I am running jellyfin in LAN on a Synology. I/O from harddisk shouldn’t be a problem being SSD on the same NAS. And WiFi should sustain a 4K stream. I have tried only web clients. How can I optimize the stream for such large file? Or how can I debug the bottleneck?
from the jellyfin website discussion: When it comes to 4K SDR 10bits movies, most of the clients supports only 1080p, JellyFin transcodes it to a 1080p / 8bits file and the main quality loss is felt by that “bitmiss”.
maybe try VLC or Kodi?