我正试图在Linux中检索(可能稍后设置)主音量.我正在使用PulseAudio,但理想情况下它也适用于ALSA.
我找到了关于如何设置音量的this非常有用的帖子,从中我能够推断出snd_mixer_selem_get_playback_volume()的存在以检索当前设置.然而,在我的系统上,这似乎给了我错误的读数 – 混音器程序显示100％,最高约66％.
如果我打开pavucontrol,我可以看到这个输出设备的音量与我从这里得到的读数相匹配,所以我假设它给了我硬件音量设置,而不是我想要的全局主音量.
解决方法:
使用gcc audio_volume.c -o audio_volume -lasound或使用gcc audio_volume.c -o audio_volume_oss -DOSSCONTROL编译以下代码. OSS版本写得很粗糙,并没有给出精确的结果.在我的系统中将音量设置为100可设置97％的音量. ALSA版本适用于我和openSUSE中的PulseAudio.需要一些清理和爱,但我希望它是你需要的,我允许在WTFPL license上使用它.
#include
#include
#ifdef OSSCONTROL
#define MIXER_DEV "/dev/dsp"
#include
#include
#include
#else
#include
#endif
typedef enum {
AUDIO_VOLUME_SET,
AUDIO_VOLUME_GET,
} audio_volume_action;
/*
Drawbacks. Sets volume on both channels but gets volume on one. Can be easily adapted.
*/
int audio_volume(audio_volume_action action, long* outvol)
{
#ifdef OSSCONTROL
int ret = 0;
int fd, devs;
if ((fd = open(MIXER_DEV, O_WRONLY)) > 0)
{
if(action == AUDIO_VOLUME_SET) {
if(*outvol < 0 || *outvol > 100)
return -2;
*outvol = (*outvol << 8) | *outvol;
ioctl(fd, SOUND_MIXER_WRITE_VOLUME, outvol);
}
else if(action == AUDIO_VOLUME_GET) {
ioctl(fd, SOUND_MIXER_READ_VOLUME, outvol);
*outvol = *outvol & 0xff;
}
close(fd);
return 0;
}
return -1;;
#else
snd_mixer_t* handle;
snd_mixer_elem_t* elem;
snd_mixer_selem_id_t* sid;
static const char* mix_name = "Master";
static const char* card = "default";
static int mix_index = 0;
long pmin, pmax;
long get_vol, set_vol;
float f_multi;
snd_mixer_selem_id_alloca(&sid);
//sets simple-mixer index and name
snd_mixer_selem_id_set_index(sid, mix_index);
snd_mixer_selem_id_set_name(sid, mix_name);
if ((snd_mixer_open(&handle, 0)) < 0)
return -1;
if ((snd_mixer_attach(handle, card)) < 0) {
snd_mixer_close(handle);
return -2;
}
if ((snd_mixer_selem_register(handle, NULL, NULL)) < 0) {
snd_mixer_close(handle);
return -3;
}
ret = snd_mixer_load(handle);
if (ret < 0) {
snd_mixer_close(handle);
return -4;
}
elem = snd_mixer_find_selem(handle, sid);
if (!elem) {
snd_mixer_close(handle);
return -5;
}
long minv, maxv;
snd_mixer_selem_get_playback_volume_range (elem, &minv, &maxv);
fprintf(stderr, "Volume range \n", minv, maxv);
if(action == AUDIO_VOLUME_GET) {
if(snd_mixer_selem_get_playback_volume(elem, 0, outvol) < 0) {
snd_mixer_close(handle);
return -6;
}
fprintf(stderr, "Get volume %i with status %i\n", *outvol, ret);
/* make the value bound to 100 */
*outvol -= minv;
maxv -= minv;
minv = 0;
*outvol = 100 * (*outvol) / maxv; // make the value bound from 0 to 100
}
else if(action == AUDIO_VOLUME_SET) {
if(*outvol < 0 || *outvol > VOLUME_BOUND) // out of bounds
return -7;
*outvol = (*outvol * (maxv - minv) / (100-1)) + minv;
if(snd_mixer_selem_set_playback_volume(elem, 0, *outvol) < 0) {
snd_mixer_close(handle);
return -8;
}
if(snd_mixer_selem_set_playback_volume(elem, 1, *outvol) < 0) {
snd_mixer_close(handle);
return -9;
}
fprintf(stderr, "Set volume %i with status %i\n", *outvol, ret);
}
snd_mixer_close(handle);
return 0;
#endif
}
int main(void)
{
long vol = -1;
printf("Ret %i\n", audio_volume(AUDIO_VOLUME_GET, &vol));
printf("Master volume is %i\n", vol);
vol = 100;
printf("Ret %i\n", audio_volume(AUDIO_VOLUME_SET, &vol));
return 0;
}
标签：c-3,linux,audio,alsa,api
来源： https://codeday.me/bug/20190521/1147473.html
