SDL_AudioPostmixCallback - A callback that fires when data is about to be fed to an audio device.

       This datatype is available since SDL 3.2.0.

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

       This callback should run as quickly as possible and not block for any significant time, as this  callback
       delays submission of data to the audio device, which can cause audio playback problems.

       The  postmix  callback _must_ be able to handle any audio data format specified in spec, which can change
       between callbacks if the audio device changed. However, this only covers  frequency  and  channel  count;
       data is always provided here in SDL_AUDIO_F32 format.

       The postmix callback runs _after_ logical device gain and audiostream gain have been applied, which is to
       say you can make the output data louder at this point than the gain settings would suggest.

userdata
              a pointer provided by the app through SDL_SetAudioPostmixCallback, for its own use.

       spec   the current format of audio that is to be submitted to the audio device.

       buffer the buffer of audio samples to be submitted. The callback can inspect and/or modify this data.

       buflen the size of buffer in bytes.

       SDL_AudioPostmixCallback - A callback that fires when data is about to be fed to an audio device.

SDL_SetAudioPostmixCallback(3)

Simple Directmedia Layer                           SDL 3.2.20                    SDL_AudioPostmixCallback(3type)

#include<SDL3/SDL_audio.h>typedefvoid(SDLCALL*SDL_AudioPostmixCallback)(void*userdata,constSDL_AudioSpec*spec,float*buffer,intbuflen);

       This will run from a background thread owned by SDL. The application is responsible for locking resources
       the callback touches that need to be protected.