SDL Library Documentation
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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\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 */
    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`

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SDL_BuildAudioCVT | Up | SDL_MixAudio