AMD GPU Transcoding on Docker container

Hello, first of all I am no expert in Linux so I might say some stupid things.
I’m running OpenMediaVault on a computer with a i7 4700 and a AMD r9 290. I’m running Docker on it, in which I am executing a Jellyfin container. The hardware acceleration works good if I use the CPU, but I’m trying to get hardware acceleration working using the GPU. I’ve been searching Google for some days now but I can’t figure how to get it working. I think I have installed my GPU drivers now (Even though I’m not sure I have the good ones) as well as VAAPI and Xorg server.
Video wont start when I enable hardware acceleration like this:

Thanks in advance!