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