Added mute logic to VideoTrackRenderers.

talk/app/webrtc/videotrackrenderers.cc

 /*
  * libjingle
  * Copyright 2012 Google Inc.
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 #include "talk/app/webrtc/videotrackrenderers.h"
-#include "talk/media/base/videoframe.h"
+#include "talk/media/webrtc/webrtcvideoframe.h"
 
 namespace webrtc {
 
 VideoTrackRenderers::VideoTrackRenderers() : enabled_(true) {
 }
 
 VideoTrackRenderers::~VideoTrackRenderers() {
 }
 
 void VideoTrackRenderers::AddRenderer(VideoRendererInterface* renderer) {
   if (!renderer) {
     return;
   }
   rtc::CritScope cs(&critical_section_);
   renderers_.insert(renderer);
 }
 
 void VideoTrackRenderers::RemoveRenderer(VideoRendererInterface* renderer) {
   rtc::CritScope cs(&critical_section_);
   renderers_.erase(renderer);
 }
 
 void VideoTrackRenderers::SetEnabled(bool enable) {
   rtc::CritScope cs(&critical_section_);
   enabled_ = enable;
 }
 
+// Create a black frame, with the same size, timestamp and rotation.
+static cricket::VideoFrame* CreateBlackFrame(const cricket::VideoFrame* frame) {

[perkj_webrtc, 2016/01/13 09:44:40]

static methods should be at the top of the file. And prefer anonymouse ns to
static.

+  cricket::VideoFrame* black = new cricket::WebRtcVideoFrame(

[perkj_webrtc, 2016/01/13 09:44:40]

This looks like a memory leak. Ownership is not transfered to the renderers. 
You will have to have this black frame as a member I think.

[nisse-webrtc, 2016/01/13 10:33:16]

The VideoFrameBuffer is reference counted, but I have to delete the
cricket::VideoFrame? When is that safe? As soon as the downstream RenderFrame
calls return? Then I can just allocate the object on the stack instead.

I was also thinking about caching the VideoFrameBuffer and keep using it as long
as the size is unchanged. But that might be a premature optimzation.

+      new rtc::RefCountedObject<I420Buffer>(frame->GetWidth(),
+                                            frame->GetHeight()),
+      frame->GetTimeStamp(), frame->GetVideoRotation());
+  black->SetToBlack();
+  return black;
+}
+
 bool VideoTrackRenderers::RenderFrame(const cricket::VideoFrame* frame) {
   rtc::CritScope cs(&critical_section_);
-  if (!enabled_) {
-    return true;
-  }
+  if (!enabled_)
+    frame = CreateBlackFrame(frame);
+
   for (VideoRendererInterface* renderer : renderers_) {
     renderer->RenderFrame(frame);
   }
   return true;
 }
 
 }  // namespace webrtc