In Pulseaudio Volume Control in the output devices tab you can see the volume of the currently playing audio. Is there any way I can output this to use in my own applications?
Every sink in pulseaudio has a corresponding source that ends in
pacmd list-sinks | grep name: pacmd list-sources | grep name:
and compare the names. Pulseaudio Volume Control connects to all of these and uses them to display the volume of the currently playing audio. You can do the same from your own programs, or with any existing program using pulseaudio, and of course you get to monitor the actual data of what's currently playing, not just the volume. There are different ways to compute a numerical volume value from this data, you must choose one.