Set ALSA master volume from C code

问题

I\'ve been looking for a simple C code example to set the master volume of the ALSA mixer but could not find anything simple for this supposedly common operation.

I\'m totally unfamiliar with ALSA, so making my own minimal example will take time. I would be happy if anyone could provide one.

回答1:

The following works for me. The parameter volume is to be given in the range [0, 100]. Beware, there is no error handling!

void SetAlsaMasterVolume(long volume)
{
    long min, max;
    snd_mixer_t *handle;
    snd_mixer_selem_id_t *sid;
    const char *card = "default";
    const char *selem_name = "Master";

    snd_mixer_open(&handle, 0);
    snd_mixer_attach(handle, card);
    snd_mixer_selem_register(handle, NULL, NULL);
    snd_mixer_load(handle);

    snd_mixer_selem_id_alloca(&sid);
    snd_mixer_selem_id_set_index(sid, 0);
    snd_mixer_selem_id_set_name(sid, selem_name);
    snd_mixer_elem_t* elem = snd_mixer_find_selem(handle, sid);

    snd_mixer_selem_get_playback_volume_range(elem, &min, &max);
    snd_mixer_selem_set_playback_volume_all(elem, volume * max / 100);

    snd_mixer_close(handle);
}

来源：https://stackoverflow.com/questions/6787318/set-alsa-master-volume-from-c-code