Video-Audio Software Suggestion

I would like to find software that would allow the following scenario:

Using a USB microphone, I would like video myself playing trombone (using a MacBook Pro built in video camera) while Garage band or iTunes plays a system audio track. Then I would load the whole movie into Garage Band so that I could add reverb (unless that is part of what the software can do). The end result I am looking for is:

A demo video where I am playing trombone along with a pre-recorded Aebersold track. The sound quality of the Aebersold track is system audio level quality, and the audio for the video is enhanced with reverb.

Your help will be greatly appreciated. Thanks!

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I don't see why you couldn't use Garageband to play the audio/record your playing.. while imovie shoots the video..

just drag the movie into garageband when your done.. mix it up and export...

Brilliant! It works And, of course that was obvious and easy. Many thanks Sir Derekeverett.