Provided are a method and apparatus for encoding a video and a method and apparatus for decoding a video. The method of encoding includes: determining, for a current block, bidirectional motion estimation information comprising an L0 motion vector, an L1 motion vector, an L0 reference vector, and an L1 reference picture by performing bidirectional motion estimation on the current block; determining whether to use the determined bidirectional motion estimation information as prediction information of the current block based on whether the L0 reference picture and the L1 reference picture are the same and based on a difference value between the L0 motion vector and the L1 motion vector; and in response to determining to use the determined bidirectional motion estimation information as the prediction information of the current block, encoding the determined bidirectional motion estimation information as the prediction information of the current block.