media: Add support for playback of VP8 Alpha video streams

media/filters/ffmpeg_demuxer.cc

Index: media/filters/ffmpeg_demuxer.cc
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index 56929bcf05172823e0aab9b2ba7d8fe64e4c81b2..abe82dd5e3126ca00ed364e1775f49bf0795b34b 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -70,6 +70,10 @@ FFmpegDemuxerStream::FFmpegDemuxerStream(
 }
 
 void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
+  uint8* side_data;
+  int side_data_size = 0;
+  AVPacket* pkt;

[scherkus (not reviewing), 2013/02/27 07:28:26]

nit: this is C++! we can move these closer to where we use them ;)

(i.e., lines 93-95)

[vignesh, 2013/03/28 21:45:12]

yeah, i was writing this along side when i made the ffmpeg change. hence the C
mindset :)

+
   DCHECK(message_loop_->BelongsToCurrentThread());
 
   if (stopped_ || end_of_stream_) {
@@ -83,11 +87,25 @@ void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
     LOG(ERROR) << "Format conversion failed.";
   }
 
+  // Get side data if any. For now, the only type of side_data is VP8 Alpha. We
+  // keep this generic so that other side_data types in the future can be
+  // handled the same way as well.
+  pkt = packet.get();

[scherkus (not reviewing), 2013/02/27 07:28:26]

nit: can we inline the packet.get() calls instead of storing it as a local
variable?

[vignesh, 2013/03/28 21:45:12]

Done.

+  av_packet_split_side_data(pkt);
+  side_data = av_packet_get_side_data(pkt,
+                                      AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL,

[scherkus (not reviewing), 2013/02/27 07:28:26]

is it safe to call this method with this enum for non-matroska formats? (e.g.,
mp3, mp4, avi, wav, ogg)

what happens when we do?

[vignesh, 2013/03/28 21:45:12]

we are requesting a very specific type of side data (which won't be present in
non-matroska formats of course). so, the method will return a NULL, setting
side_data_size to 0. So it is safe.

+                                      &side_data_size);
+
   // If a packet is returned by FFmpeg's av_parser_parse2() the packet will
   // reference inner memory of FFmpeg.  As such we should transfer the packet
   // into memory we control.
   scoped_refptr<DecoderBuffer> buffer;
-  buffer = DecoderBuffer::CopyFrom(packet->data, packet->size);
+  if (side_data_size > 0) {
+    buffer = DecoderBuffer::CopyFrom(pkt->data, pkt->size,
+                                     side_data, side_data_size);
+  } else {
+    buffer = DecoderBuffer::CopyFrom(pkt->data, pkt->size);
+  }
   buffer->SetTimestamp(ConvertStreamTimestamp(
       stream_->time_base, packet->pts));
   buffer->SetDuration(ConvertStreamTimestamp(