I have a friend who has been taking stop-motion pictures, applying a snapchat "art" filter to each picture, then composing them into video (with pretty awesome results). He is interested in mechanically applying filters like that to video. I assume this is relatively trivial in high end (meaning expensive) video or photo editing software. Is there an inexpensive way to do this, say using the Gimp or a similar free/cheap editing software?
Most motion graphics applications can import most video types and apply filters to them. I believe that Adobe After Effects is available for a subscription (so cheap if you use it only for a month), and Apple's Motion is available for $49 from the Mac App Store.
Or if that's too much, I believe that iMovie is only $15 and has a number of simple snapchat-like filters available.