YouTube has added support for HDR video playback on Apple's iPhone X, 8 and 8 Plus. The iPad Pro also has a display that is bright and dynamic enough for high-dynamic-range content, but MacRumor's notes that YouTube has not flipped the switch yet to enable it. HDR video is more colorful and radiant than traditional content. It's a little closer looking through a window than watching a video on a screen. But you have to have a display that can show it; Fortunately, more and more newer smartphones.
YouTube has tons of great demo material to watch the improved image itself: just search "HDR" and you'll find no shortage of exotic scenery, cityscapes, food, animals, and other demo reels. My iPhone automatically switched to HDR after streaming a video. Alternatively, you can tap the icon with three vertical dots to manually activate it. Note that you do not have to worry about 1