Output volume control

I really hope this doesn't get too difficult.

Basically, I want the program to control the OUTPUT audio (that is, what we hear when we play a song, watch a video, or whatever we do) and output the current audio level depending on what is playing.

I've seen countless examples of how to do this with INPUTS (like microphones), but nothing worked with the outputs.

Specifically, I have Winamp connected to a local radio stream. So I listen to music. I want this program to punch through everything, say 10ms, and tell me the current sound level of the song. So if it's a rock song, it can be super loud during the chorus (i.e. louder output) against the verse. If it's a soft blues song or whatever, the output will obviously not be as loud.

I know how to do all the loops, but as I said, everything I've seen for everything else has to deal with managing either the main volume bar (which doesn't help me) or input.

Is it possible? I would guess it is because people write render plugins for media players all the time (and that pretty much matches what I want to do, only I want it to display it to me as #s instead of pretty colors).