Missing ffmpeg after a bad update

[TheDreadPirate]

You might have trouble finding help because TrueNAS CORE is not an officially supported platform. I'm assuming you are using some sort of community created Jellyfin image for TrueNAS Core. And that may not include ffmpeg. The official docker image has ffmpeg bundled and does not require additional configuration.

What you COULD do is install ffmpeg directly in the host OS and then configure your jail to pass in the path to ffmpeg. Then set Jellyfin to use that path.