1. A motion prediction method, comprising: determining a plurality of candidate units corresponding to a current unit of a current frame, wherein the candidate units comprise at least a neighboring unit of the current unit and at least a reference unit related to a collocated unit of the current unit; obtaining a plurality of motion vectors of the candidate units; calculating a plurality of scaling factors of the candidate units according to a plurality of respective temporal distances depending on a plurality of reference frames of the motion vectors; scaling the motion vectors of the candidate units according to the scaling factors to obtain a plurality of scaled motion vectors; ranking the scaled motion vectors; identifying a subset of highest ranking motion vectors among the plurality of scaled motion vectors to be included in a candidate set; and selecting a motion vector predictor for motion prediction of the current unit from the candidate set according to a motion vector competition method.