9a71dbf4c39cb5ba0dce99f7a7e267d18ab11d54
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 claude-noether
|
348736eb63 |
iter2 Phase 4: plan — 10 contract clauses, ~400-line h265.c rewrite
Phase 4 plan for iter2 HEVC 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.
10 contract clauses cited from authoritative sources:
Clause 1 — Per-frame batched VIDIOC_S_EXT_CTRLS, count=5
Authority: linux/v4l2-controls.h:2090-2300 (8 HEVC stateless CIDs)
Reference impl: FFmpeg libavcodec/v4l2_request_hevc.c:505-565
(v4l2_request_hevc_queue_decode)
Empirical anchor: Phase 3 Baseline B verbatim payload
Clause 2 — v4l2_ctrl_hevc_sps layout (40 bytes)
Authority: linux/v4l2-controls.h:2096+ (struct + 9 SPS_FLAG_* bits)
Field-by-field VAAPI source mapping table; existing
h265_fill_sps logic preserved, just routed to flags bitmask
Phase 3 Baseline B BBB SPS bytes: flags=SAO|STRONG_INTRA_SMOOTHING
Clause 3 — v4l2_ctrl_hevc_pps layout (64 bytes, 19 flags)
Authority: linux/v4l2-controls.h:2126-2150
Field source: VAPictureParameterBufferHEVC + slice (for
dependent_slice_segment_flag)
Clause 4 — v4l2_ctrl_hevc_slice_params (variable; dynamic-array)
Authority: kernel exposes 0xa40a92 elems=1 dims=[600] dynamic-array
Submission shape: size = sizeof(slice_params) * num_slices_in_frame
Reference impl: FFmpeg v4l2_request_hevc.c:540-547
BEHAVIORAL CHANGE: per-slice accumulation in codec_store_buffer
(replace overwrite with append-to-array)
DPB MOVES OUT of slice_params to DECODE_PARAMS (Clause 6)
Clause 5 — v4l2_ctrl_hevc_scaling_matrix (size M; conditional)
Conditional on kernel availability (probed via VIDIOC_QUERY_EXT_CTRL
at init), NOT on bitstream flag (Phase 3 baseline corrects Phase 2
assumption)
Spec defaults from ISO/IEC 23008-2 Table 4-1 when iqmatrix_set==false
PROTOCOL: transcribe defaults from Phase 3 Baseline B verbatim
SCALING_MATRIX bytes, NOT from spec recall (per
memory feedback_review_empirical_over_theoretical.md)
Clause 6 — v4l2_ctrl_hevc_decode_params layout (328 bytes)
NEW in modern API (didn't exist in staging-era)
Contains: DPB array (16 entries), POC, num_active_dpb_entries,
num_poc_st_curr_before/after, num_poc_lt_curr,
poc_st_curr_before[8], etc.
Source: existing h265_fill_slice_params lines 269-315 logic
preserved, routed to new struct
Clause 7 — Device-wide DECODE_MODE + START_CODE menus
Set once at init via v4l2_set_controls(...request_fd=-1, 2 ctrls)
rkvdec accepts: FRAME_BASED + ANNEX_B (only options per kernel menu
constraints, Phase 0 v4l2_inventory)
Default location: extend src/context.c:142-155 device-init block
Clause 8 — config.c HEVCMain case must break;
Authority: C semantics; iter1 Bug 1 pattern verbatim
Empirical anchor: Phase 3 Baseline D scratch confirmed
Clause 9 — picture.c::codec_set_controls HEVCMain dispatch
Authority: existing MPEG-2 dispatch pattern at picture.c:186-191
Replace explicit Fourier-local: HEVC stripped reject with
h265_set_controls call
Clause 10 — Per-slice accumulation in codec_store_buffer
HEVC slice_params dynamic-array source = per-RenderPicture appends
BeginPicture resets num_slices=0; codec_store_buffer appends each
VASliceParameterBufferType to slices[N] array
Diff scope (8 files):
src/config.c — 5-line break addition (Clause 8)
src/picture.c — HEVCMain dispatch (Clause 9) + per-slice
accumulation (Clause 10) + BeginPicture
num_slices reset, ~25 lines
src/surface.h — extend params.h265 with slices[64] +
num_slices, ~17 KB extra per surface union
src/h265.c — full rewrite ~400 lines (Clauses 2-7)
src/h265.h — re-enable
src/meson.build — uncomment h265.c + h265.h
src/context.c — extend device-init for HEVC DECODE_MODE +
START_CODE
include/hevc-ctrls.h — leave as-is (9-line shim, lower-risk path
per iter1 Phase 5 Nit 6 deferral)
Phase 6 implementation order (2 logical commits + optional fix-forward):
A: src/config.c HEVCMain break only (substrate fix in isolation;
Phase 3 Baseline D already verified collateral safe)
B: h265.c rewrite + picture.c dispatch + slice_params accumulation +
meson re-enable + surface.h extension + context.c device-init
C: optional fix-forward if Phase 7 surfaces a regression
Phase 7 verification harness (full Bash incantations in plan body):
Criterion 1: vainfo lists VAProfileHEVCMain on rkvdec
Criterion 2: vaCreateConfig(VAProfileHEVCMain) = SUCCESS via libva trace
Criterion 3: ffmpeg -hwaccel vaapi exit 0, no Failed-to-create
Criterion 4: mpv --hwdec=vaapi --vo=image at +02s; HW=SW byte-identical
(DMA-BUF GL cache-coherency-safe path per memory
feedback_rockchip_pixel_verify_path.md)
Criterion 5: iter1 MPEG-2 + T4 H.264 reference hashes still match
Bonus: byte-compare post-fix S_EXT_CTRLS payload vs Baseline B
Pre-identified Phase 7 → Phase 4 loopback triggers:
1. S_EXT_CTRLS EINVAL post-fix → check struct sizes (pahole),
reserved zeroing, SCALING_MATRIX size encoding
2. HW pixel hash mismatch → DPB ordering, slice_params bit_offset,
SPS/PPS flags bit positions, SCALING_MATRIX values
3. mpv --hwdec=vaapi filters HEVC out → fall-forward to ffmpeg
-vf hwdownload (less likely; vaapi engaged MPEG-2 in iter1)
4. iter1/T4 regression → verify diffs scoped right
5. Slice_params dynamic-array submission shape rejected → cross-
validator size encoding anchor
6. SCALING_MATRIX availability detection wrong → defensive
QUERY_EXT_CTRL probe in h265_init_device_controls
7. Latent bug B3 hits HEVC differently than MPEG-2 → byte 240 in
h265.picture; ffmpeg-vaapi sends VAPictureParameterBufferType
per frame so masking holds
Out-of-scope (LOCKED): VP9/VP8; HEVC Main 10 / Main Still Picture /
range ext / tile-wavefront; perf metrics; long-duration stress;
SLICE_BASED decode mode (rkvdec FRAME_BASED only); Phase 4 cross-
cutting backlog (B1 device-discovery, B3 BeginPicture profile-aware,
B4 context.c log suppression, B5 vbv_buffer_size, L3 vaDeriveImage
cache-stale); chromium-fourier 149 install; upstream engagement;
hevc-ctrls.h deletion (Phase 5 Nit 6 lower-risk path continues).
Predicted Phase 8 close: 4-6 commits on the fork (vs iter1's 4).
Iter2 ~3x larger codebase delta than iter1 (mpeg2.c rewrite was
~120 lines; h265.c rewrite is ~400 lines).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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