Solaris  - SDL_ConvertAudio (3)


SDL_ConvertAudio- Convert audio data to a desired audio format.



#include "SDL.h"

int SDL_ConvertAudio(SDL_AudioCVT *cvt);




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.


/* 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 */ . . . .


SDL_BuildAudioCVT, SDL_AudioCVT

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SDL SDL_ConvertAudio (3) Tue 11 Sep 2001, 22:58
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