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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