RESOURCE_UTILIZATION in VideoFrameMetadata, a consumer feedback signal.

media/cast/sender/video_sender.cc

 // Copyright 2014 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.
 
 #include "media/cast/sender/video_sender.h"
 
 #include <algorithm>
 #include <cstring>
 
 #include "base/bind.h"
@@ skipping 190 matching lines @@
                                        frames_in_encoder_ + 1,
                                        last_reported_deadline_utilization_,
                                        last_reported_lossy_utilization_,
                                        video_frame.get());
 
   if (video_encoder_->EncodeVideoFrame(
           video_frame,
           reference_time,
           base::Bind(&VideoSender::OnEncodedVideoFrame,
                      weak_factory_.GetWeakPtr(),
+                     video_frame,
                      bitrate))) {
     frames_in_encoder_++;
     duration_in_encoder_ += duration_added_by_next_frame;
     last_enqueued_frame_rtp_timestamp_ = rtp_timestamp;
     last_enqueued_frame_reference_time_ = reference_time;
   } else {
     VLOG(1) << "Encoder rejected a frame.  Skipping...";
   }
 }
 
@@ skipping 13 matching lines @@
   } else {
     return duration_in_encoder_;
   }
 }
 
 void VideoSender::OnAck(uint32 frame_id) {
   video_encoder_->LatestFrameIdToReference(frame_id);
 }
 
 void VideoSender::OnEncodedVideoFrame(
+    const scoped_refptr<media::VideoFrame>& video_frame,
     int encoder_bitrate,
     scoped_ptr<SenderEncodedFrame> encoded_frame) {
   DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
 
   frames_in_encoder_--;
   DCHECK_GE(frames_in_encoder_, 0);
 
   duration_in_encoder_ =
       last_enqueued_frame_reference_time_ - encoded_frame->reference_time;
 
   last_reported_deadline_utilization_ = encoded_frame->deadline_utilization;
   last_reported_lossy_utilization_ = encoded_frame->lossy_utilization;
-  // TODO(miu): Plumb-in a utilization feedback signal back to the producer of
-  // the video frames.  http://crbug.com/156767
+
+  // Report the stress level for non-key frames.  Key frames are excepted
+  // because their utilization measurements are atypical compared to the other
+  // frames in the stream, and this can misguide the producer of the input video
+  // frames.

[hubbe, 2015/06/02 00:23:22]

I really wish we could include key frames too.
Not sure how to do that in a *good* way though.

[miu, 2015/06/02 03:07:34]

Done.  I thought about this for awhile, and there really isn't a good way. 
Instead of providing nothing, I've explicitly capped the value to 1.0 to avoid
throwing things off.

+  if (encoded_frame->dependency != EncodedFrame::KEY) {
+    // Take the greater of the two utilization values and attenuate them such
+    // that 75% utilization is reported as the maximum sustainable stress
+    // level.  This provides "wiggle room," ensuring there will be sufficient
+    // CPU and bandwidth available to handle the occasional more-complex frames.
+    static const double kAttenuationFactor = 0.75;
+    const double attenuated_stress_level =
+        std::max(last_reported_deadline_utilization_,
+                 last_reported_lossy_utilization_) / kAttenuationFactor;
+    if (attenuated_stress_level >= 0.0) {
+      video_frame->metadata()->SetDouble(
+          media::VideoFrameMetadata::STRESS_LEVEL, attenuated_stress_level);
+    }
+  }
 
   SendEncodedFrame(encoder_bitrate, encoded_frame.Pass());
 }
 
 }  // namespace cast
 }  // namespace media