SDL_mixer is a sound mixing library that is used with the SDL library. It allows a programmer to use multiple samples along with music; it simplifies the handling of loading and playing samples and music from different kinds of file formats. It supports the following formats.

File Format	Comments
WAVE/RIFF	( .wav )
AIFF	( .aiff )
VOC	( .voc )
MOD	(.mod .xm .s3m .669 .it .med and more) using including mikmod
MIDI	(.mid) using timidity or native midi hardware
OggVorbis	(.ogg) requiring ogg/vorbis libraries on system
MP3	(.mp3) requiring SMPEG library on system
also any command-line player, which is not mixed by SDL_mixer...

To use the mixer library, you have to include the header file "SDL_mixer.h" in your program:

• Open the audio device
• Load samples into memory
• Play them when necessary
• Clean up

AUDIO_U8	Unsigned 8-bit samples
AUDIO_S8	Signed 8-bit samples
AUDIO_U16LSB &nssp;	Unsigned 16-bit samples, in little-endian byte order
AUDIO_S16LSB	Signed 16-bit samples, in little-endian byte order
AUDIO_U16MSB	Unsigned 16-bit samples, in big-endian byte order
AUDIO_S16MSB	Signed 16-bit samples, in big-endian byte order
AUDIO_U16	same as AUDIO_U16LSB (for backwards compatibility probably)
AUDIO_S16	same as AUDIO_S16LSB (for backwards compatability probably)
AUDIO_U16SYS	Unsigned 16-bit samples, in system byte order
AUDIO_S16SYS	Signed 16-bit samples, in system byte order

The following are some of the more commonly used mixer functions.

The following piece of code, music.cpp presents the usage of SDL_mixer functions to load an ogg file and plays the music. The ogg format is open-source sound data compression standard which achieves better compression than the popular MP3. Detailed information about it can be found at http://www.vorbis.com/

The code is simple and straight forward. The playing parameters are hard-coded with the playback frequency set to 22050 Hz and audio sample size set to 16-bit. The function Mix_OpenAudio() initializes the SDL_mixer with the chosen audio settings and Mix_LoadMUS() loads and uncompresses the data from the music file "music.ogg" into memory. The music will be played repeatedly as the loops parameter in Mix_PlayMusic() is set to -1. When the key 'p' is pressed, the function Mix_Pause() is called to pause playing, and playing can be resumed by pressing the key 'r', which calls Mix_ResumeMusic() to resume playing the music.

/* music.cpp -- demo program for producing music and sound Compile: g++ -o music music.cpp -I/usr/include -L/usr/local/lib -lSDL -lSDL_mixer Execute: ./music ( need the file music.ogg to play ) See http://www.webkinesia.com/games/sdl-sdl1.php or http://www.libsdl.org/projects/docs/SDL_mixer/SDL_mixer.html for tutorials of using SDL_mixer */ #include "SDL/SDL.h" #include "SDL/SDL_image.h" #include "SDL/SDL_mixer.h" #include <string> #include <iostream> #include <stdlib.h> using namespace std; bool musicPlaying = true; void musicFinished() { //Music is done! musicPlaying = false; } int main () { SDL_Surface *screen; SDL_Event event; int status, key; bool quit = false; // Fire up SDL, init VIDEO as well as AUDIO if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO ) < 0) { printf("Error initializing SDL: %s\n", SDL_GetError()); return 1; } atexit(SDL_Quit); // Set a video mode. Force 16-bit hicolor. if ((screen = SDL_SetVideoMode(640, 480, 16, 0)) == NULL) { printf("Error setting a video, 16-bit video mode: %s\n", SDL_GetError()); return 1; } Mix_Music *music; //Pointer to our music, in memory int audio_rate = 22050; //Frequency of audio playback Uint16 audio_format = AUDIO_S16SYS; //Format of the audio we're playing int audio_channels = 2; //2 channels = stereo int audio_buffers = 4096; //Size of the audio buffers in memory //Initialize SDL_mixer with our chosen audio settings if(Mix_OpenAudio(audio_rate, audio_format, audio_channels, audio_buffers) != 0) { printf("Unable to initialize audio: %s\n", Mix_GetError()); return 1; } //Load our OGG file from disk music = Mix_LoadMUS("music.ogg"); if(music == NULL) { printf("Unable to load OGG file: %s\n", Mix_GetError()); return 1; } //Play that funky music! // -1 in argument means play music again and again, if 0, means play once if(Mix_PlayMusic(music, -1) == -1) { printf("Unable to play OGG file: %s\n", Mix_GetError()); return 1; } //Make sure that the musicFinished() function is called when the music stops playing Mix_HookMusicFinished(musicFinished); while ( !quit ) { status = SDL_WaitEvent(&event); //wait indefinitely for an event to occur //event will be removed from event queue if ( !status ) { //Error has occured while waiting printf("SDL_WaitEvent error: %s\n", SDL_GetError()); quit = true; break; } switch(event.type) { case SDL_QUIT: quit = true; break; case SDL_KEYDOWN: key = event.key.keysym.sym; if ( key == SDLK_p ) { //key 'p' pressed to pause music Mix_PauseMusic(); //pause music musicPlaying = false; } else if ( key == SDLK_r ) { //key 'r' pressed to resume music if ( !musicPlaying ) { Mix_ResumeMusic(); //resume playing music musicPlaying = true; } } else if ( key == SDLK_ESCAPE ) //quit if 'ESC' pressed quit = true; break; } //switch SDL_Delay ( 100 ); //give up some cpu time for others } //while ( !quit ) //quit may be set to true when 'ESC' is pressed //Release the memory allocated to our music Mix_FadeOutMusic( 1000 ); //fade out music in 1 sec Mix_HaltMusic(); //stop the music Mix_FreeMusic(music); //free up the allocated resources //Need to make sure that SDL_mixer and SDL have a chance to clean up Mix_CloseAudio(); return 1; }