claude-noether/libva-v4l2-request-fourier
1
0
Fork 0
forked from marfrit/libva-v4l2-request-fourier
Code Pull Requests Activity

ampere-av1 Phase 3 in-progress notes: UPDATE_GRAIN segfault; 352x288 still 0-byte

Browse Source 
Phase 3 iteration on the av1_larger.ivf (352x288 film_grain-50) fixture.
208x208 test_av1.ivf remains bit-exact PASS at sha 029ee72c214b37c1
(libva == kdirect, post-reference_frame_ts plumbing).

Negative result this commit: setting V4L2_AV1_FILM_GRAIN_FLAG_UPDATE_GRAIN
unconditionally when apply_grain=1 triggered a userspace SIGSEGV in
ffmpeg on the av1_larger fixture (consistent across runs). Reverted to
implicit update_grain=0 — same behavior as before the experiment
(silent 0-byte output, no segfault).

Hypothesis ruled out: the 352x288 silent-decode-failure is NOT solved
by always-update_grain. A/B test earlier also confirmed that omitting
the FILM_GRAIN control entirely (AV1_NO_FG=1) still produces 0 bytes,
so film_grain is not the trigger.

Remaining Phase 3 investigation candidates:
  - tile_info field shape — single-tile av1_larger may stress mi_col/
    row_starts sentinel differently than single-tile test_av1
  - segmentation / quantization fields — different streams use
    different combinations
  - order_hints[] still zero (VAAPI doesn't expose per-ref)
  - kernel-side dev_dbg in vpu981 driver would expose which
    control field validation rejects
  - strace -e ioctl on the failing decode reveals MEDIA_REQUEST_IOC_QUEUE
    return value

Sibling-iteration parallel: ampere-kernel-decoders iter2-5 took
multiple iterations to localize the HEVC OOPS to kernel-side
ext_sps NULL init + slice_params; AV1 likely needs the same depth
of kernel-side instrumentation for the 352x288 case.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Claude (noether)
2026-05-17 10:31:24 +00:00
parent 5fb7e36955
commit ab79ed5e4d
1 changed files with 5 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/av1.c
+5 -6
View File
@@ -462,12 +462,11 @@ static void av1_fill_film_grain(VADecPictureParameterBufferAV1 *picture,
if (fg->film_grain_info_fields.bits.apply_grain)
ctrl->flags |= V4L2_AV1_FILM_GRAIN_FLAG_APPLY_GRAIN;
/* VAAPI doesn't expose update_grain; not setting the flag means
* "reuse params from film_grain_params_ref_idx" — defaulting to
* "update with submitted params" (which is what apply_grain implies
* when set). The flag's omission is safe for vpu981 which derives
* grain state from the submitted control payload, not from a
* separate reuse signal. */
/* VAAPI doesn't expose update_grain; not setting it means
* "reuse from film_grain_params_ref_idx (=0)". A previous test
* with UPDATE_GRAIN=1 unconditional triggered a segfault on the
* 352x288 film_grain-50 fixture — keep update_grain implicit-zero
* here and revisit during Phase 3 deeper investigation. */
if (fg->film_grain_info_fields.bits.chroma_scaling_from_luma)
ctrl->flags |= V4L2_AV1_FILM_GRAIN_FLAG_CHROMA_SCALING_FROM_LUMA;
if (fg->film_grain_info_fields.bits.overlap_flag)