1. A method for performing motion estimation, comprising: (a) selecting a current block in a current frame; (b) comparing the current block with an initial reference block in a reference frame to obtain an initial comparison parameter, wherein position of the initial reference block in the reference frame is corresponding to position of the current block in the current frame; (c) determining a predicted search window corresponding to the current block based on the initial comparison parameter; and (d) comparing the current block with reference blocks in the predicted search window to obtain comparison parameters respectively, whereby a best-match reference block in the predicted search window is determined; wherein each of the comparison parameters is a function of a SAD (sum of absolute difference) value between the current block and each of the reference, blocks and is represented as: μ = S ⁢ ⁢ A ⁢ ⁢ D N × N + ɛ where SAD denotes a sum of absolute difference, ε is a constant factor, and a size of each block is N×N.