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_
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "media/cast/cast_environment.h"
 #include "media/cast/net/rtcp/rtcp.h"
 #include "media/cast/sender/congestion_control.h"
 
 namespace media {
 namespace cast {
 
+// Starting playout time when we enter interactive mode.
+const int kInteractiveModeStartPlayoutTimeMs = 120;

[miu, 2015/12/01 21:15:27]

Rather than as constants, these should be plumbed-in as Audio/VideoSenderConfig,
and all the way up through to the extension API.  See media/cast/cast_config.h,
chrome/common/extensions/api/cast_streaming_rtp_stream.idl, and
chrome/renderer/media/cast_rtp_stream.cc.  This will allow us to run experiments
to determine ideal values, and also to turn on/off this new feature with Cast
Extension releases.

[Irfan, 2015/12/02 22:32:44]

I thought about this and have gone with following:

- We can levarage min as the starting point for interactive mode (since a value
less than that does not make much sense)

- Added a new animated playout delay value that is in between min and max so we
can adjust for movie playback dynamically

+
+// Starting playout time when we encounter a need to drop a frame while in
+// non-interactive mode. This is chosen to be a value that is known to work
+// well for animation content in order to minimize freezing while switching
+// between interactive and non-interactive mode.
+const int kNonInteractiveModeStartPlayoutTimeMs = 400;
+
 struct SenderEncodedFrame;
 
 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,
@@ skipping 139 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_