Recording piano notes on a Mac?

[VenalWinfrey]

Bit of a weird one this, but, here goes! I have a youtube channel, and I upload videos of myself playing piano. What I want to do is be able to superimpose a frame on top of the videos, showing the notes that I am playing on the keyboard as I go.

I know this can be done because I have seen others do it! But I use an iMac, and I don't have Final Cut, just iMovie. Does anyone know if this can be done through iMovie? I also have Garageband of course, but I can't work out a way to do it.

If anyone knows of a free movie editor software I could obtain, or of course a way I could do it through my existing tools, I'd REALLY appreciate that. It's for people that ask me for the scores to my recordings, and I just play by ear, so this would be a good way for others to see what I'm actually playing.

Thanks as usual for any help on this!

p.s. my iMovie version is '08.