Assign correct track ids to buffers emitted from StreamParsers

media/formats/mpeg/mpeg_audio_stream_parser_base.cc

Index: media/formats/mpeg/mpeg_audio_stream_parser_base.cc
diff --git a/media/formats/mpeg/mpeg_audio_stream_parser_base.cc b/media/formats/mpeg/mpeg_audio_stream_parser_base.cc
index b0bb515b58e1d52e042f112965d9aa138cda8756..944225a653c3d5b68b6a87f835110b23f767a5f7 100644
--- a/media/formats/mpeg/mpeg_audio_stream_parser_base.cc
+++ b/media/formats/mpeg/mpeg_audio_stream_parser_base.cc
@@ -19,6 +19,8 @@
 
 namespace media {
 
+static const int kMpegAudioTrackId = 1;
+
 static const uint32_t kICYStartCode = 0x49435920;  // 'ICY '
 
 // Arbitrary upper bound on the size of an IceCast header before it
@@ -222,7 +224,7 @@ int MPEGAudioStreamParserBase::ParseFrame(const uint8_t* data,
 
     std::unique_ptr<MediaTracks> media_tracks(new MediaTracks());
     if (config_.IsValidConfig()) {
-      media_tracks->AddAudioTrack(config_, 1, "main", "", "");
+      media_tracks->AddAudioTrack(config_, kMpegAudioTrackId, "main", "", "");
     }
     if (!config_cb_.Run(std::move(media_tracks), TextTrackConfigMap()))
       return -1;
@@ -241,9 +243,8 @@ int MPEGAudioStreamParserBase::ParseFrame(const uint8_t* data,
   // TODO(wolenetz/acolwell): Validate and use a common cross-parser TrackId
   // type and allow multiple audio tracks, if applicable. See
   // https://crbug.com/341581.
-  scoped_refptr<StreamParserBuffer> buffer =
-      StreamParserBuffer::CopyFrom(data, frame_size, true,
-                                   DemuxerStream::AUDIO, 0);
+  scoped_refptr<StreamParserBuffer> buffer = StreamParserBuffer::CopyFrom(
+      data, frame_size, true, DemuxerStream::AUDIO, kMpegAudioTrackId);
   buffer->set_timestamp(timestamp_helper_->GetTimestamp());
   buffer->set_duration(timestamp_helper_->GetFrameDuration(sample_count));
   buffers->push_back(buffer);