media/audio/audio_parameters.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_AUDIO_AUDIO_PARAMETERS_H_
   6 #define MEDIA_AUDIO_AUDIO_PARAMETERS_H_
   7
   8 #include <string>
   9
  10 #include "base/basictypes.h"
  11 #include "base/time/time.h"
  12 #include "media/base/channel_layout.h"
  13 #include "media/base/media_export.h"
  14
  15 namespace media {
  16
  17 struct MEDIA_EXPORT AudioInputBufferParameters {
  18   double volume;
  19   uint32 size;
  20   bool key_pressed;
  21 };
  22
  23 // Use a struct-in-struct approach to ensure that we can calculate the required
  24 // size as sizeof(AudioInputBufferParameters) + #(bytes in audio buffer) without
  25 // using packing.
  26 struct MEDIA_EXPORT AudioInputBuffer {
  27   AudioInputBufferParameters params;
  28   int8 audio[1];
  29 };
  30
  31 class MEDIA_EXPORT AudioParameters {
  32  public:
  33   // TODO(miu): Rename this enum to something that correctly reflects its
  34   // semantics, such as "TransportScheme."
  35   enum Format {
  36     AUDIO_PCM_LINEAR = 0,     // PCM is 'raw' amplitude samples.
  37     AUDIO_PCM_LOW_LATENCY,    // Linear PCM, low latency requested.
  38     AUDIO_FAKE,               // Creates a fake AudioOutputStream object.
  39     AUDIO_LAST_FORMAT         // Only used for validation of format.
  40   };
  41
  42   enum {
  43     // Telephone quality sample rate, mostly for speech-only audio.
  44     kTelephoneSampleRate = 8000,
  45     // CD sampling rate is 44.1 KHz or conveniently 2x2x3x3x5x5x7x7.
  46     kAudioCDSampleRate = 44100,
  47   };
  48
  49   // Bitmasks to determine whether certain platform (typically hardware) audio
  50   // effects should be enabled.
  51   enum PlatformEffectsMask {
  52     NO_EFFECTS = 0x0,
  53     ECHO_CANCELLER = 0x1,
  54     DUCKING = 0x2,  // Enables ducking if the OS supports it.
  55     KEYBOARD_MIC = 0x4,
  56     HOTWORD = 0x8,
  57   };
  58
  59   AudioParameters();
  60   AudioParameters(Format format, ChannelLayout channel_layout,
  61                   int sample_rate, int bits_per_sample,
  62                   int frames_per_buffer);
  63   AudioParameters(Format format, ChannelLayout channel_layout,
  64                   int sample_rate, int bits_per_sample,
  65                   int frames_per_buffer, int effects);
  66   AudioParameters(Format format, ChannelLayout channel_layout,
  67                   int channels, int sample_rate, int bits_per_sample,
  68                   int frames_per_buffer, int effects);
  69
  70   void Reset(Format format, ChannelLayout channel_layout,
  71              int channels, int sample_rate, int bits_per_sample,
  72              int frames_per_buffer);
  73
  74   // Checks that all values are in the expected range. All limits are specified
  75   // in media::Limits.
  76   bool IsValid() const;
  77
  78   // Returns a human-readable string describing |*this|.  For debugging & test
  79   // output only.
  80   std::string AsHumanReadableString() const;
  81
  82   // Returns size of audio buffer in bytes.
  83   int GetBytesPerBuffer() const;
  84
  85   // Returns the number of bytes representing one second of audio.
  86   int GetBytesPerSecond() const;
  87
  88   // Returns the number of bytes representing a frame of audio.
  89   int GetBytesPerFrame() const;
  90
  91   // Returns the duration of this buffer as calculated from frames_per_buffer()
  92   // and sample_rate().
  93   base::TimeDelta GetBufferDuration() const;
  94
  95   // Comparison with other AudioParams.
  96   bool Equals(const AudioParameters& other) const;
  97
  98   Format format() const { return format_; }
  99   ChannelLayout channel_layout() const { return channel_layout_; }
 100   int sample_rate() const { return sample_rate_; }
 101   int bits_per_sample() const { return bits_per_sample_; }
 102   int frames_per_buffer() const { return frames_per_buffer_; }
 103   int channels() const { return channels_; }
 104   int effects() const { return effects_; }
 105
 106  private:
 107   // These members are mutable to support entire struct assignment. They should
 108   // not be mutated individually.
 109   Format format_;                 // Format of the stream.
 110   ChannelLayout channel_layout_;  // Order of surround sound channels.
 111   int sample_rate_;               // Sampling frequency/rate.
 112   int bits_per_sample_;           // Number of bits per sample.
 113   int frames_per_buffer_;         // Number of frames in a buffer.
 114
 115   int channels_;                  // Number of channels. Value set based on
 116                                   // |channel_layout|.
 117   int effects_;                   // Bitmask using PlatformEffectsMask.
 118 };
 119
 120 // Comparison is useful when AudioParameters is used with std structures.
 121 inline bool operator<(const AudioParameters& a, const AudioParameters& b) {
 122   if (a.format() != b.format())
 123     return a.format() < b.format();
 124   if (a.channels() != b.channels())
 125     return a.channels() < b.channels();
 126   if (a.sample_rate() != b.sample_rate())
 127     return a.sample_rate() < b.sample_rate();
 128   if (a.bits_per_sample() != b.bits_per_sample())
 129     return a.bits_per_sample() < b.bits_per_sample();
 130   return a.frames_per_buffer() < b.frames_per_buffer();
 131 }
 132
 133 }  // namespace media
 134
 135 #endif  // MEDIA_AUDIO_AUDIO_PARAMETERS_H_