435 lines
17 KiB
C++
435 lines
17 KiB
C++
/*
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* Copyright (c) 2014 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 "media/engine/simulcast.h"
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#include <stdint.h>
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#include <stdio.h>
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#include <algorithm>
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#include <string>
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#include "absl/types/optional.h"
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#include "api/video/video_codec_constants.h"
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#include "media/base/media_constants.h"
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#include "modules/video_coding/utility/simulcast_rate_allocator.h"
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#include "rtc_base/arraysize.h"
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#include "rtc_base/checks.h"
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#include "rtc_base/experiments/min_video_bitrate_experiment.h"
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#include "rtc_base/experiments/normalize_simulcast_size_experiment.h"
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#include "rtc_base/experiments/rate_control_settings.h"
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#include "rtc_base/logging.h"
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#include "system_wrappers/include/field_trial.h"
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namespace cricket {
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namespace {
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constexpr webrtc::DataRate Interpolate(const webrtc::DataRate& a,
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const webrtc::DataRate& b,
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float rate) {
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return a * (1.0 - rate) + b * rate;
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}
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constexpr char kUseLegacySimulcastLayerLimitFieldTrial[] =
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"WebRTC-LegacySimulcastLayerLimit";
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// Limits for legacy conference screensharing mode. Currently used for the
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// lower of the two simulcast streams.
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constexpr webrtc::DataRate kScreenshareDefaultTl0Bitrate =
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webrtc::DataRate::KilobitsPerSec(200);
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constexpr webrtc::DataRate kScreenshareDefaultTl1Bitrate =
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webrtc::DataRate::KilobitsPerSec(1000);
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// Min/max bitrate for the higher one of the two simulcast stream used for
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// screen content.
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constexpr webrtc::DataRate kScreenshareHighStreamMinBitrate =
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webrtc::DataRate::KilobitsPerSec(600);
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constexpr webrtc::DataRate kScreenshareHighStreamMaxBitrate =
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webrtc::DataRate::KilobitsPerSec(1250);
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} // namespace
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struct SimulcastFormat {
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int width;
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int height;
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// The maximum number of simulcast layers can be used for
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// resolutions at |widthxheigh| for legacy applications.
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size_t max_layers;
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// The maximum bitrate for encoding stream at |widthxheight|, when we are
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// not sending the next higher spatial stream.
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webrtc::DataRate max_bitrate;
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// The target bitrate for encoding stream at |widthxheight|, when this layer
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// is not the highest layer (i.e., when we are sending another higher spatial
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// stream).
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webrtc::DataRate target_bitrate;
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// The minimum bitrate needed for encoding stream at |widthxheight|.
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webrtc::DataRate min_bitrate;
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};
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// These tables describe from which resolution we can use how many
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// simulcast layers at what bitrates (maximum, target, and minimum).
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// Important!! Keep this table from high resolution to low resolution.
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constexpr const SimulcastFormat kSimulcastFormats[] = {
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{1920, 1080, 3, webrtc::DataRate::KilobitsPerSec(5000),
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webrtc::DataRate::KilobitsPerSec(4000),
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webrtc::DataRate::KilobitsPerSec(800)},
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{1280, 720, 3, webrtc::DataRate::KilobitsPerSec(2500),
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webrtc::DataRate::KilobitsPerSec(2500),
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webrtc::DataRate::KilobitsPerSec(600)},
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{960, 540, 3, webrtc::DataRate::KilobitsPerSec(1200),
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webrtc::DataRate::KilobitsPerSec(1200),
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webrtc::DataRate::KilobitsPerSec(350)},
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{640, 360, 2, webrtc::DataRate::KilobitsPerSec(700),
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webrtc::DataRate::KilobitsPerSec(500),
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webrtc::DataRate::KilobitsPerSec(150)},
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{480, 270, 2, webrtc::DataRate::KilobitsPerSec(450),
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webrtc::DataRate::KilobitsPerSec(350),
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webrtc::DataRate::KilobitsPerSec(150)},
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{320, 180, 1, webrtc::DataRate::KilobitsPerSec(200),
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webrtc::DataRate::KilobitsPerSec(150),
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webrtc::DataRate::KilobitsPerSec(30)},
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{0, 0, 1, webrtc::DataRate::KilobitsPerSec(200),
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webrtc::DataRate::KilobitsPerSec(150),
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webrtc::DataRate::KilobitsPerSec(30)}};
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const int kMaxScreenshareSimulcastLayers = 2;
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// Multiway: Number of temporal layers for each simulcast stream.
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int DefaultNumberOfTemporalLayers(int simulcast_id, bool screenshare) {
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RTC_CHECK_GE(simulcast_id, 0);
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RTC_CHECK_LT(simulcast_id, webrtc::kMaxSimulcastStreams);
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const int kDefaultNumTemporalLayers = 3;
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const int kDefaultNumScreenshareTemporalLayers = 2;
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int default_num_temporal_layers = screenshare
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? kDefaultNumScreenshareTemporalLayers
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: kDefaultNumTemporalLayers;
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const std::string group_name =
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screenshare ? webrtc::field_trial::FindFullName(
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"WebRTC-VP8ScreenshareTemporalLayers")
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: webrtc::field_trial::FindFullName(
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"WebRTC-VP8ConferenceTemporalLayers");
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if (group_name.empty())
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return default_num_temporal_layers;
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int num_temporal_layers = default_num_temporal_layers;
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if (sscanf(group_name.c_str(), "%d", &num_temporal_layers) == 1 &&
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num_temporal_layers > 0 &&
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num_temporal_layers <= webrtc::kMaxTemporalStreams) {
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return num_temporal_layers;
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}
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RTC_LOG(LS_WARNING) << "Attempt to set number of temporal layers to "
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"incorrect value: "
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<< group_name;
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return default_num_temporal_layers;
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}
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int FindSimulcastFormatIndex(int width, int height) {
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RTC_DCHECK_GE(width, 0);
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RTC_DCHECK_GE(height, 0);
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for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
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if (width * height >=
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kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
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return i;
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}
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}
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RTC_NOTREACHED();
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return -1;
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}
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// Round size to nearest simulcast-friendly size.
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// Simulcast stream width and height must both be dividable by
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// |2 ^ (simulcast_layers - 1)|.
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int NormalizeSimulcastSize(int size, size_t simulcast_layers) {
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int base2_exponent = static_cast<int>(simulcast_layers) - 1;
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const absl::optional<int> experimental_base2_exponent =
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webrtc::NormalizeSimulcastSizeExperiment::GetBase2Exponent();
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if (experimental_base2_exponent &&
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(size > (1 << *experimental_base2_exponent))) {
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base2_exponent = *experimental_base2_exponent;
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}
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return ((size >> base2_exponent) << base2_exponent);
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}
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SimulcastFormat InterpolateSimulcastFormat(int width, int height) {
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const int index = FindSimulcastFormatIndex(width, height);
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if (index == 0)
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return kSimulcastFormats[index];
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const int total_pixels_up =
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kSimulcastFormats[index - 1].width * kSimulcastFormats[index - 1].height;
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const int total_pixels_down =
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kSimulcastFormats[index].width * kSimulcastFormats[index].height;
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const int total_pixels = width * height;
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const float rate = (total_pixels_up - total_pixels) /
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static_cast<float>(total_pixels_up - total_pixels_down);
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size_t max_layers = kSimulcastFormats[index].max_layers;
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webrtc::DataRate max_bitrate =
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Interpolate(kSimulcastFormats[index - 1].max_bitrate,
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kSimulcastFormats[index].max_bitrate, rate);
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webrtc::DataRate target_bitrate =
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Interpolate(kSimulcastFormats[index - 1].target_bitrate,
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kSimulcastFormats[index].target_bitrate, rate);
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webrtc::DataRate min_bitrate =
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Interpolate(kSimulcastFormats[index - 1].min_bitrate,
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kSimulcastFormats[index].min_bitrate, rate);
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return {width, height, max_layers, max_bitrate, target_bitrate, min_bitrate};
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}
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webrtc::DataRate FindSimulcastMaxBitrate(int width, int height) {
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return InterpolateSimulcastFormat(width, height).max_bitrate;
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}
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webrtc::DataRate FindSimulcastTargetBitrate(int width, int height) {
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return InterpolateSimulcastFormat(width, height).target_bitrate;
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}
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webrtc::DataRate FindSimulcastMinBitrate(int width, int height) {
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return InterpolateSimulcastFormat(width, height).min_bitrate;
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}
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void BoostMaxSimulcastLayer(webrtc::DataRate max_bitrate,
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std::vector<webrtc::VideoStream>* layers) {
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if (layers->empty())
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return;
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const webrtc::DataRate total_bitrate = GetTotalMaxBitrate(*layers);
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// We're still not using all available bits.
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if (total_bitrate < max_bitrate) {
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// Spend additional bits to boost the max layer.
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const webrtc::DataRate bitrate_left = max_bitrate - total_bitrate;
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layers->back().max_bitrate_bps += bitrate_left.bps();
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}
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}
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webrtc::DataRate GetTotalMaxBitrate(
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const std::vector<webrtc::VideoStream>& layers) {
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if (layers.empty())
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return webrtc::DataRate::Zero();
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int total_max_bitrate_bps = 0;
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for (size_t s = 0; s < layers.size() - 1; ++s) {
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total_max_bitrate_bps += layers[s].target_bitrate_bps;
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}
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total_max_bitrate_bps += layers.back().max_bitrate_bps;
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return webrtc::DataRate::BitsPerSec(total_max_bitrate_bps);
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}
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size_t LimitSimulcastLayerCount(int width,
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int height,
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size_t need_layers,
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size_t layer_count) {
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if (!webrtc::field_trial::IsDisabled(
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kUseLegacySimulcastLayerLimitFieldTrial)) {
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size_t adaptive_layer_count = std::max(
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need_layers,
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kSimulcastFormats[FindSimulcastFormatIndex(width, height)].max_layers);
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if (layer_count > adaptive_layer_count) {
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RTC_LOG(LS_WARNING) << "Reducing simulcast layer count from "
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<< layer_count << " to " << adaptive_layer_count;
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layer_count = adaptive_layer_count;
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}
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}
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return layer_count;
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}
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std::vector<webrtc::VideoStream> GetSimulcastConfig(
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size_t min_layers,
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size_t max_layers,
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int width,
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int height,
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double bitrate_priority,
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int max_qp,
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bool is_screenshare_with_conference_mode,
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bool temporal_layers_supported) {
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RTC_DCHECK_LE(min_layers, max_layers);
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RTC_DCHECK(max_layers > 1 || is_screenshare_with_conference_mode);
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const bool base_heavy_tl3_rate_alloc =
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webrtc::RateControlSettings::ParseFromFieldTrials()
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.Vp8BaseHeavyTl3RateAllocation();
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if (is_screenshare_with_conference_mode) {
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return GetScreenshareLayers(max_layers, width, height, bitrate_priority,
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max_qp, temporal_layers_supported,
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base_heavy_tl3_rate_alloc);
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} else {
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// Some applications rely on the old behavior limiting the simulcast layer
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// count based on the resolution automatically, which they can get through
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// the WebRTC-LegacySimulcastLayerLimit field trial until they update.
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max_layers =
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LimitSimulcastLayerCount(width, height, min_layers, max_layers);
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return GetNormalSimulcastLayers(max_layers, width, height, bitrate_priority,
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max_qp, temporal_layers_supported,
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base_heavy_tl3_rate_alloc);
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}
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}
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std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
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size_t layer_count,
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int width,
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int height,
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double bitrate_priority,
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int max_qp,
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bool temporal_layers_supported,
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bool base_heavy_tl3_rate_alloc) {
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std::vector<webrtc::VideoStream> layers(layer_count);
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// Format width and height has to be divisible by |2 ^ num_simulcast_layers -
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// 1|.
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width = NormalizeSimulcastSize(width, layer_count);
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height = NormalizeSimulcastSize(height, layer_count);
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// Add simulcast streams, from highest resolution (|s| = num_simulcast_layers
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// -1) to lowest resolution at |s| = 0.
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for (size_t s = layer_count - 1;; --s) {
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layers[s].width = width;
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layers[s].height = height;
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// TODO(pbos): Fill actual temporal-layer bitrate thresholds.
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layers[s].max_qp = max_qp;
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layers[s].num_temporal_layers =
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temporal_layers_supported ? DefaultNumberOfTemporalLayers(s, false) : 1;
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layers[s].max_bitrate_bps = FindSimulcastMaxBitrate(width, height).bps();
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layers[s].target_bitrate_bps =
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FindSimulcastTargetBitrate(width, height).bps();
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int num_temporal_layers = DefaultNumberOfTemporalLayers(s, false);
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if (s == 0) {
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// If alternative temporal rate allocation is selected, adjust the
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// bitrate of the lowest simulcast stream so that absolute bitrate for
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// the base temporal layer matches the bitrate for the base temporal
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// layer with the default 3 simulcast streams. Otherwise we risk a
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// higher threshold for receiving a feed at all.
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float rate_factor = 1.0;
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if (num_temporal_layers == 3) {
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if (base_heavy_tl3_rate_alloc) {
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// Base heavy allocation increases TL0 bitrate from 40% to 60%.
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rate_factor = 0.4 / 0.6;
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}
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} else {
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rate_factor =
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webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(
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3, 0, /*base_heavy_tl3_rate_alloc=*/false) /
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webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(
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num_temporal_layers, 0, /*base_heavy_tl3_rate_alloc=*/false);
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}
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layers[s].max_bitrate_bps =
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static_cast<int>(layers[s].max_bitrate_bps * rate_factor);
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layers[s].target_bitrate_bps =
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static_cast<int>(layers[s].target_bitrate_bps * rate_factor);
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}
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layers[s].min_bitrate_bps = FindSimulcastMinBitrate(width, height).bps();
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layers[s].max_framerate = kDefaultVideoMaxFramerate;
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width /= 2;
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height /= 2;
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if (s == 0) {
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break;
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}
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}
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// Currently the relative bitrate priority of the sender is controlled by
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// the value of the lowest VideoStream.
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// TODO(bugs.webrtc.org/8630): The web specification describes being able to
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// control relative bitrate for each individual simulcast layer, but this
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// is currently just implemented per rtp sender.
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layers[0].bitrate_priority = bitrate_priority;
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return layers;
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}
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std::vector<webrtc::VideoStream> GetScreenshareLayers(
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size_t max_layers,
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int width,
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int height,
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double bitrate_priority,
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int max_qp,
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bool temporal_layers_supported,
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bool base_heavy_tl3_rate_alloc) {
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auto max_screenshare_layers = kMaxScreenshareSimulcastLayers;
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size_t num_simulcast_layers =
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std::min<int>(max_layers, max_screenshare_layers);
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std::vector<webrtc::VideoStream> layers(num_simulcast_layers);
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// For legacy screenshare in conference mode, tl0 and tl1 bitrates are
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// piggybacked on the VideoCodec struct as target and max bitrates,
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// respectively. See eg. webrtc::LibvpxVp8Encoder::SetRates().
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layers[0].width = width;
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layers[0].height = height;
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layers[0].max_qp = max_qp;
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layers[0].max_framerate = 5;
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layers[0].min_bitrate_bps = webrtc::kDefaultMinVideoBitrateBps;
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layers[0].target_bitrate_bps = kScreenshareDefaultTl0Bitrate.bps();
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layers[0].max_bitrate_bps = kScreenshareDefaultTl1Bitrate.bps();
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layers[0].num_temporal_layers = temporal_layers_supported ? 2 : 1;
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// With simulcast enabled, add another spatial layer. This one will have a
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// more normal layout, with the regular 3 temporal layer pattern and no fps
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// restrictions. The base simulcast layer will still use legacy setup.
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if (num_simulcast_layers == kMaxScreenshareSimulcastLayers) {
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// Add optional upper simulcast layer.
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const int num_temporal_layers = DefaultNumberOfTemporalLayers(1, true);
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int max_bitrate_bps;
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bool using_boosted_bitrate = false;
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if (!temporal_layers_supported) {
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// Set the max bitrate to where the base layer would have been if temporal
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// layers were enabled.
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max_bitrate_bps = static_cast<int>(
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kScreenshareHighStreamMaxBitrate.bps() *
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webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(
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num_temporal_layers, 0, base_heavy_tl3_rate_alloc));
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} else if (DefaultNumberOfTemporalLayers(1, true) != 3 ||
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base_heavy_tl3_rate_alloc) {
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// Experimental temporal layer mode used, use increased max bitrate.
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max_bitrate_bps = kScreenshareHighStreamMaxBitrate.bps();
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using_boosted_bitrate = true;
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} else {
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// Keep current bitrates with default 3tl/8 frame settings.
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// Lowest temporal layers of a 3 layer setup will have 40% of the total
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// bitrate allocation for that simulcast layer. Make sure the gap between
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// the target of the lower simulcast layer and first temporal layer of the
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// higher one is at most 2x the bitrate, so that upswitching is not
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// hampered by stalled bitrate estimates.
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max_bitrate_bps = 2 * ((layers[0].target_bitrate_bps * 10) / 4);
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}
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layers[1].width = width;
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layers[1].height = height;
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layers[1].max_qp = max_qp;
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layers[1].max_framerate = kDefaultVideoMaxFramerate;
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layers[1].num_temporal_layers =
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temporal_layers_supported ? DefaultNumberOfTemporalLayers(1, true) : 1;
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layers[1].min_bitrate_bps = using_boosted_bitrate
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? kScreenshareHighStreamMinBitrate.bps()
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: layers[0].target_bitrate_bps * 2;
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// Cap max bitrate so it isn't overly high for the given resolution.
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int resolution_limited_bitrate =
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std::max<int>(FindSimulcastMaxBitrate(width, height).bps(),
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layers[1].min_bitrate_bps);
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max_bitrate_bps =
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std::min<int>(max_bitrate_bps, resolution_limited_bitrate);
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layers[1].target_bitrate_bps = max_bitrate_bps;
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layers[1].max_bitrate_bps = max_bitrate_bps;
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}
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// The bitrate priority currently implemented on a per-sender level, so we
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// just set it for the first simulcast layer.
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layers[0].bitrate_priority = bitrate_priority;
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return layers;
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}
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} // namespace cricket
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