| CPC H04N 19/137 (2014.11) [H04N 19/105 (2014.11); H04N 19/176 (2014.11); H04N 19/70 (2014.11)] | 20 Claims | 

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               1. A method of processing video data, comprising: 
            determining, for a conversion between a block of a current picture of a video and a bitstream of the video, that a first coding mode is applied to the block based on a derivation process of two target reference pictures of the current picture, wherein the derivation process includes: 
                performing a first step for searching a forward target reference picture in a reference picture list 0 and searching a backward target reference picture in a reference picture list 1, 
                  in response to at least one of the two target reference pictures not being found in the first step, resetting both target reference picture indices to be unavailable before a second step is invoked, and 
                  performing the 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; and 
                performing the conversion based on the determination, 
                wherein in the first coding mode, a syntax structure indicating a motion vector difference of a reference picture list X is not present in the bitstream, and the motion vector difference of the reference picture list X is derived based on a motion vector difference of a reference picture list (1−X), wherein X is equal to 0 or 1. 
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