installation

[TheDreadPirate]

We would need to see your jellyfin and ffmpeg logs. But it sounds like it is trying to transcode but can't. It wants to transcode because there is some incompatibility with the codec. Jellyfin Media Player relies on the underlying hardware supporting accelerated decoding of whatever codec you are using. We I would also need to know what hardware is in the computer you are trying to play on and info about the media (codecs).