205 lines
7.5 KiB
C++
205 lines
7.5 KiB
C++
/*
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* Copyright (c) 2019 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 "video/encoder_overshoot_detector.h"
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#include <algorithm>
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namespace webrtc {
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namespace {
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// The buffer level for media-rate utilization is allowed to go below zero,
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// down to
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// -(|kMaxMediaUnderrunFrames| / |target_framerate_fps_|) * |target_bitrate_|.
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static constexpr double kMaxMediaUnderrunFrames = 5.0;
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} // namespace
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EncoderOvershootDetector::EncoderOvershootDetector(int64_t window_size_ms)
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: window_size_ms_(window_size_ms),
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time_last_update_ms_(-1),
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sum_network_utilization_factors_(0.0),
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sum_media_utilization_factors_(0.0),
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target_bitrate_(DataRate::Zero()),
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target_framerate_fps_(0),
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network_buffer_level_bits_(0),
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media_buffer_level_bits_(0) {}
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EncoderOvershootDetector::~EncoderOvershootDetector() = default;
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void EncoderOvershootDetector::SetTargetRate(DataRate target_bitrate,
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double target_framerate_fps,
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int64_t time_ms) {
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// First leak bits according to the previous target rate.
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if (target_bitrate_ != DataRate::Zero()) {
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LeakBits(time_ms);
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} else if (target_bitrate != DataRate::Zero()) {
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// Stream was just enabled, reset state.
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time_last_update_ms_ = time_ms;
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utilization_factors_.clear();
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sum_network_utilization_factors_ = 0.0;
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sum_media_utilization_factors_ = 0.0;
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network_buffer_level_bits_ = 0;
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media_buffer_level_bits_ = 0;
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}
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target_bitrate_ = target_bitrate;
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target_framerate_fps_ = target_framerate_fps;
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}
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void EncoderOvershootDetector::OnEncodedFrame(size_t bytes, int64_t time_ms) {
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// Leak bits from the virtual pacer buffer, according to the current target
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// bitrate.
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LeakBits(time_ms);
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// Ideal size of a frame given the current rates.
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const int64_t ideal_frame_size_bits = IdealFrameSizeBits();
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if (ideal_frame_size_bits == 0) {
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// Frame without updated bitrate and/or framerate, ignore it.
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return;
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}
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const double network_utilization_factor = HandleEncodedFrame(
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bytes * 8, ideal_frame_size_bits, time_ms, &network_buffer_level_bits_);
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const double media_utilization_factor = HandleEncodedFrame(
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bytes * 8, ideal_frame_size_bits, time_ms, &media_buffer_level_bits_);
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sum_network_utilization_factors_ += network_utilization_factor;
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sum_media_utilization_factors_ += media_utilization_factor;
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utilization_factors_.emplace_back(network_utilization_factor,
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media_utilization_factor, time_ms);
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}
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double EncoderOvershootDetector::HandleEncodedFrame(
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size_t frame_size_bits,
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int64_t ideal_frame_size_bits,
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int64_t time_ms,
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int64_t* buffer_level_bits) const {
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// Add new frame to the buffer level. If doing so exceeds the ideal buffer
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// size, penalize this frame but cap overshoot to current buffer level rather
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// than size of this frame. This is done so that a single large frame is not
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// penalized if the encoder afterwards compensates by dropping frames and/or
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// reducing frame size. If however a large frame is followed by more data,
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// we cannot pace that next frame out within one frame space.
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const int64_t bitsum = frame_size_bits + *buffer_level_bits;
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int64_t overshoot_bits = 0;
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if (bitsum > ideal_frame_size_bits) {
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overshoot_bits =
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std::min(*buffer_level_bits, bitsum - ideal_frame_size_bits);
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}
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// Add entry for the (over) utilization for this frame. Factor is capped
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// at 1.0 so that we don't risk overshooting on sudden changes.
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double utilization_factor;
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if (utilization_factors_.empty()) {
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// First frame, cannot estimate overshoot based on previous one so
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// for this particular frame, just like as size vs optimal size.
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utilization_factor = std::max(
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1.0, static_cast<double>(frame_size_bits) / ideal_frame_size_bits);
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} else {
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utilization_factor =
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1.0 + (static_cast<double>(overshoot_bits) / ideal_frame_size_bits);
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}
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// Remove the overshot bits from the virtual buffer so we don't penalize
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// those bits multiple times.
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*buffer_level_bits -= overshoot_bits;
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*buffer_level_bits += frame_size_bits;
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return utilization_factor;
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}
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absl::optional<double>
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EncoderOvershootDetector::GetNetworkRateUtilizationFactor(int64_t time_ms) {
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CullOldUpdates(time_ms);
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// No data points within window, return.
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if (utilization_factors_.empty()) {
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return absl::nullopt;
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}
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// TODO(sprang): Consider changing from arithmetic mean to some other
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// function such as 90th percentile.
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return sum_network_utilization_factors_ / utilization_factors_.size();
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}
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absl::optional<double> EncoderOvershootDetector::GetMediaRateUtilizationFactor(
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int64_t time_ms) {
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CullOldUpdates(time_ms);
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// No data points within window, return.
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if (utilization_factors_.empty()) {
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return absl::nullopt;
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}
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return sum_media_utilization_factors_ / utilization_factors_.size();
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}
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void EncoderOvershootDetector::Reset() {
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time_last_update_ms_ = -1;
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utilization_factors_.clear();
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target_bitrate_ = DataRate::Zero();
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sum_network_utilization_factors_ = 0.0;
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sum_media_utilization_factors_ = 0.0;
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target_framerate_fps_ = 0.0;
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network_buffer_level_bits_ = 0;
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media_buffer_level_bits_ = 0;
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}
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int64_t EncoderOvershootDetector::IdealFrameSizeBits() const {
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if (target_framerate_fps_ <= 0 || target_bitrate_ == DataRate::Zero()) {
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return 0;
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}
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// Current ideal frame size, based on the current target bitrate.
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return static_cast<int64_t>(
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(target_bitrate_.bps() + target_framerate_fps_ / 2) /
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target_framerate_fps_);
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}
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void EncoderOvershootDetector::LeakBits(int64_t time_ms) {
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if (time_last_update_ms_ != -1 && target_bitrate_ > DataRate::Zero()) {
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int64_t time_delta_ms = time_ms - time_last_update_ms_;
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// Leak bits according to the current target bitrate.
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const int64_t leaked_bits = (target_bitrate_.bps() * time_delta_ms) / 1000;
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// Network buffer may not go below zero.
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network_buffer_level_bits_ =
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std::max<int64_t>(0, network_buffer_level_bits_ - leaked_bits);
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// Media buffer my go down to minus |kMaxMediaUnderrunFrames| frames worth
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// of data.
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const double max_underrun_seconds =
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std::min(kMaxMediaUnderrunFrames, target_framerate_fps_) /
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target_framerate_fps_;
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media_buffer_level_bits_ = std::max<int64_t>(
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-max_underrun_seconds * target_bitrate_.bps<int64_t>(),
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media_buffer_level_bits_ - leaked_bits);
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}
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time_last_update_ms_ = time_ms;
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}
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void EncoderOvershootDetector::CullOldUpdates(int64_t time_ms) {
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// Cull old data points.
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const int64_t cutoff_time_ms = time_ms - window_size_ms_;
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while (!utilization_factors_.empty() &&
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utilization_factors_.front().update_time_ms < cutoff_time_ms) {
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// Make sure sum is never allowed to become negative due rounding errors.
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sum_network_utilization_factors_ = std::max(
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0.0, sum_network_utilization_factors_ -
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utilization_factors_.front().network_utilization_factor);
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sum_media_utilization_factors_ = std::max(
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0.0, sum_media_utilization_factors_ -
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utilization_factors_.front().media_utilization_factor);
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utilization_factors_.pop_front();
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}
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}
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} // namespace webrtc
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