Refactored incoming bitrate estimator.

webrtc/modules/congestion_controller/acknowledge_bitrate_estimator.cc

+/*
+ *  Copyright (c) 2017 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/acknowledge_bitrate_estimator.h"
+
+#include <cmath>
+
+#include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
+
+namespace webrtc {
+
+namespace {
+constexpr int kInitialRateWindowMs = 500;
+constexpr int kRateWindowMs = 150;
+}  // namespace
+
+AcknowledgedBitrateEstimator::AcknowledgedBitrateEstimator()
+    : sum_(0),
+      current_win_ms_(0),
+      prev_time_ms_(-1),
+      bitrate_estimate_(-1.0f),
+      bitrate_estimate_var_(50.0f) {}
+
+void AcknowledgedBitrateEstimator::IncomingPacketFeedbackVector(
+    const std::vector<PacketFeedback>& packet_feedback_vector) {
+  RTC_DCHECK(std::is_sorted(packet_feedback_vector.begin(),
+                            packet_feedback_vector.end(),
+                            PacketFeedbackComparator()));
+  for (const auto& packet : packet_feedback_vector)
+    Update(packet.arrival_time_ms, packet.payload_size);
+}
+
+void AcknowledgedBitrateEstimator::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 AcknowledgedBitrateEstimator::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> AcknowledgedBitrateEstimator::bitrate_bps() const {
+  if (bitrate_estimate_ < 0.f)
+    return rtc::Optional<uint32_t>();
+  return rtc::Optional<uint32_t>(bitrate_estimate_ * 1000);
+}
+
+}  // namespace webrtc