Refactor VideoTracks to forward all sinks to its source

webrtc/media/base/videobroadcaster.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 47 matching lines @@
 
 VideoSinkWants VideoBroadcaster::wants() const {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   rtc::CritScope cs(&sinks_and_wants_lock_);
   return current_wants_;
 }
 
 void VideoBroadcaster::OnFrame(const cricket::VideoFrame& frame) {
   rtc::CritScope cs(&sinks_and_wants_lock_);
   for (auto& sink_pair : sinks_) {
-    sink_pair.sink->OnFrame(frame);
+    if (sink_pair.wants.black_frames) {
+      sink_pair.sink->OnFrame(GetBlackFrame(frame));
+    } else {
+      sink_pair.sink->OnFrame(frame);
+    }
   }
 }
 
 VideoBroadcaster::SinkPair* VideoBroadcaster::FindSinkPair(
     const VideoSinkInterface<cricket::VideoFrame>* sink) {
   auto sink_pair_it = std::find_if(
       sinks_.begin(), sinks_.end(),
       [sink](const SinkPair& sink_pair) { return sink_pair.sink == sink; });
   if (sink_pair_it != sinks_.end()) {
     return &*sink_pair_it;
@@ skipping 26 matching lines @@
     }
   }
 
   if (wants.max_pixel_count && wants.max_pixel_count_step_up &&
       *wants.max_pixel_count_step_up >= *wants.max_pixel_count) {
     wants.max_pixel_count_step_up = Optional<int>();
   }
   current_wants_ = wants;
 }
 
+const cricket::VideoFrame& VideoBroadcaster::GetBlackFrame(
+    const cricket::VideoFrame& frame) {
+  if (black_frame_ && black_frame_->GetWidth() == frame.GetWidth() &&
+      black_frame_->GetHeight() == frame.GetHeight() &&
+      black_frame_->GetVideoRotation() == frame.GetVideoRotation()) {
+    black_frame_->SetTimeStamp(frame.GetTimeStamp());
+    return *black_frame_;
+  }
+  black_frame_.reset(new cricket::WebRtcVideoFrame(
+      new rtc::RefCountedObject<webrtc::I420Buffer>(
+          static_cast<int>(frame.GetWidth()),
+          static_cast<int>(frame.GetHeight())),
+      frame.GetTimeStamp(), frame.GetVideoRotation()));
+  black_frame_->SetToBlack();
+  return *black_frame_;
+}
+
 }  // namespace rtc