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..adc4e3618b60bab8e6159c1b73cf7c4d9b817647 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 +1315,14 @@ 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 a

[stefan-webrtc, 2016/11/24 10:40:45]

for an

[michaelt, 2016/11/24 13:47:18]

Done.

+  // expensional filter (bitrate_smoother use an exponential filter) with the

[stefan-webrtc, 2016/11/24 10:40:46]

exponential

[michaelt, 2016/11/24 13:47:18]

Done.

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

[stefan-webrtc, 2016/11/24 10:40:45]

Move to the line above.

an amplitude

[michaelt, 2016/11/24 13:47:18]

Done.

+  // 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) {