Source code
Revision control
Copy as Markdown
Other Tools
/*
* Copyright (c) 2018 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 "modules/video_coding/codecs/vp9/svc_config.h"
#include <algorithm>
#include <cmath>
#include <memory>
#include <vector>
#include "media/base/video_common.h"
#include "modules/video_coding/codecs/vp9/include/vp9_globals.h"
#include "modules/video_coding/svc/create_scalability_structure.h"
#include "modules/video_coding/svc/scalability_mode_util.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
namespace webrtc {
namespace {
const size_t kMinVp9SvcBitrateKbps = 30;
const size_t kMaxNumLayersForScreenSharing = 3;
const float kMaxScreenSharingLayerFramerateFps[] = {5.0, 10.0, 30.0};
const size_t kMinScreenSharingLayerBitrateKbps[] = {30, 200, 500};
const size_t kTargetScreenSharingLayerBitrateKbps[] = {150, 350, 950};
const size_t kMaxScreenSharingLayerBitrateKbps[] = {250, 500, 950};
// Gets limited number of layers for given resolution.
size_t GetLimitedNumSpatialLayers(size_t width, size_t height) {
const bool is_landscape = width >= height;
const size_t min_width = is_landscape ? kMinVp9SpatialLayerLongSideLength
: kMinVp9SpatialLayerShortSideLength;
const size_t min_height = is_landscape ? kMinVp9SpatialLayerShortSideLength
: kMinVp9SpatialLayerLongSideLength;
const size_t num_layers_fit_horz = static_cast<size_t>(
std::floor(1 + std::max(0.0f, std::log2(1.0f * width / min_width))));
const size_t num_layers_fit_vert = static_cast<size_t>(
std::floor(1 + std::max(0.0f, std::log2(1.0f * height / min_height))));
return std::min(num_layers_fit_horz, num_layers_fit_vert);
}
} // namespace
std::vector<SpatialLayer> ConfigureSvcScreenSharing(size_t input_width,
size_t input_height,
float max_framerate_fps,
size_t num_spatial_layers) {
num_spatial_layers =
std::min(num_spatial_layers, kMaxNumLayersForScreenSharing);
std::vector<SpatialLayer> spatial_layers;
for (size_t sl_idx = 0; sl_idx < num_spatial_layers; ++sl_idx) {
SpatialLayer spatial_layer = {0};
spatial_layer.width = input_width;
spatial_layer.height = input_height;
spatial_layer.maxFramerate =
std::min(kMaxScreenSharingLayerFramerateFps[sl_idx], max_framerate_fps);
spatial_layer.numberOfTemporalLayers = 1;
spatial_layer.minBitrate =
static_cast<int>(kMinScreenSharingLayerBitrateKbps[sl_idx]);
spatial_layer.maxBitrate =
static_cast<int>(kMaxScreenSharingLayerBitrateKbps[sl_idx]);
spatial_layer.targetBitrate =
static_cast<int>(kTargetScreenSharingLayerBitrateKbps[sl_idx]);
spatial_layer.active = true;
spatial_layers.push_back(spatial_layer);
}
return spatial_layers;
}
std::vector<SpatialLayer> ConfigureSvcNormalVideo(
size_t input_width,
size_t input_height,
float max_framerate_fps,
size_t first_active_layer,
size_t num_spatial_layers,
size_t num_temporal_layers,
absl::optional<ScalableVideoController::StreamLayersConfig> config) {
RTC_DCHECK_LT(first_active_layer, num_spatial_layers);
// Limit number of layers for given resolution.
size_t limited_num_spatial_layers =
GetLimitedNumSpatialLayers(input_width, input_height);
if (limited_num_spatial_layers < num_spatial_layers) {
RTC_LOG(LS_WARNING) << "Reducing number of spatial layers from "
<< num_spatial_layers << " to "
<< limited_num_spatial_layers
<< " due to low input resolution.";
num_spatial_layers = limited_num_spatial_layers;
}
// First active layer must be configured.
num_spatial_layers = std::max(num_spatial_layers, first_active_layer + 1);
// Ensure top layer is even enough.
int required_divisiblity = 1 << (num_spatial_layers - first_active_layer - 1);
if (config) {
required_divisiblity = 1;
for (size_t sl_idx = 0; sl_idx < num_spatial_layers; ++sl_idx) {
required_divisiblity = cricket::LeastCommonMultiple(
required_divisiblity, config->scaling_factor_den[sl_idx]);
}
}
input_width = input_width - input_width % required_divisiblity;
input_height = input_height - input_height % required_divisiblity;
std::vector<SpatialLayer> spatial_layers;
for (size_t sl_idx = first_active_layer; sl_idx < num_spatial_layers;
++sl_idx) {
SpatialLayer spatial_layer = {0};
spatial_layer.width = input_width >> (num_spatial_layers - sl_idx - 1);
spatial_layer.height = input_height >> (num_spatial_layers - sl_idx - 1);
spatial_layer.maxFramerate = max_framerate_fps;
spatial_layer.numberOfTemporalLayers = num_temporal_layers;
spatial_layer.active = true;
if (config) {
spatial_layer.width = input_width * config->scaling_factor_num[sl_idx] /
config->scaling_factor_den[sl_idx];
spatial_layer.height = input_height * config->scaling_factor_num[sl_idx] /
config->scaling_factor_den[sl_idx];
}
// minBitrate and maxBitrate formulas were derived from
// subjective-quality data to determing bit rates below which video
// quality is unacceptable and above which additional bits do not provide
// benefit. The formulas express rate in units of kbps.
// TODO(ssilkin): Add to the comment PSNR/SSIM we get at encoding certain
// video to min/max bitrate specified by those formulas.
const size_t num_pixels = spatial_layer.width * spatial_layer.height;
int min_bitrate =
static_cast<int>((600. * std::sqrt(num_pixels) - 95000.) / 1000.);
min_bitrate = std::max(min_bitrate, 0);
spatial_layer.minBitrate =
std::max(static_cast<size_t>(min_bitrate), kMinVp9SvcBitrateKbps);
spatial_layer.maxBitrate =
static_cast<int>((1.6 * num_pixels + 50 * 1000) / 1000);
spatial_layer.targetBitrate =
(spatial_layer.minBitrate + spatial_layer.maxBitrate) / 2;
spatial_layers.push_back(spatial_layer);
}
// A workaround for situation when single HD layer is left with minBitrate
// about 500kbps. This would mean that there will always be at least 500kbps
// allocated to video regardless of how low is the actual BWE.
// Also, boost maxBitrate for the first layer to account for lost ability to
// predict from previous layers.
if (first_active_layer > 0) {
spatial_layers[0].minBitrate = kMinVp9SvcBitrateKbps;
// TODO(ilnik): tune this value or come up with a different formula to
// ensure that all singlecast configurations look good and not too much
// bitrate is added.
spatial_layers[0].maxBitrate *= 1.1;
}
return spatial_layers;
}
// Uses scalability mode to configure spatial layers.
std::vector<SpatialLayer> GetVp9SvcConfig(VideoCodec& codec) {
RTC_DCHECK_EQ(codec.codecType, kVideoCodecVP9);
absl::optional<ScalabilityMode> scalability_mode = codec.GetScalabilityMode();
RTC_DCHECK(scalability_mode.has_value());
bool requested_single_spatial_layer =
ScalabilityModeToNumSpatialLayers(*scalability_mode) == 1;
// Limit number of spatial layers for given resolution.
int limited_num_spatial_layers =
GetLimitedNumSpatialLayers(codec.width, codec.height);
if (limited_num_spatial_layers <
ScalabilityModeToNumSpatialLayers(*scalability_mode)) {
ScalabilityMode limited_scalability_mode =
LimitNumSpatialLayers(*scalability_mode, limited_num_spatial_layers);
RTC_LOG(LS_WARNING)
<< "Reducing number of spatial layers due to low input resolution: "
<< ScalabilityModeToString(*scalability_mode) << " to "
<< ScalabilityModeToString(limited_scalability_mode);
scalability_mode = limited_scalability_mode;
codec.SetScalabilityMode(limited_scalability_mode);
}
codec.VP9()->interLayerPred =
ScalabilityModeToInterLayerPredMode(*scalability_mode);
absl::optional<ScalableVideoController::StreamLayersConfig> info =
ScalabilityStructureConfig(*scalability_mode);
if (!info.has_value()) {
RTC_LOG(LS_WARNING) << "Failed to create structure "
<< ScalabilityModeToString(*scalability_mode);
return {};
}
// TODO(bugs.webrtc.org/11607): Add support for screensharing.
std::vector<SpatialLayer> spatial_layers =
GetSvcConfig(codec.width, codec.height, codec.maxFramerate,
/*first_active_layer=*/0, info->num_spatial_layers,
info->num_temporal_layers, /*is_screen_sharing=*/false,
codec.GetScalabilityMode() ? info : absl::nullopt);
RTC_DCHECK(!spatial_layers.empty());
spatial_layers[0].minBitrate = kMinVp9SvcBitrateKbps;
// Use codec bitrate limits if spatial layering is not requested.
if (requested_single_spatial_layer) {
SpatialLayer& spatial_layer = spatial_layers[0];
spatial_layer.minBitrate = codec.minBitrate;
spatial_layer.maxBitrate = codec.maxBitrate;
spatial_layer.targetBitrate = codec.maxBitrate;
}
return spatial_layers;
}
std::vector<SpatialLayer> GetSvcConfig(
size_t input_width,
size_t input_height,
float max_framerate_fps,
size_t first_active_layer,
size_t num_spatial_layers,
size_t num_temporal_layers,
bool is_screen_sharing,
absl::optional<ScalableVideoController::StreamLayersConfig> config) {
RTC_DCHECK_GT(input_width, 0);
RTC_DCHECK_GT(input_height, 0);
RTC_DCHECK_GT(num_spatial_layers, 0);
RTC_DCHECK_GT(num_temporal_layers, 0);
if (is_screen_sharing) {
return ConfigureSvcScreenSharing(input_width, input_height,
max_framerate_fps, num_spatial_layers);
} else {
return ConfigureSvcNormalVideo(input_width, input_height, max_framerate_fps,
first_active_layer, num_spatial_layers,
num_temporal_layers, config);
}
}
} // namespace webrtc