1. A method of determining motion vectors and a reference picture index for a current block in a picture to be decoded, comprising: obtaining first and second motion vectors and a reference picture index of a block other than the current block; determining first and second motion vectors of the current block using the first and second motion vectors of the other block such that the first motion vector of the current block has a same direction as the first motion vector of the other block and the second motion vector of the current block has a same direction as the second motion vector of the other block; determining a reference picture index of the current block using the reference picture index of the other block; determining a direction of a reference picture for the current block based on the determined reference picture index.