Reading audio levels from the PC audio output

[Davide Perini]

Hi all,
I know that with d3d11desktopdupsrc, ximagesrc or avfvideosrc I can 
screen capture my PC using Windows, Linux or Mac.

Is there something similar to "audio capture" the audio?

I would like to get the "Audio Level" of the current audio output for 
example speakers or headphones.

The idea is to get the audio level from everything that is producing a 
sound on the PC,
example: spotify, youtube, a videogame, a generic media player, ecc. ecc...

I don't want to capture the audio of a specific software or of a 
specific audio/video file,
I want to capture the audio from the system audio output.

It is possible for the video since I can screen capture it, is this 
possible for audio?

Thanks you
Davide