sdl_audiocvt(3) [redhat man page]

SDL_AudioCVT(3) 						 SDL API Reference						   SDL_AudioCVT(3)

NAME

       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

       needed		   Set to one if the conversion is possible

       src_format	   Audio format of the source

       dest_format	   Audio format of the destination

       rate_incr	   Rate conversion increment

       buf		   Audio buffer

       len		   Length of the original audio buffer in bytes

       len_cvt		   Length of converted audio buffer in bytes (calculated)

       len_mult 	   buf must be len*len_mult bytes in size(calculated)

       len_ratio	   Final audio size is len*len_ratio

       filters[10](..)	   Pointers to functions needed for this conversion

       filter_index	   Current conversion function

DESCRIPTION

       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

       int len

       int len_mult

       double len_ratio

SEE ALSO

       SDL_BuildAudioCVT, SDL_ConvertAudio, SDL_AudioSpec

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

SDL_ConvertAudio(3)						 SDL API Reference					       SDL_ConvertAudio(3)

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. Remem-
       ber, 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
       ", 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 */
       .
       .
       .
       .

SEE ALSO

       SDL_BuildAudioCVT, SDL_AudioCVT

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