I've been working with something that may be somewhat related, basically there is a gstreamer plugin 'level' that should give you access to what you need, but obviously what you want is a nice UI on top of it.

http://www.gstreamer.net/data/doc/gs...ins-level.html

I'd been using it to make a simple input level monitor for a recording app, just a moving bar with a peak fall off, but it looks like the kind of data you'd be looking for.

You just need a pretty simple gst pipeline from input through level to null running that you can attach to for reading the values from.