在 Linux 中用 C 语言获取主音量

Get master sound volume in C in Linux

提问by Rena

I'm trying to retrieve (and probably later set) the master sound volume in Linux. I'm using PulseAudio, but ideally it should work for ALSA too.

我正在尝试在 Linux 中检索（并且可能稍后设置）主音量。我正在使用 PulseAudio，但理想情况下它也适用于 ALSA。

I found thisvery helpful post on how to set the volume, and from that I was able to deduce the existence of snd_mixer_selem_get_playback_volume() to retrieve the current setting. However on my system, this seems to be giving me wrong readings - where mixer programs show 100%, this tops out at about 66%.

我发现这篇关于如何设置音量的帖子非常有用，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%，最高约为 66%。

If I open pavucontrol I can see the volume for this output device matches the readings I get from here, so I assume it's giving me the hardware volume setting, not the global master volume that I wanted.

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。

回答by RushPL

Compile the below code with gcc audio_volume.c -o audio_volume -lasoundor altenatively with gcc audio_volume.c -o audio_volume_oss -DOSSCONTROL. OSS version is written very crudely and does not give precise results. Setting volume to 100 sets 97% volume in my system. ALSA version works for me and PulseAudio in openSUSE. Needs some cleanup and love but I hope it is what you need, I grant the permission to use it on the WTFPL license.

使用gcc audio_volume.c -o audio_volume -lasound或替代地编译以下代码gcc audio_volume.c -o audio_volume_oss -DOSSCONTROL。OSS 版本写的很粗糙，没有给出准确的结果。在我的系统中将音量设置为 100 会设置 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，我授予在WTFPL 许可证上使用它的许可。

#include <unistd.h>
#include <fcntl.h>

#ifdef OSSCONTROL
#define MIXER_DEV "/dev/dsp"

#include <sys/soundcard.h>
#include <sys/ioctl.h>
#include <stdio.h>
#else
#include <alsa/asoundlib.h>
#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 <%i,%i>\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;
}