view docs/man3/SDL_ConvertAudio.3 @ 2938:2929ed239d2a

Adjusted default choice of audio driver. If a driver can definitely see available devices, it is chosen. Otherwise, we'll take the first driver that initializes but saw no devices...this might be because it can't enumerate them, or there really aren't any available. This prevents the dsp driver from hogging control when there are no /dev/dsp* nodes (for example, on a Linux box with ALSA and no OSS emulation).
author Ryan C. Gordon <icculus@icculus.org>
date Thu, 01 Jan 2009 07:54:58 +0000
parents 546f7c1eb755
children 1238da4a7112
line wrap: on
line source

.TH "SDL_ConvertAudio" "3" "Tue 11 Sep 2001, 22:58" "SDL" "SDL API Reference" 
.SH "NAME"
SDL_ConvertAudio \- Convert audio data to a desired audio format\&.
.SH "SYNOPSIS"
.PP
\fB#include "SDL\&.h"
.sp
\fBint \fBSDL_ConvertAudio\fP\fR(\fBSDL_AudioCVT *cvt\fR);
.SH "DESCRIPTION"
.PP
\fBSDL_ConvertAudio\fP takes one parameter, \fBcvt\fR, which was previously initilized\&. Initilizing a \fI\fBSDL_AudioCVT\fR\fR is a two step process\&. First of all, the structure must be passed to \fI\fBSDL_BuildAudioCVT\fP\fR along with source and destination format parameters\&. Secondly, the \fBcvt\fR->\fBbuf\fR and \fBcvt\fR->\fBlen\fR fields must be setup\&. \fBcvt\fR->\fBbuf\fR should point to the audio data and \fBcvt\fR->\fBlen\fR should be set to the length of the audio data in bytes\&. Remember, the length of the buffer pointed to by \fBbuf\fR show be \fBlen\fR*\fBlen_mult\fR bytes in length\&.
.PP
Once the \fBSDL_AudioCVT\fRstructure is initilized then we can pass it to \fBSDL_ConvertAudio\fP, which will convert the audio data pointer to by \fBcvt\fR->\fBbuf\fR\&. If \fBSDL_ConvertAudio\fP returned \fB0\fR then the conversion was completed successfully, otherwise \fB-1\fR is returned\&.
.PP
If the conversion completed successfully then the converted audio data can be read from \fBcvt\fR->\fBbuf\fR\&. The amount of valid, converted, audio data in the buffer is equal to \fBcvt\fR->\fBlen\fR*\fBcvt\fR->\fBlen_ratio\fR\&.
.SH "EXAMPLES"
.PP
.nf
\f(CW/* 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 */
\&.
\&.
\&.
\&.

\fR
.fi
.PP
.SH "SEE ALSO"
.PP
\fI\fBSDL_BuildAudioCVT\fP\fR, \fI\fBSDL_AudioCVT\fP\fR
...\" created by instant / docbook-to-man, Tue 11 Sep 2001, 22:58