Cast: First stab at implementing adaptive latency

media/cast/sender/frame_sender.cc

Index: media/cast/sender/frame_sender.cc
diff --git a/media/cast/sender/frame_sender.cc b/media/cast/sender/frame_sender.cc
index 300e8146ed8e0157b875a4edf9c0c869b4710d9c..b6b60f66d4088fbe1365fbe04014c7ba2afe039c 100644
--- a/media/cast/sender/frame_sender.cc
+++ b/media/cast/sender/frame_sender.cc
@@ -12,6 +12,7 @@ namespace {
 
 const int kMinSchedulingDelayMs = 1;
 const int kNumAggressiveReportsSentAtStart = 100;
+const size_t kRTTWindow = 1200;
 
 }  // namespace
 
@@ -22,12 +23,15 @@ FrameSender::FrameSender(scoped_refptr<CastEnvironment> cast_environment,
                          int rtp_timebase,
                          uint32 ssrc,
                          double max_frame_rate,
-                         base::TimeDelta playout_delay,
+                         base::TimeDelta min_playout_delay,
+                         base::TimeDelta max_playout_delay,
                          CongestionControl* congestion_control)
     : cast_environment_(cast_environment),
       transport_sender_(transport_sender),
       ssrc_(ssrc),
       rtcp_interval_(rtcp_interval),
+      min_playout_delay_(min_playout_delay),
+      max_playout_delay_(max_playout_delay),
       max_frame_rate_(max_frame_rate),
       num_aggressive_rtcp_reports_sent_(0),
       last_sent_frame_id_(0),
@@ -40,7 +44,7 @@ FrameSender::FrameSender(scoped_refptr<CastEnvironment> cast_environment,
   DCHECK(transport_sender_);
   DCHECK_GT(rtp_timebase_, 0);
   DCHECK(congestion_control_);
-  SetTargetPlayoutDelay(playout_delay);
+  SetTargetPlayoutDelay(min_playout_delay);
   send_target_playout_delay_ = false;
   memset(frame_rtp_timestamps_, 0, sizeof(frame_rtp_timestamps_));
 }
@@ -91,10 +95,24 @@ void FrameSender::SendRtcpReport(bool schedule_future_reports) {
 void FrameSender::OnMeasuredRoundTripTime(base::TimeDelta rtt) {
   DCHECK(rtt > base::TimeDelta());
   current_round_trip_time_ = rtt;
+  recent_round_trip_times_.push_back(rtt);
+  recent_round_trip_times_sum_ += rtt;
+  if (recent_round_trip_times_.size() > kRTTWindow) {
+    recent_round_trip_times_sum_ -= recent_round_trip_times_[0];
+    recent_round_trip_times_.pop_front();
+  }
+}
+
+base::TimeDelta FrameSender::AverageRTT() {
+  return recent_round_trip_times_sum_ / recent_round_trip_times_.size();
 }
 
 void FrameSender::SetTargetPlayoutDelay(
     base::TimeDelta new_target_playout_delay) {
+  new_target_playout_delay = std::max(new_target_playout_delay,
+                                      min_playout_delay_);
+  new_target_playout_delay = std::min(new_target_playout_delay,
+                                      max_playout_delay_);
   target_playout_delay_ = new_target_playout_delay;
   max_unacked_frames_ =
       std::min(kMaxUnackedFrames,