Mixer音量調節

Mixer音量調節

const char *sound_device_names[] = SOUND_DEVICE_NAMES;
int fd;
int devmask, stereodevs;
char *name;

void usage()
{
int i;
fprintf(stderr, "usage: %s \n"
" %s \n\n"
"Where is one of:\n", name, name);

for (i = 0 ; i < SOUND_MIXER_NRDEVICES ; i++)
if ((1 << i) & devmask)
fprintf(stderr, "%s ", sound_device_names[i]);
fprintf(stderr, "\n");
exit(1);
}

int main(int argc, char *argv[])
{
int left, right, level;
int status;
int device;
char *dev;
int i;

name = argv[0];
fd = open("/dev/mixer", O_RDONLY);
if (fd == -1) {
perror("unable to open /dev/mixer");
exit(1);
}

status = ioctl(fd, SOUND_MIXER_READ_DEVMASK, &devmask);
if (status == -1)
perror("SOUND_MIXER_READ_DEVMASK ioctl failed");
status = ioctl(fd, SOUND_MIXER_READ_STEREODEVS, &stereodevs);
if (status == -1)
perror("SOUND_MIXER_READ_STEREODEVS ioctl failed");

if (argc != 3 && argc != 4)
usage();
dev = argv[1];

for (i = 0 ; i < SOUND_MIXER_NRDEVICES ; i++)
if (((1 << i) & devmask) && !strcmp(dev, sound_device_names[i]))
break;

if (i == SOUND_MIXER_NRDEVICES) {
fprintf(stderr, "%s is not a valid mixer device\n", dev);
usage();
}

device = i;
if (argc == 4) {
left = atoi(argv[2]);
right = atoi(argv[3]);
} else {
left = atoi(argv[2]);

right = atoi(argv[2]);
}

if ((left != right) && !((1 << i) & stereodevs)) {
fprintf(stderr, "warning: %s is not a stereo device\n", dev);
}

level = (right << 8) + left;
status = ioctl(fd, MIXER_WRITE(device), &level);
if (status == -1) {
perror("MIXER_WRITE ioctl failed");
exit(1);
}
left = level & 0xff;
right = (level & 0xff00) >> 8;
fprintf(stderr, "%s gain set to %d%% / %d%%\n", dev, left, right);
close(fd);
return 0;
}