Implemented Multiple video track recoding.

media/capture/webm_muxer.cc

Index: media/capture/webm_muxer.cc
diff --git a/media/capture/webm_muxer.cc b/media/capture/webm_muxer.cc
index c59bbae805293bc02d0463dc9fb37c5f1960756b..97422969418a2b97d9a8f7dc16ca2c4e88794dde 100644
--- a/media/capture/webm_muxer.cc
+++ b/media/capture/webm_muxer.cc
@@ -26,10 +26,17 @@ static double GetFrameRate(const scoped_refptr<VideoFrame>& video_frame) {
 }
 
 WebmMuxer::WebmMuxer(const WriteDataCB& write_data_callback)
-    : track_index_(0),
-      write_data_callback_(write_data_callback),
-      position_(0) {
+    : write_data_callback_(write_data_callback), position_(0) {
   DCHECK(!write_data_callback_.is_null());
+
+  segment_.Init(this);
+  segment_.set_mode(mkvmuxer::Segment::kLive);
+  segment_.OutputCues(false);
+
+  mkvmuxer::SegmentInfo* const info = segment_.GetSegmentInfo();
+  info->set_writing_app("Chrome");
+  info->set_muxing_app("Chrome");
+
   // Creation is done on a different thread than main activities.
   thread_checker_.DetachFromThread();
 }
@@ -41,46 +48,49 @@ WebmMuxer::~WebmMuxer() {
   segment_.Finalize();
 }
 
-void WebmMuxer::OnEncodedVideo(const scoped_refptr<VideoFrame>& video_frame,
+void WebmMuxer::OnEncodedVideo(int track_index,
+                               const scoped_refptr<VideoFrame>& video_frame,
                                scoped_ptr<std::string> encoded_data,
                                base::TimeTicks timestamp,
                                bool is_key_frame) {
   DVLOG(1) << __FUNCTION__ << " - " << encoded_data->size() << "B";
   DCHECK(thread_checker_.CalledOnValidThread());
-  if (!track_index_) {
-    // |track_index_|, cannot be zero (!), initialize WebmMuxer in that case.
+  int args_size = video_muxer_args_.size();
+  DCHECK(track_index <= args_size);
+
+  if (args_size == 0 || args_size == track_index) {
+    // If the track is not added muxer, add it in here.
     // http://www.matroska.org/technical/specs/index.html#Tracks
-    AddVideoTrack(video_frame->visible_rect().size(),
-                  GetFrameRate(video_frame));
-    first_frame_timestamp_ = timestamp;
+    uint64 track_num = AddVideoTrack(video_frame->visible_rect().size(),
+                                     GetFrameRate(video_frame));
+    video_muxer_args_.emplace_back(VideoMuxerArg(timestamp, track_num));
   }
-  segment_.AddFrame(reinterpret_cast<const uint8_t*>(encoded_data->data()),
-                    encoded_data->size(),
-                    track_index_,
-                    (timestamp - first_frame_timestamp_).InMicroseconds() *
-                        base::Time::kNanosecondsPerMicrosecond,
-                    is_key_frame);
-}
 
-void WebmMuxer::AddVideoTrack(const gfx::Size& frame_size, double frame_rate) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  DCHECK_EQ(track_index_, 0u) << "WebmMuxer can only be initialised once.";
+  base::TimeDelta timestamp_delta =
+      timestamp - video_muxer_args_[track_index].first_frame_timestamp;
+  segment_.AddFrame(
+      reinterpret_cast<const uint8_t*>(encoded_data->data()),
+      encoded_data->size(),
+      video_muxer_args_[track_index].track_number,
+      timestamp_delta.InMicroseconds() * base::Time::kNanosecondsPerMicrosecond,
+      is_key_frame);
+}
 
-  segment_.Init(this);
-  segment_.set_mode(mkvmuxer::Segment::kLive);
-  segment_.OutputCues(false);
+int WebmMuxer::GetNextVideoTrackIndex() {
+  return video_muxer_args_.size();
+}
 
-  mkvmuxer::SegmentInfo* const info = segment_.GetSegmentInfo();
-  info->set_writing_app("Chrome");
-  info->set_muxing_app("Chrome");
+uint64 WebmMuxer::AddVideoTrack(
+    const gfx::Size& frame_size, double frame_rate) {
+  DCHECK(thread_checker_.CalledOnValidThread());
 
-  track_index_ =
+  uint64 track_num =
       segment_.AddVideoTrack(frame_size.width(), frame_size.height(), 0);
-  DCHECK_GT(track_index_, 0u);
+  DCHECK_GT(track_num, 0u);
 
   mkvmuxer::VideoTrack* const video_track =
       reinterpret_cast<mkvmuxer::VideoTrack*>(
-          segment_.GetTrackByNumber(track_index_));
+          segment_.GetTrackByNumber(track_num));
   DCHECK(video_track);
   video_track->set_codec_id(mkvmuxer::Tracks::kVp8CodecId);
   DCHECK_EQ(video_track->crop_right(), 0ull);
@@ -94,6 +104,8 @@ void WebmMuxer::AddVideoTrack(const gfx::Size& frame_size, double frame_rate) {
   // Segment's timestamps should be in milliseconds, DCHECK it. See
   // http://www.webmproject.org/docs/container/#muxer-guidelines
   DCHECK_EQ(segment_.GetSegmentInfo()->timecode_scale(), 1000000ull);
+
+  return track_num;
 }
 
 mkvmuxer::int32 WebmMuxer::Write(const void* buf, mkvmuxer::uint32 len) {