如何监听默认声卡上主通道音量的变化?我希望通过dbus或回调函数等方式得到通知,告知音量已经发生变化。
我尝试查找ALSA和PulseAudio的API,但它们似乎只允许您设置和获取音量,而不能监听音量的变化。
任何编程语言都可以。
如何监听默认声卡上主通道音量的变化?我希望通过dbus或回调函数等方式得到通知,告知音量已经发生变化。
我尝试查找ALSA和PulseAudio的API,但它们似乎只允许您设置和获取音量,而不能监听音量的变化。
任何编程语言都可以。
编辑:在第二个示例中,当音量低于5%或高于100%时,对我而言不会生成事件。据我所知,第一个示例完美运行。
pactl subscribe
将在音量更改时打印有关sinks的数据。现在我正在将输出导入到一个小型C程序中,该程序将运行一个脚本。
run.sh:
pactl subscribe | grep --line-buffered "sink" | ./prog
或者对于特定的接收器,例如3:
pactl subscribe | grep --line-buffered "sink #3" | ./prog
prog.c:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[]){
while(1){
while(getchar() != '\n');
system("./volume_notify.sh");
}
}
当水槽的音量改变时,pactl
会打印一行内容,这将导致程序运行脚本。#include <stdio.h>
#include <alsa/asoundlib.h>
#define MAX_CARDS 256
int monitor_native(char const *name);
int open_ctl(const char *name, snd_ctl_t **ctlp);
void close_all(snd_ctl_t* ctls[], int ncards);
int main(int argc, char* argv[]){
const char *ctl_name = "hw:0";
while(monitor_native(ctl_name) == 1){
//volume has been changed, do something
system("~/.volume_notify.sh");
}
return 0;
}
int monitor_native(char const *name) {
snd_ctl_t *ctls[MAX_CARDS];
int ncards = 0;
int i, err = 0;
if (!name) {
int card = -1;
while (snd_card_next(&card) >= 0 && card >= 0) {
char cardname[16];
if (ncards >= MAX_CARDS) {
fprintf(stderr, "alsactl: too many cards\n");
close_all(ctls, ncards);
return -E2BIG;
}
sprintf(cardname, "hw:%d", card);
err = open_ctl(cardname, &ctls[ncards]);
if (err < 0) {
close_all(ctls, ncards);
return err;
}
ncards++;
}
} else {
err = open_ctl(name, &ctls[0]);
if (err < 0) {
close_all(ctls, ncards);
return err;
}
ncards++;
}
for (;ncards > 0;) {
pollfd* fds = new pollfd[ncards];
for (i = 0; i < ncards; i++) {
snd_ctl_poll_descriptors(ctls[i], &fds[i], 1);
}
err = poll(fds, ncards, -1);
if (err <= 0) {
err = 0;
break;
}
for (i = 0; i < ncards; i++) {
unsigned short revents;
snd_ctl_poll_descriptors_revents(ctls[i], &fds[i], 1, &revents);
if (revents & POLLIN) {
snd_ctl_event_t *event;
snd_ctl_event_alloca(&event);
if (snd_ctl_read(ctls[i], event) < 0) {
continue;
}
if (snd_ctl_event_get_type(event) != SND_CTL_EVENT_ELEM) {
continue;
}
unsigned int mask = snd_ctl_event_elem_get_mask(event);
if (mask & SND_CTL_EVENT_MASK_VALUE) {
close_all(ctls, ncards);
return 1;
}
}
}
}
close_all(ctls, ncards);
return 0;
}
int open_ctl(const char *name, snd_ctl_t **ctlp) {
snd_ctl_t *ctl;
int err;
err = snd_ctl_open(&ctl, name, SND_CTL_READONLY);
if (err < 0) {
fprintf(stderr, "Cannot open ctl %s\n", name);
return err;
}
err = snd_ctl_subscribe_events(ctl, 1);
if (err < 0) {
fprintf(stderr, "Cannot open subscribe events to ctl %s\n", name);
snd_ctl_close(ctl);
return err;
}
*ctlp = ctl;
return 0;
}
void close_all(snd_ctl_t* ctls[], int ncards) {
for (ncards -= 1; ncards >= 0; --ncards) {
snd_ctl_close(ctls[ncards]);
}
}
snd_ctl_subscribe_events()
启用事件。
然后使用snd_ctl_read()
读取事件;要等待它们,请使用阻塞模式或poll()
。
如果事件类型为SND_CTL_EVENT_ELEM
,并且其事件位掩码包含SND_CTL_EVENT_MASK_VALUE
,则该元素的值已更改。amixer monitor
实现。pactl subscribe | grep --line-buffered "sink" | xargs -n1 ./volume_notify.sh
pactl subscribe | grep --line-buffered "sink" | while read -r UNUSED_LINE; do ./volume_notify.sh; done
- Ivan Mikhnovich