Re: [Alsa-user] Mixer controls added by application

[Takashi S. <o-t...@sa...>]

Hi,

On Dec 12 2016 16:14, pet...@ya... wrote:
> I'd like to provide mixer controls such as 'Master Playback Volume' for a sound card
> where the driver does not natively support these controls.
> Is it possible to write an application to add mixer controls for a given sound card?
> I am thinking about using the alsa-lib or providing an alsa-plugin (not softvol).

You can achieve it by using some APIs in alsa-lib. Source of the library 
includes a sample program for this purpose. I wish it helps your work.
http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=test/user-ctl-element-set.c;h=75083d219fe6725870ad73ccf8aa758eb66e6d7d;hb=HEAD

For a design of ALSA control interface, code document will help you.
http://git.alsa-project.org/?p=alsa-lib.git;a=blob;f=src/control/control.c;h=134ba4c8ebea40dc088a4d94db7f8119703e4cc1;hb=HEAD#l31

I note that Linux kernel 4.0 or former includes some bugs for this feature.


Regards

Takashi Sakamoto