Release the camera when WebRTC is not visible in Android

content/browser/renderer_host/media/video_capture_controller.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // VideoCaptureController is the glue between a VideoCaptureDevice and all
 // VideoCaptureHosts that have connected to it. A controller exists on behalf of
 // one (and only one) VideoCaptureDevice; both are owned by the
 // VideoCaptureManager.
 //
 // The VideoCaptureController is responsible for:
@@ skipping 78 matching lines @@
                  media::VideoCaptureSessionId session_id,
                  const media::VideoCaptureParams& params);
 
   // Stop video capture. This will take back all buffers held by by
   // |event_handler|, and |event_handler| shouldn't use those buffers any more.
   // Returns the session_id of the stopped client, or
   // kInvalidMediaCaptureSessionId if the indicated client was not registered.
   int RemoveClient(const VideoCaptureControllerID& id,
                    VideoCaptureControllerEventHandler* event_handler);
 
+  // Pause or resume the video capture for specified client.

[tommi (sloooow) - chröme, 2014/10/01 07:17:03]

Can you document the side effects of this?
(assuming my understanding is correct) If we pause, we don't hold on to the
camera anymore, so resuming might fail and might also take much longer than
pause/play usually does (which I'm guessing is the reason you're calling it
'resume' which I think is good).

[michaelbai, 2014/10/01 22:09:33]

Thanks, I added the side effect in VideoCaptureManager::ResumeCaptureForClient()
because the camera is allocated there.

There is another issue here, if we can't allocate the camera, the error state
will be send out, the video capture can not be resumed automatically any more,
because all information was cleaned up. I were thinking developer could handle
this case by hooking into page visibility API and tried to recreate the video
channel, sounds good?

If we want video capture still resume-able, we need a way to let user know the
camera is occupied by other app so the camera could be released, it seems to me
we don't have that event in JavaScript API ( I assume VIDEO_CAPTURE_STATE_ERROR
is not suitable for this). If we don't notify this to user, there are less
chance camera will be released.

Actually, this issue is not critical, I will explain to you offline.  


On 2014/10/01 07:17:03, tommi wrote:

+  void PauseOrResumeClient(const VideoCaptureControllerID& id,
+                           VideoCaptureControllerEventHandler* event_handler,
+                           bool pause);
+
   int GetClientCount();
 
+  // Return the number of client that isn't paused.
+  int GetActiveClientCount();

[tommi (sloooow) - chröme, 2014/10/01 07:17:03]

const?

[michaelbai, 2014/10/01 22:09:33]

Done.

+
   // API called directly by VideoCaptureManager in case the device is
   // prematurely closed.
   void StopSession(int session_id);
 
   // Return a buffer with id |buffer_id| previously given in
   // VideoCaptureControllerEventHandler::OnBufferReady. In the case that the
   // buffer was backed by a texture, |sync_point| will be waited on before
   // destroying or recycling the texture, to synchronize with texture users in
   // the renderer process.
   void ReturnBuffer(const VideoCaptureControllerID& id,
@@ skipping 46 matching lines @@
   media::VideoCaptureFormat video_capture_format_;
 
   base::WeakPtrFactory<VideoCaptureController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureController);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_VIDEO_CAPTURE_CONTROLLER_H_