Set max bitrate for audio send stream based on RtpParameters.

webrtc/media/engine/webrtcvoiceengine.cc

Index: webrtc/media/engine/webrtcvoiceengine.cc
diff --git a/webrtc/media/engine/webrtcvoiceengine.cc b/webrtc/media/engine/webrtcvoiceengine.cc
index 7c6d7940f685cd9e11aa4f90227b93582ccf6ce0..49ec50fdec5a9f951f831e6a0ff2e52f85a462b9 100644
--- a/webrtc/media/engine/webrtcvoiceengine.cc
+++ b/webrtc/media/engine/webrtcvoiceengine.cc
@@ -1388,7 +1388,14 @@ class WebRtcVoiceMediaChannel::WebRtcAudioSendStream
     RTC_DCHECK(!stream_);
     if (webrtc::field_trial::IsEnabled("WebRTC-Audio-SendSideBwe")) {
       config_.min_bitrate_bps = kOpusMinBitrateBps;
-      config_.max_bitrate_bps = kOpusBitrateFbBps;
+
+      // This means that when RtpParameters is reset, we may change the
+      // encoder's bit rate immediately (through call_->CreateAudioSendStream),
+      // meanwhile change the cap to the output of BWE.
+      // TODO(minyue): remove dependency on RtpParameters when the signaling to
+      // BWE is done through a dedicated API.

[stefan-webrtc, 2017/03/24 15:09:14]

I think this is something that should be here even after we add a BWE api. It's
still possible that someone would want to change the allocation of audio
bitrate.

[minyue-webrtc, 2017/03/24 21:13:59]

right, I will remove this todo now.

+      config_.max_bitrate_bps = rtp_parameters_.encodings[0].max_bitrate_bps ?
+          *rtp_parameters_.encodings[0].max_bitrate_bps : kOpusBitrateFbBps;
       // TODO(mflodman): Keep testing this and set proper values.
       // Note: This is an early experiment currently only supported by Opus.
       if (send_side_bwe_with_overhead_) {
@@ -1421,8 +1428,8 @@ class WebRtcVoiceMediaChannel::WebRtcAudioSendStream
           int max_overhead_bps =
               kOverheadPerPacket * 8 * 1000 / min_packet_size_ms;
 
-          config_.min_bitrate_bps = kOpusMinBitrateBps + min_overhead_bps;
-          config_.max_bitrate_bps = kOpusBitrateFbBps + max_overhead_bps;
+          config_.min_bitrate_bps += min_overhead_bps;
+          config_.max_bitrate_bps += max_overhead_bps;

[minyue-webrtc, 2017/03/24 21:13:59]

I see a problem here. To make sure that the payload rate will never go above 
rtp_parameters_.encodings[0].max_bitrate_bps, we have to add min_overhead_bps.

The other one is add max_overhead_bps.

[stefan-webrtc, 2017/03/27 12:11:46]

Sounds good to me. As long as the max BWE is set high enough to allow some
overhead it shouldn't affect calls on good networks.

         }
       }
     }