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/*
* 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) {
double diff = 0.0;
for (auto& layer : config->simulcast_layers) {
double min_dist = std::numeric_limits<double>::max();
double new_scale = 1.0;
for (int i = requested_alignment; i <= alignment;
i += requested_alignment) {
double dist = std::abs(layer.scale_resolution_down_by -
alignment / static_cast<double>(i));
if (dist <= min_dist) {
min_dist = dist;
new_scale = alignment / static_cast<double>(i);
}
}
diff += std::abs(layer.scale_resolution_down_by - new_scale);
if (update_config) {
RTC_LOG(LS_INFO) << "scale_resolution_down_by "
<< layer.scale_resolution_down_by << " -> " << new_scale;
layer.scale_resolution_down_by = new_scale;
}
}
return diff;
}
} // 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) {
const int requested_alignment = encoder_info.requested_resolution_alignment;
if (!encoder_info.apply_alignment_to_all_simulcast_layers) {
return requested_alignment;
}
if (requested_alignment < 1 || config->number_of_streams <= 1 ||
config->simulcast_layers.size() <= 1) {
return requested_alignment;
}
// Update alignment to also apply to simulcast layers.
const bool has_scale_resolution_down_by = absl::c_any_of(
config->simulcast_layers, [](const webrtc::VideoStream& layer) {
return layer.scale_resolution_down_by >= 1.0;
});
if (!has_scale_resolution_down_by) {
// Default resolution downscaling used (scale factors: 1, 2, 4, ...).
size_t size = config->simulcast_layers.size();
if (max_layers && *max_layers > 0 && *max_layers < size) {
size = *max_layers;
}
return requested_alignment * (1 << (size - 1));
}
// Get alignment for downscaled layers.
// Adjust `scale_resolution_down_by` to a common multiple to limit the
// alignment value (to avoid largely cropped frames and possibly with an
// aspect ratio far from the original).
const int kMaxAlignment = 16;
for (auto& layer : config->simulcast_layers) {
layer.scale_resolution_down_by =
std::max(layer.scale_resolution_down_by, 1.0);
layer.scale_resolution_down_by =
std::min(layer.scale_resolution_down_by, 10000.0);
}
// Decide on common multiple to use.
double min_diff = std::numeric_limits<double>::max();
int best_alignment = 1;
for (int alignment = requested_alignment; alignment <= kMaxAlignment;
++alignment) {
double diff = RoundToMultiple(alignment, requested_alignment, config,
/*update_config=*/false);
if (diff < min_diff) {
min_diff = diff;
best_alignment = alignment;
}
}
RoundToMultiple(best_alignment, requested_alignment, config,
/*update_config=*/true);
return std::max(best_alignment, requested_alignment);
}
} // namespace webrtc
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