Pass time constant to bwe smoothing filter.

webrtc/voice_engine/channel.cc

Index: webrtc/voice_engine/channel.cc
diff --git a/webrtc/voice_engine/channel.cc b/webrtc/voice_engine/channel.cc
index f3021fef6fec31f8e727fa3698158628dc1d89ee..375a02d2e7801d9828e0b39e811b751419ac2da3 100644
--- a/webrtc/voice_engine/channel.cc
+++ b/webrtc/voice_engine/channel.cc
@@ -1304,7 +1304,7 @@ int32_t Channel::SetSendCodec(const CodecInst& codec) {
   return 0;
 }
 
-void Channel::SetBitRate(int bitrate_bps) {
+void Channel::SetBitRate(int bitrate_bps, int64_t probing_interval_ms) {
   WEBRTC_TRACE(kTraceInfo, kTraceVoice, VoEId(_instanceId, _channelId),
                "Channel::SetBitRate(bitrate_bps=%d)", bitrate_bps);
   audio_coding_->ModifyEncoder([&](std::unique_ptr<AudioEncoder>* encoder) {
@@ -1315,10 +1315,13 @@ void Channel::SetBitRate(int bitrate_bps) {
 
   // We give smoothed bitrate allocation to audio network adaptor as
   // the uplink bandwidth.
-  // TODO(michaelt) : Remove kDefaultBitrateSmoothingTimeConstantMs as soon as
-  // we pass the probing interval to this function.
-  constexpr int64_t kDefaultBitrateSmoothingTimeConstantMs = 20000;
-  bitrate_smoother_.SetTimeConstantMs(kDefaultBitrateSmoothingTimeConstantMs);
+  // The probing spikes should not affect the bitrate smoother more than 25%.
+  // To simplify the calculations we use a step response as input signal.
+  // The calculation show a step response for an
+  // exponential filter (bitrate_smoother use an exponential filter) with the

[minyue-webrtc, 2016/11/28 12:00:00]

merge this line with up

[michaelt, 2016/11/28 13:03:38]

Changed description according to the offline discussion. 

+  // length of probing_interval and an amplitude of 1.

[minyue-webrtc, 2016/11/28 12:00:00]

and put |var| around variables, no need in equation though (so as to avoid
confusion with abs)

[michaelt, 2016/11/28 13:03:37]

Changed description according to the offline discussion. 

+  // 0.22 = 1 - e^(-t/probing_interval * 4) | t = probing_interval.
+  bitrate_smoother_.SetTimeConstantMs(probing_interval_ms * 4);
   bitrate_smoother_.AddSample(bitrate_bps);
   audio_coding_->ModifyEncoder([&](std::unique_ptr<AudioEncoder>* encoder) {
     if (*encoder) {