In Gimp, open an animated .gif (this just for purposes of illustration). Open up the file dialogue and mouse down to "video". It seems that Gimp will (relatively) cheerfully take a series of jpegs and export them as an mpeg movie (given the mpeg2encode libraries)
Well now it could be that I've an mpeg2encode library around that interfaces to Squeak, but somehow the murky laws about licensing etc kinda made me not publish it. Now if someone want to clarify that, one could do a mpeg encoder in Squeak too.