nx_av1_frame.nx

nx_av1_frame.nx -- AV1/AV2 frame-header parameter blocks, writer and reader. Layer five. quantization_params() and cdef_params() are the two blocks that decide, respectively, how coefficients are scaled and how the constrained directional enhancement filter is applied. Both are read straight off the uncompressed header, both are shared verbatim with AV2, and both are self-contained enough to prove by round-trip. su() IS TWO'S COMPLEMENT AT AN ARBITRARY WIDTH. A delta-Q is su(1+6) -- a SEVEN bit signed field, not eight. Sign-extending from the wrong bit turns -1 into +63 and every negative delta into a large positive one, which does not error: it just makes the whole frame come out at the wrong quantiser. THE CDEF SECONDARY STRENGTH SKIPS 3. The field is two bits, and a coded 3 means strength FOUR -- the set is {0, 1, 2, 4} and strength 3 does not exist. A writer that stores 4 verbatim overflows the field; one that stores 3 silently means 4. This module maps on write and remaps on read, and REFUSES an attempt to encode strength 3, which is unrepresentable rather than merely unusual. genealogy_id: av1_spec_5_9_12_quantization_params lineage_id: nx_av1_frame_v1 license_tier: ORIGINAL