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henrika2250b052019-07-04 09:27:521/*
2 * Copyright (c) 2019 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#ifndef AUDIO_UTILITY_CHANNEL_MIXER_H_
12#define AUDIO_UTILITY_CHANNEL_MIXER_H_
13
14#include <stddef.h>
15#include <stdint.h>
Jonas Olssona4d87372019-07-05 17:08:3316
henrika2250b052019-07-04 09:27:5217#include <memory>
18#include <vector>
19
20#include "api/audio/audio_frame.h"
21#include "api/audio/channel_layout.h"
22
23namespace webrtc {
24
25// ChannelMixer is for converting audio between channel layouts. The conversion
26// matrix is built upon construction and used during each Transform() call. The
27// algorithm works by generating a conversion matrix mapping each output channel
28// to list of input channels. The transform renders all of the output channels,
29// with each output channel rendered according to a weighted sum of the relevant
30// input channels as defined in the matrix.
31// This file is derived from Chromium's media/base/channel_mixer.h.
32class ChannelMixer {
33 public:
34 // To mix two channels into one and preserve loudness, we must apply
35 // (1 / sqrt(2)) gain to each.
36 static constexpr float kHalfPower = 0.707106781186547524401f;
37
38 ChannelMixer(ChannelLayout input_layout, ChannelLayout output_layout);
39 ~ChannelMixer();
40
Artem Titovb0ea6372021-07-26 09:47:0741 // Transforms all input channels corresponding to the selected `input_layout`
42 // to the number of channels in the selected `output_layout`.
henrika2250b052019-07-04 09:27:5243 // Example usage (downmix from stereo to mono):
44 //
45 // ChannelMixer mixer(CHANNEL_LAYOUT_STEREO, CHANNEL_LAYOUT_MONO);
46 // AudioFrame frame;
47 // frame.samples_per_channel_ = 160;
48 // frame.num_channels_ = 2;
49 // EXPECT_EQ(2u, frame.channels());
50 // mixer.Transform(&frame);
51 // EXPECT_EQ(1u, frame.channels());
52 //
53 void Transform(AudioFrame* frame);
54
55 private:
56 bool IsUpMixing() const { return output_channels_ > input_channels_; }
57
58 // Selected channel layouts.
59 const ChannelLayout input_layout_;
60 const ChannelLayout output_layout_;
61
62 // Channel counts for input and output.
63 const size_t input_channels_;
64 const size_t output_channels_;
65
66 // 2D matrix of output channels to input channels.
67 std::vector<std::vector<float> > matrix_;
68
69 // 1D array used as temporary storage during the transformation.
70 std::unique_ptr<int16_t[]> audio_vector_;
71
Artem Titovb0ea6372021-07-26 09:47:0772 // Number of elements allocated for `audio_vector_`.
henrika2250b052019-07-04 09:27:5273 size_t audio_vector_size_ = 0;
74
75 // Optimization case for when we can simply remap the input channels to output
Artem Titovb0ea6372021-07-26 09:47:0776 // channels, i.e., when all scaling factors in `matrix_` equals 1.0.
henrika2250b052019-07-04 09:27:5277 bool remapping_;
78
79 // Delete the copy constructor and assignment operator.
80 ChannelMixer(const ChannelMixer& other) = delete;
81 ChannelMixer& operator=(const ChannelMixer& other) = delete;
82};
83
84} // namespace webrtc
85
86#endif // AUDIO_UTILITY_CHANNEL_MIXER_H_