Plan subagent with model: sonnet, open-consultation pattern. Raw
verbatim review text — operator transcribes to DokuWiki.
Headlines:
- Phase 0 substrate: process not defective, but "end-to-end" framing
conflated libva engagement with pixel output. New invariant for V4L2
stateless work: pixel-content check via cache-invalidating path is
mandatory Phase 0 deliverable.
- Phase 4 plan: correctly scoped, surface-export bug was undiagnosable
before decode landed (all-zeros NV12 produces solid colors regardless
of export geometry).
- Slice-header parser: correct, no off-by-one. Two non-bugs to comment
(MMCO 5 implicitly handled, POC type 2 implicitly correct).
- Phase 7 criterion: right. Both vaapi and vaapi-copy paths required.
chromium-fourier 149 should be removed from libva corpus (it uses
chromium's own internal V4L2 decoder, bypasses libva entirely).
- Slice-header parser in-fork is right call vs upstream VAAPI lobbying.
- DEBUG patches stay until DMA-BUF path works end-to-end, then clean
sweep before any bootlin snapshot.
- FRAME_BASED hardcode is correct for ohm; revisit at fresnel/boltzmann.
Surface-export attack plan (5 load-bearing items):
1. Log RequestExportSurfaceHandle descriptor (object size, plane
offsets, pitches, fd).
2. Log format_width/height from v4l2_get_format — confirm 1088 not 1080.
3. Run mpv --hwdec=vaapi --msg-level=vd=v --msg-level=vo=v, capture
what mesa reports about imported DRM format/modifier/geometry.
4. Verify UV offset matches 1920×1088 (=2,088,960). If format_height
is 1080 (=2,073,600), UV plane reads start 8 rows into Y data —
most likely structural bug.
5. Read FFmpeg's hwcontext_drm.c for NV12 nb_objects + UV-offset
computation pattern.
Six previously-unsurfaced findings:
7.1 EACCES on VIDIOC_G_EXT_CTRLS deserves one more probe (try moving
readback to before MEDIA_REQUEST_IOC_QUEUE).
7.2 num_ref_idx_l0/l1_default_active_minus1 from VASlice is wrong for
multi-slice streams with per-slice override (defer).
7.3 SET_FORMAT_OF_OUTPUT_ONCE global breaks multi-resolution use
(latent bug, document).
7.4 // HACK in surface.c is architecturally wrong for multi-codec
consumers (latent bug, document).
7.5 Firefox non-IDR first frame (mid-stream seek) handling unverified.
7.6 fourier_attribution cell A wheat verdict mechanism is now Step 2
chromium-internal V4L2 decoder, not Step 1 libva.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
