Resizing/transcoding video

I have a Nikon Coolpix 8800 which, like many digital cameras, has a video clip mode. I would like to have Gallery transcode/resize the videos after upload so that, like pictures, the user can select more than one size. The original Quicktime video can be (ahem) rather large even for folks with broadband, but a transcoded version is quite viewable. And like my photos, it's kind of nice to have one place to store the "finished" product for potential reuse.

The question is, where would have I to start poking to do this? The "cheap" solution would be to have some job that watches the files on the backend which would get me the resized version immediately, but no access to the original (which I don't want to lose unless explicitly deleted).