channel_mixing_matrix.h

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/*

 *  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_MIXING_MATRIX_H_

#define AUDIO_UTILITY_CHANNEL_MIXING_MATRIX_H_

#include <vector>

#include "api/audio/channel_layout.h"

namespace webrtc {

class ChannelMixingMatrix {

 public:

  ChannelMixingMatrix(ChannelLayout input_layout,

                      int input_channels,

                      ChannelLayout output_layout,

                      int output_channels);

  ~ChannelMixingMatrix();

  // Create the transformation matrix of input channels to output channels.

  // Updates the empty matrix with the transformation, and returns true

  // if the transformation is just a remapping of channels (no mixing).

  // The size of `matrix` is `output_channels` x `input_channels`, i.e., the

  // number of rows equals the number of output channels and the number of

  // columns corresponds to the number of input channels.

  // This file is derived from Chromium's media/base/channel_mixing_matrix.h.

  bool CreateTransformationMatrix(std::vector<std::vector<float>>* matrix);

 private:

  // Result transformation of input channels to output channels

  std::vector<std::vector<float>>* matrix_;

  // Input and output channel layout provided during construction.

  const ChannelLayout input_layout_;

  const int input_channels_;

  const ChannelLayout output_layout_;

  const int output_channels_;

  // Helper variable for tracking which inputs are currently unaccounted,

  // should be empty after construction completes.

  std::vector<Channels> unaccounted_inputs_;

  // Helper methods for managing unaccounted input channels.

  void AccountFor(Channels ch);

  bool IsUnaccounted(Channels ch) const;

  // Helper methods for checking if `ch` exists in either `input_layout_` or

  // `output_layout_` respectively.

  bool HasInputChannel(Channels ch) const;

  bool HasOutputChannel(Channels ch) const;

  // Helper methods for updating `matrix_` with the proper value for

  // mixing `input_ch` into `output_ch`.  MixWithoutAccounting() does not

  // remove the channel from `unaccounted_inputs_`.

  void Mix(Channels input_ch, Channels output_ch, float scale);

  void MixWithoutAccounting(Channels input_ch, Channels output_ch, float scale);

  // Delete the copy constructor and assignment operator.

  ChannelMixingMatrix(const ChannelMixingMatrix& other) = delete;

  ChannelMixingMatrix& operator=(const ChannelMixingMatrix& other) = delete;

};

}  // namespace webrtc

#endif  // AUDIO_UTILITY_CHANNEL_MIXING_MATRIX_H_