DRAFT |
SDL_AudioSpec
A structure that contains the audio output format. It also contains a callback that is called when the audio device needs more data.
Contents
Data Fields
int |
freq |
DSP frequency (samples per second); see Remarks for details |
format |
audio data format; see Remarks for details |
|
Uint8 |
channels |
number of separate sound channels: 1 = mono, 2 = stereo |
Uint8 |
silence |
audio buffer silence value (calculated) |
Uint16 |
samples |
audio buffer size in samples (power of 2); see Remarks for details |
Uint32 |
size |
audio buffer size in bytes (calculated) |
SDL_AudioCallback |
callback |
the function to call when the audio device needs more data; see Remarks for details |
void* |
userdata |
a pointer that is passed to callback |
Code Examples
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Remarks
*
The SDL_AudioSpec structure is used to describe the format of some audio data. This structure is used by SDL_OpenAudio() and SDL_LoadWAV(). While all fields are used by SDL_OpenAudio(), only freq, format, channels, and samples are used by SDL_LoadWAV().
freq specifies the number of samples sent to the sound device per second. Common values are 11025, 22050 and 44100. The higher the better.
format specifies the size and type of each sample element and may be one of the following:
Defaults to LSB byte order -or- Basic ???
AUDIO_U8
unsigned 8-bit samples.
AUDIO_S8
signed 8-bit samples.
AUDIO_U16 or AUDIO_U16LSB
not supported by all hardware (unsigned 16-bit little-endian)
AUDIO_S16 or AUDIO_S16LSB
not supported by all hardware (signed 16-bit little-endian)
AUDIO_U16MSB
not supported by all hardware (unsigned 16-bit big-endian)
AUDIO_S16MSB
not supported by all hardware (signed 16-bit big-endian)
int32 support
AUDIO_S32 or AUDIO_S32LSB
32-bit integer samples
AUDIO_S32MSB
as above, but big-endian byte order
float32 support
AUDIO_F32 or AUDIO_F32LSB
32-bit floating point samples
AUDIO_F32MSB
as above, but big-endian byte order
Native audio byte ordering
AUDIO_U16SYS
either AUDIO_U16LSB or AUDIO_U16MSB depending on hardware CPU endianness
AUDIO_S16SYS
either AUDIO_S16LSB or AUDIO_S16MSB depending on hardware CPU endianness
AUDIO_S32SYS
either AUDIO_S32LSB or AUDIO_S32MSB depending on hardware CPU endianness
AUDIO_F32SYS
either AUDIO_F32LSB or AUDIO_F32MSB depending on hardware CPU endianness
samples specifies a unit of audio data. When used with SDL_OpenAudio() this refers to the size of the audio buffer in samples. A sample is a chunk of audio data of the size specified in format multiplied by the number of channels. When the SDL_AudioSpec is used with SDL_LoadWAV() samples is set to 4096.
*
The values silence and size are calculated by SDL_OpenAudio().
Stereo samples are stored in a LRLRLR ordering.
The function prototype for callback is:
void SDL_AudioCallback(void* userdata, Uint8* stream, int len)
- where its parameters are:
userdata
an application-specific parameter saved in the SDL_AudioSpec structure
stream
a pointer to the audio data buffer filled in by SDL_AudioCallback()
len
the length of that buffer in bytes
Once the callback returns, the buffer will no longer be valid.