Refactored incoming bitrate estimator.

webrtc/modules/congestion_controller/delay_based_bwe.cc

Index: webrtc/modules/congestion_controller/delay_based_bwe.cc
diff --git a/webrtc/modules/congestion_controller/delay_based_bwe.cc b/webrtc/modules/congestion_controller/delay_based_bwe.cc
index fca5143bb12881211f83372773489c549e4933cc..154634829ba821d3e3478569e589750a9945d9e8 100644
--- a/webrtc/modules/congestion_controller/delay_based_bwe.cc
+++ b/webrtc/modules/congestion_controller/delay_based_bwe.cc
@@ -38,8 +38,6 @@ constexpr double kTimestampToMs =
 // This ssrc is used to fulfill the current API but will be removed
 // after the API has been changed.
 constexpr uint32_t kFixedSsrc = 0;
-constexpr int kInitialRateWindowMs = 500;
-constexpr int kRateWindowMs = 150;
 
 // Parameters for linear least squares fit of regression line to noisy data.
 constexpr size_t kDefaultTrendlineWindowSize = 20;
@@ -81,85 +79,16 @@ void SortPacketFeedbackVector(const std::vector<webrtc::PacketFeedback>& input,
 
 namespace webrtc {
 
-DelayBasedBwe::BitrateEstimator::BitrateEstimator()
-    : sum_(0),
-      current_win_ms_(0),
-      prev_time_ms_(-1),
-      bitrate_estimate_(-1.0f),
-      bitrate_estimate_var_(50.0f) {}
-
-void DelayBasedBwe::BitrateEstimator::Update(int64_t now_ms, int bytes) {
-  int rate_window_ms = kRateWindowMs;
-  // We use a larger window at the beginning to get a more stable sample that
-  // we can use to initialize the estimate.
-  if (bitrate_estimate_ < 0.f)
-    rate_window_ms = kInitialRateWindowMs;
-  float bitrate_sample = UpdateWindow(now_ms, bytes, rate_window_ms);
-  if (bitrate_sample < 0.0f)
-    return;
-  if (bitrate_estimate_ < 0.0f) {
-    // This is the very first sample we get. Use it to initialize the estimate.
-    bitrate_estimate_ = bitrate_sample;
-    return;
-  }
-  // Define the sample uncertainty as a function of how far away it is from the
-  // current estimate.
-  float sample_uncertainty =
-      10.0f * std::abs(bitrate_estimate_ - bitrate_sample) / bitrate_estimate_;
-  float sample_var = sample_uncertainty * sample_uncertainty;
-  // Update a bayesian estimate of the rate, weighting it lower if the sample
-  // uncertainty is large.
-  // The bitrate estimate uncertainty is increased with each update to model
-  // that the bitrate changes over time.
-  float pred_bitrate_estimate_var = bitrate_estimate_var_ + 5.f;
-  bitrate_estimate_ = (sample_var * bitrate_estimate_ +
-                       pred_bitrate_estimate_var * bitrate_sample) /
-                      (sample_var + pred_bitrate_estimate_var);
-  bitrate_estimate_var_ = sample_var * pred_bitrate_estimate_var /
-                          (sample_var + pred_bitrate_estimate_var);
-}
-
-float DelayBasedBwe::BitrateEstimator::UpdateWindow(int64_t now_ms,
-                                                    int bytes,
-                                                    int rate_window_ms) {
-  // Reset if time moves backwards.
-  if (now_ms < prev_time_ms_) {
-    prev_time_ms_ = -1;
-    sum_ = 0;
-    current_win_ms_ = 0;
-  }
-  if (prev_time_ms_ >= 0) {
-    current_win_ms_ += now_ms - prev_time_ms_;
-    // Reset if nothing has been received for more than a full window.
-    if (now_ms - prev_time_ms_ > rate_window_ms) {
-      sum_ = 0;
-      current_win_ms_ %= rate_window_ms;
-    }
-  }
-  prev_time_ms_ = now_ms;
-  float bitrate_sample = -1.0f;
-  if (current_win_ms_ >= rate_window_ms) {
-    bitrate_sample = 8.0f * sum_ / static_cast<float>(rate_window_ms);
-    current_win_ms_ -= rate_window_ms;
-    sum_ = 0;
-  }
-  sum_ += bytes;
-  return bitrate_sample;
-}
-
-rtc::Optional<uint32_t> DelayBasedBwe::BitrateEstimator::bitrate_bps() const {
-  if (bitrate_estimate_ < 0.f)
-    return rtc::Optional<uint32_t>();
-  return rtc::Optional<uint32_t>(bitrate_estimate_ * 1000);
-}
-
-DelayBasedBwe::DelayBasedBwe(RtcEventLog* event_log, const Clock* clock)
+DelayBasedBwe::DelayBasedBwe(
+    RtcEventLog* event_log,
+    IncomingBitrateEstimator* const receiver_incoming_bitrate,
+    const Clock* clock)
     : event_log_(event_log),
       clock_(clock),
       inter_arrival_(),
       trendline_estimator_(),
       detector_(),
-      receiver_incoming_bitrate_(),
+      receiver_incoming_bitrate_(receiver_incoming_bitrate),
       last_seen_packet_ms_(-1),
       uma_recorded_(false),
       probe_bitrate_estimator_(event_log),
@@ -244,8 +173,8 @@ void DelayBasedBwe::IncomingPacketFeedback(
     const PacketFeedback& packet_feedback) {
   int64_t now_ms = clock_->TimeInMilliseconds();
 
-  receiver_incoming_bitrate_.Update(packet_feedback.arrival_time_ms,
-                                    packet_feedback.payload_size);
+  receiver_incoming_bitrate_->Update(packet_feedback.arrival_time_ms,
+                                     packet_feedback.payload_size);
   Result result;
   // Reset if the stream has timed out.
   if (last_seen_packet_ms_ == -1 ||
@@ -294,7 +223,7 @@ DelayBasedBwe::Result DelayBasedBwe::MaybeUpdateEstimate(bool overusing) {
   int64_t now_ms = clock_->TimeInMilliseconds();
 
   rtc::Optional<uint32_t> acked_bitrate_bps =
-      receiver_incoming_bitrate_.bitrate_bps();
+      receiver_incoming_bitrate_->bitrate_bps();
   rtc::Optional<int> probe_bitrate_bps =
       probe_bitrate_estimator_.FetchAndResetLastEstimatedBitrateBps();
   // Currently overusing the bandwidth.