1. A method of determining a motion vector of a block of at least of part of a video frame with respect to a reference video frame, the reference video frame comprising a plurality of pixels, the method comprising: defining an interpolated version of the reference video frame, comprised of the pixels and interpolated pixels, the interpolated pixels being generated by interpolation of at least two pixels, the interpolated pixels being located adjacent to at least one of the pixels being exploited for the interpolation; defining a region within the interpolated reference video frame, the dimension of the region being determined by a predetermined maximal length of the motion vector; calculating mathematical norms of the block at a plurality of positions defined by the region in the interpolated version of the reference video frame, wherein the interpolated pixels are calculated when a norm calculation in such a position requires the interpolated pixels; and selecting the motion vector having the lowest norm.