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/*
* 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 "modules/congestion_controller/bitrate_estimator.h"
#include <cmath>
#include "modules/remote_bitrate_estimator/test/bwe_test_logging.h"
#include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
namespace webrtc {
namespace {
constexpr int kInitialRateWindowMs = 500;
constexpr int kRateWindowMs = 150;
} // namespace
BitrateEstimator::BitrateEstimator()
: sum_(0),
current_win_ms_(0),
prev_time_ms_(-1),
bitrate_estimate_(-1.0f),
bitrate_estimate_var_(50.0f) {}
BitrateEstimator::~BitrateEstimator() = default;
void 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);
BWE_TEST_LOGGING_PLOT(1, "acknowledged_bitrate", now_ms,
bitrate_estimate_ * 1000);
}
float 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> BitrateEstimator::bitrate_bps() const {
if (bitrate_estimate_ < 0.f)
return rtc::nullopt;
return bitrate_estimate_ * 1000;
}
void BitrateEstimator::ExpectFastRateChange() {
// By setting the bitrate-estimate variance to a higher value we allow the
// bitrate to change fast for the next few samples.
bitrate_estimate_var_ += 200;
}
} // namespace webrtc