Cast: increase the maximum outstanding audio frames

In the case of high latency congestion period, RTT is high and audio
frames are mostly delivered on time. We do no want to drop audio frames
frequently.

This change sends up to three times of target delay worth of audio
frames. It does not any harmful effect because audio packets are small
and receiver has the ability to drop any one of them.

Review URL: https://codereview.chromium.org/360103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@280724 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 14 insertions, 5 deletions

diff --git a/media/cast/audio_sender/audio_sender.cc b/media/cast/audio_sender/audio_sender.cc
index 02e12a87..f1e2d19 100644
--- a/media/cast/audio_sender/audio_sender.cc
+++ b/media/cast/audio_sender/audio_sender.cc
@@ -14,6 +14,7 @@
 
 namespace media {
 namespace cast {
+namespace {
 
 const int kNumAggressiveReportsSentAtStart = 100;
 const int kMinSchedulingDelayMs = 1;
@@ -23,17 +24,25 @@ const int kMinSchedulingDelayMs = 1;
 // well.
 const int kAudioFrameRate = 100;
 
+// Helper function to compute the maximum unacked audio frames that is sent.
+int GetMaxUnackedFrames(base::TimeDelta target_delay) {
+  // As long as it doesn't go over |kMaxUnackedFrames|, it is okay to send more
+  // audio data than the target delay would suggest. Audio packets are tiny and
+  // receiver has the ability to drop any one of the packets.
+  // We send up to three times of the target delay of audio frames.
+  int frames =
+      1 + 3 * target_delay * kAudioFrameRate / base::TimeDelta::FromSeconds(1);
+  return std::min(kMaxUnackedFrames, frames);
+}
+}  // namespace
+
 AudioSender::AudioSender(scoped_refptr<CastEnvironment> cast_environment,
                          const AudioSenderConfig& audio_config,
                          transport::CastTransportSender* const transport_sender)
     : cast_environment_(cast_environment),
       target_playout_delay_(audio_config.target_playout_delay),
       transport_sender_(transport_sender),
-      max_unacked_frames_(
-          std::min(kMaxUnackedFrames,
-                   1 + static_cast<int>(target_playout_delay_ *
-                                        kAudioFrameRate /
-                                        base::TimeDelta::FromSeconds(1)))),
+      max_unacked_frames_(GetMaxUnackedFrames(target_playout_delay_)),
       configured_encoder_bitrate_(audio_config.bitrate),
       rtcp_(cast_environment,
             this,