Plex never hardware-transcoded on esh-pve-nas LXC 105 despite correct passthrough,
cgroups, group membership, authenticated HuC firmware, a lifetime Plex Pass,
HardwareAcceleratedCodecs=1, and the Arc already selected as HardwareDevicePath.
Root cause sat below all of that: intel-media-va-driver 22.3.1 (Apr 2023, stock
jammy) predates Arc/DG2 support and exports only __vaDriverInit_1_14, against the
libva 2.22 that Plex bundles and loads via RPATH rather than the system one. A
half-finished prior attempt at the same fix was also present -- libva and libva-drm
hand-installed at 2.22 with libva-x11 left at 2.14, breaking every X11 VA-API
consumer on va_fool_postp.
Fixed with Intel's client-GPU repo: iHD 24.3.4 (__vaDriverInit_1_22, an exact ABI
match) plus a consistent libva 2.22.0.2-87 set, which also brings the orphaned
manual install back under dpkg. The repo track is rolling, so the six packages are
pinned in /etc/apt/preferences.d/intel-gpu-pin and apt-mark held; verified by a
simulated upgrade that moves 152 packages and touches none of them.
Two findings worth more than the fix:
pct snapshot refuses on a guest with a bind mount and still exits 0, so a script
guarding a change with it proceeds without the rollback point it believes it has.
The ZFS dataset snapshot is the working path, verified by reading it back.
A synthetic Plex Transcoder invocation is not a valid test of Plex's transcode
path. Plex bundles its own libc among 61 libraries; the harness produced three
distinct failure modes that were artifacts of not reproducing that runtime, and it
failed identically before and after a fix that worked. With no positive control its
negatives carried no information. Only a forced transcode settles it, and PASS is
recognisable by Plex naming the device. The original empty decoder/encoder line was
an absence of evidence rather than evidence of failure -- TranscodeSession was 0.
Jellyfin LXC 107 has the same stale stack and the same Arc available; left alone
per the operator, and it ships its own ffmpeg so this may not transfer verbatim.
vh
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