If I remember correctly, the QuickSync option in Jellyfin is only for Windows. The equilevant under linux is VAAPI. It should work with that as long as you have mounted /dev/dri/ to the container.
Yep, I changed to VAAPI and with the additional lines from the compose file above, it’s now working perfectly! Thank you.
I was having the same issue until it was pointed out that VAAPI is the option you need.
If you have the render node exposed you will be able to see /dev/dri/renderD128 as your VA API Device.
Here is my docker-compose file. Also, after you configured dev/dri device, you have to go to server dashboard/transcoding and choose the device that will do the work.
[/dev/dri] # ll