With only the performance of a scripting language, Ruby isn't considered a particularly suitable choice for intense video work (direct transcoding, encoding, and the like.). Nonetheless, there are a handful of Ruby libraries and Ruby-based technologies you can use to work with video and movie files - primarily through interacting with faster tools or libraries.
RMov (Ruby Quicktime Library)
RMov is an awesome new Ruby library by Ryan Bates that wraps around Apple's QuickTime API and allows you to open, edit, and export QuickTime movies from within Ruby. It is, unfortunately, OS X only.