LibMedia: Let the Matroska LanguageBCP47 element override Language

The Matroska spec indicates that this field should always override the
Language element when it is present.

Author: Zaggy1024

Libraries/LibMedia/Containers/Matroska/Document.h

@@ -120,6 +120,8 @@ class TrackEntry : public RefCounted<TrackEntry> {
     void set_name(String const& name) { m_name = name; }
     String language() const { return m_language; }
     void set_language(String const& language) { m_language = language; }
+    Optional<String> const& language_bcp_47() const { return m_language_bcp_47; }
+    void set_language_bcp_47(String const& language_bcp_47) { m_language_bcp_47 = language_bcp_47; }
     String codec_id() const { return m_codec_id; }
     void set_codec_id(String const& codec_id) { m_codec_id = codec_id; }
     ReadonlyBytes codec_private_data() const LIFETIME_BOUND { return m_codec_private_data.span(); }
@@ -155,6 +157,7 @@ class TrackEntry : public RefCounted<TrackEntry> {
     TrackType m_track_type { Invalid };
     String m_name;
     String m_language = "eng"_string;
+    Optional<String> m_language_bcp_47;
     String m_codec_id;
     FixedArray<u8> m_codec_private_data;
     double m_timestamp_scale { 1 };

Libraries/LibMedia/Containers/Matroska/MatroskaDemuxer.cpp

@@ -68,7 +68,13 @@ static TrackType track_type_from_matroska_track_type(TrackEntry::TrackType type)
 static Track track_from_track_entry(TrackEntry const& track_entry)
 {
     auto name = Utf16String::from_utf8(track_entry.name());
-    auto language = Utf16String::from_utf8(track_entry.language());
+    auto language = [&] {
+        // LanguageBCP47 - The language of the track, in the BCP47 form; see basics on language codes. If this Element is used,
+        // then any Language Elements used in the same TrackEntry MUST be ignored.
+        if (track_entry.language_bcp_47().has_value())
+            return Utf16String::from_utf8(track_entry.language_bcp_47().value());
+        return Utf16String::from_utf8(track_entry.language());
+    }();
     Track track(track_type_from_matroska_track_type(track_entry.track_type()), track_entry.track_number(), name, language);
 
     if (track.type() == TrackType::Video) {

Libraries/LibMedia/Containers/Matroska/Reader.cpp

@@ -52,6 +52,7 @@ constexpr u32 TRACK_UID_ID = 0x73C5;
 constexpr u32 TRACK_TYPE_ID = 0x83;
 constexpr u32 TRACK_NAME_ID = 0x536E;
 constexpr u32 TRACK_LANGUAGE_ID = 0x22B59C;
+constexpr u32 TRACK_LANGUAGE_BCP_47_ID = 0x22B59D;
 constexpr u32 TRACK_CODEC_ID = 0x86;
 constexpr u32 TRACK_CODEC_PRIVATE_ID = 0x63A2;
 constexpr u32 TRACK_CODEC_DELAY_ID = 0x56AA;
@@ -485,6 +486,10 @@ static DecoderErrorOr<NonnullRefPtr<TrackEntry>> parse_track_entry(Streamer& str
             track_entry->set_language(DECODER_TRY_ALLOC(String::from_byte_string(TRY_READ(streamer.read_string()))));
             dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's Language attribute: {}", track_entry->language());
             break;
+        case TRACK_LANGUAGE_BCP_47_ID:
+            track_entry->set_language_bcp_47(DECODER_TRY_ALLOC(String::from_byte_string(TRY_READ(streamer.read_string()))));
+            dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's LanguageBCP47 attribute: {}", track_entry->language());
+            break;
         case TRACK_CODEC_ID:
             track_entry->set_codec_id(DECODER_TRY_ALLOC(String::from_byte_string(TRY_READ(streamer.read_string()))));
             dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's CodecID attribute: {}", track_entry->codec_id());