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..560ac26c4d56aeb6b4e32f79b06a32dd526454c1 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_);
 
   // Used by chrome/browser/extension/api/cast_streaming/performance_test.cc
   TRACE_EVENT_INSTANT1(
@@ -387,8 +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);
-        current_requested_bitrate_ = new_bitrate;
+        UpdateBitrate(new_bitrate);
       }
     }
     // We only count duplicate ACKs when we have sent newer frames.
@@ -414,8 +415,7 @@ 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);
-      current_requested_bitrate_ = new_bitrate;
+      UpdateBitrate(new_bitrate);
     }
   }
   ReceivedAck(cast_feedback.ack_frame_id_);
@@ -467,6 +467,12 @@ 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_);
   }
@@ -482,5 +488,11 @@ void VideoSender::ResendFrame(uint32 resend_frame_id) {
   transport_sender_->ResendPackets(false, missing_frames_and_packets);
 }
 
+void VideoSender::UpdateBitrate(int new_bitrate) {
+  new_bitrate /= current_bitrate_divider_;

[Alpha Left Google, 2014/05/08 23:48:30]

Please have a check here such that we don't go too low for the bitrate.

[hubbe, 2014/05/08 23:55:02]

What is "too low" ?

[hubbe, 2014/05/08 23:58:17]

Done.

+  video_encoder_->SetBitRate(new_bitrate);
+  current_requested_bitrate_ = new_bitrate;
+}
+
 }  // namespace cast
 }  // namespace media