 claude-noether
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898544a29c
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iter3 Phase 2: situation analysis — VP8 backend gaps + contract surface
Source-read of every file the iter3 patch series will touch, plus the
kernel UAPI + VAAPI + downstream FFmpeg + kernel hantro reference
sources. Conducted on noether against fork tip 8d71e20 (iter2 Phase 6
commit B); fresnel.vpn was unreachable so Phase 3 baseline empirical
capture defers until laptop reachable.
Bug enumeration (10 sites the patch series must touch):
B1 config.c::RequestQueryConfigProfiles enumeration block missing
B2 config.c::RequestCreateConfig VP8 case label missing
B3 config.c::RequestQueryConfigEntrypoints VP8 case missing
B4 src/vp8.c new file ~160-220 LOC
B5 src/vp8.h new file ~35-45 LOC
B6 picture.c::codec_set_controls VP8 dispatch missing
B7 picture.c::codec_store_buffer 4 buffer-type cases +
VAProbabilityDataBufferType
outer case missing
B8 picture.c::RequestBeginPicture per-frame reset additions
B9 surface.h::object_surface::params union vp8 member missing
B10 meson.build vp8.c/vp8.h not in lists
Non-bugs (intentionally untouched):
- context.c (no DECODE_MODE/START_CODE menus for VP8)
- video.c (CAPTURE-side format list; VP8 is OUTPUT-side)
- v4l2.c (fourcc-agnostic helpers)
- buffer.c (buffer registry is type-agnostic)
- include/hevc-ctrls.h (already includes <linux/v4l2-controls.h>
which holds V4L2_CID_STATELESS_VP8_FRAME)
Contract surface cited verbatim:
- V4L2_CID_STATELESS_VP8_FRAME = V4L2_CID_CODEC_STATELESS_BASE+200
= 0x00a409c8 (matches Phase 0 V4L2 inventory)
- struct v4l2_ctrl_vp8_frame at <linux/v4l2-controls.h>:1929-1958
+ 5 sub-structs (segment, lf, quant, entropy, coder_state) at
1785-1888
- VAAPI VAPictureParameterBufferVP8 + VASliceParameterBufferVP8 +
VAProbabilityDataBufferVP8 + VAIQMatrixBufferVP8 at
references/libva/va/va_dec_vp8.h
- FFmpeg v4l2_request_vp8.c reference: single batched S_EXT_CTRLS
at end_frame, count=1, no init-time menus
- Kernel hantro_vp8.c::hantro_vp8_prob_update reads 9 fields from
hdr (skip/intra/last/gf probs, segment_probs, entropy.{y,uv,mv,
coeff}_probs)
VAAPI → V4L2 mapping table: 30 fields enumerated. Open questions for
Phase 3 baseline (6 items: first_part_header_bits derivation, num_
dct_parts off-by-one, DPB timestamp 0-sentinel handling, show_frame
default, lf.flags FILTER_TYPE_SIMPLE bit, first-frame DPB sentinel).
Patch-shape prediction: ~260-340 LOC across 6 modified + 2 new
files. Medium-sized iter — between iter1's 120 LOC (3 modified +
1 deleted) and iter2's 470 LOC (5 modified). The new file dominates.
Phase 3 baseline targets queued: cross-validator strace verbatim
S_EXT_CTRLS payload capture, VAAPI consumer trace, mpv-SW reference
JPEG capture for criterion 4 byte-compare anchor.
Phase 4 plan structure anticipated: 10-clause template per iter2.
Refs:
phase0_findings_iter3.md (Phase 1 lock)
phase8_iteration2_close.md (predecessor close)
src/mpeg2.c (iter1 single-codec template; iter3 will mirror shape)
src/h265.c (iter2 dispatcher pattern; iter3 takes structure cues)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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2026-05-08 17:27:06 +00:00 |
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