1. A method of decoding a video signal, comprising: generating a merge candidate list of a current prediction block, the merge candidate list comprising at least one spatial merge candidate block; and performing inter prediction of the current prediction block based on the merge candidate list; wherein the spatial merge candidate block includes at least one of neighboring blocks adjacent to the current prediction block, the neighboring blocks including a left neighboring block, a top neighboring block, a top-right neighboring block, a left-bottom neighboring block or a top-left neighboring block, wherein when a size of a MER (Motion Estimation Region) is 8×8 and a size of a coding block is 8×8, at least one of the neighboring blocks is replaced to a replacement block located outside the MER, the coding block including the current prediction block whose a size is 8×4 or 4×8, and wherein when the size of the MER is not 8×8 and the size of the coding block is not 8×8, none of the neighboring blocks is replaced to the replacement block located outside the MER.