1. A method of processing video data comprising the steps of: encoding video data representing a series of images using motion compensated prediction on at least some of the images being encoded, the step of encoding the video data including the step of generating motion vectors for first and second image areas, the step of generating motion vectors for the first image area including the step of: limiting the generation of motion vectors for first image areas so that coded pixels in the first image areas are limited to be a function of coded pixels of corresponding first image areas of preceding or subsequent images.