That is a function that belongs on the display device and is usually there in the form of stretch or zoom or some such.
However since you asked about roVideoPlayer I think you are developing a channel and therefore this question really belongs in the developer forum.
Two Roku Ultras, three Roku 3s and a Roku 1
"Part of the secret of success in life is to eat what you like and let the food fight it out inside." Mark Twain
Van Roy's Law: An unbreakable toy is useful for breaking other toys.