SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK - Man Page

#include <SDL3/SDL_audio.h>

#define SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK ((SDL_AudioDeviceID) 0xFFFFFFFFu)

Several functions that require an SDL_AudioDeviceID will accept this value to signify the app just wants the system to choose a default device instead of the app providing a specific one.

This macro is available since SDL 3.2.0.