Reland of Add framerate to VideoSinkWants and ability to signal on overuse

webrtc/video_send_stream.h

 /*
  *  Copyright (c) 2013 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 196 matching lines @@
 
   // Starts stream activity.
   // When a stream is active, it can receive, process and deliver packets.
   virtual void Start() = 0;
   // Stops stream activity.
   // When a stream is stopped, it can't receive, process or deliver packets.
   virtual void Stop() = 0;
 
   // Based on the spec in
   // https://w3c.github.io/webrtc-pc/#idl-def-rtcdegradationpreference.
+  // These options are enforced on a best-effort basis. For instance, all of
+  // these options may suffer some frame drops in order to avoid queuing.
+  // TODO(sprang): Look into possibility of more strictly enforcing the
+  // maintain-framerate option.
   enum class DegradationPreference {
+    // Don't take any actions based on over-utilization signals.
+    kDegradationDisabled,
+    // On over-use, request lost resolution, possibly causing down-scaling.
     kMaintainResolution,
-    // TODO(perkj): Implement kMaintainFrameRate. kBalanced will drop frames
-    // if the encoder overshoots or the encoder can not encode fast enough.
+    // On over-use, request lower frame rate, possible causing frame drops.
+    kMaintainFramerate,
+    // Try to strike a "pleasing" balance between frame rate or resolution.
     kBalanced,
   };
+
   virtual void SetSource(
       rtc::VideoSourceInterface<webrtc::VideoFrame>* source,
       const DegradationPreference& degradation_preference) = 0;
 
   // Set which streams to send. Must have at least as many SSRCs as configured
   // in the config. Encoder settings are passed on to the encoder instance along
   // with the VideoStream settings.
   virtual void ReconfigureVideoEncoder(VideoEncoderConfig config) = 0;
 
   virtual Stats GetStats() = 0;
@@ skipping 14 matching lines @@
     EnableEncodedFrameRecording(std::vector<rtc::PlatformFile>(), 0);
   }
 
  protected:
   virtual ~VideoSendStream() {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_VIDEO_SEND_STREAM_H_