A method for decoding a video, the method comprising: determining a first reference picture and a second reference picture of a current block based on respective reference picture index information decoded from a bitstream; obtaining, based on a first motion vector and the first reference picture, a first prediction block of the current block; obtaining, based on a second motion vector and the second reference picture, a second prediction block of the current block; obtaining a weighted prediction parameter of the current block, the weighted prediction parameter being representative of a second weight applying to the second prediction block; determining a first weight applying to the first prediction block the first weight having a value subtracting the second weight from 1 and obtaining a final prediction block of the current block based on a weighted sum of the first prediction block and the second prediction block, characterised in that: the weighted prediction parameter is selected based on index information indicating one of weighted prediction parameter candidates included in a first weighted prediction parameter set or a second weighted prediction parameter set, the index information being explicitly signaled via a bitstream, each of the first weighted prediction parameter set and the second weighted prediction parameter set being composed of a plurality of weighted prediction parameter candidates, a number of weighted prediction parameter candidates included in the first weighted prediction parameter set is different from a number of weighted prediction parameter candidates included in the second weighted prediction parameter set, and one of the first weighted prediction parameter set and the second weighted prediction parameter set is selected based on temporal directions of the first reference picture and the second reference picture, a temporal direction representing whether an output order of a reference picture is previous to or subsequent to a current picture. determining a first reference picture and a second reference picture of a current block based on respective reference picture index information decoded from a bitstream; obtaining, based on a first motion vector and the first reference picture, a first prediction block of the current block; obtaining, based on a second motion vector and the second reference picture, a second prediction block of the current block; obtaining a weighted prediction parameter of the current block, the weighted prediction parameter being representative of a second weight applying to the second prediction block; determining a first weight applying to the first prediction block the first weight having a value subtracting the second weight from 1 and obtaining a final prediction block of the current block based on a weighted sum of the first prediction block and the second prediction block, characterised in that: the weighted prediction parameter is selected based on index information indicating one of weighted prediction parameter candidates included in a first weighted prediction parameter set or a second weighted prediction parameter set, the index information being explicitly signaled via a bitstream, each of the first weighted prediction parameter set and the second weighted prediction parameter set being composed of a plurality of weighted prediction parameter candidates, a number of weighted prediction parameter candidates included in the first weighted prediction parameter set is different from a number of weighted prediction parameter candidates included in the second weighted prediction parameter set, and one of the first weighted prediction parameter set and the second weighted prediction parameter set is selected based on temporal directions of the first reference picture and the second reference picture, a temporal direction representing whether an output order of a reference picture is previous to or subsequent to a current picture. the weighted prediction parameter is selected based on index information indicating one of weighted prediction parameter candidates included in a first weighted prediction parameter set or a second weighted prediction parameter set, the index information being explicitly signaled via a bitstream, each of the first weighted prediction parameter set and the second weighted prediction parameter set being composed of a plurality of weighted prediction parameter candidates, a number of weighted prediction parameter candidates included in the first weighted prediction parameter set is different from a number of weighted prediction parameter candidates included in the second weighted prediction parameter set, and one of the first weighted prediction parameter set and the second weighted prediction parameter set is selected based on temporal directions of the first reference picture and the second reference picture, a temporal direction representing whether an output order of a reference picture is previous to or subsequent to a current picture.