127 lines
4.5 KiB
C++
127 lines
4.5 KiB
C++
/*
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* Copyright (c) 2020 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 "video/alignment_adjuster.h"
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#include <algorithm>
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#include <limits>
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#include "absl/algorithm/container.h"
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#include "rtc_base/logging.h"
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namespace webrtc {
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namespace {
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// Round each scale factor to the closest rational in form alignment/i where i
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// is a multiple of `requested_alignment`. Each resolution divisible by
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// `alignment` will be divisible by `requested_alignment` after the scale factor
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// is applied.
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double RoundToMultiple(int alignment,
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int requested_alignment,
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VideoEncoderConfig* config,
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bool update_config) {
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double diff = 0.0;
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for (auto& layer : config->simulcast_layers) {
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double min_dist = std::numeric_limits<double>::max();
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double new_scale = 1.0;
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for (int i = requested_alignment; i <= alignment;
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i += requested_alignment) {
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double dist = std::abs(layer.scale_resolution_down_by -
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alignment / static_cast<double>(i));
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if (dist <= min_dist) {
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min_dist = dist;
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new_scale = alignment / static_cast<double>(i);
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}
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}
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diff += std::abs(layer.scale_resolution_down_by - new_scale);
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if (update_config) {
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RTC_LOG(LS_INFO) << "scale_resolution_down_by "
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<< layer.scale_resolution_down_by << " -> " << new_scale;
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layer.scale_resolution_down_by = new_scale;
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}
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}
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return diff;
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}
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} // namespace
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// Input: encoder_info.requested_resolution_alignment (K)
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// Input: encoder_info.apply_alignment_to_all_simulcast_layers (B)
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// Input: vector config->simulcast_layers.scale_resolution_down_by (S[i])
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// Output:
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// If B is false, returns K and does not adjust scaling factors.
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// Otherwise, returns adjusted alignment (A), adjusted scaling factors (S'[i])
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// are written in `config` such that:
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//
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// A / S'[i] are integers divisible by K
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// sum abs(S'[i] - S[i]) -> min
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// A integer <= 16
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//
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// Solution chooses closest S'[i] in a form A / j where j is a multiple of K.
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int AlignmentAdjuster::GetAlignmentAndMaybeAdjustScaleFactors(
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const VideoEncoder::EncoderInfo& encoder_info,
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VideoEncoderConfig* config,
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absl::optional<size_t> max_layers) {
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const int requested_alignment = encoder_info.requested_resolution_alignment;
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if (!encoder_info.apply_alignment_to_all_simulcast_layers) {
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return requested_alignment;
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}
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if (requested_alignment < 1 || config->number_of_streams <= 1 ||
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config->simulcast_layers.size() <= 1) {
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return requested_alignment;
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}
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// Update alignment to also apply to simulcast layers.
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const bool has_scale_resolution_down_by = absl::c_any_of(
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config->simulcast_layers, [](const webrtc::VideoStream& layer) {
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return layer.scale_resolution_down_by >= 1.0;
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});
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if (!has_scale_resolution_down_by) {
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// Default resolution downscaling used (scale factors: 1, 2, 4, ...).
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size_t size = config->simulcast_layers.size();
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if (max_layers && *max_layers > 0 && *max_layers < size) {
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size = *max_layers;
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}
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return requested_alignment * (1 << (size - 1));
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}
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// Get alignment for downscaled layers.
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// Adjust `scale_resolution_down_by` to a common multiple to limit the
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// alignment value (to avoid largely cropped frames and possibly with an
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// aspect ratio far from the original).
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const int kMaxAlignment = 16;
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for (auto& layer : config->simulcast_layers) {
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layer.scale_resolution_down_by =
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std::max(layer.scale_resolution_down_by, 1.0);
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layer.scale_resolution_down_by =
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std::min(layer.scale_resolution_down_by, 10000.0);
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}
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// Decide on common multiple to use.
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double min_diff = std::numeric_limits<double>::max();
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int best_alignment = 1;
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for (int alignment = requested_alignment; alignment <= kMaxAlignment;
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++alignment) {
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double diff = RoundToMultiple(alignment, requested_alignment, config,
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/*update_config=*/false);
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if (diff < min_diff) {
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min_diff = diff;
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best_alignment = alignment;
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}
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}
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RoundToMultiple(best_alignment, requested_alignment, config,
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/*update_config=*/true);
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return std::max(best_alignment, requested_alignment);
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}
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} // namespace webrtc
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