MP4: Add support for NI STEM (#1299)

tests/CMakeLists.txt

@@ -131,6 +131,7 @@ IF(WITH_MP4)
     test_mp4.cpp
     test_mp4item.cpp
     test_mp4coverart.cpp
+    test_mp4stem.cpp
   )
 ENDIF()
 IF(WITH_ASF)

tests/test_mp4stem.cpp

@@ -0,0 +1,153 @@
+/***************************************************************************
+    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 <string>
+
+#include "tag.h"
+#include "mp4file.h"
+#include <cppunit/extensions/HelperMacros.h>
+#include "utils.h"
+
+using namespace std;
+using namespace TagLib;
+
+namespace {
+const String STEM_KEY("STEM");
+}
+
+class TestMP4Stem : public CppUnit::TestFixture
+{
+  CPPUNIT_TEST_SUITE(TestMP4Stem);
+  CPPUNIT_TEST(testCreate);
+  CPPUNIT_TEST(testUpdate);
+  CPPUNIT_TEST(testRemove);
+  CPPUNIT_TEST_SUITE_END();
+
+protected:
+  static void createTestFile(ScopedFileCopy &copy){
+    MP4::File f(copy.fileName().c_str());
+    CPPUNIT_ASSERT(!f.hasMP4Tag());
+    auto &tag = *f.tag();
+    CPPUNIT_ASSERT_EQUAL(0U, tag.complexProperties(STEM_KEY).size());
+    CPPUNIT_ASSERT(tag.setComplexProperties(STEM_KEY, List<VariantMap>({{{"manifest", ByteVector("{some text data}")}}})));
+    f.save();
+  }
+
+public:
+
+  void testCreate()
+  {
+    ScopedFileCopy copy("no-tags", ".m4a");
+    createTestFile(copy);
+
+    // Assert whether the newly created stem content is as expected
+    {
+      MP4::File f(copy.fileName().c_str());
+      auto &tag = *f.tag();
+      CPPUNIT_ASSERT(f.hasMP4Tag());
+      auto stems = tag.complexProperties(STEM_KEY);
+      CPPUNIT_ASSERT_EQUAL(1U, stems.size());
+      CPPUNIT_ASSERT(stems.front().contains("manifest"));
+      CPPUNIT_ASSERT_EQUAL(Variant(ByteVector("{some text data}")), stems.front().find("manifest")->second);
+    }
+  }
+
+  void testUpdate()
+  {
+    ScopedFileCopy copy("no-tags", ".m4a");
+    createTestFile(copy);
+
+    // Prepare so large test data, to ensure that free padding is correctly used
+    char *buffer = new char[1025]{'X'};
+    buffer[1024] = '\0';
+    String artist(buffer);
+    std::memset(buffer, 'Y', 1024);
+    String title(buffer);
+    std::memset(buffer, 'Z', 1024);
+    ByteVector newStem(buffer);
+    delete [] buffer;
+
+    // Update tags and stems to force atom offset recalculation
+    {
+      MP4::File f(copy.fileName().c_str());
+      CPPUNIT_ASSERT(f.setComplexProperties("PICTURE", List<VariantMap>({
+        {
+          {"data", ByteVector("DummyData")},
+          {"pictureType", "Front Cover"},
+          {"mimeType", String("image/png")},
+          {"description", String("Test")}
+        }
+      })));
+      CPPUNIT_ASSERT(f.tag()->setComplexProperties(STEM_KEY, List<VariantMap>({{{"manifest", newStem}}})));
+      f.tag()->setArtist(artist);
+      f.tag()->setTitle(title);
+      f.save();
+    }
+    // Reload the file to assert its tags
+    {
+      MP4::File f(copy.fileName().c_str());
+      CPPUNIT_ASSERT(f.hasMP4Tag());
+
+      auto stems = f.tag()->complexProperties(STEM_KEY);
+      CPPUNIT_ASSERT_EQUAL(1U, stems.size());
+      CPPUNIT_ASSERT(stems.front().contains("manifest"));
+      CPPUNIT_ASSERT_EQUAL(Variant(newStem), stems.front().find("manifest")->second);
+
+      auto pictures = f.tag()->complexProperties("PICTURE");
+      CPPUNIT_ASSERT_EQUAL(1U, pictures.size());
+      CPPUNIT_ASSERT_EQUAL(VariantMap({
+        {
+          {"data", ByteVector("DummyData")},
+          {"mimeType", String("image/png")},
+        }
+      }), pictures.front());
+
+      CPPUNIT_ASSERT_EQUAL(title, f.tag()->title());
+      CPPUNIT_ASSERT_EQUAL(artist, f.tag()->artist());
+    }
+  }
+
+  void testRemove()
+  {
+    ScopedFileCopy copy("no-tags", ".m4a");
+    createTestFile(copy);
+
+    // Remove the stem
+    {
+      MP4::File f(copy.fileName().c_str());
+      CPPUNIT_ASSERT(f.hasMP4Tag());
+      CPPUNIT_ASSERT(f.tag()->setComplexProperties(STEM_KEY, List<VariantMap>()));
+      f.save();
+    }
+    {
+      MP4::File f(copy.fileName().c_str());
+      CPPUNIT_ASSERT(!f.hasMP4Tag());
+      CPPUNIT_ASSERT(!f.tag()->complexPropertyKeys().contains(STEM_KEY));
+    }
+  }
+
+};
+
+CPPUNIT_TEST_SUITE_REGISTRATION(TestMP4Stem);