Fix issue with BWE value proposition (#81)

Author: taste1981

modules/congestion_controller/goog_cc/send_side_bandwidth_estimation.cc

@@ -247,6 +247,7 @@ SendSideBandwidthEstimation::SendSideBandwidthEstimation(
   if (LossBasedBandwidthEstimatorV2Enabled()) {
     loss_based_bandwidth_estimator_v2_.SetMinBitrate(min_bitrate_configured_);
   }
+  is_low_latency_mode_ = field_trial::IsEnabled("OWT-LowLatencyMode");
 }
 
 SendSideBandwidthEstimation::~SendSideBandwidthEstimation() {}
@@ -462,6 +463,9 @@ void SendSideBandwidthEstimation::UpdateRtt(TimeDelta rtt, Timestamp at_time) {
 
 void SendSideBandwidthEstimation::UpdateEstimate(Timestamp at_time) {
   if (rtt_backoff_.CorrectedRtt(at_time) > rtt_backoff_.rtt_limit_) {
+    // If last decrease happens before 1 second, and current target is larger than
+    // 5kbps, and we decided an RTT backoff is neccessary, we drop current target by
+    // 0.8 and use that as estimation result.
     if (at_time - time_last_decrease_ >= rtt_backoff_.drop_interval_ &&
         current_target_ > rtt_backoff_.bandwidth_floor_) {
       time_last_decrease_ = at_time;
@@ -663,7 +667,10 @@ void SendSideBandwidthEstimation::MaybeLogLossBasedEvent(Timestamp at_time) {
 
 void SendSideBandwidthEstimation::UpdateTargetBitrate(DataRate new_bitrate,
                                                       Timestamp at_time) {
-  new_bitrate = std::min(new_bitrate, GetUpperLimit());
+  if (is_low_latency_mode_)
+    new_bitrate = GetUpperLimit();
+  else
+    new_bitrate = std::min(new_bitrate, GetUpperLimit());
   if (new_bitrate < min_bitrate_configured_) {
     MaybeLogLowBitrateWarning(new_bitrate, at_time);
     new_bitrate = min_bitrate_configured_;

modules/congestion_controller/goog_cc/send_side_bandwidth_estimation.h

@@ -202,6 +202,7 @@ class SendSideBandwidthEstimation {
   LossBasedBandwidthEstimation loss_based_bandwidth_estimator_v1_;
   LossBasedBweV2 loss_based_bandwidth_estimator_v2_;
   FieldTrialFlag disable_receiver_limit_caps_only_;
+  bool is_low_latency_mode_;
 };
 }  // namespace webrtc
 #endif  // MODULES_CONGESTION_CONTROLLER_GOOG_CC_SEND_SIDE_BANDWIDTH_ESTIMATION_H_