Google Play Movies & TV has quietly gained 4K HDR support today, following the rollout of non-HDR 4K content late last year. So if you have a device (or TV) that supports 4K HDR, you can now take advantage of that great image quality if Play Movies is your thing. This may work with HDR-capable phones such as the Sony Xperia XZ Premium, LG G6 and Samsung Galaxy S8, but Google's focus is on HDR-compatible TVs with Cast built-in. If you don't own one of those, you can still see HDR if you use a Chromecast Ultra plugged into an HDR TV. Oddly enough, HDR isn't supported in Android TV...
Source: http://www.gsmarena.com/google_play_movies_now_supports_4k_hdr_playback-news-26156.php
