SDL_AudioCVT(3) SDL API Reference SDL_AudioCVT(3)NAME
SDL_AudioCVT - Audio Conversion Structure
STRUCTURE DEFINITION
typedef struct{
int needed;
Uint16 src_format;
Uint16 dest_format;
double rate_incr;
Uint8 *buf;
int len;
int len_cvt;
int len_mult;
double len_ratio;
void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
int filter_index;
} SDL_AudioCVT;
STRUCTURE DATA
needed Set to one if the conversion is possible
src_format Audio format of the source
dest_format Audio format of the destination
rate_incr Rate conversion increment
buf Audio buffer
len Length of the original audio buffer in bytes
len_cvt Length of converted audio buffer in bytes (calculated)
len_mult buf must be len*len_mult bytes in size(calculated)
len_ratio Final audio size is len*len_ratio
filters[10](..) Pointers to functions needed for this conversion
filter_index Current conversion function
DESCRIPTION
The SDL_AudioCVT is used to convert audio data between different formats. A SDL_AudioCVT structure is created with the SDL_BuildAudioCVT
function, while the actual conversion is done by the SDL_ConvertAudio function.
Many of the fields in the SDL_AudioCVT structure should be considered private and their function will not be discussed here.
Uint8 *buf
int len
int len_mult
double len_ratio
SEE ALSO
SDL_BuildAudioCVT, SDL_ConvertAudio, SDL_AudioSpec
SDL Tue 11 Sep 2001, 22:58 SDL_AudioCVT(3)
Check Out this Related Man Page
SDL_ConvertAudio(3) SDL API Reference SDL_ConvertAudio(3)NAME
SDL_ConvertAudio - Convert audio data to a desired audio format.
SYNOPSIS
#include "SDL.h"
int SDL_ConvertAudio(SDL_AudioCVT *cvt);
DESCRIPTION
SDL_ConvertAudio takes one parameter, cvt, which was previously initilized. Initilizing a SDL_AudioCVT is a two step process. First of all,
the structure must be passed to SDL_BuildAudioCVT along with source and destination format parameters. Secondly, the cvt->buf and cvt->len
fields must be setup. cvt->buf should point to the audio data and cvt->len should be set to the length of the audio data in bytes. Remem-
ber, the length of the buffer pointed to by buf show be len*len_mult bytes in length.
Once the SDL_AudioCVTstructure is initilized then we can pass it to SDL_ConvertAudio, which will convert the audio data pointer to by
cvt->buf. If SDL_ConvertAudio returned 0 then the conversion was completed successfully, otherwise -1 is returned.
If the conversion completed successfully then the converted audio data can be read from cvt->buf. The amount of valid, converted, audio
data in the buffer is equal to cvt->len*cvt->len_ratio.
EXAMPLES
/* Converting some WAV data to hardware format */
void my_audio_callback(void *userdata, Uint8 *stream, int len);
SDL_AudioSpec *desired, *obtained;
SDL_AudioSpec wav_spec;
SDL_AudioCVT wav_cvt;
Uint32 wav_len;
Uint8 *wav_buf;
int ret;
/* Allocated audio specs */
desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));
/* Set desired format */
desired->freq=22050;
desired->format=AUDIO_S16LSB;
desired->samples=8192;
desired->callback=my_audio_callback;
desired->userdata=NULL;
/* Open the audio device */
if ( SDL_OpenAudio(desired, obtained) < 0 ){
fprintf(stderr, "Couldn't open audio: %s
", SDL_GetError());
exit(-1);
}
free(desired);
/* Load the test.wav */
if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buf, &wav_len) == NULL ){
fprintf(stderr, "Could not open test.wav: %s
", SDL_GetError());
SDL_CloseAudio();
free(obtained);
exit(-1);
}
/* Build AudioCVT */
ret = SDL_BuildAudioCVT(&wav_cvt,
wav_spec.format, wav_spec.channels, wav_spec.freq,
obtained->format, obtained->channels, obtained->freq);
/* Check that the convert was built */
if(ret==-1){
fprintf(stderr, "Couldn't build converter!
");
SDL_CloseAudio();
free(obtained);
SDL_FreeWAV(wav_buf);
}
/* Setup for conversion */
wav_cvt.buf=(Uint8 *)malloc(wav_len*wav_cvt.len_mult);
wav_cvt.len=wav_len;
memcpy(wav_cvt.buf, wav_buf, wav_len);
/* We can delete to original WAV data now */
SDL_FreeWAV(wav_buf);
/* And now we're ready to convert */
SDL_ConvertAudio(&wav_cvt);
/* do whatever */
.
.
.
.
SEE ALSO
SDL_BuildAudioCVT, SDL_AudioCVT
SDL Tue 11 Sep 2001, 22:58 SDL_ConvertAudio(3)