Update RateStatistics to handle too-little-data case.

webrtc/common_video/bitrate_adjuster.cc

 /*
  *  Copyright 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 52 matching lines @@
 uint32_t BitrateAdjuster::GetTargetBitrateBps() const {
   rtc::CritScope cs(&crit_);
   return target_bitrate_bps_;
 }
 
 uint32_t BitrateAdjuster::GetAdjustedBitrateBps() const {
   rtc::CritScope cs(&crit_);
   return adjusted_bitrate_bps_;
 }
 
-uint32_t BitrateAdjuster::GetEstimatedBitrateBps() {
+rtc::Optional<uint32_t> BitrateAdjuster::GetEstimatedBitrateBps() {
   rtc::CritScope cs(&crit_);
   return bitrate_tracker_.Rate(clock_->TimeInMilliseconds());
 }
 
 void BitrateAdjuster::Update(size_t frame_size) {
   rtc::CritScope cs(&crit_);
   uint32_t current_time_ms = clock_->TimeInMilliseconds();
   bitrate_tracker_.Update(frame_size, current_time_ms);
   UpdateBitrate(current_time_ms);
 }
@@ skipping 30 matching lines @@
 
 void BitrateAdjuster::UpdateBitrate(uint32_t current_time_ms) {
   uint32_t time_since_last_update_ms =
       current_time_ms - last_bitrate_update_time_ms_;
   // Don't attempt to update bitrate unless enough time and frames have passed.
   ++frames_since_last_update_;
   if (time_since_last_update_ms < kBitrateUpdateIntervalMs ||
       frames_since_last_update_ < kBitrateUpdateFrameInterval) {
     return;
   }
-  float estimated_bitrate_bps = bitrate_tracker_.Rate(current_time_ms);
   float target_bitrate_bps = target_bitrate_bps_;
+  float estimated_bitrate_bps =
+      bitrate_tracker_.Rate(current_time_ms).value_or(target_bitrate_bps);
   float error = target_bitrate_bps - estimated_bitrate_bps;
 
   // Adjust if we've overshot by any amount or if we've undershot too much.
   if (estimated_bitrate_bps > target_bitrate_bps ||
       error > kBitrateTolerancePct * target_bitrate_bps) {
     // Adjust the bitrate by a fraction of the error.
     float adjustment = .5 * error;
     float adjusted_bitrate_bps = target_bitrate_bps + adjustment;
 
     // Clamp the adjustment.
@@ skipping 16 matching lines @@
                       << static_cast<uint32_t>(adjusted_bitrate_bps);
       adjusted_bitrate_bps_ = adjusted_bitrate_bps;
     }
   }
   last_bitrate_update_time_ms_ = current_time_ms;
   frames_since_last_update_ = 0;
   last_adjusted_target_bitrate_bps_ = target_bitrate_bps_;
 }
 
 }  // namespace webrtc