[Xiaomi Mi Mix 2 Questions & Answers] ylair:
Whatever you want, but what do you want

Before anything else, I think you need to realize that if you get a bezeless phone, you are going to have viewing differences then phones with a bezel, as it's a wider viewing area then the ratio most phones take video in (explained in more detail below). However, that does not mean it's changing the video from the way it's currently captured on your bezeled phone to the way it would be captured on a bezeless phone. The only thing that impacts the video capture is hardware such as the camera, megapixels of the camera and recording resolution or in terms of viewing, screen resolution and dpi. Therefore, that is probably what you should make any phone buying decisions based off of and you can use a handy website like gsmarena..com to get full specs on phones from all around the world in addition to a bunch of other useful tools like size comparisons.

With that said, if all your concerned with is cosmetics, then the Mi Mix 2 still has you covered as you literally get a button that says fullscreen. Tap it on, the video stretches to fill the screen, tap it off, it retains its proper ratio in letterbox (black bars). As that feature demonstrates though it's purely for looks, which is why I would caution you from making any decisions based off of it. It's like deciding whether a phone is right for you based on a phone case, which has nothing to do with the fact that your buying a pocket computer and ignores what it's used for or in your case what size pictures/video you want. The Mi Mix 2 takes video in 4k, 3840x2160 at it's highest resolution, that is a 16:9 ratio. Phone sizes are not typically made in 16:9 ratios, they are wider, but 16:9 is the most common ratio used across the entertainment industry from video distributed in movie theaters, TV, YouTube, to video being captured on most phones.. Consequently, any bezeless phone will have a wider viewing area then the video they capture in 16:9, yielding black bars.. However, does that matter? Have you ever decided on buying a computer based on whether you have black bars when watching YouTube in fullscreen, probably not, and most likely you do have black bars at the top and bottom of videos because computers tend to use more square ratios. Therefore, regardless of any cosmetic differences, which can be achieved by stretching a video to fill the screen (a technique often used when broadcasting non standard ratios on TV and even a setting you can trigger on most TVs through the display menu), the Mi Mix 2 captures video in the most widely used and distributed ratio of 16:9. Therefore, if you watch your recorded videos on most TVs, it will fill the entire screen and since the Mi Mix 2 shoots in 4k UHD, the resolution will be pretty good too.

Hope that helps. I own a Mi Mix 2 and honestly it's a fantastic phone all around, although the explanation above is really for any bezeless phone and for anyone making decisions in a similar fashion. Essentially you should decide what you need out of a phone first then judge how things look, which will help inform why they look that way and how much weight you should afford to any cosmetic aspect. I also work in the film industry and realize most people don't know or necessarily pay attention to things like video ratios, so I'm happy to share, but as mentioned above, regardless of your knowledge, you should not take for granted the fact that phones nowadays are massively powerful pocket computers capable of incredible things and instead reduce them to "black bars".