DRAFT |
SDL_ConvertAudio
Use this function to convert audio data to a desired audio format.
Syntax
int SDL_ConvertAudio(SDL_AudioCVT* cvt)
Function Parameters
cvt |
an SDL_AudioCVT structure that was previously set up; see Remarks for details |
Return Value
Returns 0 if the conversion was completed successfully or a negative error code on failure; call SDL_GetError() for more information.
Code 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 = malloc(sizeof(SDL_AudioSpec));
obtained = 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\n", 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\n", 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!\n");
SDL_CloseAudio();
free(obtained);
SDL_FreeWAV(wav_buf);
}
/* Setup for conversion, copy original data to new buffer*/
wav_cvt.buf = 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 */
.
.
.
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Remarks
Does SDL_BuildAudioCVT() initialize the structure create the buffer and fill it with audio data or does it require other actions to create the buffer and fill it with data? If the function does all of the above then the second paragraph below should probably replace the first. If not then the first paragraph below should be kept and possibly modified to include information about how to create the buffer and fill it.
Once you have initialized the cvt structure using SDL_BuildAudioCVT(), created an audio buffer cvt->buf, and filled it with cvt->len bytes of audio data in the source format, the structure can be passed to this function which will convert it in-place to the desired format.
-or-
Once you have initialized the cvt structure, created an audio buffer cvt->buf, and filled it with cvt->len bytes of audio data in the source format using SDL_BuildAudioCVT(), the structure can be passed to this function which will convert it in-place to the desired format.
How do you allocate the buffer? Should that info be included here or is that common knowledge?
The data conversion may expand the size of the audio data, so the buffer cvt->buf should be allocated after the cvt structure is initialized by SDL_BuildAudioCVT(), and should be cvt->len*cvt->len_mult bytes long.
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.
