media/base/channel_mixer.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_BASE_CHANNEL_MIXER_H_
   6 #define MEDIA_BASE_CHANNEL_MIXER_H_
   7
   8 #include <vector>
   9
  10 #include "base/macros.h"
  11 #include "media/base/channel_layout.h"
  12 #include "media/base/media_export.h"
  13
  14 namespace media {
  15
  16 class AudioBus;
  17 class AudioParameters;
  18
  19 // ChannelMixer is for converting audio between channel layouts.  The conversion
  20 // matrix is built upon construction and used during each Transform() call.  The
  21 // algorithm works by generating a conversion matrix mapping each output channel
  22 // to list of input channels.  The transform renders all of the output channels,
  23 // with each output channel rendered according to a weighted sum of the relevant
  24 // input channels as defined in the matrix.
  25 class MEDIA_EXPORT ChannelMixer {
  26  public:
  27   ChannelMixer(ChannelLayout input_layout, ChannelLayout output_layout);
  28   ChannelMixer(const AudioParameters& input, const AudioParameters& output);
  29   ~ChannelMixer();
  30
  31   // Transforms all channels from |input| into |output| channels.
  32   void Transform(const AudioBus* input, AudioBus* output);
  33
  34  private:
  35   void Initialize(ChannelLayout input_layout, int input_channels,
  36                   ChannelLayout output_layout, int output_channels);
  37
  38   // 2D matrix of output channels to input channels.
  39   std::vector< std::vector<float> > matrix_;
  40
  41   // Optimization case for when we can simply remap the input channels to output
  42   // channels and don't need to do a multiply-accumulate loop over |matrix_|.
  43   bool remapping_;
  44
  45   DISALLOW_COPY_AND_ASSIGN(ChannelMixer);
  46 };
  47
  48 }  // namespace media
  49
  50 #endif  // MEDIA_BASE_CHANNEL_MIXER_H_