1. An apparatus, comprising: an encoder for encoding a multi-prediction picture from a combination of two or more reference pictures by respectively predicting a motion vector for a particular one of the two or more reference pictures in a motion estimation process while initializing motion vectors for remaining ones of the two or more reference pictures to a predefined value for use by the motion estimation process, wherein the predefined value, to which the motion vectors for the remaining ones of the two or more reference pictures are initialized, is constrained to a value representative of the remaining ones of the two or more reference pictures being stationary, and wherein said encoder jointly computes the motion vectors for the two or more reference pictures based on the two or more reference pictures having identical motion with respect to the multi-prediction picture to be encoded.