SDL_mixer is an add‑on library for SDL2 that simplifies loading and playing sound effects and music in multiple formats (WAV, OGG, MP3, FLAC, MOD, etc.). It wraps lower‑level SDL_Audio APIs with a higher‑level mixer, channels, and music interface.

Link with -lSDL2_mixer and include <SDL_mixer.h>.

macOS (Homebrew)

brew install sdl2_mixer

Ubuntu / Debian

sudo apt-get install libsdl2-mixer-dev

Ensure matching SDL2 and SDL_mixer versions.

SDL_Init(SDL_INIT_AUDIO);

int flags   = MIX_INIT_MP3 | MIX_INIT_OGG | MIX_INIT_FLAC;
int initted = Mix_Init(flags);

if ((initted & flags) != flags) {
    fprintf(stderr, "Mix_Init: failed to load some codecs → %s\n", Mix_GetError());
}

int freq     = 48000;           /* Output sample rate         */
Uint16 format = MIX_DEFAULT_FORMAT; /* AUDIO_S16LSB               */
int channels = 2;               /* Stereo                     */
int chunks   = 1024;            /* Internal chunk size        */

if (Mix_OpenAudio(freq, format, channels, chunks) < 0) {
    fprintf(stderr, "Mix_OpenAudio: %s\n", Mix_GetError());
}

Parameters

• Mix_Init
  • flags – bitmask of codecs to enable (MIX_INIT_*).
  • Return – bitmask of codecs actually initialized (check with &).
• Mix_OpenAudio
  • freq – desired output sample rate (Hz).
  • format – AUDIO_S16SYS, AUDIO_F32SYS, etc. Use MIX_DEFAULT_FORMAT (signed 16‑bit).
  • channels – 1 = mono, 2 = stereo.
  • chunksize – mixer buffer size in samples. Power of two recommended; affects latency.

Chunk (short sound)

Mix_Chunk* pew = Mix_LoadWAV("laser.wav");

Music (streamed)

Mix_Music* bgm = Mix_LoadMUS("theme.ogg");

Parameters

• Mix_LoadWAV/Mix_LoadMUS
  • file – path to audio file (WAV recommended for FX; OGG/MP3 for music).
  • Return – pointer to loaded Mix_Chunk / Mix_Music or NULL on error.

Sound Effect

int channel = Mix_PlayChannel(-1, pew, 0);

Music

Mix_PlayMusic(bgm, -1);  /* loop indefinitely */

Parameters

• Mix_PlayChannel
  • channel – -1 = first free channel or index 0‑7 etc.
  • chunk – pointer to Mix_Chunk.
  • loops – 0 = play once; n = loop n extra times; -1 = forever.
• Mix_PlayMusic
  • music – pointer to Mix_Music.
  • loops – -1 infinite; 0 once; n loops n extra.

Mix_Volume(channel, 64);       /* 0‑128 for this channel */
Mix_VolumeChunk(pew, 90);    /* affects all future plays */
Mix_VolumeMusic(32);         /* music volume             */

Mix_Pause(channel);
Mix_Resume(channel);
Mix_HaltChannel(channel);

Mix_PauseMusic();
Mix_ResumeMusic();
Mix_FadeOutMusic(2000);  /* ms fade‑out */

Important Parameters

• Volume range: 0 silent → 128 max.
• Mix_FadeOutMusic – milliseconds to fade.

if (Mix_Playing(channel)) {
    /* still playing */
}

if (!Mix_PlayingMusic()) {
    /* music finished */
}

Use Mix_Paused/Mix_PausedMusic similarly.

Mix_FreeChunk(pew);
Mix_FreeMusic(bgm);

Mix_CloseAudio();
Mix_Quit();

Call after all audio usage to release resources.

fprintf(stderr, "SDL_mixer error: %s\n", Mix_GetError());

Always check return values & print Mix_GetError() on failure.