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Mirrors phase6/step1/ from the ohm_gl_fix campaign. Contract-correct
hantro multi-planar / chromium-149-era stateless H.264 port of
bootlin's libva-v4l2-request, patches 0001..0018 + fourier-local.
Honest characterisation in README:
- Builds cleanly on chromium-builder LXC (boltzmann)
- vainfo enumerates H.264 profiles cleanly with LIBVA_DRIVER_NAME=v4l2_request
- NOT on Brave's decode path on ohm_gl_fix stack — Brave uses
Chromium's own V4L2VideoDecoder in media/gpu/v4l2/.
- Most likely useful for a future Firefox-via-libavcodec-vaapi
campaign, modulo a separate Mesa-panfrost WSI pitch issue.
- DEBUG patches (0010, 0011, 0014) intentionally kept in series
for development; remove for cleaner production runs.
Audit trail in the source repo at ohm_gl_fix:
phase6/step1/audit_0008_decode_params_2026-05-01.md
phase6/step1/api_contract_findings_2026-05-01.md
phase3_remeasure_2026-05-02/B3_decoder_discovery.md (why this
isn't on Brave's path)
59 lines
2.5 KiB
Markdown
59 lines
2.5 KiB
Markdown
# libva-v4l2-request-ohm-gl-fix
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Bootlin's libva-v4l2-request VA-API backend, with hantro-vpu
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multi-planar + chromium-149-era stateless H.264 patches developed
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in the [ohm_gl_fix campaign](../../../ohm_gl_fix/) Phase 6 Step 1
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(2026-05-01..2026-05-02).
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Patches 0001-0018 are contract-correct against the kernel V4L2
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stateless H.264 UAPI, validated by inspection against
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hantro_h264.c and v4l2_h264_init_reflist_builder() in linux 6.19.x.
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See ohm_gl_fix's `phase6/step1/audit_0008_decode_params_2026-05-01.md`
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and `phase6/step1/api_contract_findings_2026-05-01.md` for the
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audit trail.
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## Honest characterisation
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This package compiles cleanly, installs cleanly, and `vainfo` with
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`LIBVA_DRIVER_NAME=v4l2_request LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1`
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enumerates all H.264 profiles. It is, however, **not on Brave's
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critical decode path** on the ohm_gl_fix Step-1+Step-2 stack —
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Brave/Chromium uses its own `V4L2VideoDecoder` in
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`media/gpu/v4l2/`, opens `/dev/video1` directly, and never loads
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libva. See `phase3_remeasure_2026-05-02/B3_decoder_discovery.md`
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in the ohm_gl_fix repo for the strace/maps evidence.
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For libva consumers that DO route through libva (mpv with
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`--hwdec=vaapi`, ffmpeg-vaapi, Firefox with
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`media.ffmpeg.vaapi.enabled=true`), this backend would in
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principle engage hantro hardware decode — but each consumer hits
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its own downstream issue:
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- mpv `--vo=gpu-next`: blocked by a Mesa-panfrost WSI pitch bug
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during EGL dmabuf import (out of scope for this package; see
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`phase3_remeasure_2026-05-02/A3_mesa_wsi_pitch.md`).
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- mpv `--vo=image`: silently falls back to libavcodec SW decode
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rather than engaging the libva session (see
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`phase3_remeasure_2026-05-02/A1_morning_pass_disambiguation.md`).
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Reason not yet diagnosed.
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The most likely use case where this backend cleanly delivers
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hardware decode end-to-end is **Firefox via libavcodec-vaapi**, on
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a stack that also has the Mesa pitch issue resolved (or that
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doesn't hit the EGL import path because Firefox's video element
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composites differently). Untested at time of writing.
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## DEBUG patches in the series
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`0010-DEBUG-hex-dump-output-capture.patch`,
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`0011-DEBUG-sentinel-capture-buffer.patch`, and
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`0014-DEBUG-vapic-bytes-dump.patch` produce verbose stderr output
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useful for diagnosing decode-path issues but excessive for
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production. They are intentionally kept in the applied series
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during development; remove for cleaner runs.
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## Status
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Tagged stable as of 2026-05-02 against chromium-149 / linux-6.19.10
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/ libva-2.22.0. Contract-correct; ecosystem-validation-pending.
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