When i reboot i need to use chmod for transcoding to work

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Compose V3 doesn't support group_add. It doesn't work how people expect it to anyway. Everybody wants to use it to add the group ID of video/render outside the container. This might work, but not always. That flag adds the user inside the container to a group inside the container, so IDs need to be verified within the container for groups or semantic group names should be used. Just to reiterate, group_add won't work if you're specifying Compose V3.

Make sure your host user is the ID you expect and that it has been added to BOTH the video and render groups. If you don't see video and render (should be correct for Debian I think?) listed in the groups list for the host user, add them with...

Code:

usermod -aG <group_id or name>

This requires sudo privileges. I might also specify exactly which device you're using in as I've had issues using the generic /dev/dri path (iGPU will be /dev/dri/renderD128 and /dev/dri/card0). You can add both in your devices block by specifying the same designation on both sides of a colon; essentially copy what you have and add the specific devices.