Transcoding Causing Fatal Error

[TheDreadPirate]

With Docker, the container is only aware of the hardware and storage you tell it about and give permission to access it. So you told Jellyfin to use a GPU for transcoding, but there wasn't a GPU present within the reference frame of the container.

That check box tells Docker to give the container access to your GPUs and now Jellyfin can see the GPU and use it appropriately.