In one embodiment, the method includes selecting a list 1 motion vector of the co-located block in a first reference picture if the co-located block only has the list 1 motion vector. The first reference picture is a type of reference picture permitted to be located temporally before or after a current picture. The current picture includes the bi-predictive block. The method further includes deriving at least one motion vector of the bi-predictive block by applying a bit operation to the selected motion vector. The bit operation includes 8 bits right shift.