The YouTube app for iOS has received an update that supports video with a high dynamic range on the iPhone XS and iPhone XS Max, but it also lacks an option to watch video with 4K resolution.
The update to version 13.37 of the iOS YouTube app adds new options to the video quality settings, with compatible clips that now show the letters "HDR" next to the resolution to indicate the contents of the high dynamic range. HDR options can be manually selected, but the Auto Quality option also enables HDR if it is available for the currently viewed video.
HDR allows a wider range of colors in a video to be displayed on a compatible screen, as is the case for the Apple TV 4K and a supported 4K TV with HDR support. The effect can provide a brighter, more detailed and vivid image, with fewer color strips and other digital approximation artifacts.
The OLED screens used in the iPhone XS and XR offer high contrast ratio, making it suitable for displaying HDR content, both made by the built-in cameras and those downloaded or streamed to the device via online services.
The addition of HDR to the app has not been announced by YouTube. The release notes for the app version simply state that it contains bug fixes and has improved its performance without mentioning additional device support for HDR.
Although HDR support is likely to be acclaimed by users, the app will continue to avoid providing options with higher resolution than 1080p, with 4K content displayed on an encrypted resolution on the iPhones. The problem is not only limited to iPhones, because iPads with higher resolution screens and the Apple TV can not play 4K 4K or higher than 1080p content.
The problem is also clear on macOS, while Chrome can offer YouTube video with resolution up to 4K, but Safari is up to just 1080p.
The problem is probably due to the lack of OS level support for Google's VP9 codec, used by YouTube. Although it is still unclear when Apple will include the VP9 support in its software and devices, it is also unknown whether Google will use Apple's decision not to use the codec in the software, as with the Xbox One. 4K or 1440p video streams on hardware that it could play.