ohm task (b): Brave reached vaCreateContext, blocked on multiplanar libva

End-to-end status of browser HW decode:

- Built bootlin libva-v4l2-request-git from AUR with local patches:
  - HEVC stripped (old V4L2_CID_MPEG_VIDEO_HEVC_* names; kernel renamed
    them to V4L2_CID_STATELESS_HEVC_*; ohm has no HW HEVC anyway)
  - Missing #include "utils.h" in h264.c added
  - config.c probe extended to try both OUTPUT and OUTPUT_MPLANE types
  (patch archive parked on ohm at ~/fourier-test/libva-patches/)
- vainfo enumerates MPEG-2 + H.264 profiles (Main/High/ConstrainedBaseline/
  MultiviewHigh/StereoHigh) via LIBVA_DRIVER_NAME=v4l2_request
  LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1.
- Brave with --enable-features=VaapiVideoDecoder,VaapiIgnoreDriverChecks,
  AcceleratedVideoDecodeLinuxGL + --use-gl=angle --use-angle=gl-egl picks
  up VAAPI in the GPU process and calls vaCreateContext on the video.
- vaCreateContext fails. Root cause: bootlin library was written for
  Allwinner sunxi-cedrus (single-plane V4L2); context.c / picture.c / v4l2.c
  hardcode single-plane paths that don't match Rockchip hantro multiplanar.
  Profile probe is now multiplanar-aware (my patch), but buffer setup and
  frame-submission paths aren't.

Decision: browser HW video decode on ohm parked until a multiplanar port
of libva-v4l2-request exists. Non-browser paths (gst v4l2codecs, ffmpeg
v4l2-request) are unaffected. Patch set on ohm is a starting point for
anyone picking up the multiplanar rework; also a candidate for a future
marfrit libva-v4l2-request-fourier PKGBUILD once multiplanar works.

Also updated the Status line with fermi CI success: first push built,
signed, and published ffmpeg-v4l2-request-git-2:8.1.r123329.b57fbbe-1
on packages.reauktion.de in one shot.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -160,10 +160,12 @@ picks up rkvdec2 patches.
 
 **Status 2026-04-24**: ohm reachable; steps 1 + 2 + 3 + 4 done for H.264 on
 ohm (GStreamer `v4l2slh264dec → waylandsink` at 7 % CPU with zero-copy
-dmabuf NV12). Step 5 scaffold landed
-(`marfrit-packages/arch/ffmpeg-v4l2-request-git/` on `main`, commit
-`9994c4e`, unpushed — fermi CI build + ohm install still to run).
-Immediate next: push, build, install, validate the ffmpeg path.
+dmabuf NV12). Step 5 scaffold pushed; fermi CI **built + signed +
+published** `ffmpeg-v4l2-request-git-2:8.1.r123329.b57fbbe-1-aarch64` on
+first push. Immediate next: install on ohm via `pacman -Sy`, validate the
+ffmpeg v4l2-request hwaccel path, compare CPU / fps to the GStreamer
+numbers. Task (b) (Brave HW decode) blocked on multiplanar
+`libva-v4l2-request` rework — see section below.
 
 ### Baseline numbers (2026-04-24, ohm, `bbb_1080p30_h264.mp4`)
 
@@ -203,6 +205,53 @@ Reading:
   position advances 1:1 with wall clock for the full 62 s run — zero
   drops, full 24 fps delivery.
 
+### Browser HW decode (Brave / Chromium) — partially wired, library-blocked
+
+Attempted as task (b) on 2026-04-24. State reached:
+
+- Installed bootlin `libva-v4l2-request-git` from AUR with local patches
+  (patch archive on ohm: `~/fourier-test/libva-patches/fourier-local.patch`):
+  - HEVC stripped from the build (`h265.c` + `h265.h` removed from
+    `src/meson.build`, HEVC case in `picture.c` returns
+    `UNSUPPORTED_PROFILE`). The library's HEVC UAPI binding predates the
+    mainline rename (`V4L2_CID_MPEG_VIDEO_HEVC_*` → `V4L2_CID_STATELESS_HEVC_*`)
+    and ohm has no HW HEVC anyway.
+  - Missing `#include "utils.h"` added to `src/h264.c` (pre-existing bug
+    the library grew into as compilers got stricter about implicit
+    declarations).
+  - `src/config.c` probe extended to try both `V4L2_BUF_TYPE_VIDEO_OUTPUT`
+    and `V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE` when enumerating profiles.
+- `vainfo LIBVA_DRIVER_NAME=v4l2_request LIBVA_V4L2_REQUEST_VIDEO_PATH=/dev/video1`
+  enumerates profiles: **MPEG-2 Simple/Main + H.264 Main/High/ConstrainedBaseline/
+  MultiviewHigh/StereoHigh**. Library is up and talking to the hantro
+  decoder.
+- Brave launched with `--enable-features=VaapiVideoDecoder,VaapiIgnoreDriverChecks,AcceleratedVideoDecodeLinuxGL --use-gl=angle --use-angle=gl-egl --ozone-platform=wayland`
+  visibly activates VaapiVideoDecoder in the GPU process argv and attempts
+  VA context creation on the video file.
+
+Failure mode:
+```
+ERROR:media/gpu/vaapi/vaapi_wrapper.cc:2407] vaCreateContext failed,
+  VA error: operation failed
+ERROR:media/gpu/vaapi/vaapi_video_decoder.cc:1219] failed creating VAContext
+```
+
+Root cause: the bootlin `libva-v4l2-request` was written for Allwinner's
+sunxi-cedrus (single-plane V4L2). The probe patch gets it past format
+enumeration, but `context.c` / `picture.c` / `v4l2.c` still hardcode
+single-plane buffer setup, `VIDIOC_S_FMT` paths, and request-API frame
+submission in ways that don't match a multiplanar decoder. A real port to
+multiplanar is a side project — the upstream is effectively unmaintained
+(last meaningful commit years ago; Collabora talked about a replacement
+but it has not shipped).
+
+Decision: **browser HW video decode on ohm is parked until a multiplanar
+`libva-v4l2-request` rework exists**, either ours or someone else's.
+Non-browser HW decode (GStreamer `v4l2codecs`, FFmpeg via
+`ffmpeg-v4l2-request-git`) is unaffected and works. The patch set on
+ohm is a useful starting point for anyone who wants to pick up the
+multiplanar port.
+
 ### Acceptance criterion
 
 **1080p @ 30 fps, no dropped frames.** Applies to every device and every