LibMedia: Adjust Matroska seeking based on SeekPreRoll

This is important for seeking Opus tracks, as Opus needs to decode a
certain amount of input data before its output converges. Without this,
audio after a seek can sound muffled briefly.

Author: Zaggy1024

Libraries/LibMedia/Containers/Matroska/Document.h

@@ -135,6 +135,8 @@ class TrackEntry : public RefCounted<TrackEntry> {
     void set_timestamp_scale(double timestamp_scale) { m_timestamp_scale = timestamp_scale; }
     u64 codec_delay() const { return m_codec_delay; }
     void set_codec_delay(u64 codec_delay) { m_codec_delay = codec_delay; }
+    u64 seek_pre_roll() const { return m_seek_pre_roll; }
+    void set_seek_pre_roll(u64 seek_pre_roll) { m_seek_pre_roll = seek_pre_roll; }
     u64 timestamp_offset() const { return m_timestamp_offset; }
     void set_timestamp_offset(u64 timestamp_offset) { m_timestamp_offset = timestamp_offset; }
     Optional<VideoTrack> video_track() const { return m_video_track; }
@@ -153,6 +155,7 @@ class TrackEntry : public RefCounted<TrackEntry> {
     FixedArray<u8> m_codec_private_data;
     double m_timestamp_scale { 1 };
     u64 m_codec_delay { 0 };
+    u64 m_seek_pre_roll { 0 };
     u64 m_timestamp_offset { 0 };
     Optional<VideoTrack> m_video_track;
     Optional<AudioTrack> m_audio_track;

Libraries/LibMedia/Containers/Matroska/Reader.cpp

@@ -57,6 +57,7 @@ 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;
+constexpr u32 TRACK_SEEK_PRE_ROLL_ID = 0x56BB;
 constexpr u32 TRACK_TIMESTAMP_SCALE_ID = 0x23314F;
 constexpr u32 TRACK_OFFSET_ID = 0x537F;
 constexpr u32 TRACK_VIDEO_ID = 0xE0;
@@ -512,6 +513,10 @@ static DecoderErrorOr<NonnullRefPtr<TrackEntry>> parse_track_entry(Streamer& str
             track_entry->set_codec_delay(TRY_READ(streamer.read_u64()));
             dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's CodecDelay attribute: {}", track_entry->codec_delay());
             break;
+        case TRACK_SEEK_PRE_ROLL_ID:
+            track_entry->set_seek_pre_roll(TRY_READ(streamer.read_u64()));
+            dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's SeekPreRoll attribute: {}", track_entry->seek_pre_roll());
+            break;
         case TRACK_TIMESTAMP_SCALE_ID:
             track_entry->set_timestamp_scale(TRY_READ(streamer.read_float()));
             dbgln_if(MATROSKA_TRACE_DEBUG, "Read Track's TrackTimestampScale attribute: {}", track_entry->timestamp_scale());
@@ -1090,6 +1095,8 @@ DecoderErrorOr<bool> Reader::has_cues_for_track(u64 track_number)
 
 DecoderErrorOr<SampleIterator> Reader::seek_to_random_access_point(SampleIterator iterator, AK::Duration timestamp)
 {
+    timestamp -= AK::Duration::from_nanoseconds(AK::clamp_to<i64>(iterator.m_track->seek_pre_roll()));
+
     if (TRY(has_cues_for_track(iterator.m_track->track_number()))) {
         TRY(seek_to_cue_for_timestamp(iterator, timestamp));
         VERIFY(iterator.last_timestamp().has_value());