feat: Add album artist and track number metadata embedding

- Add aART atom for album artist
- Add trkn atom with binary track number format
- Update JNI signature to accept new parameters

Author: alltechdev

coverart_jni.cpp

@@ -26,10 +26,32 @@ static void addTextMetadata(AP4_ContainerAtom* ilst, AP4_Atom::Type type, const
     ilst->AddChild(container);
 }
 
+// Helper to add track number metadata (trkn atom - binary format)
+// Format: [2 bytes reserved=0][2 bytes track][2 bytes total][2 bytes reserved=0]
+static void addTrackNumber(AP4_ContainerAtom* ilst, int trackNumber, int totalTracks) {
+    if (trackNumber <= 0) return;
+
+    // Remove existing trkn atom
+    ilst->DeleteChild(AP4_ATOM_TYPE_TRKN);
+
+    // Build 8-byte binary data
+    AP4_UI08 data[8] = {0};
+    data[2] = (trackNumber >> 8) & 0xFF;  // track high byte
+    data[3] = trackNumber & 0xFF;          // track low byte
+    data[4] = (totalTracks >> 8) & 0xFF;  // total high byte
+    data[5] = totalTracks & 0xFF;          // total low byte
+
+    AP4_ContainerAtom* container = new AP4_ContainerAtom(AP4_ATOM_TYPE_TRKN);
+    AP4_BinaryMetaDataValue value(AP4_MetaData::Value::TYPE_BINARY, data, 8);
+    AP4_DataAtom* dataAtom = new AP4_DataAtom(value);
+    container->AddChild(dataAtom);
+    ilst->AddChild(container);
+}
+
 extern "C" {
 
 /**
- * Embed metadata (cover art, title, artist, album, year) into an M4A/MP4 file.
+ * Embed metadata (cover art, title, artist, album, year, album artist, track number) into an M4A/MP4 file.
  * Uses a two-pass approach: first parse to build modified moov, then rebuild file.
  * All text is stored as UTF-8 (supports Hebrew, Arabic, and all Unicode).
  */
@@ -43,7 +65,10 @@ Java_com_metrolist_music_utils_CoverArtNative_embedMetadata(
         jstring titleStr,
         jstring artistStr,
         jstring albumStr,
-        jstring yearStr) {
+        jstring yearStr,
+        jstring albumArtistStr,
+        jint trackNumber,
+        jint totalTracks) {
 
     const char *input = env->GetStringUTFChars(inputPath, nullptr);
     const char *output = env->GetStringUTFChars(outputPath, nullptr);
@@ -61,12 +86,15 @@ Java_com_metrolist_music_utils_CoverArtNative_embedMetadata(
     const char *artist = artistStr ? env->GetStringUTFChars(artistStr, nullptr) : nullptr;
     const char *album = albumStr ? env->GetStringUTFChars(albumStr, nullptr) : nullptr;
     const char *year = yearStr ? env->GetStringUTFChars(yearStr, nullptr) : nullptr;
+    const char *albumArtist = albumArtistStr ? env->GetStringUTFChars(albumArtistStr, nullptr) : nullptr;
 
     LOGI("Embedding metadata: %s -> %s (%d bytes artwork)", input, output, artworkSize);
     if (title) LOGI("  Title: %s", title);
     if (artist) LOGI("  Artist: %s", artist);
     if (album) LOGI("  Album: %s", album);
     if (year) LOGI("  Year: %s", year);
+    if (albumArtist) LOGI("  Album Artist: %s", albumArtist);
+    if (trackNumber > 0) LOGI("  Track: %d/%d", trackNumber, totalTracks);
 
     bool success = false;
 
@@ -170,11 +198,13 @@ Java_com_metrolist_music_utils_CoverArtNative_embedMetadata(
             LOGI("Created ilst atom");
         }
 
-        // Add text metadata (©nam = title, ©ART = artist, ©alb = album, ©day = year)
+        // Add text metadata (©nam = title, ©ART = artist, ©alb = album, ©day = year, aART = album artist)
         addTextMetadata(ilst, AP4_ATOM_TYPE_cNAM, title);   // Title
         addTextMetadata(ilst, AP4_ATOM_TYPE_cART, artist);  // Artist
         addTextMetadata(ilst, AP4_ATOM_TYPE_cALB, album);   // Album
         addTextMetadata(ilst, AP4_ATOM_TYPE_cDAY, year);    // Year
+        addTextMetadata(ilst, AP4_ATOM_TYPE_aART, albumArtist);  // Album Artist
+        addTrackNumber(ilst, trackNumber, totalTracks);     // Track Number
         LOGI("Added text metadata atoms");
 
         // Add cover art if provided
@@ -260,6 +290,7 @@ Java_com_metrolist_music_utils_CoverArtNative_embedMetadata(
     if (artist) env->ReleaseStringUTFChars(artistStr, artist);
     if (album) env->ReleaseStringUTFChars(albumStr, album);
     if (year) env->ReleaseStringUTFChars(yearStr, year);
+    if (albumArtist) env->ReleaseStringUTFChars(albumArtistStr, albumArtist);
 
     return success ? JNI_TRUE : JNI_FALSE;
 }