SOLVED: Proxmox LXC Hardware Transcoding

[C0nfigurator]

Hello everyone,

after a day of troubleshooting and looking at tutorials and forum posts I decided I will ask here, sorry I know this topic has been opened a million times by now. So I try to get Intel QSV inside a Proxmox priviledged LXC to work. I successfully passed through my gpu, but when enabling Hardware transcoding in Jellyfin, I am left with a playback error. Looking in the LOGs, I can find the following entries:

[2025-01-06 18:24:31.463 +00:00] [ERR] FFmpeg exited with code 234
[2025-01-06 18:24:31.562 +00:00] [ERR] Error processing request. URL "GET" "/videos/1d3a78ff-a07f-0173-c6b8-b26e7159a051/hls1/main/-1.mp4".
MediaBrowser.Common.FfmpegException: FFmpeg exited with code 234


LXC Config file:
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arch: amd64
cores: 4
features: mount=cifs,nesting=1
hostname: jellyfin-prox
memory: 4098
net0: name=eth0,bridge=vmbr0,firewall=1,gw=192.168.178.1,hwaddr=BC:24:11:3E95,ip=192.168.178.11/24,type=veth
ostype: ubuntu
rootfs: DIR01:900/vm-900-disk-0.raw,size=64G
swap: 2048
lxc.cgroup2.devices.allow: c 226:0 rwm
lxc.cgroup2.devices.allow: c 226:128 rwm
lxc.mount.entry: /dev/dri/renderD128 dev/dri/renderD128 none bind,optional,create=file
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In the LXC I can see the renderD128 device. vainfo displays me the correct driver as well:
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vainfo: Driver version: Intel iHD driver for Intel® Gen Graphics - 24.1.0 () in both the LXC and the Host.
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I also can see all the supported profiles.

Jellyfin is part of the render group:
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root@jellyfin-prox:~# members render
jellyfin
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When using intel-gpu-top inside the jellyfin container I can read the current power usage and it is the same as on the proxmox host.
The driver intel-media-va-driver-non-free is installed on both, the Host and LXC.

The thing is, and I think there is my problem that I dont't fully understand as to how you modify the GID. The example on the Jellyfin Docs is:
lxc.cgroup2.devices.allow: c 226:0 rwm
lxc.cgroup2.devices.allow: c 226:128 rwm

But the GID of renderr on my Proxmox host is 104 and in my jellyfin container 993. I guess this could be my problem?