How to make a video play in a multiplayer lobby?

Unity has a VideoPlayer that you can use. It will render onto a material or render texture. It will take a URL but not a YouTube URL unfortunately because YouTube blocks that type of usage. The VideoPlayer has a property that you can set the current position of the video from the start of the video in milliseconds (or some similarly small measurement). You just need to send an RPC to all the clients with a string of the URL to start the videos playing. It is more complicated than that because of network delays. Once the video has started playing, you will want the Master Client to send another RPC to the clients shortly thereafter telling them what position it is currently at and along with a UTC time stamp (something that includes milliseconds). The clients receiving the message will look at the video position sent by the Master Client and calculate the UTC time difference from the timestamp sent along with the RPC to then set the current position of it's local Video Player to be the same as the Master Client's video position. The Master Client should keep sending that same RPC message every so often (once a minute or so) telling the clients it's position and the clients only need to apply it if they see that they are outside of a range of time (maybe half a second or something) because you don't want to make the video stutter from constant updates - as long as you are within a certain time delta of less than a second you don't want to do anything.