you see the black bars on both sides when the video’s aspect ratio mismatches with YouTube’s recommended 16:9. If you watch a video with a 1:1 or 4:3 aspect ratio on YouTube, you will see ...

or at a typical 16:9 or similar common aspect ratio. That gets the job done, but it means that you end up playing a game on your mobile device with black bars around the sides as most modern ...