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/basictypes.h"
  11 #include "media/base/channel_layout.h"
  12 #include "media/base/media_export.h"
  13
  14 namespace media {
  15
  16 class AudioBus;
  17
  18 // ChannelMixer is for converting audio between channel layouts.  The conversion
  19 // matrix is built upon construction and used during each Transform() call.  The
  20 // algorithm works by generating a conversion matrix mapping each output channel
  21 // to list of input channels.  The transform renders all of the output channels,
  22 // with each output channel rendered according to a weighted sum of the relevant
  23 // input channels as defined in the matrix.
  24 class MEDIA_EXPORT ChannelMixer {
  25  public:
  26   ChannelMixer(ChannelLayout input, ChannelLayout output);
  27   ~ChannelMixer();
  28
  29   // Transforms all channels from |input| into |output| channels.
  30   void Transform(const AudioBus* input, AudioBus* output);
  31
  32  private:
  33   // Constructor helper methods for managing unaccounted input channels.
  34   void AccountFor(Channels ch);
  35   bool IsUnaccounted(Channels ch);
  36
  37   // Helper methods for checking if |ch| exists in either |input_layout_| or
  38   // |output_layout_| respectively.
  39   bool HasInputChannel(Channels ch);
  40   bool HasOutputChannel(Channels ch);
  41
  42   // Constructor helper methods for updating |matrix_| with the proper value for
  43   // mixing |input_ch| into |output_ch|.  MixWithoutAccounting() does not remove
  44   // the channel from |unaccounted_inputs_|.
  45   void Mix(Channels input_ch, Channels output_ch, float scale);
  46   void MixWithoutAccounting(Channels input_ch, Channels output_ch, float scale);
  47
  48   // Input and output channel layout provided during construction.
  49   ChannelLayout input_layout_;
  50   ChannelLayout output_layout_;
  51
  52   // Helper variable for tracking which inputs are currently unaccounted, should
  53   // be empty after construction completes.
  54   std::vector<Channels> unaccounted_inputs_;
  55
  56   // 2D matrix of output channels to input channels.
  57   std::vector< std::vector<float> > matrix_;
  58
  59   // Optimization case for when we can simply remap the input channels to output
  60   // channels and don't need to do a multiply-accumulate loop over |matrix_|.
  61   bool remapping_;
  62
  63   DISALLOW_COPY_AND_ASSIGN(ChannelMixer);
  64 };
  65
  66 }  // namespace media
  67
  68 #endif  // MEDIA_BASE_CHANNEL_MIXER_H_