Implemented Multiple video track recoding.

media/capture/webm_muxer.h

Index: media/capture/webm_muxer.h
diff --git a/media/capture/webm_muxer.h b/media/capture/webm_muxer.h
index 2d25c46a66a40342f8f2e4484dafee2662bf677e..4474c12547f4d0566bde154b8e751f3692c54e73 100644
--- a/media/capture/webm_muxer.h
+++ b/media/capture/webm_muxer.h
@@ -36,6 +36,12 @@ class VideoFrame;
 // TODO(mcasas): Add support for Audio muxing.
 class MEDIA_EXPORT WebmMuxer : public NON_EXPORTED_BASE(mkvmuxer::IMkvWriter) {
  public:
+  using EncodedVideoCB =
+      base::Callback<void(const scoped_refptr<VideoFrame>& video_frame,
+                          scoped_ptr<std::string> encoded_data,
+                          base::TimeTicks timestamp,
+                          bool is_key_frame)>;
+
   // Callback to be called when WebmMuxer is ready to write a chunk of data,
   // either any file header or a SingleBlock.
   using WriteDataCB = base::Callback<void(base::StringPiece)>;
@@ -43,20 +49,34 @@ class MEDIA_EXPORT WebmMuxer : public NON_EXPORTED_BASE(mkvmuxer::IMkvWriter) {
   explicit WebmMuxer(const WriteDataCB& write_data_callback);
   ~WebmMuxer() override;
 
+  EncodedVideoCB GenerateOnEncodedVideoCallback();
+
+ private:
+  friend class WebmMuxerTest;
+  struct VideoMuxerArg {
+    VideoMuxerArg(
+        const base::TimeTicks& first_frame_timestamp, uint64 track_number)
+        : first_frame_timestamp(first_frame_timestamp),
+          track_number(track_number) {}
+
+    base::TimeTicks first_frame_timestamp;
+    uint64 track_number;
+  };
+
   // Adds a |video_frame| with |encoded_data.data()| to WebM Segment.
-  void OnEncodedVideo(const scoped_refptr<VideoFrame>& video_frame,
+  void OnEncodedVideo(int track_index,
+                      const scoped_refptr<VideoFrame>& video_frame,
                       scoped_ptr<std::string> encoded_data,
                       base::TimeTicks timestamp,
                       bool is_key_frame);
 
- private:
-  friend class WebmMuxerTest;
+  int GetNextVideoTrackIndex() const;
 
   // Creates and adds a new video track. Called upon receiving the first
   // frame of a given Track, adds |frame_size| and |frame_rate| to the Segment
   // info, although individual frames passed to OnEncodedVideo() can have any
   // frame size.
-  void AddVideoTrack(const gfx::Size& frame_size, double frame_rate);
+  uint64 AddVideoTrack(const gfx::Size& frame_size, double frame_rate);
 
   // IMkvWriter interface.
   mkvmuxer::int32 Write(const void* buf, mkvmuxer::uint32 len) override;
@@ -69,12 +89,8 @@ class MEDIA_EXPORT WebmMuxer : public NON_EXPORTED_BASE(mkvmuxer::IMkvWriter) {
   // Used to DCHECK that we are called on the correct thread.
   base::ThreadChecker thread_checker_;
 
-  // A caller-side identifier to interact with |segment_|, initialised upon
-  // first frame arrival by AddVideoTrack().
-  uint64_t track_index_;
-
-  // Origin of times for frame timestamps.
-  base::TimeTicks first_frame_timestamp_;
+  // Arguments for each tracks to mkvmuxer.
+  std::vector<VideoMuxerArg> video_muxer_args_;
 
   // Callback to dump written data as being called by libwebm.
   const WriteDataCB write_data_callback_;