On certain machines running Windows 10, RV cannot be set as the default for a file type. If you set a file to open in RV by right clicking, it will open the file once, but not set RV as the default player. It also won't work to set it through the control panel. When you go to choose an app to assign to a specific file type it'll immediately switch it to windows media player.
RV won't stick as the default player for file types