1. A method for decoding a video picture comprising at least a video block in a reference area, the method comprising: selecting a subset of N motion vectors from a plurality of M motion vectors of the video blocks in the reference area, wherein selecting N motion vectors from M motion vectors comprises comparing the reference vector with the M motion vectors to select the N motion vectors by: executing a vector subtraction on the reference vector and the M motion vectors respectively to calculate M judgment vectors; selecting N judgment vectors that are smaller in magnitude than the M judgment vectors; and determining N motion vectors according to the N judgment vectors; and decoding the video blocks according to the N motion vectors.