nx_h264_mvgrid.nx

nx_h264_mvgrid.nx -- H.264 per-4x4 motion-vector grid + neighbour gathering (8.4.1.3). Maintains three parallel grids over the whole picture (lbW x lbH 4x4 blocks): gref[idx] : reference index of the block. -2 == NOT-YET-DECODED or out-of-picture (geometrically unavailable -> triggers D-substitution for the C neighbour); -1 == DECODED but intra (available, refIdxN=-1, mvN=0); >=0 == inter reference index. Distinguishing -2 from -1 matters only for sub-partition (8x8) neighbours whose top-right may be undecoded. gmvx/gmvy : the block's L0 motion vector (quarter-pel units). Gathering A(left)/B(top)/C(top-right; D=top-left substitutes when C unavailable) for a partition then calling the median/directional predictor (nx_h264_mvp / _directional). Reusable by the P-frame reconstructor. genealogy_id: itu_t_h264_sec8_4_1_3_mvgrid license_tier: ORIGINAL