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/*
* Copyright (c) 2019 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 "video/encoder_bitrate_adjuster.h"
#include <algorithm>
#include <memory>
#include <vector>
#include "rtc_base/experiments/rate_control_settings.h"
#include "rtc_base/logging.h"
#include "rtc_base/time_utils.h"
#include "system_wrappers/include/field_trial.h"
namespace webrtc {
namespace {
// Helper struct with metadata for a single spatial layer.
struct LayerRateInfo {
double link_utilization_factor = 0.0;
double media_utilization_factor = 0.0;
DataRate target_rate = DataRate::Zero();
DataRate WantedOvershoot() const {
// If there is headroom, allow bitrate to go up to media rate limit.
// Still limit media utilization to 1.0, so we don't overshoot over long
// runs even if we have headroom.
const double max_media_utilization =
std::max(1.0, media_utilization_factor);
if (link_utilization_factor > max_media_utilization) {
return (link_utilization_factor - max_media_utilization) * target_rate;
}
return DataRate::Zero();
}
};
} // namespace
constexpr int64_t EncoderBitrateAdjuster::kWindowSizeMs;
constexpr size_t EncoderBitrateAdjuster::kMinFramesSinceLayoutChange;
constexpr double EncoderBitrateAdjuster::kDefaultUtilizationFactor;
EncoderBitrateAdjuster::EncoderBitrateAdjuster(const VideoCodec& codec_settings)
: utilize_bandwidth_headroom_(RateControlSettings::ParseFromFieldTrials()
.BitrateAdjusterCanUseNetworkHeadroom()),
frames_since_layout_change_(0),
min_bitrates_bps_{} {
if (codec_settings.codecType == VideoCodecType::kVideoCodecVP9) {
for (size_t si = 0; si < codec_settings.VP9().numberOfSpatialLayers; ++si) {
if (codec_settings.spatialLayers[si].active) {
min_bitrates_bps_[si] =
std::max(codec_settings.minBitrate * 1000,
codec_settings.spatialLayers[si].minBitrate * 1000);
}
}
} else {
for (size_t si = 0; si < codec_settings.numberOfSimulcastStreams; ++si) {
if (codec_settings.simulcastStream[si].active) {
min_bitrates_bps_[si] =
std::max(codec_settings.minBitrate * 1000,
codec_settings.simulcastStream[si].minBitrate * 1000);
}
}
}
}
EncoderBitrateAdjuster::~EncoderBitrateAdjuster() = default;
VideoBitrateAllocation EncoderBitrateAdjuster::AdjustRateAllocation(
const VideoEncoder::RateControlParameters& rates) {
current_rate_control_parameters_ = rates;
// First check that overshoot detectors exist, and store per spatial layer
// how many active temporal layers we have.
size_t active_tls_[kMaxSpatialLayers] = {};
for (size_t si = 0; si < kMaxSpatialLayers; ++si) {
active_tls_[si] = 0;
for (size_t ti = 0; ti < kMaxTemporalStreams; ++ti) {
// Layer is enabled iff it has both positive bitrate and framerate target.
if (rates.bitrate.GetBitrate(si, ti) > 0 &&
current_fps_allocation_[si].size() > ti &&
current_fps_allocation_[si][ti] > 0) {
++active_tls_[si];
if (!overshoot_detectors_[si][ti]) {
overshoot_detectors_[si][ti] =
std::make_unique<EncoderOvershootDetector>(kWindowSizeMs);
frames_since_layout_change_ = 0;
}
} else if (overshoot_detectors_[si][ti]) {
// Layer removed, destroy overshoot detector.
overshoot_detectors_[si][ti].reset();
frames_since_layout_change_ = 0;
}
}
}
// Next poll the overshoot detectors and populate the adjusted allocation.
const int64_t now_ms = rtc::TimeMillis();
VideoBitrateAllocation adjusted_allocation;
std::vector<LayerRateInfo> layer_infos;
DataRate wanted_overshoot_sum = DataRate::Zero();
for (size_t si = 0; si < kMaxSpatialLayers; ++si) {
layer_infos.emplace_back();
LayerRateInfo& layer_info = layer_infos.back();
layer_info.target_rate =
DataRate::BitsPerSec(rates.bitrate.GetSpatialLayerSum(si));
// Adjustment is done per spatial layer only (not per temporal layer).
if (frames_since_layout_change_ < kMinFramesSinceLayoutChange) {
layer_info.link_utilization_factor = kDefaultUtilizationFactor;
layer_info.media_utilization_factor = kDefaultUtilizationFactor;
} else if (active_tls_[si] == 0 ||
layer_info.target_rate == DataRate::Zero()) {
// No signaled temporal layers, or no bitrate set. Could either be unused
// spatial layer or bitrate dynamic mode; pass bitrate through without any
// change.
layer_info.link_utilization_factor = 1.0;
layer_info.media_utilization_factor = 1.0;
} else if (active_tls_[si] == 1) {
// A single active temporal layer, this might mean single layer or that
// encoder does not support temporal layers. Merge target bitrates for
// this spatial layer.
RTC_DCHECK(overshoot_detectors_[si][0]);
layer_info.link_utilization_factor =
overshoot_detectors_[si][0]
->GetNetworkRateUtilizationFactor(now_ms)
.value_or(kDefaultUtilizationFactor);
layer_info.media_utilization_factor =
overshoot_detectors_[si][0]
->GetMediaRateUtilizationFactor(now_ms)
.value_or(kDefaultUtilizationFactor);
} else if (layer_info.target_rate > DataRate::Zero()) {
// Multiple temporal layers enabled for this spatial layer. Update rate
// for each of them and make a weighted average of utilization factors,
// with bitrate fraction used as weight.
// If any layer is missing a utilization factor, fall back to default.
layer_info.link_utilization_factor = 0.0;
layer_info.media_utilization_factor = 0.0;
for (size_t ti = 0; ti < active_tls_[si]; ++ti) {
RTC_DCHECK(overshoot_detectors_[si][ti]);
const absl::optional<double> ti_link_utilization_factor =
overshoot_detectors_[si][ti]->GetNetworkRateUtilizationFactor(
now_ms);
const absl::optional<double> ti_media_utilization_factor =
overshoot_detectors_[si][ti]->GetMediaRateUtilizationFactor(now_ms);
if (!ti_link_utilization_factor || !ti_media_utilization_factor) {
layer_info.link_utilization_factor = kDefaultUtilizationFactor;
layer_info.media_utilization_factor = kDefaultUtilizationFactor;
break;
}
const double weight =
static_cast<double>(rates.bitrate.GetBitrate(si, ti)) /
layer_info.target_rate.bps();
layer_info.link_utilization_factor +=
weight * ti_link_utilization_factor.value();
layer_info.media_utilization_factor +=
weight * ti_media_utilization_factor.value();
}
} else {
RTC_NOTREACHED();
}
if (layer_info.link_utilization_factor < 1.0) {
// TODO(sprang): Consider checking underuse and allowing it to cancel some
// potential overuse by other streams.
// Don't boost target bitrate if encoder is under-using.
layer_info.link_utilization_factor = 1.0;
} else {
// Don't reduce encoder target below 50%, in which case the frame dropper
// should kick in instead.
layer_info.link_utilization_factor =
std::min(layer_info.link_utilization_factor, 2.0);
// Keep track of sum of desired overshoot bitrate.
wanted_overshoot_sum += layer_info.WantedOvershoot();
}
}
// Available link headroom that can be used to fill wanted overshoot.
DataRate available_headroom = DataRate::Zero();
if (utilize_bandwidth_headroom_) {
available_headroom = rates.bandwidth_allocation -
DataRate::BitsPerSec(rates.bitrate.get_sum_bps());
}
// All wanted overshoots are satisfied in the same proportion based on
// available headroom.
const double granted_overshoot_ratio =
wanted_overshoot_sum == DataRate::Zero()
? 0.0
: std::min(1.0, available_headroom.bps<double>() /
wanted_overshoot_sum.bps());
for (size_t si = 0; si < kMaxSpatialLayers; ++si) {
LayerRateInfo& layer_info = layer_infos[si];
double utilization_factor = layer_info.link_utilization_factor;
DataRate allowed_overshoot =
granted_overshoot_ratio * layer_info.WantedOvershoot();
if (allowed_overshoot > DataRate::Zero()) {
// Pretend the target bitrate is higher by the allowed overshoot.
// Since utilization_factor = actual_bitrate / target_bitrate, it can be
// done by multiplying by old_target_bitrate / new_target_bitrate.
utilization_factor *= layer_info.target_rate.bps<double>() /
(allowed_overshoot.bps<double>() +
layer_info.target_rate.bps<double>());
}
if (min_bitrates_bps_[si] > 0 &&
layer_info.target_rate > DataRate::Zero() &&
DataRate::BitsPerSec(min_bitrates_bps_[si]) < layer_info.target_rate) {
// Make sure rate adjuster doesn't push target bitrate below minimum.
utilization_factor =
std::min(utilization_factor, layer_info.target_rate.bps<double>() /
min_bitrates_bps_[si]);
}
if (layer_info.target_rate > DataRate::Zero()) {
RTC_LOG(LS_VERBOSE) << "Utilization factors for spatial index " << si
<< ": link = " << layer_info.link_utilization_factor
<< ", media = " << layer_info.media_utilization_factor
<< ", wanted overshoot = "
<< layer_info.WantedOvershoot().bps()
<< " bps, available headroom = "
<< available_headroom.bps()
<< " bps, total utilization factor = "
<< utilization_factor;
}
// Populate the adjusted allocation with determined utilization factor.
if (active_tls_[si] == 1 &&
layer_info.target_rate >
DataRate::BitsPerSec(rates.bitrate.GetBitrate(si, 0))) {
// Bitrate allocation indicates temporal layer usage, but encoder
// does not seem to support it. Pipe all bitrate into a single
// overshoot detector.
uint32_t adjusted_layer_bitrate_bps =
std::min(static_cast<uint32_t>(
layer_info.target_rate.bps() / utilization_factor + 0.5),
layer_info.target_rate.bps<uint32_t>());
adjusted_allocation.SetBitrate(si, 0, adjusted_layer_bitrate_bps);
} else {
for (size_t ti = 0; ti < kMaxTemporalStreams; ++ti) {
if (rates.bitrate.HasBitrate(si, ti)) {
uint32_t adjusted_layer_bitrate_bps = std::min(
static_cast<uint32_t>(
rates.bitrate.GetBitrate(si, ti) / utilization_factor + 0.5),
rates.bitrate.GetBitrate(si, ti));
adjusted_allocation.SetBitrate(si, ti, adjusted_layer_bitrate_bps);
}
}
}
// In case of rounding errors, add bitrate to TL0 until min bitrate
// constraint has been met.
const uint32_t adjusted_spatial_layer_sum =
adjusted_allocation.GetSpatialLayerSum(si);
if (layer_info.target_rate > DataRate::Zero() &&
adjusted_spatial_layer_sum < min_bitrates_bps_[si]) {
adjusted_allocation.SetBitrate(si, 0,
adjusted_allocation.GetBitrate(si, 0) +
min_bitrates_bps_[si] -
adjusted_spatial_layer_sum);
}
// Update all detectors with the new adjusted bitrate targets.
for (size_t ti = 0; ti < kMaxTemporalStreams; ++ti) {
const uint32_t layer_bitrate_bps = adjusted_allocation.GetBitrate(si, ti);
// Overshoot detector may not exist, eg for ScreenshareLayers case.
if (layer_bitrate_bps > 0 && overshoot_detectors_[si][ti]) {
// Number of frames in this layer alone is not cumulative, so
// subtract fps from any low temporal layer.
const double fps_fraction =
static_cast<double>(
current_fps_allocation_[si][ti] -
(ti == 0 ? 0 : current_fps_allocation_[si][ti - 1])) /
VideoEncoder::EncoderInfo::kMaxFramerateFraction;
if (fps_fraction <= 0.0) {
RTC_LOG(LS_WARNING)
<< "Encoder config has temporal layer with non-zero bitrate "
"allocation but zero framerate allocation.";
continue;
}
overshoot_detectors_[si][ti]->SetTargetRate(
DataRate::BitsPerSec(layer_bitrate_bps),
fps_fraction * rates.framerate_fps, now_ms);
}
}
}
// Since no spatial layers or streams are toggled by the adjustment
// bw-limited flag stays the same.
adjusted_allocation.set_bw_limited(rates.bitrate.is_bw_limited());
return adjusted_allocation;
}
void EncoderBitrateAdjuster::OnEncoderInfo(
const VideoEncoder::EncoderInfo& encoder_info) {
// Copy allocation into current state and re-allocate.
for (size_t si = 0; si < kMaxSpatialLayers; ++si) {
current_fps_allocation_[si] = encoder_info.fps_allocation[si];
}
// Trigger re-allocation so that overshoot detectors have correct targets.
AdjustRateAllocation(current_rate_control_parameters_);
}
void EncoderBitrateAdjuster::OnEncodedFrame(DataSize size,
int spatial_index,
int temporal_index) {
++frames_since_layout_change_;
// Detectors may not exist, for instance if ScreenshareLayers is used.
auto& detector = overshoot_detectors_[spatial_index][temporal_index];
if (detector) {
detector->OnEncodedFrame(size.bytes(), rtc::TimeMillis());
}
}
void EncoderBitrateAdjuster::Reset() {
for (size_t si = 0; si < kMaxSpatialLayers; ++si) {
for (size_t ti = 0; ti < kMaxTemporalStreams; ++ti) {
overshoot_detectors_[si][ti].reset();
}
}
// Call AdjustRateAllocation() with the last know bitrate allocation, so that
// the appropriate overuse detectors are immediately re-created.
AdjustRateAllocation(current_rate_control_parameters_);
}
} // namespace webrtc