alsa-volume-monitor is a simple program written in C that listens to ALSA events and emits a DBus signal when something has been changed (e.g. volume).

It was created for use with Awesome WM in volume indicator widgets.

./alsa-volume-monitor hw:0, where hw:0 is the name of your audio card.

dbus.request_name("session", "com.ch1p.avm")
dbus.add_match("session", "interface='com.ch1p.avm',member='valueChanged'")
dbus.connect_signal("com.ch1p.avm", function(...)
        -- Update your widget here
    end
)

To build the app on Ubuntu, you need to install libasound2-dev and libdbus-1-dev.

This require libalsa and dbus

cd /tmp
wget https://raw.githubusercontent.com/ndgnuh/alsa-volume-monitor/master/PKGBUILD
makepkg -si

GPLv2