Use ifVideoPlayer.SetDestinationRect(x as Integer, y as Integer, w as Integer, h as Integer) to set the window size to the full screen, and then set it back to the window when the user clicks OK again.
To expose the videoplayer you have to Place a transparent layer directly over it You can create a transparent layer by creating A target rect with full transparent color above the video player. It has to be at the Same coordinates and the same size as The destination rect of the player To see any of your changes you need to Refresh any changed layers by calling setlayer Again. Your better off using roscreen For what you are trying to accomplish You are going to be disappointed in the Performance with the imagecanvas
My Channels: 2D API Framework Presentation: https://owner.roku.com/add/2M9LCVC Updated: 11-11-2015 - Completed Keyboard interface The Joel Channel ( Final Beta )