A method of decoding a video signal, comprising: determining whether a spatial merge candidate block is not decoded yet; determining whether the spatial merge candidate block is included in a same Motion Estimation Region, MER, as a current block to be decoded; when the spatial merge candidate block is already decoded and is not included in the same MER as the current block, determining that the spatial merge candidate block is an available merge candidate block for inter prediction of the current block; determining a temporal merge candidate block; generating a merge candidate list of the current block, the merge candidate list including the available merge candidate block and the temporal merge candidate block; obtaining a prediction block of the current block by performing inter prediction based on the merge candidate list; and reconstructing the current block based on the prediction block, wherein the spatial merge candidate block includes at least one of neighbouring blocks adjacent to the current block, the neighbouring blocks including a left neighbouring block, a top neighbouring block, a top-right neighbouring block, a left-bottom neighbouring block and a top-left neighbouring block, wherein the temporal merge candidate block is one of a first collocated block and a second collocated block, wherein if a location of a point at a top-left of the current block is (xP, yP), a width of the current block is nPSW, and a height of the current block is nPSH, the first collocated block is a block including a point at (xP+nPSW, yP+nPSH) within a collocated picture, and the second collocated block is a block including a point at (xP+(nPSW>>1), yP+(nPSH>>1)), within the collocated picture, characterized in that, when a size of the MER is 8x8 and a size of the current block is 4x8, the left neighbouring block adjacent to the current block is replaced to a replacement block located outside the MER. determining whether a spatial merge candidate block is not decoded yet; determining whether the spatial merge candidate block is included in a same Motion Estimation Region, MER, as a current block to be decoded; when the spatial merge candidate block is already decoded and is not included in the same MER as the current block, determining that the spatial merge candidate block is an available merge candidate block for inter prediction of the current block; determining a temporal merge candidate block; generating a merge candidate list of the current block, the merge candidate list including the available merge candidate block and the temporal merge candidate block; obtaining a prediction block of the current block by performing inter prediction based on the merge candidate list; and reconstructing the current block based on the prediction block, wherein the spatial merge candidate block includes at least one of neighbouring blocks adjacent to the current block, the neighbouring blocks including a left neighbouring block, a top neighbouring block, a top-right neighbouring block, a left-bottom neighbouring block and a top-left neighbouring block, wherein the temporal merge candidate block is one of a first collocated block and a second collocated block, wherein if a location of a point at a top-left of the current block is (xP, yP), a width of the current block is nPSW, and a height of the current block is nPSH, the first collocated block is a block including a point at (xP+nPSW, yP+nPSH) within a collocated picture, and the second collocated block is a block including a point at (xP+(nPSW>>1), yP+(nPSH>>1)), within the collocated picture, characterized in that, when a size of the MER is 8x8 and a size of the current block is 4x8, the left neighbouring block adjacent to the current block is replaced to a replacement block located outside the MER.