Encoding a video data stream comprising a first and second frame of video data, encoding comprising the steps of: obtaining motion prediction data for a plurality of pixels, the motion prediction data indicative of the predicted relative motion of the plurality of pixels between the first and second frames of video data; obtaining a data mask comprising data indicative of relative weights to be applied for predicting pixels for the second frame; determining update data to define a relative difference between a plurality of pixels in the first frame and a corresponding plurality of pixels in the second frame, wherein said update data is based on a weighted scaling of the motion prediction data and the second frame of video data, said weighted scaling based on the data mask; and encoding the video data stream comprising at least the first frame of video data and the update data.