cast: Support for low-latency interactive mode

media/cast/sender/frame_sender.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This is the base class for an object that send frames to a receiver.
 // TODO(hclam): Refactor such that there is no separate AudioSender vs.
 // VideoSender, and the functionality of both is rolled into this class.
 
 #ifndef MEDIA_CAST_SENDER_FRAME_SENDER_H_
 #define MEDIA_CAST_SENDER_FRAME_SENDER_H_
@@ skipping 14 matching lines @@
 class FrameSender {
  public:
   FrameSender(scoped_refptr<CastEnvironment> cast_environment,
               bool is_audio,
               CastTransportSender* const transport_sender,
               int rtp_timebase,
               uint32 ssrc,
               double max_frame_rate,
               base::TimeDelta min_playout_delay,
               base::TimeDelta max_playout_delay,
+              base::TimeDelta animated_playout_delay,
               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);
 
   base::TimeDelta GetTargetPlayoutDelay() const {
@@ skipping 53 matching lines @@
   // media::cast::kMaxUnackedFrames.
   void RecordLatestFrameTimestamps(uint32 frame_id,
                                    base::TimeTicks reference_time,
                                    RtpTimestamp rtp_timestamp);
   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 GetUnacknowledgedFrameCount() const;
 
-  // The total amount of time between a frame's capture/recording on the sender
-  // and its playback on the receiver (i.e., shown to a user).  This is fixed as
-  // a value large enough to give the system sufficient time to encode,
-  // transmit/retransmit, receive, decode, and render; given its run-time
-  // environment (sender/receiver hardware performance, network conditions,
-  // etc.).
+  // Playout delay represents total amount of time between a frame's
+  // capture/recording on the sender and its playback on the receiver
+  // (i.e., shown to a user).  This should be a value large enough to
+  // give the system sufficient time to encode, transmit/retransmit,
+  // receive, decode, and render; given its run-time environment
+  // (sender/receiver hardware performance, network conditions,etc.).
+
+  // The |target_playout delay_| is the current delay that is adaptively

[miu, 2015/12/03 21:26:23]

Nice comment!  :)

+  // adjusted based on feedback from video capture engine and the congestion
+  // control. In case of interactive content, the target is adjusted to start
+  // at |min_playout_delay_| and in case of animated content, it starts out at
+  // |animated_playout_delay_| and then adaptively adjust based on feedback
+  // from congestion control.
   base::TimeDelta target_playout_delay_;
   base::TimeDelta min_playout_delay_;

[miu, 2015/12/03 21:26:23]

nit: Looks like min/max/animated_playout_delay_ could be made const.

[Irfan, 2015/12/04 22:45:37]

Done.

   base::TimeDelta max_playout_delay_;
+  // Starting playout delay for animated content.
+  base::TimeDelta animated_playout_delay_;
 
   // If true, we transmit the target playout delay to the receiver.
   bool send_target_playout_delay_;
 
   // Max encoded frames generated per second.
   double max_frame_rate_;
 
   // Counts how many RTCP reports are being "aggressively" sent (i.e., one per
   // frame) at the start of the session.  Once a threshold is reached, RTCP
   // reports are instead sent at the configured interval + random drift.
@@ skipping 45 matching lines @@
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<FrameSender> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameSender);
 };
 
 }  // namespace cast
 }  // namespace media
 
 #endif  // MEDIA_CAST_SENDER_FRAME_SENDER_H_