Adding OnReceivedOverhead to AudioEncoder.

webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc

Index: webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc
diff --git a/webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc b/webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc
index 40ad595e5c2b76b4a35236d1cfd34a267caabc48..70ce3c5718622497c07d07f750b753945159e5be 100644
--- a/webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc
+++ b/webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus.cc
@@ -15,12 +15,14 @@
 
 #include "webrtc/base/analytics/exp_filter.h"
 #include "webrtc/base/checks.h"
+#include "webrtc/base/logging.h"
 #include "webrtc/base/safe_conversions.h"
 #include "webrtc/common_types.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/audio_network_adaptor_impl.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/controller_manager.h"
 #include "webrtc/modules/audio_coding/codecs/opus/opus_interface.h"
 #include "webrtc/system_wrappers/include/clock.h"
+#include "webrtc/system_wrappers/include/field_trial.h"
 
 namespace webrtc {
 
@@ -291,10 +293,27 @@ void AudioEncoderOpus::OnReceivedUplinkPacketLossFraction(
 
 void AudioEncoderOpus::OnReceivedTargetAudioBitrate(
     int target_audio_bitrate_bps) {
-  if (!audio_network_adaptor_)
-    return SetTargetBitrate(target_audio_bitrate_bps);
-  audio_network_adaptor_->SetTargetAudioBitrate(target_audio_bitrate_bps);
-  ApplyAudioNetworkAdaptor();
+  if (audio_network_adaptor_) {
+    audio_network_adaptor_->SetTargetAudioBitrate(target_audio_bitrate_bps);
+    ApplyAudioNetworkAdaptor();
+    return;
+  }
+  if (webrtc::field_trial::FindFullName("WebRTC-SendSideBwe-WithOverhead") ==
+      "Enabled") {
+    if (!overhead_bytes_per_packet_) {
+      LOG(LS_INFO)
+          << "AudioEncoderOpus: Overhead unknown, target audio bitrate "
+          << target_audio_bitrate_bps << " bps is ignored.";
+      return;
+    }
+    int overhead_rate =
+        8 * 100 * *overhead_bytes_per_packet_ / Num10MsFramesInNextPacket();

[kwiberg-webrtc, 2016/12/03 00:30:56]

I had a hard time deciphering this calculation. Could you call the variable
"overhead_bps" or something instead?

Also, const.

[minyue-webrtc, 2016/12/06 09:04:19]

Done.

+    SetTargetBitrate(std::min(
+        kMaxBitrateBps,
+        std::max(kMinBitrateBps, target_audio_bitrate_bps - overhead_rate)));
+    return;
+  }
+  SetTargetBitrate(target_audio_bitrate_bps);

[kwiberg-webrtc, 2016/12/03 00:30:56]

I'd argue this would be easier to read if you removed the explicit returns and
did

  if (...) {
    ...
  } else if (...) {
    ...
  } else {
    ...
  }

[minyue-webrtc, 2016/12/06 09:04:19]

Done.

 }
 
 void AudioEncoderOpus::OnReceivedRtt(int rtt_ms) {
@@ -304,6 +323,15 @@ void AudioEncoderOpus::OnReceivedRtt(int rtt_ms) {
   ApplyAudioNetworkAdaptor();
 }
 
+void AudioEncoderOpus::OnReceivedOverhead(size_t overhead_bytes_per_packet) {
+  if (audio_network_adaptor_) {
+    audio_network_adaptor_->SetOverhead(overhead_bytes_per_packet);
+    ApplyAudioNetworkAdaptor();
+    return;
+  }
+  overhead_bytes_per_packet_ = rtc::Optional<size_t>(overhead_bytes_per_packet);

[kwiberg-webrtc, 2016/12/03 00:30:56]

if ... else ... instead of the explicit return.

[minyue-webrtc, 2016/12/06 09:04:19]

Done.

+}
+
 void AudioEncoderOpus::SetReceiverFrameLengthRange(int min_frame_length_ms,
                                                    int max_frame_length_ms) {
   // Ensure that |SetReceiverFrameLengthRange| is called before