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 previ-
ously initilized. Initilizing a SDL_AudioCVT is a two step
process. First of all, the structure must be passed toSDL_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 belen*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 convertedaudio 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;
SDL Last change: Tue 11 Sep 2001, 22:58 1SDL API Reference SDL_ConvertAudio(3)
/* 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 */ . . . . SDL Last change: Tue 11 Sep 2001, 22:58 2SDL API Reference SDL_ConvertAudio(3)
SEE ALSO
SDL_BuildAudioCVT, SDL_AudioCVT
SDL Last change: Tue 11 Sep 2001, 22:58 3