Cast: First stab at implementing adaptive latency

media/cast/sender/video_sender.cc

 // 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.
 
 #include "media/cast/sender/video_sender.h"
 
 #include <algorithm>
 #include <cstring>
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "media/cast/cast_defines.h"
 #include "media/cast/net/cast_transport_config.h"
 #include "media/cast/sender/external_video_encoder.h"
 #include "media/cast/sender/video_encoder_impl.h"
 
 namespace media {
 namespace cast {
 
+const int kRoundTripsNeeded = 4;

[Alpha Left Google, 2014/09/11 01:24:26]

nit: This constant needs to be more descriptive or a comment to explain what it
does. My first glance I'm thinking "round trips needed" for what?

[hubbe, 2014/09/11 19:17:19]

I actually think the name is pretty good (but I'm open to suggestions)
I added some comments to provide context instead.

+
 // 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.
 // See details: crbug.com/392086.
 VideoSender::VideoSender(
     scoped_refptr<CastEnvironment> cast_environment,
     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,
         transport_sender,
         base::TimeDelta::FromMilliseconds(video_config.rtcp_interval),
         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_
           << " for target_playout_delay="
           << target_playout_delay_.InMilliseconds() << " ms"
           << " and max_frame_rate=" << video_config.max_frame_rate;
   DCHECK_GT(max_unacked_frames_, 0);
 
   if (video_config.use_external_encoder) {
     video_encoder_.reset(new ExternalVideoEncoder(cast_environment,
                                                   video_config,
                                                   create_vea_cb,
                                                   create_video_encode_mem_cb));
   } else {
     congestion_control_.reset(
         NewAdaptiveCongestionControl(cast_environment->Clock(),
                                      video_config.max_bitrate,
                                      video_config.min_bitrate,
                                      max_unacked_frames_));
     video_encoder_.reset(new VideoEncoderImpl(
         cast_environment, video_config, max_unacked_frames_));
   }
   cast_initialization_status_ = STATUS_VIDEO_INITIALIZED;
 
   media::cast::CastTransportRtpConfig transport_config;
   transport_config.ssrc = video_config.ssrc;
   transport_config.feedback_ssrc = video_config.incoming_feedback_ssrc;
   transport_config.rtp_payload_type = video_config.rtp_payload_type;
-  transport_config.stored_frames = max_unacked_frames_;
+  transport_config.stored_frames =
+      std::min(kMaxUnackedFrames,
+               1 + static_cast<int>(max_playout_delay_ *
+                                    max_frame_rate_ /
+                                    base::TimeDelta::FromSeconds(1)));
   transport_config.aes_key = video_config.aes_key;
   transport_config.aes_iv_mask = video_config.aes_iv_mask;
 
   transport_sender->InitializeVideo(
       transport_config,
       base::Bind(&VideoSender::OnReceivedCastFeedback,
                  weak_factory_.GetWeakPtr()),
       base::Bind(&VideoSender::OnMeasuredRoundTripTime,
                  weak_factory_.GetWeakPtr()));
 }
@@ skipping 22 matching lines @@
       kFrameIdUnknown);
 
   // Used by chrome/browser/extension/api/cast_streaming/performance_test.cc
   TRACE_EVENT_INSTANT2(
       "cast_perf_test", "InsertRawVideoFrame",
       TRACE_EVENT_SCOPE_THREAD,
       "timestamp", capture_time.ToInternalValue(),
       "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;
   }
 
   uint32 bitrate = congestion_control_->GetBitrate(
         capture_time + target_playout_delay_, target_playout_delay_);
   if (bitrate != last_bitrate_) {
     video_encoder_->SetBitRate(bitrate);
     last_bitrate_ = bitrate;
   }
@@ skipping 24 matching lines @@
   DCHECK(cast_environment_->CurrentlyOn(CastEnvironment::MAIN));
 
   frames_in_encoder_--;
   DCHECK_GE(frames_in_encoder_, 0);
 
   SendEncodedFrame(encoder_bitrate, encoded_frame.Pass());
 }
 
 }  // namespace cast
 }  // namespace media