https://www.theverge.com/2018/5/10/17341656/youtube-iphone-x-8-hdr-video-streaming-now-available

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’s bright and vibrant enough for high dynamic range content, but MacRumors notes that YouTube hasn’t flipped the switch to enable it on there yet. HDR video is more colorful and more radiant than traditional content. It’s a little closer to looking through a window than watching video on a screen. But you’ve got to have a display that’s capable of showing it; thankfully more and more recent smartphones do.

YouTube has plenty of great demo material for seeing the improved picture for yourself: just search “HDR” and you’ll find no shortage of exotic scenery, cityscapes, food, animals, and other demo reel material. My iPhone switched over to HDR automatically once I started streaming a video, but you can also tap the icon with three vertical dots to manually enable it. Note that since it’s really all about color, brightness, and contrast, you don’t have to pick 1080p to enjoy HDR; it’s also supported at lower resolutions like 480p.