Best Design to Sync Video Stream Across Clients in Asp.net Application?

We are developing an Asp.net core application with a video streaming feature. The project contains an action on a controller that returns video stream. For an upcoming demo we need to mock a video stream using a single video file played in a loop for a demo. Business requirements expect the stream to appear the same on all clients, e.g. if the controller just loads the video file from the beginning when the web request starts each client will be viewing the video at different time points and it would not be synced like a live stream.

What is the best design/architecture to sync all of the clients video feeds based on a single video file stored on the webserver?