1. A motion estimation method, applied to a video signal comprising a first frame and a second frame, the method comprising: capturing a matching window from the first frame; capturing a searching area from the second frame, the searching area comprising a plurality of searching blocks each having a size equal to that of the matching window; selecting a searching block from the plurality of searching blocks; calculating a difference between pixel data of the selected searching block and pixel data of the matching window to simultaneously obtain N total differences corresponding to N different searching blocks, N being an integer greater than 1; and determining a motion vector corresponding to the matching window according to at least the N total differences, wherein selecting the searching block from the plurality of searching blocks and calculating the difference between the pixel data of the selected searching block and the pixel data of the matching window comprises: selecting a searching block sampling area from the selected searching block; defining N matching window sampling areas in the matching window, each of the N matching window sampling areas having a size equal to that of each of the searching block sampling areas; and respectively calculating a difference between the searching block sampling area and the N matching window sampling areas to obtain the N total differences corresponding to the N searching blocks.