It's determined by the client you're trying to watch the file on. The server could be run on a Raspberry Pi if you always use compatible files with your client since transcoding wouldn't be needed. The most compatible files will be x264 video and (don't quote me here) AAC audio but modern clients can also play x265 video and stuff like EAC or AC3 audio without needing to be transcoded (converted from one format to another on the server). For ease of transcoding, a GPU works best but they can be converted strictly with CPU hardware though it's more resource intensive.

The logs say something?

I would recommend giving kivata a try.

Can't really speak on open source alternative for Plex though (other than jellyfin, which I haven't used myself even). Good luck on the search!

@raccoon @nutbutter

The linux server image worked without issue for me.

You might have to let jellyfin finish scanning your stuff though. First time takes a bit.

Pretty sure Emby is open source since Jellyfin is a fork of it, but that also means you might run into the same issues if you try switching over.

I’d check if you have hardware transcoding turned on. If you have an intel cpu it should be enough to get things to work.