WebmMuxer-MediaRecorderHandler: thread hopping and data ownership

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 b913fa7501416818c31a857084d225fa66e740d1..d40b28dc9c909a6636d0a8d09211a71639341f5b 100644
--- a/media/capture/webm_muxer.cc
+++ b/media/capture/webm_muxer.cc
@@ -24,21 +24,27 @@ static double GetFrameRate(const scoped_refptr<VideoFrame>& video_frame) {
   return frame_rate;
 }
 
-WebmMuxer::WebmMuxer(const WriteDataCB& write_data_callback)
-    : track_index_(0),
+//static
+void WebmMuxer::FinalizeSegment(scoped_ptr<mkvmuxer::Segment> segment) {
+  // No need to segment_->Finalize() since is not Seekable(), i.e. a live
+  // stream, but is a good practice.
+  segment->Finalize();
+}
+
+WebmMuxer::WebmMuxer(
+    const scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
+    const WriteDataCB& write_data_callback)
+    : main_task_runner_(main_task_runner),
+      track_index_(0),
       write_data_callback_(write_data_callback),
-      position_(0) {
+      position_(0),
+      segment_(new mkvmuxer::Segment()) {
+  DCHECK(main_task_runner_);
   DCHECK(!write_data_callback_.is_null());
   // Creation is done on a different thread than main activities.
   thread_checker_.DetachFromThread();
 }
 
-WebmMuxer::~WebmMuxer() {
-  // No need to segment_.Finalize() since is not Seekable(), i.e. a live stream,
-  // but is good practice.
-  segment_.Finalize();
-}
-
 void WebmMuxer::OnEncodedVideo(const scoped_refptr<VideoFrame>& video_frame,
                                const base::StringPiece& encoded_data,
                                base::TimeTicks timestamp,
@@ -52,33 +58,39 @@ void WebmMuxer::OnEncodedVideo(const scoped_refptr<VideoFrame>& video_frame,
                   GetFrameRate(video_frame));
     first_frame_timestamp_ = timestamp;
   }
-  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);
+  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);
+}
+
+WebmMuxer::~WebmMuxer() {
+  // Guarantee destruction of |segment_| in the appropriate thread.
+  main_task_runner_->PostTask(FROM_HERE,
+      base::Bind(&WebmMuxer::FinalizeSegment, base::Passed(&segment_)));
 }
 
 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.";
 
-  segment_.Init(this);
-  segment_.set_mode(mkvmuxer::Segment::kLive);
-  segment_.OutputCues(false);
+  segment_->Init(this);
+  segment_->set_mode(mkvmuxer::Segment::kLive);
+  segment_->OutputCues(false);
 
-  mkvmuxer::SegmentInfo* const info = segment_.GetSegmentInfo();
+  mkvmuxer::SegmentInfo* const info = segment_->GetSegmentInfo();
   info->set_writing_app("Chrome");
   info->set_muxing_app("Chrome");
 
   track_index_ =
-      segment_.AddVideoTrack(frame_size.width(), frame_size.height(), 0);
+      segment_->AddVideoTrack(frame_size.width(), frame_size.height(), 0);
   DCHECK_GT(track_index_, 0u);
 
   mkvmuxer::VideoTrack* const video_track =
       reinterpret_cast<mkvmuxer::VideoTrack*>(
-          segment_.GetTrackByNumber(track_index_));
+          segment_->GetTrackByNumber(track_index_));
   DCHECK(video_track);
   video_track->set_codec_id(mkvmuxer::Tracks::kVp8CodecId);
   DCHECK_EQ(video_track->crop_right(), 0ull);
@@ -91,7 +103,7 @@ void WebmMuxer::AddVideoTrack(const gfx::Size& frame_size, double frame_rate) {
                                     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);
+  DCHECK_EQ(segment_->GetSegmentInfo()->timecode_scale(), 1000000ull);
 }
 
 mkvmuxer::int32 WebmMuxer::Write(const void* buf, mkvmuxer::uint32 len) {