master
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 claude-noether
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3e996d09e2 |
iter1 Phase 4: plan — contract clauses, diff scope, Phase 7 harness
Phase 4 plan for the iter1 MPEG-2 fix, structured per the feedback_dev_process.md Phase 6 contract-before-code worked example (0012-h264-omit-scaling-matrix-frame-based.patch shape): contract clauses with citations first, then code changes mapping 1:1 to clauses. Phase 1 criterion #3 re-locked per Phase 3 → Phase 1 loopback: Original: "mpv --hwdec=vaapi-copy ... engages backend" Adjusted: "ffmpeg -hwaccel vaapi ... engages backend" Phase 3 Baseline A established mpv silently filters MPEG-2 out before libva is loaded; the original wording was unfalsifiable. ffmpeg-direct exercises the path. mpv-driven testing → separate follow-up task. Other 4 criteria unchanged (vainfo regression, vaCreateConfig SUCCESS, DMA-BUF GL pixel verify HW=SW at +02s, T4 H.264 regression). Six contract clauses cited from authoritative sources: Clause 1 — Three split controls in one batched VIDIOC_S_EXT_CTRLS Authority: linux/v4l2-controls.h:1988-2105 Reference impl: FFmpeg libavcodec/v4l2_request_mpeg2.c:130-155 Empirical anchor: Phase 3 Baseline C verbatim payload Clause 2 — v4l2_ctrl_mpeg2_sequence layout (12 bytes) Authority: linux/v4l2-controls.h:2009-2017 Field-by-field VAAPI source mapping table Note: progressive_frame is used as proxy for progressive_sequence (VAAPI doesn't expose the latter; same bit for BBB). Clause 3 — v4l2_ctrl_mpeg2_picture layout (32 bytes) Authority: linux/v4l2-controls.h:2056-2065 reserved[5] MUST be zeroed (kernel doc 2052) 8 picture flags decoded; field-by-field VAAPI mapping Clause 4 — v4l2_ctrl_mpeg2_quantisation layout (256 bytes) Authority: linux/v4l2-controls.h:2089-2096 Matrices in zigzag scanning order; no permutation in libva backend (kernel hantro_mpeg2_dec_copy_qtable handles zigzag-to-raster) Decision: when iqmatrix_set is false, populate from MPEG-2 spec defaults (ISO/IEC 13818-2 Table 7-3) to avoid kernel rejecting a batch missing the QUANTISATION control. Clause 5 — Per-frame submission via v4l2_set_controls Authority: existing src/h264.c:986 pattern surface_object->request_fd binds controls to per-surface request Clause 6 — config.c MPEG-2 case must break; Authority: C semantics; H.264 case shape at config.c:62-63 Empirical anchor: Phase 3 Baseline B confirmed scratch-fix shape. Diff scope: src/config.c — 3 lines added (break for MPEG-2 cases) + drop stale #include <mpeg2-ctrls.h> src/mpeg2.c — full rewrite of mpeg2_set_controls against new split API; ~120 lines replaced; switches from 2× v4l2_set_control(single) to 1× batched v4l2_set_controls(3-control array) include/mpeg2-ctrls.h — DELETE (staging-era, masks kernel UAPI) src/picture.c, src/context.c, meson.build — no changes (verified Phase 2 + Phase 3) Phase 6 implementation order (3 logical commits): Commit A: config.c break — substrate fix in isolation Commit B: mpeg2.c rewrite + drop mpeg2-ctrls.h includes Commit C: delete include/mpeg2-ctrls.h Phase 7 verification harness (full Bash incantations included in plan body): Criterion 1: vainfo MPEG-2 enumeration regression check Criterion 2: vaCreateConfig SUCCESS via libva trace Criterion 3: ffmpeg -hwaccel vaapi exit 0, no Failed-to-create Criterion 4: mpv --hwdec=vaapi --vo=image at +02s seek; HW=SW byte-identical hashes for 2 distinct frames (fallback to ffmpeg hwdownload if mpv-vaapi also filters MPEG-2; criterion holds, harness adapts) Criterion 5: T4 H.264 hashes still f623d5f7... and 7d7bc6f2... Bonus: byte-compare post-fix S_EXT_CTRLS payload vs Baseline C Pre-identified Phase 7 → Phase 4 loopback triggers: 1. S_EXT_CTRLS EINVAL post-fix → check pic.reserved[5] memset, struct sizes, flag value collisions 2. Pixel hash mismatch → check f_code packing, field/frame interpretation, ref timestamps, IQ matrix order 3. mpv-vaapi filters MPEG-2 out (same as -copy) → fall-forward to ffmpeg hwdownload pixel verify (criterion holds, harness adapts; do not redefine criterion) 4. H.264 regression → re-locate the offending change in Bug 1 5. Header deletion breaks unaudited consumer → git grep audit Out of scope (LOCKED): HEVC/VP9/VP8 (later iterations); vaDerive Image cache-stale fix; chromium-fourier 149 install; perf metrics; long-duration stress; other MPEG-2 containers; mpv-hwdec follow-up; context.c H.264 device-init EINVAL (auxiliary, intentional); profile/chroma/progressive_sequence refinement; upstream engagement. Phase 5 entry: artifacts handover (no summary, raw bundle) per feedback_dev_process.md — phase0_findings_iter1.md, phase2_iter1_situation.md, phase3_iter1_baseline.md, phase4_iter1_plan.md, plus phase0_evidence/2026-05-07/iter1_phase3/. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> |