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 specifications.

       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 information and len is the length of the
       audio buffer in bytes.

       desired->userdata

       SDL_OpenAudio reads these fields from the desired  SDL_AudioSpec  structure  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 converting 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