[Cast] Limit frames in flight by duration, and not by number of frames.

media/cast/sender/frame_sender.h

Index: media/cast/sender/frame_sender.h
diff --git a/media/cast/sender/frame_sender.h b/media/cast/sender/frame_sender.h
index 89e654d81baa7c631e8d04e5e21cbf0d219d3710..1afd73eeb9b97e934a84f95b50c062cf3ada6708 100644
--- a/media/cast/sender/frame_sender.h
+++ b/media/cast/sender/frame_sender.h
@@ -9,6 +9,8 @@
 #ifndef MEDIA_CAST_SENDER_FRAME_SENDER_H_
 #define MEDIA_CAST_SENDER_FRAME_SENDER_H_
 
+#include <deque>
+
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
@@ -33,6 +35,8 @@ class FrameSender {
               CongestionControl* congestion_control);
   virtual ~FrameSender();
 
+  int rtp_timebase() const { return rtp_timebase_; }
+
   // Calling this function is only valid if the receiver supports the
   // "extra_playout_delay", rtp extension.
   void SetTargetPlayoutDelay(base::TimeDelta new_target_playout_delay);
@@ -46,9 +50,6 @@ class FrameSender {
                         scoped_ptr<EncodedFrame> encoded_frame);
 
  protected:
-  // Returns the number of frames in the encoder's backlog.
-  virtual int GetNumberOfFramesInEncoder() const = 0;
-
   // Called when we get an ACK for a frame.
   virtual void OnAck(uint32 frame_id) = 0;
 
@@ -83,12 +84,6 @@ class FrameSender {
   // Protected for testability.
   void OnReceivedCastFeedback(const RtcpCastMessage& cast_feedback);
 
-  // Returns true if there are too many frames in flight, or if the media
-  // duration of the frames in flight would be too high by sending the next
-  // frame.  The latter metric is determined from the given |capture_time|
-  // for the next frame to be encoded and sent.
-  bool ShouldDropNextFrame(base::TimeTicks capture_time) const;
-
   // Record or retrieve a recent history of each frame's timestamps.
   // Warning: If a frame ID too far in the past is requested, the getters will
   // silently succeed but return incorrect values.  Be sure to respect
@@ -99,6 +94,13 @@ class FrameSender {
   base::TimeTicks GetRecordedReferenceTime(uint32 frame_id) const;
   RtpTimestamp GetRecordedRtpTimestamp(uint32 frame_id) const;
 
+  // Returns the number of frames that were sent but not yet acknowledged.
+  int GetUnackedFrameCount() const;
+
+  // Returns the maximum media duration currently allowed in-flight.  This
+  // fluctuates in response to the currently-measured network latency.
+  base::TimeDelta GetAllowedInFlightMediaDuration() const;
+
   const base::TimeDelta rtcp_interval_;
 
   // The total amount of time between a frame's capture/recording on the sender
@@ -148,14 +150,14 @@ class FrameSender {
   // STATUS_VIDEO_INITIALIZED.
   CastInitializationStatus cast_initialization_status_;
 
-  // RTP timestamp increment representing one second.
-  const int rtp_timebase_;
-
   // This object controls how we change the bitrate to make sure the
   // buffer doesn't overflow.
   scoped_ptr<CongestionControl> congestion_control_;
 
  private:
+  // RTP timestamp increment representing one second.
+  const int rtp_timebase_;
+
   const bool is_audio_;
 
   // Ring buffers to keep track of recent frame timestamps (both in terms of
@@ -164,8 +166,16 @@ class FrameSender {
   base::TimeTicks frame_reference_times_[256];
   RtpTimestamp frame_rtp_timestamps_[256];
 
-  // The most recently measured round trip time.
+  // The most recently measured round trip time, and a recent history of
+  // maximums.
   base::TimeDelta current_round_trip_time_;
+  std::deque<base::TimeDelta> max_rtt_buckets_;
+  base::TimeTicks last_max_rtt_bucket_rotation_;
+
+  // The current maximum expected one-way trip time on the network.  This is
+  // re-computed as each RTT measurement is received, and affects the media
+  // duration allowed to be in-flight.
+  base::TimeDelta expected_max_one_way_trip_time_;
 
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<FrameSender> weak_factory_;