NAME

       SDL_SetAudioPostmixCallback - Set a callback that fires when data is about to be fed to an audio device.

HEADER FILE

       Defined in SDL3/SDL_audio.h

SYNOPSIS

       #include "SDL3/SDL.h"

       bool SDL_SetAudioPostmixCallback(SDL_AudioDeviceID devid, SDL_AudioPostmixCallback callback, void *userdata);

DESCRIPTION

       This  is  useful for accessing the final mix, perhaps for writing a visualizer or applying a final effect
       to the audio data before playback.

       The buffer is the final mix of all bound audio streams on an  opened  device;  this  callback  will  fire
       regularly for any device that is both opened and unpaused. If there is no new data to mix, either because
       no  streams  are bound to the device or all the streams are empty, this callback will still fire with the
       entire buffer set to silence.

       This callback is allowed to make changes to the data; the contents of the buffer after this call is  what
       is ultimately passed along to the hardware.

       The  callback  is always provided the data in float format (values from -1.0f to 1.0f), but the number of
       channels or sample rate may be different than the format the app requested when opening the  device;  SDL
       might  have  had  to  manage  a  conversion  behind  the scenes, or the playback might have jumped to new
       physical hardware  when  a  system  default  changed,  etc.  These  details  may  change  between  calls.
       Accordingly, the size of the buffer might change between calls as well.

       This  callback  can  run  at any time, and from any thread; if you need to serialize access to your app's
       data, you should provide and use a mutex or other synchronization device.

       All of this to say: there are specific needs this callback can  fulfill,  but  it  is  not  the  simplest
       interface. Apps should generally provide audio in their preferred format through an SDL_AudioStream
        and let SDL handle the difference.

       This  function  is extremely time-sensitive; the callback should do the least amount of work possible and
       return as quickly as it can. The longer the callback runs, the higher the risk of audio dropouts or other
       problems.

       This function will block until the audio device is in between iterations, so any existing  callback  that
       might be running will finish before this function sets the new callback and returns.

       Setting a NULL callback function disables any previously-set callback.

FUNCTION PARAMETERS

       devid  the ID of an opened audio device.

       callback
              a callback function to be called. Can be NULL.

       userdata
              app-controlled pointer passed to callback. Can be NULL.

RETURN VALUE

       Returns true on success or false on failure; call

       SDL_GetError () for more information.

THREAD SAFETY

       It is safe to call this function from any thread.

AVAILABILITY

       This function is available since SDL 3.2.0.

Simple Directmedia Layer                            SDL 3.2.8                     SDL_SetAudioPostmixCallback(3)