SDL_ConvertAudio(3)

👑 NAME 👑

SDL_ConvertAudio — converts your audio data into the audio format you actually want. 💅

okay so real quick, bestie, this page lives in the SDL API Reference, section 3, and it's literally just the glow-up step for your audio bytes. let's get into it 🫶

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✨ SYNOPSIS ✨

#include "SDL.h"

int SDL_ConvertAudio(SDL_AudioCVT *cvt);

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💖 DESCRIPTION 💖

SDL_ConvertAudio takes exactly one parameter, cvt, and that baby has to be previously initialized or we're not doing anything. no cap.

And initializing an SDL_AudioCVT is a whole two step process, so pay attention bestie:

1. First, the structure gets passed to SDL_BuildAudioCVT along with the source and destination format parameters. that's the setup era. 🌸
2. Then, the cvt->buf and cvt->len fields have to be set up. cvt->buf should point at the audio data, and cvt->len gets set to the length of that audio data in bytes.

🚨 okay this part matters: the length of the buffer that buf points to should be len*len_mult bytes long. do not skip this. not me forgetting len_mult and ruining my whole afternoon 😭

Once the SDL_AudioCVT structure is initialized, we can pass it into SDL_ConvertAudio, and it will convert the audio data pointed to by cvt->buf. iconic behavior tbh.

Now the receipts:

• if SDL_ConvertAudio returned 0, the conversion was completed successfully. slay. ✨
• otherwise, -1 is returned. 🙈

If the conversion completed successfully, the converted audio data can be read straight from cvt->buf. and the amount of valid, converted audio data sitting in that buffer is equal to cvt->len*cvt->len_ratio. yes, you do the little multiplication. 💅

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🎀 EXAMPLES 🎀

here's the whole vibe, a WAV file getting converted to hardware format:

/* 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 */
.
.
.
.

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🦋 SEE ALSO 🦋

• SDL_BuildAudioCVT — the one that builds the converter first, iykyk
• SDL_AudioCVT — the structure itself, the main character

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okay that's the whole page bestie, you ate it 💖✨

this was SDL — the SDL API Reference, dated Tue 11 Sep 2001, 22:58, filed under SDL_ConvertAudio(3). periodt. 💅🎀🦋