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Åsa Perssonc5a74ff2020-09-20 15:50:001/*
2 * Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11#include "video/alignment_adjuster.h"
12
13#include <algorithm>
14#include <limits>
15
16#include "absl/algorithm/container.h"
17#include "rtc_base/logging.h"
18
19namespace webrtc {
20namespace {
21// Round each scale factor to the closest rational in form alignment/i where i
Artem Titovab30d722021-07-27 14:22:1122// is a multiple of `requested_alignment`. Each resolution divisible by
23// `alignment` will be divisible by `requested_alignment` after the scale factor
Åsa Perssonc5a74ff2020-09-20 15:50:0024// is applied.
25double RoundToMultiple(int alignment,
26 int requested_alignment,
27 VideoEncoderConfig* config,
28 bool update_config) {
29 double diff = 0.0;
30 for (auto& layer : config->simulcast_layers) {
31 double min_dist = std::numeric_limits<double>::max();
32 double new_scale = 1.0;
33 for (int i = requested_alignment; i <= alignment;
34 i += requested_alignment) {
35 double dist = std::abs(layer.scale_resolution_down_by -
36 alignment / static_cast<double>(i));
37 if (dist <= min_dist) {
38 min_dist = dist;
39 new_scale = alignment / static_cast<double>(i);
40 }
41 }
42 diff += std::abs(layer.scale_resolution_down_by - new_scale);
43 if (update_config) {
44 RTC_LOG(LS_INFO) << "scale_resolution_down_by "
45 << layer.scale_resolution_down_by << " -> " << new_scale;
46 layer.scale_resolution_down_by = new_scale;
47 }
48 }
49 return diff;
50}
51} // namespace
52
53// Input: encoder_info.requested_resolution_alignment (K)
54// Input: encoder_info.apply_alignment_to_all_simulcast_layers (B)
55// Input: vector config->simulcast_layers.scale_resolution_down_by (S[i])
56// Output:
57// If B is false, returns K and does not adjust scaling factors.
58// Otherwise, returns adjusted alignment (A), adjusted scaling factors (S'[i])
Artem Titovab30d722021-07-27 14:22:1159// are written in `config` such that:
Åsa Perssonc5a74ff2020-09-20 15:50:0060//
61// A / S'[i] are integers divisible by K
62// sum abs(S'[i] - S[i]) -> min
63// A integer <= 16
64//
65// Solution chooses closest S'[i] in a form A / j where j is a multiple of K.
66
67int AlignmentAdjuster::GetAlignmentAndMaybeAdjustScaleFactors(
68 const VideoEncoder::EncoderInfo& encoder_info,
Åsa Perssona24d35e2021-01-19 09:25:1069 VideoEncoderConfig* config,
70 absl::optional<size_t> max_layers) {
Åsa Perssonc5a74ff2020-09-20 15:50:0071 const int requested_alignment = encoder_info.requested_resolution_alignment;
72 if (!encoder_info.apply_alignment_to_all_simulcast_layers) {
73 return requested_alignment;
74 }
75
76 if (requested_alignment < 1 || config->number_of_streams <= 1 ||
77 config->simulcast_layers.size() <= 1) {
78 return requested_alignment;
79 }
80
81 // Update alignment to also apply to simulcast layers.
82 const bool has_scale_resolution_down_by = absl::c_any_of(
83 config->simulcast_layers, [](const webrtc::VideoStream& layer) {
84 return layer.scale_resolution_down_by >= 1.0;
85 });
86
87 if (!has_scale_resolution_down_by) {
88 // Default resolution downscaling used (scale factors: 1, 2, 4, ...).
Åsa Perssona24d35e2021-01-19 09:25:1089 size_t size = config->simulcast_layers.size();
90 if (max_layers && *max_layers > 0 && *max_layers < size) {
91 size = *max_layers;
92 }
93 return requested_alignment * (1 << (size - 1));
Åsa Perssonc5a74ff2020-09-20 15:50:0094 }
95
96 // Get alignment for downscaled layers.
Artem Titovab30d722021-07-27 14:22:1197 // Adjust `scale_resolution_down_by` to a common multiple to limit the
Åsa Perssonc5a74ff2020-09-20 15:50:0098 // alignment value (to avoid largely cropped frames and possibly with an
99 // aspect ratio far from the original).
100 const int kMaxAlignment = 16;
101
102 for (auto& layer : config->simulcast_layers) {
103 layer.scale_resolution_down_by =
104 std::max(layer.scale_resolution_down_by, 1.0);
105 layer.scale_resolution_down_by =
106 std::min(layer.scale_resolution_down_by, 10000.0);
107 }
108
109 // Decide on common multiple to use.
110 double min_diff = std::numeric_limits<double>::max();
111 int best_alignment = 1;
112 for (int alignment = requested_alignment; alignment <= kMaxAlignment;
113 ++alignment) {
114 double diff = RoundToMultiple(alignment, requested_alignment, config,
115 /*update_config=*/false);
116 if (diff < min_diff) {
117 min_diff = diff;
118 best_alignment = alignment;
119 }
120 }
121 RoundToMultiple(best_alignment, requested_alignment, config,
122 /*update_config=*/true);
123
124 return std::max(best_alignment, requested_alignment);
125}
126} // namespace webrtc