Let VideoRenderFrames::FrameToRender return rtc::Optional

webrtc/common_video/video_render_frames.h

 /*
  *  Copyright (c) 2012 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.
  */
 
 #ifndef WEBRTC_COMMON_VIDEO_VIDEO_RENDER_FRAMES_H_
 #define WEBRTC_COMMON_VIDEO_VIDEO_RENDER_FRAMES_H_
 
 #include <stdint.h>
 
 #include <list>
 
+#include "webrtc/base/optional.h"
 #include "webrtc/video_frame.h"
 
 namespace webrtc {
 
 // Class definitions
 class VideoRenderFrames {
  public:
   VideoRenderFrames();
 
   // Add a frame to the render queue
   int32_t AddFrame(const VideoFrame& new_frame);
 
-  // Get a frame for rendering, or a zero-size frame if it's not time to render.
-  VideoFrame FrameToRender();
+  // Get a frame for rendering, or false if it's not time to render.
+  rtc::Optional<VideoFrame> FrameToRender();
 
   // Releases all frames
   int32_t ReleaseAllFrames();
 
   // Returns the number of ms to next frame to render
   uint32_t TimeToNextFrameRelease();
 
   // Sets estimates delay in renderer
   int32_t SetRenderDelay(const uint32_t render_delay);
 
  private:
   // 10 seconds for 30 fps.
   enum { KMaxNumberOfFrames = 300 };
   // Don't render frames with timestamp older than 500ms from now.
   enum { KOldRenderTimestampMS = 500 };
   // Don't render frames with timestamp more than 10s into the future.
   enum { KFutureRenderTimestampMS = 10000 };
 
   // Sorted list with framed to be rendered, oldest first.
   std::list<VideoFrame> incoming_frames_;
 
   // Estimated delay from a frame is released until it's rendered.
   uint32_t render_delay_ms_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_VIDEO_VIDEO_RENDER_FRAMES_H_