From d1bd220c26053a09aaf07cd2f142aac93556f028 Mon Sep 17 00:00:00 2001
From: Ryan Francesconi <2917795+ryanfrancesconi@users.noreply.github.com>
Date: Sat, 31 Oct 2026 23:06:07 -0700
Subject: [PATCH] Matroska: Read SamplingFrequency and Channels defaults when
 absent (#1358)

An Audio element without SamplingFrequency or Channels now reads their
defaults (RFC 9559: 8000 Hz, one channel) instead of 0, and the track
is no longer skipped when BitDepth is absent too. A track without an
Audio element is still skipped.
---
 taglib/matroska/ebml/ebmlmktracks.cpp |  4 ++++
 tests/test_matroska.cpp               | 22 ++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/taglib/matroska/ebml/ebmlmktracks.cpp b/taglib/matroska/ebml/ebmlmktracks.cpp
index 5852d3bf..c7f1b0f6 100644
--- a/taglib/matroska/ebml/ebmlmktracks.cpp
+++ b/taglib/matroska/ebml/ebmlmktracks.cpp
@@ -67,6 +67,10 @@ void EBML::MkTracks::parse(Matroska::Properties *properties) const
       if(const Id trackEntryChildId = trackEntryChild->getId(); trackEntryChildId == Id::MkCodecID)
         codecId = element_cast<Id::MkCodecID>(trackEntryChild)->getValue();
       else if(trackEntryChildId == Id::MkAudio) {
+        // Their defaults (RFC 9559, 5.1.4.1.29), which a muxer may leave out
+        // when the value equals them (RFC 8794, 11.1.19).
+        samplingFrequency = 8000.0;
+        channels = 1;
         const auto audio = element_cast<Id::MkAudio>(trackEntryChild);
         for(const auto &audioChild : *audio) {
           if(const Id audioChildId = audioChild->getId(); audioChildId == Id::MkSamplingFrequency)
diff --git a/tests/test_matroska.cpp b/tests/test_matroska.cpp
index 3c12ab15..9717881e 100644
--- a/tests/test_matroska.cpp
+++ b/tests/test_matroska.cpp
@@ -219,6 +219,7 @@ class TestMatroska : public CppUnit::TestFixture
   CPPUNIT_TEST(testPropertiesMka);
   CPPUNIT_TEST(testPropertiesMkv);
   CPPUNIT_TEST(testPropertiesWebm);
+  CPPUNIT_TEST(testPropertiesAudioDefaults);
   CPPUNIT_TEST(testSimpleTagsAndAttachments);
   CPPUNIT_TEST(testAddRemoveTagsAttachments);
   CPPUNIT_TEST(testTagsWebm);
@@ -291,6 +292,27 @@ public:
     CPPUNIT_ASSERT(!noProps.audioProperties());
   }
 
+  void testPropertiesAudioDefaults()
+  {
+    // no-tags.mka's Audio element holds SamplingFrequency (44100) and Channels (2).
+    // Replaced by Void elements of the same size, they are absent, and their
+    // defaults apply.
+    ScopedFileCopy copy("no-tags", ".mka");
+    {
+      FileStream stream(copy.fileName().c_str());
+      const ByteVector audio("\xe1\x89\xb5\x84\x47\x2c\x44\x00\x9f\x81\x02", 11);
+      const offset_t offset = stream.readBlock(stream.length()).find(audio);
+      CPPUNIT_ASSERT(offset > 0);
+      stream.seek(offset + 2);
+      stream.writeBlock(ByteVector("\xec\x84\x00\x00\x00\x00\xec\x81\x00", 9));
+    }
+    Matroska::File f(copy.fileName().c_str());
+    CPPUNIT_ASSERT(f.audioProperties());
+    CPPUNIT_ASSERT_EQUAL(8000, f.audioProperties()->sampleRate());
+    CPPUNIT_ASSERT_EQUAL(1, f.audioProperties()->channels());
+    CPPUNIT_ASSERT_EQUAL(String("A_MPEG/L3"), f.audioProperties()->codecName());
+  }
+
   void testSimpleTagsAndAttachments()
   {
     ScopedFileCopy copy("no-tags", ".mka");