Use different restrictions of acked bitrate lag depending on operating point.

webrtc/modules/remote_bitrate_estimator/aimd_rate_control.cc

 /*
  *  Copyright (c) 2014 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 211 matching lines @@
         UpdateMaxBitRateEstimate(incoming_bitrate_kbps);
       }
       // Stay on hold until the pipes are cleared.
       ChangeState(kRcHold);
       time_last_bitrate_change_ = now_ms;
       break;
 
     default:
       assert(false);
   }
-  if ((incoming_bitrate_bps > 100000 || current_bitrate_bps > 150000) &&
-      current_bitrate_bps > 1.5 * incoming_bitrate_bps) {
-    // Allow changing the bit rate if we are operating at very low rates
-    // Don't change the bit rate if the send side is too far off
-    current_bitrate_bps = current_bitrate_bps_;
+  // Don't change the bit rate if the send side is too far off.
+  // We allow a bit more lag at very low rates to not too easily get stuck if
+  // the encoder produces uneven outputs.
+  const uint32_t max_bitrate_bps =
+      static_cast<uint32_t>(1.5f * incoming_bitrate_bps) + 10000;
+  if (current_bitrate_bps > current_bitrate_bps_ &&
+      current_bitrate_bps > max_bitrate_bps) {
+    current_bitrate_bps = std::max(current_bitrate_bps_, max_bitrate_bps);
     time_last_bitrate_change_ = now_ms;
   }
   return current_bitrate_bps;
 }
 
 uint32_t AimdRateControl::MultiplicativeRateIncrease(
     int64_t now_ms, int64_t last_ms, uint32_t current_bitrate_bps) const {
   double alpha = 1.08;
   if (last_ms > -1) {
     int time_since_last_update_ms = std::min(static_cast<int>(now_ms - last_ms),
@@ skipping 58 matching lines @@
 }
 
 void AimdRateControl::ChangeRegion(RateControlRegion region) {
   rate_control_region_ = region;
 }
 
 void AimdRateControl::ChangeState(RateControlState new_state) {
   rate_control_state_ = new_state;
 }
 }  // namespace webrtc