γ dump confirms libva reads buffer correctly; the 16x32 patch and
stride-4 UV markers appear at YUV output exactly as in the dump.
IMP-1 memset-before-QBUF test: pre-zeroing buffer does NOT change output
(identical hash). The 512 bytes ARE deterministic kernel writes, not
stale residue.
Bug root cause: rkvdec accepts libva's H.264 decode request without
error flags but writes only 16x32 of luma-neutral data + stride-4 UV
scratch. Kernel decoded a tiny bit then stopped.
Phase 3 SPS diff: libva SPS.constraint_set_flags=0x00 vs kdirect's
0x02 — likely the kernel hint that triggers rkvdec's full decode path
for Main profile. Phase 4b α-1 fix: derive constraint_set_flags per
VAProfile in h264_set_controls. ~10 LOC. Phase 5b review required.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
