[alsa-devel] Simple Mixer help

[Takashi Iwai]

At Thu, 30 Apr 2015 10:29:14 +0200,
Bram Bos wrote:
> 
> Ok, so perhaps this is not the forum to ask support for using ALSA in
> application development.

It's no wrong place, but not everybody has enough time, so be patient
:)

> Can anyone point me to a place where I can ask such questions.?
> 
> The existing ALSA documentation is not sufficient to help me out here.

The device name concept isn't written so much, although it's a quite
basic idea.  Maybe someone should work on it.

As you have already noticed, ALSA device may contain the card number.
For the control / mixer API, you can get the direct access to a
certain hardware with "hw:X" name string where X is the card number.


Takashi

> 
> Thanks!
> 
> 2015-04-29 16:15 GMT+02:00 Bram Bos <buramu at gmail.com>:
> 
> > I want to get access to the ALSA Simple Mixer interface, but rather than
> > the 'default' sound device I want to target a specific USB sound device.
> >
> > I'm at a loss how to refer to it...  I am using a modified version of the
> > code below but I have no idea what to replace the "card" and "selem_name"
> > strings with. The device name? The 'hwX.Y' string?
> >
> > And do I need to change the index#?
> >
> > Too many variables to solve this by trial and error.
> > Any hints appreciated!
> >
> > 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);}
> >
> >
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