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sdl_mixaudio(3) [opensolaris man page]

SDL_MixAudio(3) 						 SDL API Reference						   SDL_MixAudio(3)

NAME
SDL_MixAudio - Mix audio data SYNOPSIS
#include "SDL.h" void SDL_MixAudio(Uint8 *dst, Uint8 *src, Uint32 len, int volume); DESCRIPTION
This function takes two audio buffers of len bytes each of the playing audio format and mixes them, performing addition, volume adjustment, and overflow clipping. The volume ranges from 0 to SDL_MIX_MAXVOLUME and should be set to the maximum value for full audio volume. Note this does not change hardware volume. This is provided for convenience -- you can mix your own audio data. Note: 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). Use mixing functions from SDL_mixer, OpenAL, or write your own mixer instead. SEE ALSO
SDL_OpenAudio SDL
Tue 11 Sep 2001, 22:58 SDL_MixAudio(3)

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SDL_OpenAudio(3)						 SDL API Reference						  SDL_OpenAudio(3)

NAME
SDL_OpenAudio - Opens the audio device with the desired parameters. SYNOPSIS
#include "SDL.h" int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained); DESCRIPTION
This function opens the audio device with the desired parameters, and returns 0 if successful, placing the actual hardware parameters in the structure pointed to by obtained. If obtained is NULL, the audio data passed to the callback function will be guaranteed to be in the requested format, and will be automatically converted to the hardware audio format if necessary. This function returns -1 if it failed to open the audio device, or couldn't set up the audio thread. To open the audio device a desired SDL_AudioSpec must be created. SDL_AudioSpec *desired; . . desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); You must then fill this structure with your desired audio specifications. desired->freq desired->format desired->samples desired->callback void callback(void *userdata, Uint8 *stream, int len); userdata is the pointer stored in userdata field of the SDL_AudioSpec. stream is a pointer to the audio buffer you want to fill with information and len is the length of the audio buffer in bytes. desired->userdata SDL_OpenAudio reads these fields from the desired SDL_AudioSpec structure pass to the function and attempts to find an audio configuration matching your desired. As mentioned above, if the obtained parameter is NULL then SDL with convert from your desired audio settings to the hardware settings as it plays. If obtained is NULL then the desired SDL_AudioSpec is your working specification, otherwise the obtained SDL_AudioSpec becomes the working specification and the desirec specification can be deleted. The data in the working specification is used when building SDL_AudioCVT's for converting loaded data to the hardware format. SDL_OpenAudio calculates the size and silence fields for both the desired and obtained specifications. The size field stores the total size of the audio buffer in bytes, while the silence stores the value used to represent silence in the audio buffer The audio device starts out playing silence when it's opened, and should be enabled for playing by calling SDL_PauseAudio(0) when you are ready for your audio callback function to be called. Since the audio driver may modify the requested size of the audio buffer, you should allocate any local mixing buffers after you open the audio device. EXAMPLES
/* Prototype of our callback function */ void my_audio_callback(void *userdata, Uint8 *stream, int len); /* Open the audio device */ SDL_AudioSpec *desired, *obtained; SDL_AudioSpec *hardware_spec; /* Allocate a desired SDL_AudioSpec */ desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); /* Allocate space for the obtained SDL_AudioSpec */ obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); /* 22050Hz - FM Radio quality */ desired->freq=22050; /* 16-bit signed audio */ desired->format=AUDIO_S16LSB; /* Mono */ desired->channels=0; /* Large audio buffer reduces risk of dropouts but increases response time */ desired->samples=8192; /* Our callback function */ desired->callback=my_audio_callback; desired->userdata=NULL; /* Open the audio device */ if ( SDL_OpenAudio(desired, obtained) < 0 ){ fprintf(stderr, "Couldn't open audio: %s ", SDL_GetError()); exit(-1); } /* desired spec is no longer needed */ free(desired); hardware_spec=obtained; . . /* Prepare callback for playing */ . . . /* Start playing */ SDL_PauseAudio(0); SEE ALSO
SDL_AudioSpec, SDL_LockAudio, SDL_UnlockAudio, SDL_PauseAudio SDL
Tue 11 Sep 2001, 22:58 SDL_OpenAudio(3)
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