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SDL_ConvertAudio

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. Remember, 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