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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/basictypes.h"
#include "media/base/channel_layout.h"
#include "media/base/media_export.h"
namespace media {
class AudioBus;
// 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:
ChannelMixer(ChannelLayout input, ChannelLayout output);
~ChannelMixer();
// Transforms all channels from |input| into |output| channels.
void Transform(const AudioBus* input, AudioBus* output);
private:
// Constructor helper methods for managing unaccounted input channels.
void AccountFor(Channels ch);
bool IsUnaccounted(Channels ch);
// Helper methods for checking if |ch| exists in either |input_layout_| or
// |output_layout_| respectively.
bool HasInputChannel(Channels ch);
bool HasOutputChannel(Channels ch);
// Constructor 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);
// Input and output channel layout provided during construction.
ChannelLayout input_layout_;
ChannelLayout output_layout_;
// Helper variable for tracking which inputs are currently unaccounted, should
// be empty after construction completes.
std::vector<Channels> unaccounted_inputs_;
// 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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