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SDL_OpenAudio(3)	       SDL API Reference	      SDL_OpenAudio(3)

NAME
       SDL_OpenAudio - Opens the audio device with the desired parameters.

SYNOPSIS
       #include "SDL.h"

       int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained);

DESCRIPTION
       This  function  opens the audio device with the desired parameters, and
       returns 0 if successful, placing the actual hardware parameters in  the
       structure  pointed  to by obtained. If obtained is NULL, the audio data
       passed to the callback  function  will  be  guaranteed  to  be  in  the
       requested  format,  and will be automatically converted to the hardware
       audio format if necessary. This function returns -1  if	it  failed  to
       open the audio device, or couldn't set up the audio thread.

       To open the audio device a desired SDL_AudioSpec must be created.

       SDL_AudioSpec *desired;
       .
       .
       desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

	You  must  then fill this structure with your desired audio specifica-
       tions.

       desired->freq

       desired->format

       desired->samples

       desired->callback

       void callback(void *userdata, Uint8 *stream, int len);

	userdata is the pointer stored in userdata field of the SDL_AudioSpec.
       stream  is a pointer to the audio buffer you want to fill with informa-
       tion and len is the length of the audio buffer in bytes.

       desired->userdata

       SDL_OpenAudio reads these fields from the desired SDL_AudioSpec	struc-
       ture  pass  to the function and attempts to find an audio configuration
       matching your desired. As mentioned above, if the obtained parameter is
       NULL  then  SDL	with  convert  from your desired audio settings to the
       hardware settings as it plays.

       If obtained is NULL then the  desired  SDL_AudioSpec  is  your  working
       specification, otherwise the obtained SDL_AudioSpec becomes the working
       specification and the desirec specification can be deleted. The data in
       the working specification is used when building SDL_AudioCVT's for con-
       verting loaded data to the hardware format.

       SDL_OpenAudio calculates the size  and  silence	fields	for  both  the
       desired	and  obtained  specifications. The size field stores the total
       size of the audio buffer in bytes, while the silence stores  the  value
       used to represent silence in the audio buffer

       The  audio  device  starts  out	playing  silence when it's opened, and
       should be enabled for playing by calling SDL_PauseAudio(0) when you are
       ready  for  your  audio callback function to be called. Since the audio
       driver may modify the requested size of the audio  buffer,  you	should
       allocate any local mixing buffers after you open the audio device.

EXAMPLES
       /* Prototype of our callback function */
       void my_audio_callback(void *userdata, Uint8 *stream, int len);

       /* Open the audio device */
       SDL_AudioSpec *desired, *obtained;
       SDL_AudioSpec *hardware_spec;

       /* Allocate a desired SDL_AudioSpec */
       desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

       /* Allocate space for the obtained SDL_AudioSpec */
       obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec));

       /* 22050Hz - FM Radio quality */
       desired->freq=22050;

       /* 16-bit signed audio */
       desired->format=AUDIO_S16LSB;

       /* Mono */
       desired->channels=0;

       /* Large audio buffer reduces risk of dropouts but increases response time */
       desired->samples=8192;

       /* Our callback function */
       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);
       }
       /* desired spec is no longer needed */
       free(desired);
       hardware_spec=obtained;
       .
       .
       /* Prepare callback for playing */
       .
       .
       .
       /* Start playing */
       SDL_PauseAudio(0);

SEE ALSO
       SDL_AudioSpec, SDL_LockAudio, SDL_UnlockAudio, SDL_PauseAudio

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