AW3425DWN, Mac mini, not zooming

I have a Mac mini and apps and video is no problem. On the two HDMI input, I have the Apple TV, which of course has 16:9 content, so 21:9 movies are imbedded in 16:9 medium/broadcast. The Alienware monitor only stretches 16:9 content. I need Zoom function to fit 21:9 movies to FULL SCREEN while having 16:9 medium. Why can I not do this or what do I need to do to view 21:9 content without the black bars on the screen?