Methods and a decoder for video processing are provided. The method includes: a current picture is received; and a group of pictures associated with the current picture is determined. The group of pictures includes a first key picture at a first time prior to the current picture and a second key picture at a second time later than the current picture. The method includes: first and second reference pictures are generated based on the first and second key pictures. Based on the first and second reference pictures bi-directional predictive pictures in the group of pictures are determined. A motion estimation process based on the current picture and the bi-directional predictive pictures is then performed to generate motion information of the current picture.