Bad 4K Performance on Jellyfin

Hi all, looking for some help with the Jellyfin Media Player.

For background, I've used Plex for years, and I've had it working well. I'm trying out Jellyfin because of all of the reasons you're already thinking of.

One issue I'm having - I like uncompressed 4K HDR. I'm trying to play a large movie, one Plex direct plays perfectly fine to my HTPC. (2.5GB networking through and through, direct access, all the basics have checked). However Jellyfin Media Player seems to stutter and drop frames.

Not like "It stops and buffers", but more like playing a video game and it drops down to 15fps. Is there a setting somewhere I'm missing to enable GPU support or something? I toggled OpenGL on and off and it didn't seem to have an effect.

Video says it's direct play, no transcode. Not sure what else it could be beyond hardware acceleration?

Thanks!