Is it possible to adjust aspect ratio on an Android device?

I have an Android device that has a 4:3 aspect ratio. When I watch videos in full screen mode, sometimes the aspect ratio causes the video to be distorted. Is there a way to temporarily adjust the aspect ratio? I can see a couple different solutions: 1. Adjust the actual aspect ratio. 1. Add a black bar on the top / bottom of the display that effectively changes the aspect ratio.