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(This is the documentation for SDL3, which is under heavy development and the API is changing! SDL2 is the current stable version!)


Mix audio data in a specified format.

Header File

Defined in <SDL3/SDL_audio.h>


int SDL_MixAudioFormat(Uint8 * dst,
                       const Uint8 * src,
                       SDL_AudioFormat format,
                       Uint32 len, int volume);

Function Parameters

dst the destination for the mixed audio
src the source audio buffer to be mixed
format the SDL_AudioFormat structure representing the desired audio format
len the length of the audio buffer in bytes
volume ranges from 0 - 128, and should be set to SDL_MIX_MAXVOLUME for full audio volume

Return Value

Returns 0 on success or a negative error code on failure; call SDL_GetError() for more information.


This takes an audio buffer src of len bytes of format data and mixes it into dst, performing addition, volume adjustment, and overflow clipping. The buffer pointed to by dst must also be len bytes of format data.

This is provided for convenience -- you can mix your own audio data.

Do not use this function for mixing together more than two streams of sample data. The output from repeated application of this function may be distorted by clipping, because there is no accumulator with greater range than the input (not to mention this being an inefficient way of doing it).

It is a common misconception that this function is required to write audio data to an output stream in an audio callback. While you can do that, SDL_MixAudioFormat() is really only needed when you're mixing a single audio stream with a volume adjustment.

Thread Safety

It is safe to call this function from any thread.


This function is available since SDL 3.0.0.

Code Examples

void MyAudioCallback(void *udata, Uint8 *stream, int len)
    extern SDL_AudioFormat deviceFormat;
    extern const Uint8 *mixData;
    SDL_memset(stream, 0, len);  // make sure this is silence.
    // mix our audio against the silence, at 50% volume.
    SDL_MixAudioFormat(stream, mixData, deviceFormat, len, SDL_MIX_MAXVOLUME / 2);

CategoryAPI, CategoryAPIFunction, CategoryAudio

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