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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