "mp4file.h"
+#include "mp4atom.h"
+
+using namespace TagLib;
+
+namespace
+{
+  ByteVector renderAtom(const ByteVector &name, const ByteVector &data)
+  {
+    return ByteVector::fromUInt(data.size() + 8) + name + data;
+  }
+
+  // Update parent atom sizes along a path when child size changes by delta.
+  // Mirrors MP4::Tag::updateParents().
+  void updateParentSizes(TagLib::File *file, const MP4::AtomList &path,
+                         offset_t delta, int ignore = 0)
+  {
+    if(static_cast<int>(path.size()) <= ignore)
+      return;
+
+    auto itEnd = path.end();
+    std::advance(itEnd, 0 - ignore);
+
+    for(auto it = path.begin(); it != itEnd; ++it) {
+      file->seek((*it)->offset());
+      if(const long size = file->readBlock(4).toUInt(); size == 1) {
+        // 64-bit size
+        file->seek(4, TagLib::File::Current);
+        const long long longSize = file->readBlock(8).toLongLong();
+        file->seek((*it)->offset() + 8);
+        file->writeBlock(ByteVector::fromLongLong(longSize + delta));
+      }
+      else {
+        // 32-bit size
+        file->seek((*it)->offset());
+        file->writeBlock(ByteVector::fromUInt(static_cast<unsigned int>(size + delta)));
+      }
+    }
+  }
+
+  // Update stco/co64/tfhd chunk offsets when file content shifts.
+  // Mirrors MP4::Tag::updateOffsets().
+  void updateChunkOffsets(TagLib::File *file, const MP4::Atoms *atoms,
+                          offset_t delta, offset_t offset)
+  {
+    if(const MP4::Atom *moov = atoms->find("moov")) {
+      const MP4::AtomList stco = moov->findall("stco", true);
+      for(const auto &atom : stco) {
+        if(atom->offset() > offset)
+          atom->addToOffset(delta);
+        file->seek(atom->offset() + 12);
+        ByteVector data = file->readBlock(atom->length() - 12);
+        unsigned int count = data.toUInt();
+        file->seek(atom->offset() + 16);
+        unsigned int pos = 4;
+        const unsigned int maxPos = data.size() - 4;
+        while(count-- && pos <= maxPos) {
+          auto o = static_cast<offset_t>(data.toUInt(pos));
+          if(o > offset)
+            o += delta;
+          file->writeBlock(ByteVector::fromUInt(static_cast<unsigned int>(o)));
+          pos += 4;
+        }
+      }
+
+      const MP4::AtomList co64 = moov->findall("co64", true);
+      for(const auto &atom : co64) {
+        if(atom->offset() > offset)
+          atom->addToOffset(delta);
+        file->seek(atom->offset() + 12);
+        ByteVector data = file->readBlock(atom->length() - 12);
+        unsigned int count = data.toUInt();
+        file->seek(atom->offset() + 16);
+        unsigned int pos = 4;
+        const unsigned int maxPos = data.size() - 8;
+        while(count-- && pos <= maxPos) {
+          long long o = data.toLongLong(pos);
+          if(o > offset)
+            o += delta;
+          file->writeBlock(ByteVector::fromLongLong(o));
+          pos += 8;
+        }
+      }
+    }
+
+    if(const MP4::Atom *moof = atoms->find("moof")) {
+      const MP4::AtomList tfhd = moof->findall("tfhd", true);
+      for(const auto &atom : tfhd) {
+        if(atom->offset() > offset)
+          atom->addToOffset(delta);
+        file->seek(atom->offset() + 9);
+        ByteVector data = file->readBlock(atom->length() - 9);
+        if(const unsigned int flags = data.toUInt(0, 3, true);
+           flags & 1) {
+          long long o = data.toLongLong(7U);
+          if(o > offset)
+            o += delta;
+          file->seek(atom->offset() + 16);
+          file->writeBlock(ByteVector::fromLongLong(o));
+        }
+      }
+    }
+  }
+
+  // Build the binary payload for a chpl atom (version 1).
+  ByteVector renderChplData(const MP4::ChapterList &chapters)
+  {
+    const unsigned int count = std::min(chapters.size(), 255U);
+
+    ByteVector data;
+    // Version (1 byte) + flags (3 bytes) + reserved (4 bytes)
+    data.append(static_cast<char>(0x01));        // version 1
+    data.append(ByteVector(3, '\0'));             // flags
+    data.append(ByteVector(4, '\0'));             // reserved
+
+    // Chapter count
+    data.append(static_cast<char>(count & 0xFF));
+
+    unsigned int i = 0;
+    for(const auto &ch : chapters) {
+      if(i++ >= count)
+        break;
+
+      // Start time: 8 bytes big-endian, on-disk format is 100-nanosecond units
+      data.append(ByteVector::fromLongLong(ch.startTime() * 10000LL));
+
+      // Title: 1-byte length + UTF-8 bytes (max 255 bytes)
+      ByteVector titleBytes = ch.title().data(String::UTF8);
+      const unsigned int titleLen = std::min(titleBytes.size(), 255U);
+      data.append(static_cast<char>(titleLen & 0xFF));
+      if(titleLen > 0)
+        data.append(titleBytes.mid(0, titleLen));
+    }
+
+    return data;
+  }
+
+  // Parse the binary content of a chpl atom into a ChapterList.
+  MP4::ChapterList parseChplData(const ByteVector &data)
+  {
+    MP4::ChapterList chapters;
+
+    // Minimum: version(1) + flags(3) + count(1) = 5 bytes (version 0 layout)
+    if(data.size() < 5)
+      return chapters;
+
+    unsigned int pos = 0;
+    const auto version = static_cast<unsigned char>(data[pos++]);
+
+    // Skip flags (3 bytes)
+    pos += 3;
+
+    // Version 1 has 4 reserved bytes
+    if(version >= 1)
+      pos += 4;
+
+    if(pos >= data.size())
+      return chapters;
+
+    const unsigned int count = static_cast<unsigned char>(data[pos++]);
+
+    for(unsigned int i = 0; i < count && pos + 9 <= data.size(); ++i) {
+      const long long startTime100ns = data.toLongLong(pos);
+      pos += 8;
+
+      const unsigned int titleLen = static_cast<unsigned char>(data[pos++]);
+
+      String title;
+      if(titleLen > 0 && pos + titleLen <= data.size()) {
+        title = String(data.mid(pos, titleLen), String::UTF8);
+        pos += titleLen;
+      }
+
+      chapters.append(MP4::Chapter(title, startTime100ns / 10000LL));
+    }
+
+    return chapters;
+  }
+
+}  // namespace
+
+////////////////////////////////////////////////////////////////////////////////
+// public members
+////////////////////////////////////////////////////////////////////////////////
+
+bool MP4::NeroChapterList::read(TagLib::File *file)
+{
+  const Atoms atoms(file);
+
+  const Atom *chpl = atoms.find("moov", "udta", "chpl");
+  modified = false;
+  chapterList.clear();
+  if(chpl) {
+    // Read the atom content (skip 8-byte atom header)
+    file->seek(chpl->offset() + 8);
+    const ByteVector data = file->readBlock(chpl->length() - 8);
+
+    chapterList = parseChplData(data);
+    return true;
+  }
+  return false;
+}
+
+bool MP4::NeroChapterList::write(TagLib::File *file)
+{
+  // Writing an empty list is equivalent to removing the chapters.
+  if(chapterList.isEmpty())
+    return remove(file);
+
+  const Atoms atoms(file);
+
+  if(!atoms.find("moov")) {
+    debug("MP4ChapterList::write() -- No moov atom found");
+    return false;
+  }
+
+  const ByteVector chplPayload = renderChplData(chapterList);
+  const ByteVector chplAtom = renderAtom("chpl", chplPayload);
+
+  if(const Atom *existingChpl = atoms.find("moov", "udta", "chpl")) {
+    // Replace existing chpl atom
+    const offset_t offset = existingChpl->offset();
+    const offset_t oldLength = existingChpl->length();
+    const offset_t delta = static_cast<offset_t>(chplAtom.size()) - oldLength;
+
+    file->insert(chplAtom, offset, oldLength);
+
+    if(delta != 0) {
+      // Update parent sizes: moov and udta
+      const AtomList parentPath = atoms.path("moov", "udta", "chpl");
+      updateParentSizes(file, parentPath, delta, 1);  // ignore chpl itself
+      updateChunkOffsets(file, &atoms, delta, offset);
+    }
+  }
+  else {
+    // Need to insert a new chpl atom
+
+    if(AtomList udtaPath = atoms.path("moov", "udta"); udtaPath.size() == 2) {
+      // udta exists -- insert chpl at the beginning of udta's content
+      const offset_t insertOffset = udtaPath.back()->offset() + 8;
+      file->insert(chplAtom, insertOffset, 0);
+
+      updateParentSizes(file, udtaPath, chplAtom.size());
+      updateChunkOffsets(file, &atoms, chplAtom.size(), insertOffset);
+    }
+    else {
+      // No udta -- insert udta + chpl at the beginning of moov's content
+      const ByteVector udtaAtom = renderAtom("udta", chplAtom);
+
+      AtomList moovPath = atoms.path("moov");
+      if(moovPath.isEmpty()) {
+        debug("MP4ChapterList::write() -- No moov atom in path");
+        return false;
+      }
+
+      const offset_t insertOffset = moovPath.back()->offset() + 8;
+      file->insert(udtaAtom, insertOffset, 0);
+
+      updateParentSizes(file, moovPath, udtaAtom.size());
+      updateChunkOffsets(file, &atoms, udtaAtom.size(), insertOffset);
+    }
+  }
+
+  modified = false;
+  return true;
+}
+
+bool MP4::NeroChapterList::remove(TagLib::File *file)
+{
+  const Atoms atoms(file);
+  chapterList.clear();
+  modified = false;
+
+  const Atom *chpl = atoms.find("moov", "udta", "chpl");
+  if(!chpl) {
+    // No chpl atom -- nothing to remove
+    return true;
+  }
+
+  const offset_t offset = chpl->offset();
+  const offset_t length = chpl->length();
+
+  file->removeBlock(offset, length);
+
+  // Update parent sizes with negative delta
+  const AtomList parentPath = atoms.path("moov", "udta", "chpl");
+  updateParentSizes(file, parentPath, -length, 1);  // ignore chpl itself
+  updateChunkOffsets(file, &atoms, -length, offset);
+
+  return true;
+}

taglib/mp4/mp4nerochapterlist.h

@@ -0,0 +1,66 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Ryan Francesconi
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MP4CHAPTERLIST_H
+#define TAGLIB_MP4CHAPTERLIST_H
+
+#include "mp4chapterholder.h"
+
+namespace TagLib {
+  class File;
+  namespace MP4 {
+
+    /*!
+     * Reads, writes, and removes Nero-style chapter markers (chpl atom)
+     * from MP4 files.  Operates independently of MP4::Tag -- the chpl atom
+     * lives at moov/udta/chpl, a sibling of the metadata ilst path.
+     */
+    class NeroChapterList : public ChapterHolder
+    {
+    public:
+      /*!
+       * Reads chapter markers from the already-opened \a file.
+       * Returns \c false if the file has no chpl atom.
+       */
+      bool read(TagLib::File *file);
+
+      /*!
+       * Writes chapter markers to the already-opened \a file,
+       * replacing any existing chpl atom.
+       * The chapter count is capped at 255 (Nero format limit).
+       * Returns \c true on success.
+       */
+      bool write(TagLib::File *file);
+
+      /*!
+       * Removes the chpl atom from the already-opened \a file.
+       * Returns \c true on success, or if no chpl atom exists.
+       */
+      bool remove(TagLib::File *file);
+    };
+
+  }  // namespace MP4
+}  // namespace TagLib
+
+#endif

taglib/mp4/mp4properties.cpp

@@ -224,7 +224,7 @@ MP4::Properties::read(File *file, const Atoms *atoms)
         pos += 10;
         if(const unsigned int bitrateValue = data.toUInt(pos);
            bitrateValue != 0 || d->length <= 0) {
-          d->bitrate = static_cast<int>((bitrateValue + 500) / 1000.0 + 0.5);
+          d->bitrate = static_cast<int>(bitrateValue / 1000.0 + 0.5);
         }
         else {
           d->bitrate = static_cast<int>(

taglib/mp4/mp4qtchapterlist.h

@@ -0,0 +1,78 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Ryan Francesconi
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MP4QTCHAPTERLIST_H
+#define TAGLIB_MP4QTCHAPTERLIST_H
+
+#include "mp4chapterholder.h"
+
+namespace TagLib {
+  class File;
+  namespace MP4 {
+
+    /*!
+     * Reads, writes, and removes QuickTime-style chapter tracks from MP4
+     * files.  A QT chapter track is a disabled text track (\c hdlr type
+     * \c "text") referenced by a \c chap track-reference in the audio
+     * track's \c tref box.  This format is understood by QuickTime,
+     * iTunes, Final Cut, Logic, DaVinci Resolve, Twisted Wave, and most
+     * other Apple/macOS software.
+     *
+     * The existing \c MP4ChapterList class handles Nero-style \c chpl
+     * atoms, which are a different (and less widely supported) chapter
+     * format.
+     *
+     * Chapter times use the same 100-nanosecond unit convention as
+     * \c MP4ChapterList so that existing \c Chapter / \c ChapterList
+     * types can be shared.
+     */
+    class QtChapterList : public ChapterHolder
+    {
+    public:
+      /*!
+       * Reads chapter markers from the QuickTime chapter track in the
+       * already-opened \a file.
+       * Returns \c false if the file has no chapter track.
+       */
+      bool read(TagLib::File *file);
+
+      /*!
+       * Writes chapter markers as a QuickTime chapter track to the
+       * already-opened \a file, replacing any existing chapter track.
+       * Returns \c true on success.
+       */
+      bool write(TagLib::File *file);
+
+      /*!
+       * Removes the QuickTime chapter track and its \c tref/chap
+       * reference from the already-opened \a file.
+       * Returns \c true on success, or if no chapter track exists.
+       */
+      bool remove(TagLib::File *file);
+    };
+
+  }  // namespace MP4
+}  // namespace TagLib
+
+#endif

taglib/mp4/mp4stem.cpp

@@ -0,0 +1,64 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Antoine Colombier
+    email                : antoine@mixxx.org
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#include "mp4stem.h"
+
+using namespace TagLib;
+
+MP4::Stem::Stem(const ByteVector &data) :
+  d(std::make_shared<StemPrivate>())
+{
+  d->data = data;
+}
+
+MP4::Stem::Stem() = default;
+MP4::Stem::Stem(const Stem &) = default;
+MP4::Stem &MP4::Stem::operator=(const Stem &) = default;
+
+void
+MP4::Stem::swap(Stem &item) noexcept
+{
+  using std::swap;
+
+  swap(d, item.d);
+}
+
+MP4::Stem::~Stem() = default;
+
+ByteVector
+MP4::Stem::data() const
+{
+  return d->data;
+}
+
+bool MP4::Stem::operator==(const Stem &other) const
+{
+  return data() == other.data();
+}
+
+bool MP4::Stem::operator!=(const Stem &other) const
+{
+  return !(*this == other);
+}

taglib/mp4/mp4stem.h

@@ -0,0 +1,78 @@
+/**************************************************************************
+    copyright            : (C) 2026 by Antoine Colombier
+    email                : antoine@mixxx.org
+ **************************************************************************/
+
+/***************************************************************************
+ *   This library is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License version   *
+ *   2.1 as published by the Free Software Foundation.                     *
+ *                                                                         *
+ *   This library is distributed in the hope that it will be useful, but   *
+ *   WITHOUT ANY WARRANTY; without even the implied warranty of            *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU     *
+ *   Lesser General Public License for more details.                       *
+ *                                                                         *
+ *   You should have received a copy of the GNU Lesser General Public      *
+ *   License along with this library; if not, write to the Free Software   *
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA         *
+ *   02110-1301  USA                                                       *
+ *                                                                         *
+ *   Alternatively, this file is available under the Mozilla Public        *
+ *   License Version 1.1.  You may obtain a copy of the License at         *
+ *   http://www.mozilla.org/MPL/                                           *
+ ***************************************************************************/
+
+#ifndef TAGLIB_MP4STEM_H
+#define TAGLIB_MP4STEM_H
+
+#include "tbytevector.h"
+#include "taglib_export.h"
+
+namespace TagLib::MP4 {
+  //! STEM
+  class StemPrivate
+  {
+  public:
+    ByteVector data;
+  };
+
+  class TAGLIB_EXPORT Stem
+  {
+  public:
+    Stem();
+    explicit Stem(const ByteVector &data);
+    ~Stem();
+
+    Stem(const Stem &item);
+
+    /*!
+     * Copies the contents of \a item into this Stem.
+     */
+    Stem &operator=(const Stem &item);
+
+    /*!
+     * Exchanges the content of the Stem with the content of \a item.
+     */
+    void swap(Stem &item) noexcept;
+
+    //! The Stem data
+    ByteVector data() const;
+
+    /*!
+     * Returns \c true if the Stem and \a other contain the same data.
+     */
+    bool operator==(const Stem &other) const;
+
+    /*!
+     * Returns \c true if the Stem and \a other have different data.
+     */
+    bool operator!=(const Stem &other) const;
+
+  private:
+    TAGLIB_MSVC_SUPPRESS_WARNING_NEEDS_TO_HAVE_DLL_INTERFACE
+    std::shared_ptr<StemPrivate> d;
+  };
+} // namespace TagLib::MP4
+
+#endif

taglib/mp4/mp4tag.cpp

@@ -32,6 +32,7 @@
 #include "mp4itemfactory.h"
 #include "mp4atom.h"
 #include "mp4coverart.h"
+#include "mp4stem.h"
 
 using namespace TagLib;
 
@@ -65,15 +66,22 @@ MP4::Tag::Tag(TagLib::File *file, MP4::Atoms *atoms,
   d->atoms = atoms;
 
   const MP4::Atom *ilst = atoms->find("moov", "udta", "meta", "ilst");
-  if(!ilst) {
-    //debug("Atom moov.udta.meta.ilst not found.");
-    return;
+  if(ilst) {
+    for(const auto &atom : ilst->children()) {
+      file->seek(atom->offset() + 8);
+      ByteVector data = d->file->readBlock(atom->length() - 8);
+      if(const auto &[name, itm] = d->factory->parseItem(atom, data);
+        itm.isValid()) {
+        addItem(name, itm);
+      }
+    }
   }
 
-  for(const auto &atom : ilst->children()) {
-    file->seek(atom->offset() + 8);
-    ByteVector data = d->file->readBlock(atom->length() - 8);
-    if(const auto &[name, itm] = d->factory->parseItem(atom, data);
+  const MP4::Atom *stem = atoms->find("moov", "udta", "stem");
+  if(stem) {
+    file->seek(stem->offset() + 8);
+    ByteVector data = d->file->readBlock(stem->length() - 8);
+    if(const auto &[name, itm] = d->factory->parseItem(stem, data);
        itm.isValid()) {
       addItem(name, itm);
     }
@@ -100,18 +108,33 @@ MP4::Tag::renderAtom(const ByteVector &name, const ByteVector &data) const
 bool
 MP4::Tag::save()
 {
-  ByteVector data;
+  ByteVector ilstData, stemData;
   for(const auto &[name, itm] : std::as_const(d->items)) {
-    data.append(d->factory->renderItem(name, itm));
+    if(name == "stem"){
+      stemData.append(d->factory->renderItem(name, itm));
+    } else {
+      ilstData.append(d->factory->renderItem(name, itm));
+    }
   }
-  data = renderAtom("ilst", data);
+  ilstData = renderAtom("ilst", ilstData);
 
   AtomList path = d->atoms->path("moov", "udta", "meta", "ilst");
   if(path.size() == 4) {
-    saveExisting(data, path);
+    saveExisting(ilstData, path);
   }
   else {
-    saveNew(data);
+    ByteVector metaData = renderAtom("meta", ByteVector(4, '\0') +
+                      renderAtom("hdlr", ByteVector(8, '\0') + ByteVector("mdirappl") +
+                                ByteVector(9, '\0')) +
+                      ilstData + padIlst(ilstData));
+    saveNew(metaData);
+  }
+
+  path = d->atoms->path("moov", "udta", "stem");
+  if(path.size() == 3) {
+    saveExisting(stemData, path);
+  } else if (!stemData.isEmpty()) {
+    saveNew(stemData);
   }
 
   return true;
@@ -127,6 +150,11 @@ MP4::Tag::strip()
     saveExisting(ByteVector(), path);
   }
 
+  path = d->atoms->path("moov", "udta", "stem");
+  if(path.size() == 3) {
+    saveExisting(ByteVector(), path);
+  }
+
   return true;
 }
 
@@ -172,7 +200,8 @@ MP4::Tag::updateOffsets(offset_t delta, offset_t offset)
       unsigned int count = data.toUInt();
       d->file->seek(atom->offset() + 16);
       unsigned int pos = 4;
-      while(count--) {
+      const unsigned int maxPos = data.size() - 4;
+      while(count-- && pos <= maxPos) {
         auto o = static_cast<offset_t>(data.toUInt(pos));
         if(o > offset) {
           o += delta;
@@ -192,7 +221,8 @@ MP4::Tag::updateOffsets(offset_t delta, offset_t offset)
       unsigned int count = data.toUInt();
       d->file->seek(atom->offset() + 16);
       unsigned int pos = 4;
-      while(count--) {
+      const unsigned int maxPos = data.size() - 8;
+      while(count-- && pos <= maxPos) {
         long long o = data.toLongLong(pos);
         if(o > offset) {
           o += delta;
@@ -227,11 +257,6 @@ MP4::Tag::updateOffsets(offset_t delta, offset_t offset)
 void
 MP4::Tag::saveNew(ByteVector data)
 {
-  data = renderAtom("meta", ByteVector(4, '\0') +
-                    renderAtom("hdlr", ByteVector(8, '\0') + ByteVector("mdirappl") +
-                               ByteVector(9, '\0')) +
-                    data + padIlst(data));
-
   AtomList path = d->atoms->path("moov", "udta");
   if(path.size() != 2) {
     path = d->atoms->path("moov");
@@ -510,13 +535,17 @@ StringList MP4::Tag::complexPropertyKeys() const
   if(d->items.contains("covr")) {
     keys.append("PICTURE");
   }
+  if(d->items.contains("stem")) {
+    keys.append("STEM");
+  }
   return keys;
 }
 
 List<VariantMap> MP4::Tag::complexProperties(const String &key) const
 {
   List<VariantMap> props;
-  if(const String uppercaseKey = key.upper(); uppercaseKey == "PICTURE") {
+  const String uppercaseKey = key.upper();
+  if(uppercaseKey == "PICTURE") {
     const CoverArtList pictures = d->items.value("covr").toCoverArtList();
     for(const CoverArt &picture : pictures) {
       String mimeType = "image/";
@@ -543,12 +572,20 @@ List<VariantMap> MP4::Tag::complexProperties(const String &key) const
       props.append(property);
     }
   }
+  else if(uppercaseKey == "STEM" && d->items.contains("stem")) {
+    const Stem stem = d->items.value("stem").toStem();
+
+    VariantMap property;
+    property.insert("manifest", stem.data());
+    props.append(property);
+  }
   return props;
 }
 
 bool MP4::Tag::setComplexProperties(const String &key, const List<VariantMap> &value)
 {
-  if(const String uppercaseKey = key.upper(); uppercaseKey == "PICTURE") {
+  const String uppercaseKey = key.upper();
+  if(uppercaseKey == "PICTURE") {
     CoverArtList pictures;
     for(const auto &property : value) {
       auto mimeType = property.value("mimeType").value<String>();
@@ -568,6 +605,13 @@ bool MP4::Tag::setComplexProperties(const String &key, const List<VariantMap> &v
     }
     d->items["covr"] = pictures;
   }
+  else if(uppercaseKey == "STEM") {
+    if (!value.isEmpty()) {
+      d->items["stem"] = Stem(value.front().value("manifest").value<ByteVector>());
+    } else {
+      d->items.erase("stem");
+    }
+  }
   else {
     return false;
   }