Use this function to convert audio data to a desired audio format.
int SDL_ConvertAudio(SDL_AudioCVT* cvt)
Returns 0 if the conversion was completed successfully or a negative error code on failure; call SDL_GetError() for more information.
// Change 1024 stereo sample frames at 48000Hz from Float32 to Int16. SDL_AudioCVT cvt; SDL_BuildAudioCVT(&cvt, AUDIO_F32, 2, 48000, AUDIO_S16, 2, 48000); SDL_assert(cvt.needed); // obviously, this one is always needed. cvt.len = 1024 * 2 * 4; // 1024 stereo float32 sample frames. cvt.buf = (Uint8 *) SDL_malloc(cvt.len * cvt.len_mult); // read your float32 data into cvt.buf here. SDL_ConvertAudio(&cvt); // cvt.buf has cvt.len_cvt bytes of converted data now.
This function does the actual audio data conversion, after the application has called SDL_BuildAudioCVT() to prepare the conversion information and then filled in the buffer details.
Once the application has initialized the cvt structure using SDL_BuildAudioCVT(), allocated an audio buffer and filled it with audio data in the source format, this function will convert the buffer, in-place, to the desired format.
The data conversion may go through several passes; any given pass may possibly temporarily increase the size of the data. For example, SDL might expand 16-bit data to 32 bits before resampling to a lower frequency, shrinking the data size after having grown it briefly. Since the supplied buffer will be both the source and destination, converting as necessary in-place, the application must allocate a buffer that will fully contain the data during its largest conversion pass. After SDL_BuildAudioCVT() returns, the application should set the cvt structure's len field to the size, in bytes, of the source data, and allocate a buffer that is len * len_mult bytes long for the buf field.
The source data should be copied into this buffer before the call to SDL_ConvertAudio(). Upon successful return, this buffer will contain the converted audio, and the cvt structure's len_cvt field will be the size of the converted data, in bytes. Any bytes in the buffer past len_cvt are undefined once this function returns.