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/*
* Copyright (c) 2014 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 <stdint.h>
#include <stdio.h>
#include <algorithm>
#include <string>
#include "absl/types/optional.h"
#include "api/video/video_codec_constants.h"
#include "media/base/media_constants.h"
#include "media/engine/constants.h"
#include "media/engine/simulcast.h"
#include "modules/video_coding/utility/simulcast_rate_allocator.h"
#include "rtc_base/arraysize.h"
#include "rtc_base/checks.h"
#include "rtc_base/experiments/normalize_simulcast_size_experiment.h"
#include "rtc_base/logging.h"
#include "system_wrappers/include/field_trial.h"
namespace cricket {
namespace {
constexpr char kUseBaseHeavyVP8TL3RateAllocationFieldTrial[] =
"WebRTC-UseBaseHeavyVP8TL3RateAllocation";
// Limits for legacy conference screensharing mode. Currently used for the
// lower of the two simulcast streams.
constexpr int kScreenshareDefaultTl0BitrateKbps = 200;
constexpr int kScreenshareDefaultTl1BitrateKbps = 1000;
// Min/max bitrate for the higher one of the two simulcast stream used for
// screen content.
constexpr int kScreenshareHighStreamMinBitrateBps = 600000;
constexpr int kScreenshareHighStreamMaxBitrateBps = 1250000;
static const char* kSimulcastScreenshareFieldTrialName =
"WebRTC-SimulcastScreenshare";
} // namespace
struct SimulcastFormat {
int width;
int height;
// The maximum bitrate for encoding stream at |widthxheight|, when we are
// not sending the next higher spatial stream.
int max_bitrate_kbps;
// The target bitrate for encoding stream at |widthxheight|, when this layer
// is not the highest layer (i.e., when we are sending another higher spatial
// stream).
int target_bitrate_kbps;
// The minimum bitrate needed for encoding stream at |widthxheight|.
int min_bitrate_kbps;
};
// These tables describe from which resolution we can use how many
// simulcast layers at what bitrates (maximum, target, and minimum).
// Important!! Keep this table from high resolution to low resolution.
// clang-format off
const SimulcastFormat kSimulcastFormats[] = {
{1920, 1080, 5000, 4000, 800},
{1280, 720, 2500, 2500, 600},
{960, 540, 900, 900, 450},
{640, 360, 700, 500, 150},
{480, 270, 450, 350, 150},
{320, 180, 200, 150, 30},
{0, 0, 200, 150, 30}
};
// clang-format on
const int kMaxScreenshareSimulcastLayers = 2;
// Multiway: Number of temporal layers for each simulcast stream.
int DefaultNumberOfTemporalLayers(int simulcast_id, bool screenshare) {
RTC_CHECK_GE(simulcast_id, 0);
RTC_CHECK_LT(simulcast_id, webrtc::kMaxSimulcastStreams);
const int kDefaultNumTemporalLayers = 3;
const int kDefaultNumScreenshareTemporalLayers = 2;
int default_num_temporal_layers = screenshare
? kDefaultNumScreenshareTemporalLayers
: kDefaultNumTemporalLayers;
const std::string group_name =
screenshare ? webrtc::field_trial::FindFullName(
"WebRTC-VP8ScreenshareTemporalLayers")
: webrtc::field_trial::FindFullName(
"WebRTC-VP8ConferenceTemporalLayers");
if (group_name.empty())
return default_num_temporal_layers;
int num_temporal_layers = default_num_temporal_layers;
if (sscanf(group_name.c_str(), "%d", &num_temporal_layers) == 1 &&
num_temporal_layers > 0 &&
num_temporal_layers <= webrtc::kMaxTemporalStreams) {
return num_temporal_layers;
}
RTC_LOG(LS_WARNING) << "Attempt to set number of temporal layers to "
"incorrect value: "
<< group_name;
return default_num_temporal_layers;
}
int FindSimulcastFormatIndex(int width, int height) {
RTC_DCHECK_GE(width, 0);
RTC_DCHECK_GE(height, 0);
for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
if (width * height >=
kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
return i;
}
}
RTC_NOTREACHED();
return -1;
}
// Simulcast stream width and height must both be dividable by
// |2 ^ (simulcast_layers - 1)|.
int NormalizeSimulcastSize(int size, size_t simulcast_layers) {
int base2_exponent = static_cast<int>(simulcast_layers) - 1;
const absl::optional<int> experimental_base2_exponent =
webrtc::NormalizeSimulcastSizeExperiment::GetBase2Exponent();
if (experimental_base2_exponent &&
(size > (1 << *experimental_base2_exponent))) {
base2_exponent = *experimental_base2_exponent;
}
return ((size >> base2_exponent) << base2_exponent);
}
int FindSimulcastMaxBitrateBps(int width, int height) {
const int format_index = FindSimulcastFormatIndex(width, height);
return kSimulcastFormats[format_index].max_bitrate_kbps * 1000;
}
int FindSimulcastTargetBitrateBps(int width, int height) {
const int format_index = FindSimulcastFormatIndex(width, height);
return kSimulcastFormats[format_index].target_bitrate_kbps * 1000;
}
int FindSimulcastMinBitrateBps(int width, int height) {
const int format_index = FindSimulcastFormatIndex(width, height);
return kSimulcastFormats[format_index].min_bitrate_kbps * 1000;
}
void BoostMaxSimulcastLayer(int max_bitrate_bps,
std::vector<webrtc::VideoStream>* layers) {
if (layers->empty())
return;
// Spend additional bits to boost the max layer.
int bitrate_left_bps = max_bitrate_bps - GetTotalMaxBitrateBps(*layers);
if (bitrate_left_bps > 0) {
layers->back().max_bitrate_bps += bitrate_left_bps;
}
}
int GetTotalMaxBitrateBps(const std::vector<webrtc::VideoStream>& layers) {
if (layers.empty())
return 0;
int total_max_bitrate_bps = 0;
for (size_t s = 0; s < layers.size() - 1; ++s) {
total_max_bitrate_bps += layers[s].target_bitrate_bps;
}
total_max_bitrate_bps += layers.back().max_bitrate_bps;
return total_max_bitrate_bps;
}
std::vector<webrtc::VideoStream> GetSimulcastConfig(
size_t max_layers,
int width,
int height,
double bitrate_priority,
int max_qp,
bool is_screenshare,
bool temporal_layers_supported) {
if (is_screenshare) {
return GetScreenshareLayers(max_layers, width, height, bitrate_priority,
max_qp, ScreenshareSimulcastFieldTrialEnabled(),
temporal_layers_supported);
} else {
return GetNormalSimulcastLayers(max_layers, width, height, bitrate_priority,
max_qp, temporal_layers_supported);
}
}
std::vector<webrtc::VideoStream> GetNormalSimulcastLayers(
size_t layer_count,
int width,
int height,
double bitrate_priority,
int max_qp,
bool temporal_layers_supported) {
std::vector<webrtc::VideoStream> layers(layer_count);
// Format width and height has to be divisible by |2 ^ num_simulcast_layers -
// 1|.
width = NormalizeSimulcastSize(width, layer_count);
height = NormalizeSimulcastSize(height, layer_count);
// Add simulcast streams, from highest resolution (|s| = num_simulcast_layers
// -1) to lowest resolution at |s| = 0.
for (size_t s = layer_count - 1;; --s) {
layers[s].width = width;
layers[s].height = height;
// TODO(pbos): Fill actual temporal-layer bitrate thresholds.
layers[s].max_qp = max_qp;
layers[s].num_temporal_layers =
temporal_layers_supported ? DefaultNumberOfTemporalLayers(s, false) : 0;
layers[s].max_bitrate_bps = FindSimulcastMaxBitrateBps(width, height);
layers[s].target_bitrate_bps = FindSimulcastTargetBitrateBps(width, height);
int num_temporal_layers = DefaultNumberOfTemporalLayers(s, false);
if (s == 0) {
// If alternative temporal rate allocation is selected, adjust the
// bitrate of the lowest simulcast stream so that absolute bitrate for
// the base temporal layer matches the bitrate for the base temporal
// layer with the default 3 simulcast streams. Otherwise we risk a
// higher threshold for receiving a feed at all.
float rate_factor = 1.0;
if (num_temporal_layers == 3) {
if (webrtc::field_trial::IsEnabled(
kUseBaseHeavyVP8TL3RateAllocationFieldTrial)) {
// Base heavy allocation increases TL0 bitrate from 40% to 60%.
rate_factor = 0.4 / 0.6;
}
} else {
rate_factor =
webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(3, 0) /
webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(
num_temporal_layers, 0);
}
layers[s].max_bitrate_bps =
static_cast<int>(layers[s].max_bitrate_bps * rate_factor);
layers[s].target_bitrate_bps =
static_cast<int>(layers[s].target_bitrate_bps * rate_factor);
}
layers[s].min_bitrate_bps = FindSimulcastMinBitrateBps(width, height);
layers[s].max_framerate = kDefaultVideoMaxFramerate;
width /= 2;
height /= 2;
if (s == 0) {
break;
}
}
// Currently the relative bitrate priority of the sender is controlled by
// the value of the lowest VideoStream.
// TODO(bugs.webrtc.org/8630): The web specification describes being able to
// control relative bitrate for each individual simulcast layer, but this
// is currently just implemented per rtp sender.
layers[0].bitrate_priority = bitrate_priority;
return layers;
}
std::vector<webrtc::VideoStream> GetScreenshareLayers(
size_t max_layers,
int width,
int height,
double bitrate_priority,
int max_qp,
bool screenshare_simulcast_enabled,
bool temporal_layers_supported) {
auto max_screenshare_layers =
screenshare_simulcast_enabled ? kMaxScreenshareSimulcastLayers : 1;
size_t num_simulcast_layers =
std::min<int>(max_layers, max_screenshare_layers);
std::vector<webrtc::VideoStream> layers(num_simulcast_layers);
// For legacy screenshare in conference mode, tl0 and tl1 bitrates are
// piggybacked on the VideoCodec struct as target and max bitrates,
// respectively. See eg. webrtc::LibvpxVp8Encoder::SetRates().
layers[0].width = width;
layers[0].height = height;
layers[0].max_qp = max_qp;
layers[0].max_framerate = 5;
layers[0].min_bitrate_bps = kMinVideoBitrateBps;
layers[0].target_bitrate_bps = kScreenshareDefaultTl0BitrateKbps * 1000;
layers[0].max_bitrate_bps = kScreenshareDefaultTl1BitrateKbps * 1000;
layers[0].num_temporal_layers = temporal_layers_supported ? 2 : 0;
// With simulcast enabled, add another spatial layer. This one will have a
// more normal layout, with the regular 3 temporal layer pattern and no fps
// restrictions. The base simulcast layer will still use legacy setup.
if (num_simulcast_layers == kMaxScreenshareSimulcastLayers) {
// Add optional upper simulcast layer.
const int num_temporal_layers = DefaultNumberOfTemporalLayers(1, true);
int max_bitrate_bps;
bool using_boosted_bitrate = false;
if (!temporal_layers_supported) {
// Set the max bitrate to where the base layer would have been if temporal
// layers were enabled.
max_bitrate_bps = static_cast<int>(
kScreenshareHighStreamMaxBitrateBps *
webrtc::SimulcastRateAllocator::GetTemporalRateAllocation(
num_temporal_layers, 0));
} else if (DefaultNumberOfTemporalLayers(1, true) != 3 ||
webrtc::field_trial::IsEnabled(
kUseBaseHeavyVP8TL3RateAllocationFieldTrial)) {
// Experimental temporal layer mode used, use increased max bitrate.
max_bitrate_bps = kScreenshareHighStreamMaxBitrateBps;
using_boosted_bitrate = true;
} else {
// Keep current bitrates with default 3tl/8 frame settings.
// Lowest temporal layers of a 3 layer setup will have 40% of the total
// bitrate allocation for that simulcast layer. Make sure the gap between
// the target of the lower simulcast layer and first temporal layer of the
// higher one is at most 2x the bitrate, so that upswitching is not
// hampered by stalled bitrate estimates.
max_bitrate_bps = 2 * ((layers[0].target_bitrate_bps * 10) / 4);
}
layers[1].width = width;
layers[1].height = height;
layers[1].max_qp = max_qp;
layers[1].max_framerate = kDefaultVideoMaxFramerate;
layers[1].num_temporal_layers =
temporal_layers_supported ? DefaultNumberOfTemporalLayers(1, true) : 0;
layers[1].min_bitrate_bps = using_boosted_bitrate
? kScreenshareHighStreamMinBitrateBps
: layers[0].target_bitrate_bps * 2;
// Cap max bitrate so it isn't overly high for the given resolution.
int resolution_limited_bitrate = std::max(
FindSimulcastMaxBitrateBps(width, height), layers[1].min_bitrate_bps);
max_bitrate_bps =
std::min<int>(max_bitrate_bps, resolution_limited_bitrate);
layers[1].target_bitrate_bps = max_bitrate_bps;
layers[1].max_bitrate_bps = max_bitrate_bps;
}
// The bitrate priority currently implemented on a per-sender level, so we
// just set it for the first simulcast layer.
layers[0].bitrate_priority = bitrate_priority;
return layers;
}
bool ScreenshareSimulcastFieldTrialEnabled() {
return !webrtc::field_trial::IsDisabled(kSimulcastScreenshareFieldTrialName);
}
} // namespace cricket