1. A method for decoding a video signal comprising: deriving, based on a position and a size of a first prediction block, at least one merging candidate relating to the first prediction block, wherein when a size of a block indicated by parallel merge level information is equal to or greater than a first size and a size of a coding block which comprising the first prediction block is equal to a second size, the position of the first prediction block is set equal to a position of the coding block and the size of the first prediction block is set equal to the size of the coding block; generating a merging candidate list for the first prediction block based on the at least one merging candidate; determining motion prediction information of the first prediction block based on the merging candidate list and a merge index, the motion prediction information of the first prediction block being derived from a merging candidate indicated by the merge index, and obtaining prediction samples of the first prediction block based on the motion prediction information.