What is volumemixer?

VolumeMixer is a small shell script for Linux that gives you a way to control volume for individual applications, not just the whole system at once. It comes with its own on screen volume bar that shows up as a pop up, and that bar keeps working even when another application is running in fullscreen. You run it from the command line with one of four commands: next, up, down, or mute. The next command lets you cycle through your currently running applications, so you can pick which one's volume you want to adjust, and once you have landed on either an application or the overall system volume, the up, down, and mute commands change that selection's level. The README describes this as being usable with keyboard macros or a physical rotary knob, so you could bind these commands to hardware controls or hotkeys rather than typing them each time. Under the hood it relies on pactl, the command line tool for PipeWire's PulseAudio compatibility layer or for PulseAudio itself, along with a JSON processing tool called jq to read and track which application is currently selected. An optional dependency, libnotify, lets it show desktop notification popups if you want them, in addition to or instead of its own on screen bar. Because VolumeMixer shows its own volume interface, the README recommends turning off your desktop's built in volume notifications, since the two would otherwise show up at the same time and conflict with each other. The README itself is quite short and does not go into detail about installation steps, configuration options, or how to bind the commands to a rotary knob in practice, so some of that setup work is left for the user to figure out.