Now probe for x3 and x6 the initial start bitrate.

webrtc/modules/congestion_controller/probe_bitrate_estimator.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.
  */
 
 #include "webrtc/modules/congestion_controller/probe_bitrate_estimator.h"
 
 #include <algorithm>
 
 #include "webrtc/base/checks.h"
 #include "webrtc/base/logging.h"
 
 namespace {
 // The minumum number of probes we need for a valid cluster.
 constexpr int kMinNumProbesValidCluster = 4;
 
 // The maximum (receive rate)/(send rate) ratio for a valid estimate.
-constexpr float kValidRatio = 1.2f;
+constexpr float kValidRatio = 2.0f;
 
 // The maximum time period over which the cluster history is retained.
 // This is also the maximum time period beyond which a probing burst is not
 // expected to last.
 constexpr int kMaxClusterHistoryMs = 1000;
 
 // The maximum time interval between first and the last probe on a cluster
 // on the sender side as well as the receive side.
 constexpr int kMaxProbeIntervalMs = 1000;
 }  // namespace
@@ skipping 84 matching lines @@
 void ProbeBitrateEstimator::EraseOldClusters(int64_t timestamp_ms) {
   for (auto it = clusters_.begin(); it != clusters_.end();) {
     if (it->second.last_receive_ms < timestamp_ms) {
       it = clusters_.erase(it);
     } else {
       ++it;
     }
   }
 }
 }  // namespace webrtc