GTK-Mixer is GTK based volume control tool ("mixer").

GUI from xfce4-mixer: https://gitlab.xfce.org/apps/xfce4-mixer but
xfce4 and gstreamer does not used.

Features
- plugins for support different sound backens
- change system default sound card
- set volume per line/channel
- enable/disable lines (mute/unmute)
- detect sound cards connect/disconnect
- detect default sound card change