Phase 0 deep-strace yielded a critical narrowing:
- Post-DPB DECODE_PARAMS bytes (512-559): IDENTICAL libva vs kdirect
- PPS: IDENTICAL
- SPS: identical except inert constraint_set_flags
- DPB[0] beyond reference_ts: IDENTICAL after α-2
The ONLY remaining wire-byte diff between libva (broken) and kdirect
(working) is reference_ts magnitude. libva uses gettimeofday giving
~1.78e18 ns; kdirect uses an internal counter giving ~10000 ns.
α-7 hypothesis: V4L2 stateless decoder (rkvdec) reference-resolution
fails for very large reference_ts values. Possible mechanisms:
M-A: vb2_find_buffer_by_timestamp truncates/overflows on giant values.
M-B: V4L2 framework transforms OUTPUT QBUF ts before storing on CAPTURE
but DPB.reference_ts left untransformed → mismatch.
M-C: gettimeofday + v4l2_timeval_to_ns produce slightly different ns
values than the kernel computes from the timeval QBUF.
Fix: ~10 LOC. Add timestamp_counter to driver_data; replace
gettimeofday in EndPicture with monotonic counter.
If α-7 works → iter9 PASS, Bug 4 closed.
If α-7 doesn't → iter9 PARTIAL, wire-byte search space effectively
exhausted.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
