Cast: Reduce bitrate drastically when close to unacked frame limit

media/cast/video_sender/video_sender.cc

Index: media/cast/video_sender/video_sender.cc
diff --git a/media/cast/video_sender/video_sender.cc b/media/cast/video_sender/video_sender.cc
index 29859db18853226b0a775b234c79a27d00f699da..924e0135671880103eb1e668432ee789963d9a20 100644
--- a/media/cast/video_sender/video_sender.cc
+++ b/media/cast/video_sender/video_sender.cc
@@ -65,6 +65,7 @@ VideoSender::VideoSender(
       duplicate_ack_(0),
       last_skip_count_(0),
       current_requested_bitrate_(video_config.start_bitrate),
+      current_bitrate_divider_(1),
       congestion_control_(cast_environment->Clock(),
                           video_config.congestion_control_back_off,
                           video_config.max_bitrate,
@@ -184,7 +185,8 @@ void VideoSender::SendEncodedVideoFrameMainThread(
   cast_environment_->Logging()->InsertEncodedFrameEvent(
       last_send_time_, kVideoFrameEncoded, encoded_frame->rtp_timestamp,
       frame_id, static_cast<int>(encoded_frame->data.size()),
-      encoded_frame->key_frame, current_requested_bitrate_);
+      encoded_frame->key_frame,
+      current_requested_bitrate_ / current_bitrate_divider_);

[Alpha Left Google, 2014/05/08 23:22:34]

Can we have a helper method to compute this instead of duplicating the divide?

[hubbe, 2014/05/08 23:44:04]

Done.

 
   // Used by chrome/browser/extension/api/cast_streaming/performance_test.cc
   TRACE_EVENT_INSTANT1(
@@ -387,7 +389,7 @@ void VideoSender::OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback) {
         cast_feedback.ack_frame_id_) {
       uint32 new_bitrate = 0;
       if (congestion_control_.OnAck(rtt, &new_bitrate)) {
-        video_encoder_->SetBitRate(new_bitrate);
+        video_encoder_->SetBitRate(new_bitrate / current_bitrate_divider_);

[Alpha Left Google, 2014/05/08 23:22:34]

This should really be a helper method.

[hubbe, 2014/05/08 23:44:04]

Done.

         current_requested_bitrate_ = new_bitrate;
       }
     }
@@ -414,7 +416,7 @@ void VideoSender::OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback) {
         false, cast_feedback.missing_frames_and_packets_);
     uint32 new_bitrate = 0;
     if (congestion_control_.OnNack(rtt, &new_bitrate)) {
-      video_encoder_->SetBitRate(new_bitrate);
+      video_encoder_->SetBitRate(new_bitrate / current_bitrate_divider_);

[Alpha Left Google, 2014/05/08 23:22:34]

Same here this should be a helper method.

[hubbe, 2014/05/08 23:44:04]

Done.

       current_requested_bitrate_ = new_bitrate;
     }
   }
@@ -467,6 +469,12 @@ void VideoSender::UpdateFramesInFlight() {
     if (frames_in_flight >= max_unacked_frames_) {
       video_encoder_->SkipNextFrame(true);
       return;
+    } else if (frames_in_flight > max_unacked_frames_ * 4 / 5) {
+      current_bitrate_divider_ = 3;
+    } else if (frames_in_flight > max_unacked_frames_ * 2 / 3) {
+      current_bitrate_divider_ = 2;
+    } else {
+      current_bitrate_divider_ = 1;
     }
     DCHECK(frames_in_flight <= max_unacked_frames_);
   }