(This is the documentation for SDL3, which is the current stable version. SDL2 was the previous version!)

SDL_AudioStreamCallback

A callback that fires when data passes through an SDL_AudioStream.

Header File

Syntax

typedef void (SDLCALL *SDL_AudioStreamCallback)(void *userdata, SDL_AudioStream *stream, int additional_amount, int total_amount);

Function Parameters

stream	the SDL audio stream associated with this callback.
additional_amount	the amount of data, in bytes, that is needed right now.
total_amount	the total amount of data requested, in bytes, that is requested or available.
userdata	an opaque pointer provided by the app for their personal use.

Remarks

Apps can (optionally) register a callback with an audio stream that is called when data is added with SDL_PutAudioStreamData, or requested with SDL_GetAudioStreamData.

Two values are offered here: one is the amount of additional data needed to satisfy the immediate request (which might be zero if the stream already has enough data queued) and the other is the total amount being requested. In a Get call triggering a Put callback, these values can be different. In a Put call triggering a Get callback, these values are always the same.

Byte counts might be slightly overestimated due to buffering or resampling, and may change from call to call.

This callback is not required to do anything. Generally this is useful for adding/reading data on demand, and the app will often put/get data as appropriate, but the system goes on with the data currently available to it if this callback does nothing.

Thread Safety

This callbacks may run from any thread, so if you need to protect shared data, you should use SDL_LockAudioStream to serialize access; this lock will be held before your callback is called, so your callback does not need to manage the lock explicitly.

Version

This datatype is available since SDL 3.1.3.