media/base/audio_converter.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 // AudioConverter is a complete mixing, resampling, buffering, and channel
   6 // mixing solution for converting data from one set of AudioParameters to
   7 // another.
   8 //
   9 // For efficiency, pieces are only invoked when necessary; i.e.,
  10 //    - The resampler is only used if sample rates differ.
  11 //    - The FIFO is only used if buffer sizes differ.
  12 //    - The channel mixer is only used if channel layouts differ.
  13 //
  14 // Additionally, since resampling is the most expensive operation, input mixing
  15 // and channel down mixing are done prior to resampling.  Likewise, channel up
  16 // mixing is performed after resampling.
  17
  18 #ifndef MEDIA_BASE_AUDIO_CONVERTER_H_
  19 #define MEDIA_BASE_AUDIO_CONVERTER_H_
  20
  21 #include <list>
  22
  23 #include "base/callback.h"
  24 #include "base/memory/scoped_ptr.h"
  25 #include "base/time/time.h"
  26 #include "media/audio/audio_parameters.h"
  27 #include "media/base/media_export.h"
  28
  29 namespace media {
  30
  31 class AudioBus;
  32 class AudioPullFifo;
  33 class ChannelMixer;
  34 class MultiChannelResampler;
  35
  36 // Converts audio data between two AudioParameters formats.  Sample usage:
  37 //   AudioParameters input(...), output(...);
  38 //   AudioConverter ac(input, output);
  39 //   scoped_ptr<AudioBus> output_audio_bus = AudioBus::Create(output);
  40 //   ac.AddInput(<AudioConverter::InputCallback* 1>);
  41 //   ac.AddInput(<AudioConverter::InputCallback* 2>);
  42 //   ac.Convert(output_audio_bus.get());
  43 //
  44 // Convert() will ask for input audio data from each InputCallback and convert
  45 // the data into the provided AudioBus.
  46 class MEDIA_EXPORT AudioConverter {
  47  public:
  48   // Interface for inputs into the converter.  Each InputCallback is added or
  49   // removed from Convert() processing via AddInput() and RemoveInput().
  50   class MEDIA_EXPORT InputCallback {
  51    public:
  52     // Method for providing more data into the converter.  Expects |audio_bus|
  53     // to be completely filled with data upon return; zero padded if not enough
  54     // frames are available to satisfy the request.  The return value is the
  55     // volume level of the provided audio data.  If a volume level of zero is
  56     // returned no further processing will be done on the provided data, else
  57     // the volume level will be used to scale the provided audio data.
  58     virtual double ProvideInput(AudioBus* audio_bus,
  59                                 base::TimeDelta buffer_delay) = 0;
  60
  61    protected:
  62     virtual ~InputCallback() {}
  63   };
  64
  65   // Constructs an AudioConverter for converting between the given input and
  66   // output parameters.  Specifying |disable_fifo| means all InputCallbacks are
  67   // capable of handling arbitrary buffer size requests; i.e. one call might ask
  68   // for 10 frames of data (indicated by the size of AudioBus provided) and the
  69   // next might ask for 20.  In synthetic testing, disabling the FIFO yields a
  70   // ~20% speed up for common cases.
  71   AudioConverter(const AudioParameters& input_params,
  72                  const AudioParameters& output_params,
  73                  bool disable_fifo);
  74   ~AudioConverter();
  75
  76   // Converts audio from all inputs into the |dest|. If an |initial_delay| is
  77   // specified, it will be propagated to each input.
  78   void Convert(AudioBus* dest);
  79   void ConvertWithDelay(const base::TimeDelta& initial_delay, AudioBus* dest);
  80
  81   // Adds or removes an input from the converter.  RemoveInput() will call
  82   // Reset() if no inputs remain after the specified input is removed.
  83   void AddInput(InputCallback* input);
  84   void RemoveInput(InputCallback* input);
  85
  86   // Flushes all buffered data.
  87   void Reset();
  88
  89   // The maximum size in frames that guarantees we will only make a single call
  90   // to each input's ProvideInput for more data.
  91   int ChunkSize() const;
  92
  93  private:
  94   // Provides input to the MultiChannelResampler.  Called by the resampler when
  95   // more data is necessary.
  96   void ProvideInput(int resampler_frame_delay, AudioBus* audio_bus);
  97
  98   // Provides input to the AudioPullFifo.  Called by the fifo when more data is
  99   // necessary.
 100   void SourceCallback(int fifo_frame_delay, AudioBus* audio_bus);
 101
 102   // (Re)creates the temporary |unmixed_audio_| buffer if necessary.
 103   void CreateUnmixedAudioIfNecessary(int frames);
 104
 105   // Set of inputs for Convert().
 106   typedef std::list<InputCallback*> InputCallbackSet;
 107   InputCallbackSet transform_inputs_;
 108
 109   // Used to buffer data between the client and the output device in cases where
 110   // the client buffer size is not the same as the output device buffer size.
 111   scoped_ptr<AudioPullFifo> audio_fifo_;
 112   int chunk_size_;
 113
 114   // Handles resampling.
 115   scoped_ptr<MultiChannelResampler> resampler_;
 116
 117   // Handles channel transforms.  |unmixed_audio_| is a temporary destination
 118   // for audio data before it goes into the channel mixer.
 119   scoped_ptr<ChannelMixer> channel_mixer_;
 120   scoped_ptr<AudioBus> unmixed_audio_;
 121
 122   // Temporary AudioBus destination for mixing inputs.
 123   scoped_ptr<AudioBus> mixer_input_audio_bus_;
 124
 125   // Since resampling is expensive, figure out if we should downmix channels
 126   // before resampling.
 127   bool downmix_early_;
 128
 129   // Used to calculate buffer delay information for InputCallbacks.
 130   base::TimeDelta input_frame_duration_;
 131   base::TimeDelta output_frame_duration_;
 132   base::TimeDelta initial_delay_;
 133   int resampler_frame_delay_;
 134
 135   // Number of channels of input audio data.  Set during construction via the
 136   // value from the input AudioParameters class.  Preserved to recreate internal
 137   // AudioBus structures on demand in response to varying frame size requests.
 138   const int input_channel_count_;
 139
 140   DISALLOW_COPY_AND_ASSIGN(AudioConverter);
 141 };
 142
 143 }  // namespace media
 144
 145 #endif  // MEDIA_BASE_AUDIO_CONVERTER_H_