1. A method of processing video data, comprising: providing a frame of video data, the frame of video data comprising a plurality of blocks of pixels, the blocks being addressable in a two-dimensional array of rows and columns; selecting alternating blocks of the frame of video data and estimating a motion vector for the selected blocks; selecting at least one block of the frame of video data for which a motion vector has not been estimated, and determining whether a block to the left or a block to the right of the selected at least one block has an estimated zero motion vector, and determining whether the selected at least one block had an estimated zero motion vector in a previous frame; and providing, if the determinations are affirmative, a predetermined motion vector to the selected at least one block.