Just in case it might be useful for anyone.
It is againgst the rules to play YouTube videos out of YouTube apps. To stream without resctricitons, you need the direct video URL. To get direct video streaming URL, you need to host your video content into a server and create video streaming URL. HISPlayer now includes Video Upload & Hosting solution that allows you to host your local videos and convert them into HLS or DASH streaming URLs. You can then play those video URLs anywhere inside Unreal projects.