US Patent 11463703 Symmetric motion vector difference coding

Symmetric motion vector difference coding is described. One example video processing method includes determining, for a conversion between a block of a current picture of video and a bitstream representation of the block, whether a symmetric motion vector difference (SMVD) mode is allowable for the block, wherein whether the SMVD mode is allowable depends on a derivation process of two target reference pictures of the current picture, which includes a first step for searching a forward target reference picture in the reference picture list 0 and searching a backward target reference picture in the reference picture list 1, and a second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1, outputs of the first step and the second step being independent of each other; and performing the conversion based on the determination.