audio_converter.h revision 2a99a7e74a7f215066514fe81d2bfa6639d9eddd 
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_AUDIO_CONVERTER_H_
6#define MEDIA_BASE_AUDIO_CONVERTER_H_
7
8#include <list>
9
10#include "base/callback.h"
11#include "base/time.h"
12#include "media/audio/audio_parameters.h"
13#include "media/base/media_export.h"
14
15namespace media {
16
17class AudioBus;
18class AudioPullFifo;
19class ChannelMixer;
20class MultiChannelResampler;
21
22// AudioConverter is a complete mixing, resampling, buffering, and channel
23// mixing solution for converting data from one set of AudioParameters to
24// another.  For efficiency pieces are only invoked when necessary; e.g. the
25// resampler is only used if the input and output sample rates differ.  Mixing
26// and channel down mixing are done prior to resampling to maximize efficiency.
27class MEDIA_EXPORT AudioConverter {
28 public:
29  class MEDIA_EXPORT InputCallback {
30   public:
31    // Method for providing more data into the converter.  Expects |audio_bus|
32    // to be completely filled with data upon return; zero padded if not enough
33    // frames are available to satisfy the request.  The return value is the
34    // volume level of the provided audio data.  If a volume level of zero is
35    // returned no further processing will be done on the provided data, else
36    // the volume level will be used to scale the provided audio data.
37    virtual double ProvideInput(AudioBus* audio_bus,
38                                base::TimeDelta buffer_delay) = 0;
39
40   protected:
41    virtual ~InputCallback() {}
42  };
43
44  // Construct an AudioConverter for converting between the given input and
45  // output parameters.  Specifying |disable_fifo| means all InputCallbacks are
46  // capable of handling arbitrary buffer size requests; i.e. one call might ask
47  // for 10 frames of data (indicated by the size of AudioBus provided) and the
48  // next might ask for 20.  In synthetic testing, disabling the FIFO yields a
49  // ~20% speed up for common cases.
50  AudioConverter(const AudioParameters& input_params,
51                 const AudioParameters& output_params,
52                 bool disable_fifo);
53  ~AudioConverter();
54
55  // Converts audio from all inputs into the |dest|.  |dest| must be sized for
56  // data matching the output AudioParameters provided during construction.
57  void Convert(AudioBus* dest);
58
59  // Add or remove an input from the converter.
60  void AddInput(InputCallback* input);
61  void RemoveInput(InputCallback* input);
62
63  // Flush all buffered data.  Automatically called when all inputs are removed.
64  void Reset();
65
66 private:
67  // Called by MultiChannelResampler when more data is necessary.
68  void ProvideInput(int resampler_frame_delay, AudioBus* audio_bus);
69
70  // Called by AudioPullFifo when more data is necessary.
71  void SourceCallback(int fifo_frame_delay, AudioBus* audio_bus);
72
73  // Set of inputs for Convert().
74  typedef std::list<InputCallback*> InputCallbackSet;
75  InputCallbackSet transform_inputs_;
76
77  // Used to buffer data between the client and the output device in cases where
78  // the client buffer size is not the same as the output device buffer size.
79  scoped_ptr<AudioPullFifo> audio_fifo_;
80
81  // Handles resampling.
82  scoped_ptr<MultiChannelResampler> resampler_;
83
84  // Handles channel transforms.  |unmixed_audio_| is a temporary destination
85  // for audio data before it goes into the channel mixer.
86  scoped_ptr<ChannelMixer> channel_mixer_;
87  scoped_ptr<AudioBus> unmixed_audio_;
88
89  // Temporary AudioBus destination for mixing inputs.
90  scoped_ptr<AudioBus> mixer_input_audio_bus_;
91
92  // Since resampling is expensive, figure out if we should downmix channels
93  // before resampling.
94  bool downmix_early_;
95
96  // Used to calculate buffer delay information for InputCallbacks.
97  base::TimeDelta input_frame_duration_;
98  base::TimeDelta output_frame_duration_;
99  int resampler_frame_delay_;
100
101  const int input_channel_count_;
102
103  DISALLOW_COPY_AND_ASSIGN(AudioConverter);
104};
105
106}  // namespace media
107
108#endif  // MEDIA_BASE_AUDIO_CONVERTER_H_
109