Empirical byte-diff of libva vs kdirect VP8 control payloads on
current substrate:
- Keyframe (payloads 0+1): BYTE-IDENTICAL (0 diffs / 1232 bytes)
- Inter frames: only 24 bytes diff at offset 1200-1223, which are
the 3 reference-frame timestamps. libva uses gettimeofday→ns
(large values), kdirect uses pts-derived (small). Both internally
consistent; kernel uses them as keys, absolute values don't matter.
Verdict: Bug 6 is NOT in vp8.c control generation. The bytes match.
With identical controls and same hardware, libva produces 0.4% pixel
match for keyframe — bug lives in slice-data path, bytesused, cache
coherency, or CAPTURE slot rotation.
5 hypotheses (H-A..H-E) for Phase 3 to narrow:
- H-A slice data corruption in libva path (picture.c memcpy)
- H-B slices_size wrong on OUTPUT QBUF
- H-C cache coherency on OUTPUT mmap before kernel DMA read
- H-D CAPTURE slot rotation mismatch
- H-E other (deeper kernel-side)
Pre-iter5b masked all of these via the OUTPUT format mismatch
producing all-zero output. β fixed format → kernel actually decodes →
underlying bug now visible.
iter3's transitive proof verified specific control fields. Did not
verify slice data, bytesused, cache state, or slot rotation. Same
pattern as iter2's HEVC transitive PASS missing Bug 5. Future
transitive PASS claims must enumerate non-verified artifacts.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
