87 lines
2.9 KiB
C
87 lines
2.9 KiB
C
|
/*
|
||
|
|
* Copyright (c) 2019 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.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#ifndef AUDIO_UTILITY_CHANNEL_MIXER_H_
|
||
|
|
#define AUDIO_UTILITY_CHANNEL_MIXER_H_
|
||
|
|
|
||
|
|
#include <stddef.h>
|
||
|
|
#include <stdint.h>
|
||
|
|
|
||
|
|
#include <memory>
|
||
|
|
#include <vector>
|
||
|
|
|
||
|
|
#include "api/audio/audio_frame.h"
|
||
|
|
#include "api/audio/channel_layout.h"
|
||
|
|
|
||
|
|
namespace webrtc {
|
||
|
|
|
||
|
|
// ChannelMixer is for converting audio between channel layouts. The conversion
|
||
|
|
// matrix is built upon construction and used during each Transform() call. The
|
||
|
|
// algorithm works by generating a conversion matrix mapping each output channel
|
||
|
|
// to list of input channels. The transform renders all of the output channels,
|
||
|
|
// with each output channel rendered according to a weighted sum of the relevant
|
||
|
|
// input channels as defined in the matrix.
|
||
|
|
// This file is derived from Chromium's media/base/channel_mixer.h.
|
||
|
|
class ChannelMixer {
|
||
|
|
public:
|
||
|
|
// To mix two channels into one and preserve loudness, we must apply
|
||
|
|
// (1 / sqrt(2)) gain to each.
|
||
|
|
static constexpr float kHalfPower = 0.707106781186547524401f;
|
||
|
|
|
||
|
|
ChannelMixer(ChannelLayout input_layout, ChannelLayout output_layout);
|
||
|
|
~ChannelMixer();
|
||
|
|
|
||
|
|
// Transforms all input channels corresponding to the selected |input_layout|
|
||
|
|
// to the number of channels in the selected |output_layout|.
|
||
|
|
// Example usage (downmix from stereo to mono):
|
||
|
|
//
|
||
|
|
// ChannelMixer mixer(CHANNEL_LAYOUT_STEREO, CHANNEL_LAYOUT_MONO);
|
||
|
|
// AudioFrame frame;
|
||
|
|
// frame.samples_per_channel_ = 160;
|
||
|
|
// frame.num_channels_ = 2;
|
||
|
|
// EXPECT_EQ(2u, frame.channels());
|
||
|
|
// mixer.Transform(&frame);
|
||
|
|
// EXPECT_EQ(1u, frame.channels());
|
||
|
|
//
|
||
|
|
void Transform(AudioFrame* frame);
|
||
|
|
|
||
|
|
private:
|
||
|
|
bool IsUpMixing() const { return output_channels_ > input_channels_; }
|
||
|
|
|
||
|
|
// Selected channel layouts.
|
||
|
|
const ChannelLayout input_layout_;
|
||
|
|
const ChannelLayout output_layout_;
|
||
|
|
|
||
|
|
// Channel counts for input and output.
|
||
|
|
const size_t input_channels_;
|
||
|
|
const size_t output_channels_;
|
||
|
|
|
||
|
|
// 2D matrix of output channels to input channels.
|
||
|
|
std::vector<std::vector<float> > matrix_;
|
||
|
|
|
||
|
|
// 1D array used as temporary storage during the transformation.
|
||
|
|
std::unique_ptr<int16_t[]> audio_vector_;
|
||
|
|
|
||
|
|
// Number of elements allocated for |audio_vector_|.
|
||
|
|
size_t audio_vector_size_ = 0;
|
||
|
|
|
||
|
|
// Optimization case for when we can simply remap the input channels to output
|
||
|
|
// channels, i.e., when all scaling factors in |matrix_| equals 1.0.
|
||
|
|
bool remapping_;
|
||
|
|
|
||
|
|
// Delete the copy constructor and assignment operator.
|
||
|
|
ChannelMixer(const ChannelMixer& other) = delete;
|
||
|
|
ChannelMixer& operator=(const ChannelMixer& other) = delete;
|
||
|
|
};
|
||
|
|
|
||
|
|
} // namespace webrtc
|
||
|
|
|
||
|
|
#endif // AUDIO_UTILITY_CHANNEL_MIXER_H_
|