Add framerate to VideoSinkWants and ability to signal on overuse

webrtc/video_send_stream.h

Index: webrtc/video_send_stream.h
diff --git a/webrtc/video_send_stream.h b/webrtc/video_send_stream.h
index 680eb02bc46805ae701342faabd54a81d3581f87..8a82a6df4d81a447f708f9d5c56673a61e2e123b 100644
--- a/webrtc/video_send_stream.h
+++ b/webrtc/video_send_stream.h
@@ -214,12 +214,21 @@ class VideoSendStream {
 
   // 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;