Video Streaming from Linux

As part of a set-top video project, I looked into streaming. Just local streaming: we have a fileserver in one part of the house, running Linux, and the set-top box by the TV (also running Linux though that part is less important); how can I stream a video from the fileserver and play it using mpv on the set-top box? I thought that would be a dead simple question to answer. But there's…