The video player in 📝Topia (found in the 'Specials' folder of the Topia Asset Library) enables you to place a video in-world. It can be a .mp4 or .webm file, not a Youtube video.
The video playing is not synced between people. However, if you get everyone around the video and then open it and uncheck / recheck the 'show video', it'll be synced for everyone.