438 lines
14 KiB
C++
438 lines
14 KiB
C++
/*
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* Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "modules/video_coding/jitter_estimator.h"
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#include <assert.h>
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#include <math.h>
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#include <string.h>
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#include <algorithm>
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#include <cstdint>
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#include "absl/types/optional.h"
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#include "modules/video_coding/internal_defines.h"
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#include "modules/video_coding/rtt_filter.h"
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#include "rtc_base/experiments/jitter_upper_bound_experiment.h"
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#include "rtc_base/numerics/safe_conversions.h"
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#include "system_wrappers/include/clock.h"
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#include "system_wrappers/include/field_trial.h"
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namespace webrtc {
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namespace {
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static constexpr uint32_t kStartupDelaySamples = 30;
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static constexpr int64_t kFsAccuStartupSamples = 5;
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static constexpr double kMaxFramerateEstimate = 200.0;
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static constexpr int64_t kNackCountTimeoutMs = 60000;
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static constexpr double kDefaultMaxTimestampDeviationInSigmas = 3.5;
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} // namespace
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VCMJitterEstimator::VCMJitterEstimator(Clock* clock)
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: _phi(0.97),
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_psi(0.9999),
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_alphaCountMax(400),
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_thetaLow(0.000001),
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_nackLimit(3),
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_numStdDevDelayOutlier(15),
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_numStdDevFrameSizeOutlier(3),
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_noiseStdDevs(2.33), // ~Less than 1% chance
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// (look up in normal distribution table)...
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_noiseStdDevOffset(30.0), // ...of getting 30 ms freezes
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_rttFilter(),
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fps_counter_(30), // TODO(sprang): Use an estimator with limit based on
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// time, rather than number of samples.
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time_deviation_upper_bound_(
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JitterUpperBoundExperiment::GetUpperBoundSigmas().value_or(
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kDefaultMaxTimestampDeviationInSigmas)),
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enable_reduced_delay_(
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!field_trial::IsEnabled("WebRTC-ReducedJitterDelayKillSwitch")),
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clock_(clock) {
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Reset();
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}
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VCMJitterEstimator::~VCMJitterEstimator() {}
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VCMJitterEstimator& VCMJitterEstimator::operator=(
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const VCMJitterEstimator& rhs) {
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if (this != &rhs) {
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memcpy(_thetaCov, rhs._thetaCov, sizeof(_thetaCov));
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memcpy(_Qcov, rhs._Qcov, sizeof(_Qcov));
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_avgFrameSize = rhs._avgFrameSize;
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_varFrameSize = rhs._varFrameSize;
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_maxFrameSize = rhs._maxFrameSize;
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_fsSum = rhs._fsSum;
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_fsCount = rhs._fsCount;
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_lastUpdateT = rhs._lastUpdateT;
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_prevEstimate = rhs._prevEstimate;
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_prevFrameSize = rhs._prevFrameSize;
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_avgNoise = rhs._avgNoise;
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_alphaCount = rhs._alphaCount;
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_filterJitterEstimate = rhs._filterJitterEstimate;
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_startupCount = rhs._startupCount;
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_latestNackTimestamp = rhs._latestNackTimestamp;
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_nackCount = rhs._nackCount;
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_rttFilter = rhs._rttFilter;
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clock_ = rhs.clock_;
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}
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return *this;
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}
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// Resets the JitterEstimate.
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void VCMJitterEstimator::Reset() {
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_theta[0] = 1 / (512e3 / 8);
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_theta[1] = 0;
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_varNoise = 4.0;
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_thetaCov[0][0] = 1e-4;
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_thetaCov[1][1] = 1e2;
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_thetaCov[0][1] = _thetaCov[1][0] = 0;
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_Qcov[0][0] = 2.5e-10;
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_Qcov[1][1] = 1e-10;
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_Qcov[0][1] = _Qcov[1][0] = 0;
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_avgFrameSize = 500;
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_maxFrameSize = 500;
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_varFrameSize = 100;
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_lastUpdateT = -1;
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_prevEstimate = -1.0;
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_prevFrameSize = 0;
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_avgNoise = 0.0;
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_alphaCount = 1;
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_filterJitterEstimate = 0.0;
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_latestNackTimestamp = 0;
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_nackCount = 0;
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_latestNackTimestamp = 0;
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_fsSum = 0;
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_fsCount = 0;
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_startupCount = 0;
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_rttFilter.Reset();
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fps_counter_.Reset();
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}
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// Updates the estimates with the new measurements.
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void VCMJitterEstimator::UpdateEstimate(int64_t frameDelayMS,
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uint32_t frameSizeBytes,
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bool incompleteFrame /* = false */) {
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if (frameSizeBytes == 0) {
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return;
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}
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int deltaFS = frameSizeBytes - _prevFrameSize;
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if (_fsCount < kFsAccuStartupSamples) {
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_fsSum += frameSizeBytes;
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_fsCount++;
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} else if (_fsCount == kFsAccuStartupSamples) {
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// Give the frame size filter.
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_avgFrameSize = static_cast<double>(_fsSum) / static_cast<double>(_fsCount);
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_fsCount++;
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}
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if (!incompleteFrame || frameSizeBytes > _avgFrameSize) {
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double avgFrameSize = _phi * _avgFrameSize + (1 - _phi) * frameSizeBytes;
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if (frameSizeBytes < _avgFrameSize + 2 * sqrt(_varFrameSize)) {
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// Only update the average frame size if this sample wasn't a key frame.
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_avgFrameSize = avgFrameSize;
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}
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// Update the variance anyway since we want to capture cases where we only
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// get key frames.
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_varFrameSize = VCM_MAX(
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_phi * _varFrameSize + (1 - _phi) * (frameSizeBytes - avgFrameSize) *
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(frameSizeBytes - avgFrameSize),
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1.0);
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}
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// Update max frameSize estimate.
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_maxFrameSize =
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VCM_MAX(_psi * _maxFrameSize, static_cast<double>(frameSizeBytes));
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if (_prevFrameSize == 0) {
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_prevFrameSize = frameSizeBytes;
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return;
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}
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_prevFrameSize = frameSizeBytes;
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// Cap frameDelayMS based on the current time deviation noise.
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int64_t max_time_deviation_ms =
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static_cast<int64_t>(time_deviation_upper_bound_ * sqrt(_varNoise) + 0.5);
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frameDelayMS = std::max(std::min(frameDelayMS, max_time_deviation_ms),
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-max_time_deviation_ms);
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// Only update the Kalman filter if the sample is not considered an extreme
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// outlier. Even if it is an extreme outlier from a delay point of view, if
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// the frame size also is large the deviation is probably due to an incorrect
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// line slope.
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double deviation = DeviationFromExpectedDelay(frameDelayMS, deltaFS);
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if (fabs(deviation) < _numStdDevDelayOutlier * sqrt(_varNoise) ||
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frameSizeBytes >
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_avgFrameSize + _numStdDevFrameSizeOutlier * sqrt(_varFrameSize)) {
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// Update the variance of the deviation from the line given by the Kalman
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// filter.
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EstimateRandomJitter(deviation, incompleteFrame);
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// Prevent updating with frames which have been congested by a large frame,
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// and therefore arrives almost at the same time as that frame.
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// This can occur when we receive a large frame (key frame) which has been
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// delayed. The next frame is of normal size (delta frame), and thus deltaFS
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// will be << 0. This removes all frame samples which arrives after a key
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// frame.
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if ((!incompleteFrame || deviation >= 0.0) &&
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static_cast<double>(deltaFS) > -0.25 * _maxFrameSize) {
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// Update the Kalman filter with the new data
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KalmanEstimateChannel(frameDelayMS, deltaFS);
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}
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} else {
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int nStdDev =
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(deviation >= 0) ? _numStdDevDelayOutlier : -_numStdDevDelayOutlier;
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EstimateRandomJitter(nStdDev * sqrt(_varNoise), incompleteFrame);
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}
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// Post process the total estimated jitter
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if (_startupCount >= kStartupDelaySamples) {
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PostProcessEstimate();
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} else {
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_startupCount++;
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}
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}
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// Updates the nack/packet ratio.
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void VCMJitterEstimator::FrameNacked() {
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if (_nackCount < _nackLimit) {
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_nackCount++;
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}
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_latestNackTimestamp = clock_->TimeInMicroseconds();
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}
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// Updates Kalman estimate of the channel.
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// The caller is expected to sanity check the inputs.
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void VCMJitterEstimator::KalmanEstimateChannel(int64_t frameDelayMS,
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int32_t deltaFSBytes) {
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double Mh[2];
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double hMh_sigma;
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double kalmanGain[2];
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double measureRes;
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double t00, t01;
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// Kalman filtering
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// Prediction
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// M = M + Q
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_thetaCov[0][0] += _Qcov[0][0];
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_thetaCov[0][1] += _Qcov[0][1];
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_thetaCov[1][0] += _Qcov[1][0];
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_thetaCov[1][1] += _Qcov[1][1];
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// Kalman gain
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// K = M*h'/(sigma2n + h*M*h') = M*h'/(1 + h*M*h')
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// h = [dFS 1]
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// Mh = M*h'
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// hMh_sigma = h*M*h' + R
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Mh[0] = _thetaCov[0][0] * deltaFSBytes + _thetaCov[0][1];
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Mh[1] = _thetaCov[1][0] * deltaFSBytes + _thetaCov[1][1];
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// sigma weights measurements with a small deltaFS as noisy and
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// measurements with large deltaFS as good
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if (_maxFrameSize < 1.0) {
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return;
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}
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double sigma = (300.0 * exp(-fabs(static_cast<double>(deltaFSBytes)) /
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(1e0 * _maxFrameSize)) +
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1) *
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sqrt(_varNoise);
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if (sigma < 1.0) {
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sigma = 1.0;
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}
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hMh_sigma = deltaFSBytes * Mh[0] + Mh[1] + sigma;
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if ((hMh_sigma < 1e-9 && hMh_sigma >= 0) ||
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(hMh_sigma > -1e-9 && hMh_sigma <= 0)) {
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assert(false);
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return;
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}
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kalmanGain[0] = Mh[0] / hMh_sigma;
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kalmanGain[1] = Mh[1] / hMh_sigma;
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// Correction
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// theta = theta + K*(dT - h*theta)
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measureRes = frameDelayMS - (deltaFSBytes * _theta[0] + _theta[1]);
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_theta[0] += kalmanGain[0] * measureRes;
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_theta[1] += kalmanGain[1] * measureRes;
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if (_theta[0] < _thetaLow) {
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_theta[0] = _thetaLow;
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}
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// M = (I - K*h)*M
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t00 = _thetaCov[0][0];
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t01 = _thetaCov[0][1];
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_thetaCov[0][0] = (1 - kalmanGain[0] * deltaFSBytes) * t00 -
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kalmanGain[0] * _thetaCov[1][0];
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_thetaCov[0][1] = (1 - kalmanGain[0] * deltaFSBytes) * t01 -
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kalmanGain[0] * _thetaCov[1][1];
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_thetaCov[1][0] = _thetaCov[1][0] * (1 - kalmanGain[1]) -
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kalmanGain[1] * deltaFSBytes * t00;
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_thetaCov[1][1] = _thetaCov[1][1] * (1 - kalmanGain[1]) -
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kalmanGain[1] * deltaFSBytes * t01;
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// Covariance matrix, must be positive semi-definite.
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assert(_thetaCov[0][0] + _thetaCov[1][1] >= 0 &&
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_thetaCov[0][0] * _thetaCov[1][1] -
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_thetaCov[0][1] * _thetaCov[1][0] >=
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0 &&
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_thetaCov[0][0] >= 0);
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}
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// Calculate difference in delay between a sample and the expected delay
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// estimated by the Kalman filter
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double VCMJitterEstimator::DeviationFromExpectedDelay(
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int64_t frameDelayMS,
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int32_t deltaFSBytes) const {
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return frameDelayMS - (_theta[0] * deltaFSBytes + _theta[1]);
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}
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// Estimates the random jitter by calculating the variance of the sample
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// distance from the line given by theta.
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void VCMJitterEstimator::EstimateRandomJitter(double d_dT,
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bool incompleteFrame) {
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uint64_t now = clock_->TimeInMicroseconds();
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if (_lastUpdateT != -1) {
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fps_counter_.AddSample(now - _lastUpdateT);
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}
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_lastUpdateT = now;
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if (_alphaCount == 0) {
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assert(false);
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return;
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}
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double alpha =
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static_cast<double>(_alphaCount - 1) / static_cast<double>(_alphaCount);
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_alphaCount++;
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if (_alphaCount > _alphaCountMax)
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_alphaCount = _alphaCountMax;
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// In order to avoid a low frame rate stream to react slower to changes,
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// scale the alpha weight relative a 30 fps stream.
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double fps = GetFrameRate();
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if (fps > 0.0) {
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double rate_scale = 30.0 / fps;
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// At startup, there can be a lot of noise in the fps estimate.
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// Interpolate rate_scale linearly, from 1.0 at sample #1, to 30.0 / fps
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// at sample #kStartupDelaySamples.
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if (_alphaCount < kStartupDelaySamples) {
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rate_scale =
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(_alphaCount * rate_scale + (kStartupDelaySamples - _alphaCount)) /
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kStartupDelaySamples;
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}
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alpha = pow(alpha, rate_scale);
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}
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double avgNoise = alpha * _avgNoise + (1 - alpha) * d_dT;
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double varNoise =
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alpha * _varNoise + (1 - alpha) * (d_dT - _avgNoise) * (d_dT - _avgNoise);
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if (!incompleteFrame || varNoise > _varNoise) {
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_avgNoise = avgNoise;
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_varNoise = varNoise;
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}
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if (_varNoise < 1.0) {
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// The variance should never be zero, since we might get stuck and consider
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// all samples as outliers.
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_varNoise = 1.0;
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}
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}
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double VCMJitterEstimator::NoiseThreshold() const {
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double noiseThreshold = _noiseStdDevs * sqrt(_varNoise) - _noiseStdDevOffset;
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if (noiseThreshold < 1.0) {
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noiseThreshold = 1.0;
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}
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return noiseThreshold;
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}
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// Calculates the current jitter estimate from the filtered estimates.
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double VCMJitterEstimator::CalculateEstimate() {
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double ret = _theta[0] * (_maxFrameSize - _avgFrameSize) + NoiseThreshold();
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// A very low estimate (or negative) is neglected.
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if (ret < 1.0) {
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if (_prevEstimate <= 0.01) {
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ret = 1.0;
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} else {
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ret = _prevEstimate;
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}
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}
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if (ret > 10000.0) { // Sanity
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ret = 10000.0;
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}
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_prevEstimate = ret;
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return ret;
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}
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void VCMJitterEstimator::PostProcessEstimate() {
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_filterJitterEstimate = CalculateEstimate();
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}
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void VCMJitterEstimator::UpdateRtt(int64_t rttMs) {
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_rttFilter.Update(rttMs);
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}
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// Returns the current filtered estimate if available,
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// otherwise tries to calculate an estimate.
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int VCMJitterEstimator::GetJitterEstimate(
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double rttMultiplier,
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absl::optional<double> rttMultAddCapMs) {
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double jitterMS = CalculateEstimate() + OPERATING_SYSTEM_JITTER;
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uint64_t now = clock_->TimeInMicroseconds();
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if (now - _latestNackTimestamp > kNackCountTimeoutMs * 1000)
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_nackCount = 0;
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if (_filterJitterEstimate > jitterMS)
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jitterMS = _filterJitterEstimate;
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if (_nackCount >= _nackLimit) {
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if (rttMultAddCapMs.has_value()) {
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jitterMS +=
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std::min(_rttFilter.RttMs() * rttMultiplier, rttMultAddCapMs.value());
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} else {
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jitterMS += _rttFilter.RttMs() * rttMultiplier;
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}
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}
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if (enable_reduced_delay_) {
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static const double kJitterScaleLowThreshold = 5.0;
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static const double kJitterScaleHighThreshold = 10.0;
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double fps = GetFrameRate();
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// Ignore jitter for very low fps streams.
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if (fps < kJitterScaleLowThreshold) {
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if (fps == 0.0) {
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return rtc::checked_cast<int>(std::max(0.0, jitterMS) + 0.5);
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}
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return 0;
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}
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// Semi-low frame rate; scale by factor linearly interpolated from 0.0 at
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// kJitterScaleLowThreshold to 1.0 at kJitterScaleHighThreshold.
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if (fps < kJitterScaleHighThreshold) {
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jitterMS =
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(1.0 / (kJitterScaleHighThreshold - kJitterScaleLowThreshold)) *
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(fps - kJitterScaleLowThreshold) * jitterMS;
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}
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}
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return rtc::checked_cast<int>(std::max(0.0, jitterMS) + 0.5);
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}
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double VCMJitterEstimator::GetFrameRate() const {
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if (fps_counter_.ComputeMean() <= 0.0)
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return 0;
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double fps = 1000000.0 / fps_counter_.ComputeMean();
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// Sanity check.
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assert(fps >= 0.0);
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if (fps > kMaxFramerateEstimate) {
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fps = kMaxFramerateEstimate;
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}
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return fps;
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}
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} // namespace webrtc
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