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// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef MEDIA_BASE_CHANNEL_MIXER_H_
#define MEDIA_BASE_CHANNEL_MIXER_H_
#include <vector>
#include "base/macros.h"
#include "media/base/channel_layout.h"
#include "media/base/media_export.h"
namespace media {
class AudioBus;
class AudioParameters;
// 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.
class MEDIA_EXPORT 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(const AudioParameters& input, const AudioParameters& output);
~ChannelMixer();
// Transforms all channels from |input| into |output| channels.
void Transform(const AudioBus* input, AudioBus* output);
// Transforms all channels from |input| into |output| channels, for just the
// initial part of the input. Callers can use this to avoid reallocating
// AudioBuses, if the length of the data changes frequently for their use
// case.
void TransformPartial(const AudioBus* input,
int frame_count,
AudioBus* output);
private:
void Initialize(ChannelLayout input_layout, int input_channels,
ChannelLayout output_layout, int output_channels);
// 2D matrix of output channels to input channels.
std::vector< std::vector<float> > matrix_;
// Optimization case for when we can simply remap the input channels to output
// channels and don't need to do a multiply-accumulate loop over |matrix_|.
bool remapping_;
DISALLOW_COPY_AND_ASSIGN(ChannelMixer);
};
} // namespace media
#endif // MEDIA_BASE_CHANNEL_MIXER_H_
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