nx_vcodec_subpel_ceil.nx

nx_vcodec_subpel_ceil.nx -- CEILING of the 6-tap sub-pel lever (the next real refinement after the magic-number fixes). Our qp_pixel is BILINEAR; x264 uses a 6-tap [1,-5,20,20,-5,1]/32 half-pel filter. For each genuinely- coded P-MB (non-skip, INTERIOR so the 6-tap has its +/-2..3 margin), find the best integer MV, then compare the best fractional residual SAD under BILINEAR quarter-pel (what we do) vs 6-TAP half-pel. The reduction is the prediction gain a 6-tap upgrade could realize (residual smaller -> fewer bits). Decides if the (vcv-bump, bit-exact-critical) 6-tap build is worth it. Reads /tmp/seq.y4m. CIF. license: ORIGINAL