Counting people

I'm currently doing an installation at a theatre trying to bring visualisation, sound and performance together in a foyer area. The general idea is that words drift across a corridor and slowly form a script at the other end, once the script is complete the actors perform the script. I would like to involve audience interactivity by using jitter to detect how busy the room is from a camera source.

I have had one idea that will use a camera placed across the corridor as people enter and then use cv.track, from the computer vision package, to track a person past the camera and then reset once the point hits the far end, increment a value and continue this process thus creating a variable that can be passed to a flash animation controlling the speed/amount of words that are being projected. In theory i think this should work though i've only really glanced at cv.track!

Does this sound reasonable or is there a better method to detect how busy a space is?

Cheers,
Josh