1. A video pre-processing method for motion estimation, comprising: receiving a first image in a video, the first image consisting of a plurality of first blocks, each of which corresponding to one of a plurality of first pixel matrices; for each of the first blocks, calculating a similarity descriptor of the first block, the similarity descriptor of the first block configured to indicate whether a plurality of pixel values of at least one pair of adjacent pixels in the corresponding first pixel matrix are identical; calculating a similarity descriptor of a second block of a second image in the video, the second block corresponding to a reference block among the first blocks and to a second pixel matrix, the similarity descriptor of the second block configured to indicate whether a plurality of pixel values of at least one pair of adjacent pixels in the second pixel matrix are identical; reaching a verdict on whether the similarity descriptor of the second block and the similarity descriptor of the reference block are identical; and selectively performing motion estimation on the second block based on the verdict.