Reduce send rate to 50% if overusing before we have an acknowledged bitrate.

webrtc/modules/congestion_controller/delay_based_bwe.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 183 matching lines @@
   int64_t now_ms = clock_->TimeInMilliseconds();
 
   rtc::Optional<int> probe_bitrate_bps =
       probe_bitrate_estimator_.FetchAndResetLastEstimatedBitrateBps();
   // Currently overusing the bandwidth.
   if (overusing) {
     if (acked_bitrate_bps &&
         rate_control_.TimeToReduceFurther(now_ms, *acked_bitrate_bps)) {
       result.updated = UpdateEstimate(now_ms, acked_bitrate_bps, overusing,
                                       &result.target_bitrate_bps);
+    } else if (!acked_bitrate_bps && rate_control_.ValidEstimate() &&
+               rate_control_.TimeToReduceFurther(
+                   now_ms, rate_control_.LatestEstimate() / 2 - 1)) {
+      // Overusing before we have a measured acknowledged bitrate. We check
+      // TimeToReduceFurther (with a fake acknowledged bitrate) to avoid
+      // reducing too often.
+      // TODO(tschumim): Improve this and/or the acknowledged bitrate estimator
+      // so that we (almost) always have a bitrate estimate.
+      rate_control_.SetEstimate(rate_control_.LatestEstimate() / 2, now_ms);
+      result.updated = true;
+      result.probe = false;
+      result.target_bitrate_bps = rate_control_.LatestEstimate();
     }
   } else {
     if (probe_bitrate_bps) {
       result.probe = true;
       result.updated = true;
       result.target_bitrate_bps = *probe_bitrate_bps;
       rate_control_.SetEstimate(*probe_bitrate_bps, now_ms);
     } else {
       result.updated = UpdateEstimate(now_ms, acked_bitrate_bps, overusing,
                                       &result.target_bitrate_bps);
@@ skipping 56 matching lines @@
 void DelayBasedBwe::SetMinBitrate(int min_bitrate_bps) {
   // Called from both the configuration thread and the network thread. Shouldn't
   // be called from the network thread in the future.
   rate_control_.SetMinBitrate(min_bitrate_bps);
 }
 
 int64_t DelayBasedBwe::GetExpectedBwePeriodMs() const {
   return rate_control_.GetExpectedBandwidthPeriodMs();
 }
 }  // namespace webrtc