Video Capture: Allow suspension of individual devices.

media/base/video_capturer_source.h

 // Copyright 2015 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.
 
 #ifndef MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_
 #define MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 68 matching lines @@
   // Asks source to send a refresh frame. In cases where source does not provide
   // a continuous rate of new frames (e.g. canvas capture, screen capture where
   // the screen's content has not changed in a while), consumers may request a
   // "refresh frame" to be delivered. For instance, this would be needed when
   // a new sink is added to a MediaStreamTrack.
   // The default implementation is a no-op and implementations are not required
   // to honor this request. If they decide to and capturing is started
   // successfully, then |new_frame_callback| should be called with a frame.
   virtual void RequestRefreshFrame() {}
 
+  // Optionally suspends frame delivery. The source may or may not honor this
+  // request. The purpose of this is to allow minimizing resource usage while
+  // there are no frame consumers present.
+  virtual void MaybeSuspend() {}

[xhwang, 2016/09/28 21:09:56]

nit: How will the caller know whether it can/should call Resume() if it doesn't
know whether "suspend" request is honored?

[miu, 2016/09/28 21:52:14]

Added explanation in comments.

+
+  // Resumes frame delivery, if it was suspended.

[xhwang, 2016/09/28 21:09:56]

nit: What if "it was not suspended"? Will it fail, no-op, or DCHECK? What if
capturing never "started"?

[miu, 2016/09/28 21:52:14]

Added explanation in comments for this too.

+  virtual void Resume() {}
+
   // Stops capturing frames and clears all callbacks including the
   // SupportedFormatsCallback callback. Note that queued frame callbacks
   // may still occur after this call, so the caller must take care to
   // use refcounted or weak references in |new_frame_callback|.
   virtual void StopCapture() = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_CAPTURER_SOURCE_H_