Use ffmpeg packet.pos for restarting reading after reenabling video

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index bd223ab9ccb8c5fb115e67bd409bd5d80d1bb65c..73500fd9438d5474950a624a5f16453cbcc719ef 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -271,6 +271,10 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
   // FFmpeg callbacks during seeking.
   void OnSeekFrameDone(int result);
 
+  // Called when FFmpeg completes seek initiated in OnSelectedVideoTrackChanged
+  // in order to restart the |stream|.
+  void OnSeekDoneForRestartingStream(FFmpegDemuxerStream* stream, int result);
+
   // FFmpeg callbacks during reading + helper method to initiate reads.
   void ReadFrameIfNeeded();
   void OnReadFrameDone(ScopedAVPacket packet, int result);
@@ -299,6 +303,16 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
 
   void SetLiveness(DemuxerStream::Liveness liveness);
 
+  // Do an FFmpeg seek such that the read position is adjusted to be able to
+  // restart playback from the |time| position. If the |preferred_stream| is not
+  // null then it is used for seeking, otherwise the preferred stream is
+  // selected by FindPreferredStreamForSeeking function. When the seek is
+  // completed the |ffmpeg_seek_done_cb| will be called with FFmpeg result.
+  using FFmpegSeekDoneCB = base::Callback<void(int ffmpeg_result)>;
+  void SeekInternal(base::TimeDelta time,
+                    FFmpegDemuxerStream* preferred_stream,
+                    const FFmpegSeekDoneCB& ffmpeg_seek_done_cb);
+
   DemuxerHost* host_;
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
@@ -379,6 +393,9 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
 
   std::map<MediaTrack::Id, FFmpegDemuxerStream*> track_id_to_demux_stream_map_;
 
+  int64_t last_packet_pos_;
+  FFmpegDemuxerStream* restarting_stream_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtr<FFmpegDemuxer> weak_this_;
   base::WeakPtrFactory<FFmpegDemuxer> cancel_pending_seek_factory_;