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sdl_convertaudio(3) [redhat man page]

SDL_ConvertAudio(3)						 SDL API Reference					       SDL_ConvertAudio(3)

SDL_ConvertAudio- Convert audio data to a desired audio format. SYNOPSIS
#include "SDL.h" int SDL_ConvertAudio(SDL_AudioCVT *cvt); DESCRIPTION
SDL_ConvertAudio takes one parameter, cvt, which was previously initilized. Initilizing a SDL_AudioCVT is a two step process. First of all, the structure must be passed to SDL_BuildAudioCVT along with source and destination format parameters. Secondly, the cvt->buf and cvt->len fields must be setup. cvt->buf should point to the audio data and cvt->len should be set to the length of the audio data in bytes. Remem- ber, the length of the buffer pointed to by buf show be len*len_mult bytes in length. Once the SDL_AudioCVTstructure is initilized then we can pass it to SDL_ConvertAudio, which will convert the audio data pointer to by cvt->buf. If SDL_ConvertAudio returned 0 then the conversion was completed successfully, otherwise -1 is returned. If the conversion completed successfully then the converted audio data can be read from cvt->buf. The amount of valid, converted, audio data in the buffer is equal to cvt->len*cvt->len_ratio. EXAMPLES
/* Converting some WAV data to hardware format */ void my_audio_callback(void *userdata, Uint8 *stream, int len); SDL_AudioSpec *desired, *obtained; SDL_AudioSpec wav_spec; SDL_AudioCVT wav_cvt; Uint32 wav_len; Uint8 *wav_buf; int ret; /* Allocated audio specs */ desired=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); obtained=(SDL_AudioSpec *)malloc(sizeof(SDL_AudioSpec)); /* Set desired format */ desired->freq=22050; desired->format=AUDIO_S16LSB; desired->samples=8192; 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); } free(desired); /* Load the test.wav */ if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buf, &wav_len) == NULL ){ fprintf(stderr, "Could not open test.wav: %s ", SDL_GetError()); SDL_CloseAudio(); free(obtained); exit(-1); } /* Build AudioCVT */ ret = SDL_BuildAudioCVT(&wav_cvt, wav_spec.format, wav_spec.channels, wav_spec.freq, obtained->format, obtained->channels, obtained->freq); /* Check that the convert was built */ if(ret==-1){ fprintf(stderr, "Couldn't build converter! "); SDL_CloseAudio(); free(obtained); SDL_FreeWAV(wav_buf); } /* Setup for conversion */ wav_cvt.buf=(Uint8 *)malloc(wav_len*wav_cvt.len_mult); wav_cvt.len=wav_len; memcpy(wav_cvt.buf, wav_buf, wav_len); /* We can delete to original WAV data now */ SDL_FreeWAV(wav_buf); /* And now we're ready to convert */ SDL_ConvertAudio(&wav_cvt); /* do whatever */ . . . . SEE ALSO
Tue 11 Sep 2001, 22:58 SDL_ConvertAudio(3)

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SDL_OpenAudio(3)						 SDL API Reference						  SDL_OpenAudio(3)

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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