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Phase 2 step 4 close: AV1 dispatch scaffolding verified

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350 LoC across 6 files in libva backend. vainfo advertises AV1.
av1_set_controls stub returns -1 cleanly; ffmpeg-vaapi falls back to
SW; no crash, no IOMMU fault.

Three devices opened at backend init (rkvdec /dev/video1 + legacy
hantro /dev/video2 + vpu981 /dev/video4) via capability-based probe.
HEVC + H264 + VP8 + MPEG2 unaffected.

Remaining: Phase 2.1 — fill_sequence (75 LoC), fill_frame (257 LoC),
fill_film_grain (67 LoC), fill_tile_group_entries + 4-control batch
submit (~50 LoC) = ~450 LoC of field-mapping work + Janet F1/F2/F3
silent-failure-mode handling. Fresh-focus session recommended.

Phase 3 test vectors locked: av1-1-b8-01-size-208x208.ivf (smoke),
av1-1-b8-23-film_grain-50.ivf (F1 multi-tile + F3 film_grain stress).
Byte-compare libva vs kdirect (Phase 0 verified bit-perfect).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Claude (noether)
2026-05-17 07:55:56 +00:00
parent 695588aaaf
commit 4ed18d6837
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# Phase 2 step 4 close — AV1 dispatch SCAFFOLDING wired and verified
Date: 2026-05-17 ~10:30. Phase 2 scaffolding complete. Stub av1_set_controls returns -1 cleanly; ffmpeg falls back to SW; no crash, no IOMMU fault.
## What's done (3 commits on libva backend branch `av1-iter1`)
| Commit | Subject | Lines |
|---|---|---|
| `bed75c0` | Phase 2 step 1: third-device fd scaffolding for vpu981 | +154 |
| `61db76e` | Phase 2 step 2: advertise VAProfileAV1Profile0 via libva | +19 |
| `78a9978` | Phase 2 step 4: AV1 dispatch scaffolding compiles and wires | +177 |
Total: 350 LoC across 6 files. Module installed at `/usr/lib/dri/v4l2_request_drv_video.so` on ampere (md5 `adab8fa005ec3187f5127d0dd6605690`).
## Verification
```
$ vainfo
VAProfileMPEG2Simple/Main, H264×5, HEVC, VP8, AV1 — all advertised
$ LIBVA_DRIVER_NAME=v4l2_request ffmpeg -hwaccel vaapi -i /tmp/test_av1.ivf ...
v4l2-request: auto-selected codec device: /dev/video1 + /dev/media0
v4l2-request: iter38: also opened hantro-vpu decoder at /dev/video2 + /dev/media1
v4l2-request: ampere-av1: vpu981 AV1 decoder at /dev/video4 + /dev/media3
v4l2-request: ampere-av1: av1_set_controls stub — Phase 2.1 will implement ...
[av1] HW accel end frame fail.
[dec:av1] Error submitting packet to decoder: Input/output error
```
Three devices opened, vpu981 found via capability probe, AV1 routed to stub, graceful fall-back to SW. Other codecs unaffected.
## Phase 2.1 remaining (the bulk — ~700 LoC)
Implement the body of `av1_set_controls` in `~/src/libva-v4l2-request-fourier/src/av1.c`:
| Function | Reference (Kwiboo) | Notes |
|---|---|---|
| `fill_sequence()` | lines 55-128 | 75 LoC — AV1 sequence flags from `VADecPictureParameterBufferAV1.seq_fields.bits.*` |
| `fill_frame()` | lines 130-385 | 257 LoC — the heavy one; F1 (mi_col/row_starts sentinel), F2 (superres_denom AV1_SUPERRES_NUM=8), F3 (loop_restoration_size USES_LR gate) ALL apply here |
| `fill_film_grain()` | lines 387-452 | 67 LoC — only if context->has_film_grain (init-time probe) |
| `fill_tile_group_entries()` | lines 481-522 | tile_group_entries[] DYNAMIC_ARRAY; size = sizeof × MAX(N,1) |
| `av1_set_controls()` body | lines 524-560 | 4-control batch + request_fd submit |
Plus context init for `has_film_grain` flag (VIDIOC_QUERY_EXT_CTRL probe at first AV1 context open).
## Phase 3 testing plan (unchanged from v3 amendment)
1. Test 208×208 (single-tile, smoke test) — `av1-1-b8-01-size-208x208.ivf`
2. Test 352×288 with film_grain + tiling — `av1-1-b8-23-film_grain-50.ivf` (F1 + F3 stress)
3. Byte-compare HW (libva) vs HW (kdirect, verified Phase 0 bit-perfect) — should be 100% identical
## Pending follow-ups
- Push av1-iter1 branch to gitea (vp9 branch had ssh sideband disconnect; may recur)
- Janet code review of completed av1.c after Phase 2.1 implementation
- Real-world 1080p AV1 stress test post-Phase 3 bit-perfect verification
## State at this checkpoint
- ampere: iter38b-vp9-iter1-base (sibling close) + Phase 2 scaffolding installed; HEVC bit-perfect retained, AV1 falls back cleanly to SW until Phase 2.1
- backend repo on ampere: branch `av1-iter1` with 3 new commits stacked on iter2 step4
- campaign repo: 4 plan docs + Phase 0 + this step4 close
## Honest assessment
Scaffolding work was 350 LoC of mostly-mechanical infrastructure (~3 hours). The remaining ~700 LoC of `av1.c` body IS the field-mapping work where Janet's F1/F2/F3 silent-failure modes lurk. That's fresh-focus territory, not "keep grinding" territory. Recommend Phase 2.1 in a separate focused session.