SDL_AudioCVT -- Audio Conversion Structure

Structure Definition

typedef struct{
  int needed;
  Uint16 src_format;
  Uint16 dest_format;
  double rate_incr;
  Uint8 *buf;
  int len;
  int len_cvt;
  int len_mult;
  double len_ratio;
  void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
  int filter_index;
} SDL_AudioCVT;

Structure Data

neededSet to one if the conversion is possible
src_formatAudio format of the source
dest_formatAudio format of the destination
rate_incrRate conversion increment
bufAudio buffer
lenLength of the original audio buffer in bytes
len_cvtLength of converted audio buffer in bytes (calculated)
len_multbuf must be len*len_mult bytes in size(calculated)
len_ratioFinal audio size is len*len_ratio
filters[10](..)Pointers to functions needed for this conversion
filter_indexCurrent conversion function


The SDL_AudioCVT is used to convert audio data between different formats. A SDL_AudioCVT structure is created with the SDL_BuildAudioCVT function, while the actual conversion is done by the SDL_ConvertAudio function.

Many of the fields in the SDL_AudioCVT structure should be considered private and their function will not be discussed here.

Uint8 *buf

This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure buf is large enough. See below.

int len

This is the length of the original audio data in bytes.

int len_mult

As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of buf should be len*len_mult.

double len_ratio

When you have finished converting your audio data, you need to know how much of your audio buffer is valid. len*len_ratio is the size of the converted audio data in bytes. This is very similar to len_mult, however when the convert audio data is shorter than the original len_mult would be 1. len_ratio, on the other hand, would be a fractional number between 0 and 1.

See Also

SDL_BuildAudioCVT, SDL_ConvertAudio, SDL_AudioSpec