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/*
* 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 <vector>
#include "modules/video_coding/codecs/vp9/svc_rate_allocator.h"
#include "modules/video_coding/include/video_codec_interface.h"
namespace webrtc {
namespace {
const size_t kMinVp9SvcBitrateKbps = 30;
const size_t kMaxNumLayersForScreenSharing = 2;
const float kMaxScreenSharingLayerFramerateFps[] = {5.0, 5.0};
const size_t kMaxScreenSharingLayerBitrateKbps[] = {200, 500};
} // 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>(kMinVp9SvcBitrateKbps);
spatial_layer.maxBitrate =
static_cast<int>(kMaxScreenSharingLayerBitrateKbps[sl_idx]);
spatial_layer.targetBitrate = spatial_layer.maxBitrate;
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 num_spatial_layers,
size_t num_temporal_layers) {
std::vector<SpatialLayer> spatial_layers;
// Limit number of layers for given resolution.
const size_t num_layers_fit_horz = static_cast<size_t>(std::floor(
1 + std::max(0.0f,
std::log2(1.0f * input_width / kMinVp9SpatialLayerWidth))));
const size_t num_layers_fit_vert = static_cast<size_t>(
std::floor(1 + std::max(0.0f, std::log2(1.0f * input_height /
kMinVp9SpatialLayerHeight))));
num_spatial_layers =
std::min({num_spatial_layers, num_layers_fit_horz, num_layers_fit_vert});
float top_fraction = 0.;
for (size_t sl_idx = 0; 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;
// 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);
top_fraction += std::pow(kSpatialLayeringRateScalingFactor, sl_idx);
}
// Compute spatial_layers[num_spatial_layers - 1].targetBitrate, which is
// used to set max_padding_bitrate_. Set max_padding_bitrate_ equal to the
// minimum total bit rate required to support all spatial layers.
spatial_layers[num_spatial_layers - 1].targetBitrate =
static_cast<unsigned int>(
spatial_layers[num_spatial_layers - 1].minBitrate * top_fraction);
return spatial_layers;
}
std::vector<SpatialLayer> GetSvcConfig(size_t input_width,
size_t input_height,
float max_framerate_fps,
size_t num_spatial_layers,
size_t num_temporal_layers,
bool is_screen_sharing) {
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,
num_spatial_layers, num_temporal_layers);
}
}
} // namespace webrtc
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