2250b05778
Two new classes are added to WebRTC from Chrome: ChannelMixer and ChannelMixingMatrix but they are not yet utilized in the audio path for WebRTC. The idea is to utilize these new classes when adding support for multi- channel encoding/decoding in WebRTC/Chrome. Adds support for a new enumerator call webrtc::ChannelLayout and some helper methods which maps between channel layout and number of channels. These parts are also copied from Chrome. Minor (cosmetic) changes are also done on the AudioFrame to prepare for upcoming work. Bug: webrtc:10783 Change-Id: I6cd7a13a3bc1c8bbfa19bc974c7a011d22d19197 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/141674 Commit-Queue: Henrik Andreassson <henrika@webrtc.org> Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#28482}
86 lines
2.9 KiB
C++
86 lines
2.9 KiB
C++
/*
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* Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef AUDIO_UTILITY_CHANNEL_MIXER_H_
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#define AUDIO_UTILITY_CHANNEL_MIXER_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <memory>
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#include <vector>
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#include "api/audio/audio_frame.h"
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#include "api/audio/channel_layout.h"
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namespace webrtc {
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// ChannelMixer is for converting audio between channel layouts. The conversion
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// matrix is built upon construction and used during each Transform() call. The
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// algorithm works by generating a conversion matrix mapping each output channel
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// to list of input channels. The transform renders all of the output channels,
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// with each output channel rendered according to a weighted sum of the relevant
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// input channels as defined in the matrix.
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// This file is derived from Chromium's media/base/channel_mixer.h.
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class ChannelMixer {
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public:
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// To mix two channels into one and preserve loudness, we must apply
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// (1 / sqrt(2)) gain to each.
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static constexpr float kHalfPower = 0.707106781186547524401f;
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ChannelMixer(ChannelLayout input_layout, ChannelLayout output_layout);
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~ChannelMixer();
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// Transforms all input channels corresponding to the selected |input_layout|
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// to the number of channels in the selected |output_layout|.
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// Example usage (downmix from stereo to mono):
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//
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// ChannelMixer mixer(CHANNEL_LAYOUT_STEREO, CHANNEL_LAYOUT_MONO);
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// AudioFrame frame;
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// frame.samples_per_channel_ = 160;
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// frame.num_channels_ = 2;
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// EXPECT_EQ(2u, frame.channels());
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// mixer.Transform(&frame);
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// EXPECT_EQ(1u, frame.channels());
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//
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void Transform(AudioFrame* frame);
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private:
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bool IsUpMixing() const { return output_channels_ > input_channels_; }
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// Selected channel layouts.
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const ChannelLayout input_layout_;
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const ChannelLayout output_layout_;
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// Channel counts for input and output.
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const size_t input_channels_;
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const size_t output_channels_;
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// 2D matrix of output channels to input channels.
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std::vector<std::vector<float> > matrix_;
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// 1D array used as temporary storage during the transformation.
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std::unique_ptr<int16_t[]> audio_vector_;
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// Number of elements allocated for |audio_vector_|.
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size_t audio_vector_size_ = 0;
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// Optimization case for when we can simply remap the input channels to output
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// channels, i.e., when all scaling factors in |matrix_| equals 1.0.
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bool remapping_;
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// Delete the copy constructor and assignment operator.
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ChannelMixer(const ChannelMixer& other) = delete;
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ChannelMixer& operator=(const ChannelMixer& other) = delete;
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};
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} // namespace webrtc
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#endif // AUDIO_UTILITY_CHANNEL_MIXER_H_
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