chromium/third_party/webrtc/video/alignment_adjuster.cc

/*
 *  Copyright (c) 2020 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 "video/alignment_adjuster.h"

#include <algorithm>
#include <limits>

#include "absl/algorithm/container.h"
#include "rtc_base/logging.h"

namespace webrtc {
namespace {
// Round each scale factor to the closest rational in form alignment/i where i
// is a multiple of `requested_alignment`. Each resolution divisible by
// `alignment` will be divisible by `requested_alignment` after the scale factor
// is applied.
double RoundToMultiple(int alignment,
                       int requested_alignment,
                       VideoEncoderConfig* config,
                       bool update_config) { … }
}  // namespace

// Input: encoder_info.requested_resolution_alignment (K)
// Input: encoder_info.apply_alignment_to_all_simulcast_layers (B)
// Input: vector config->simulcast_layers.scale_resolution_down_by (S[i])
// Output:
// If B is false, returns K and does not adjust scaling factors.
// Otherwise, returns adjusted alignment (A), adjusted scaling factors (S'[i])
// are written in `config` such that:
//
// A / S'[i] are integers divisible by K
// sum abs(S'[i] - S[i]) -> min
// A integer <= 16
//
// Solution chooses closest S'[i] in a form A / j where j is a multiple of K.

int AlignmentAdjuster::GetAlignmentAndMaybeAdjustScaleFactors(
    const VideoEncoder::EncoderInfo& encoder_info,
    VideoEncoderConfig* config,
    absl::optional<size_t> max_layers) { … }
}  // namespace webrtc