Cast: First stab at implementing adaptive latency

media/cast/sender/video_sender.cc

Index: media/cast/sender/video_sender.cc
diff --git a/media/cast/sender/video_sender.cc b/media/cast/sender/video_sender.cc
index 9f8b6f9bd2e0f9c7eaf49019d46c219e930f72e5..d51b69453918bb042a1c3509559d36a1b8a4b0e2 100644
--- a/media/cast/sender/video_sender.cc
+++ b/media/cast/sender/video_sender.cc
@@ -19,6 +19,8 @@
 namespace media {
 namespace cast {
 
+const int kRoundTripsNeeded = 4;
+
 // Note, we use a fixed bitrate value when external video encoder is used.
 // Some hardware encoder shows bad behavior if we set the bitrate too
 // frequently, e.g. quality drop, not abiding by target bitrate, etc.
@@ -28,7 +30,8 @@ VideoSender::VideoSender(
     const VideoSenderConfig& video_config,
     const CreateVideoEncodeAcceleratorCallback& create_vea_cb,
     const CreateVideoEncodeMemoryCallback& create_video_encode_mem_cb,
-    CastTransportSender* const transport_sender)
+    CastTransportSender* const transport_sender,
+    const PlayoutDelayChangeCB& playout_delay_change_cb)
     : FrameSender(
         cast_environment,
         false,
@@ -37,11 +40,13 @@ VideoSender::VideoSender(
         kVideoFrequency,
         video_config.ssrc,
         video_config.max_frame_rate,
-        video_config.target_playout_delay,
+        video_config.min_playout_delay,
+        video_config.max_playout_delay,
         NewFixedCongestionControl(
             (video_config.min_bitrate + video_config.max_bitrate) / 2)),
       frames_in_encoder_(0),
       last_bitrate_(0),
+      playout_delay_change_cb_(playout_delay_change_cb),
       weak_factory_(this) {
   cast_initialization_status_ = STATUS_VIDEO_UNINITIALIZED;
   VLOG(1) << "max_unacked_frames is " << max_unacked_frames_
@@ -113,6 +118,12 @@ void VideoSender::InsertRawVideoFrame(
       "rtp_timestamp", rtp_timestamp);
 
   if (ShouldDropNextFrame(capture_time)) {
+    base::TimeDelta new_target_delay = std::min(
+        AverageRTT() * kRoundTripsNeeded,
+        max_playout_delay_);
+    if (new_target_delay > target_playout_delay_) {
+      playout_delay_change_cb_.Run(new_target_delay);
+    }
     VLOG(1) << "Dropping frame due to too many frames currently in-flight.";
     return;
   }