From context I would guess that judder is a global effect (e.g. when the film pauses and then suddenly jerks forward playing), and that jitter is more local (e.

From context I would guess that judder is a global effect (e.g. when the film pauses and then suddenly jerks forward playing), and that jitter is more local (e.g. to do with the movements of the actual characters on screen moving with sudden velocity)