VideoSync for Chrome
More About VideoSync
To watch a video with others on VideoSync, make sure that all parties have the extension installed. Once everyone is in the same room, they can each select the video they want to watch; while it is recommended that everyone use the same video, people can choose to use different streaming providers if they want. Once everyone is ready, the video players will be sync and you can start watching the video at the same time.
Playing, pausing, rewinding, or even changing the playback speed are synchronized. The extension attempts to adjust for latency in order to keep everyone synchronized, but this may cause unexpected skipping, so if you wish to turn it off you can uncheck the "Adjust for latency" checkbox.