I am so very useless when it comes to this type of thing.
Anyway I just wanted to say that there's a fork of Gimp that's made exclusively for developing films. It used to be called "FilmGimp" but I believe it's recently had its name changed. I'm sure you'll be able to call it up on google with filmgimp as a query.
Also, my spider senses tell me you'll need Video4Linux, but I'm not sure why.
Told ya I was inept
EDIT: Ah yeah...that's the stuff... http://cinepaint.sourceforge.net/
Was previously FilmGimp...AFAIK it uses ugly gtk1.2, but apparently it's quite functional.