ffmpeg reset bitstream converters on Seek

We should not assume that the underlying decoders
keep their state after a Seek.
So for example, the SPS/PPS should be added again.

BUG=140371

Review URL: https://codereview.chromium.org/683573002

Cr-Commit-Position: refs/heads/master@{#302154}

media/filters/ffmpeg_demuxer.cc

@@ -382,6 +382,12 @@ void FFmpegDemuxerStream::SetEndOfStream() {
 void FFmpegDemuxerStream::FlushBuffers() {
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK(read_cb_.is_null()) << "There should be no pending read";
+
+  // H264 requires that we resend the header after flush.
+  // Reset its bitstream for converter to do so.
+  // This is related to chromium issue 140371 (http://crbug.com/140371).
+  ResetBitstreamConverter();
+
   buffer_queue_.Clear();
   end_of_stream_ = false;
   last_packet_timestamp_ = kNoTimestamp();
@@ -434,6 +440,16 @@ void FFmpegDemuxerStream::EnableBitstreamConverter() {
 #endif
 }
 
+void FFmpegDemuxerStream::ResetBitstreamConverter() {
+#if defined(USE_PROPRIETARY_CODECS)
+  if (!bitstream_converter_enabled_ || !bitstream_converter_)
+    return;
+
+  bitstream_converter_.reset(
+      new FFmpegH264ToAnnexBBitstreamConverter(stream_->codec));
+#endif  // defined(USE_PROPRIETARY_CODECS)
+}
+
 bool FFmpegDemuxerStream::SupportsConfigChanges() { return false; }
 
 AudioDecoderConfig FFmpegDemuxerStream::audio_decoder_config() {

media/filters/ffmpeg_demuxer.h

@@ -124,6 +124,9 @@ class FFmpegDemuxerStream : public DemuxerStream {
   static base::TimeDelta ConvertStreamTimestamp(const AVRational& time_base,
                                                 int64 timestamp);
 
+  // Resets any currently active bitstream converters.
+  void ResetBitstreamConverter();
+
   FFmpegDemuxer* demuxer_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   AVStream* stream_;