| | Open Sound System |
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Copyright (C) 4Front Technologies, 2002-2004. Released under GPLv2/CDDL.
This program opens three audio devices (hard coded in the program) and creates a syncronization group using SNDCTL_DSP_SYNCGROUP.
Next it starts all the devices joined in the group simultaneously by calling SNDCTL_DSP_SYNCSTART. Finally it will keep copying audio input from the 3rd device to the other two ones.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <soundcard.h>
#define MAX_DEV 10
int
main (int argc, char *argv[])
{
int i, id, fd[MAX_DEV], ndevs = 0;
char buf[32768] = { 0 };
oss_syncgroup group;
group.id = 0;
group.mode = PCM_ENABLE_OUTPUT;
Open the devices listed on command line
if (argc < 2)
exit (-1);
for (i = 1; i < argc; i++)
{
if ((fd[ndevs] = open (argv[i], O_WRONLY, 0)) == -1)
{
perror (argv[i]);
exit (-1);
}
if (ioctl (fd[ndevs], SNDCTL_DSP_SYNCGROUP, &group) == -1)
{
perror ("SNDCTL_DSP_SYNCGROUP");
exit (-1);
}
Note! It is very important to write some data to all output devices between calling SNDCTL_DSP_SYNCGROUP and SNDCTL_DSP_SYNCSTART. Otherwise playback will not start properly. However do not write more data than there is room in device's DMA buffer. Recommended amount of prteload data is one full fragment.
In applications that record audio, process it and then play back it's necessary to write two fragments of silence to the output device(s) before starting the group. Otherwise output device(s) will run out of data before the first read from the input device returns.
if (write (fd[ndevs], buf, sizeof (buf)) != sizeof (buf))
{
perror ("write");
exit (-1);
}
ndevs++;
}
printf ("Sync group %x created with %d devices\n", group.id, ndevs);
id = group.id;
if (ioctl (fd[0], SNDCTL_DSP_SYNCSTART, &id) == -1)
{
perror ("SNDCTL_DSP_SYNCSTART");
exit (-1);
}
while (1)
{
for (i = 0; i < ndevs; i++)
if (write (fd[i], buf, sizeof (buf)) != sizeof (buf))
{
perror ("write2");
exit (-1);
}
}
exit (0);
}