Google recently unveiled that its streaming service will support films and shows in HDR (High Dynamic Range) starting here in the USA and Canada, but perhaps eventually coming to other territories like the United Kingdom and Australia as well.
Netflix, for example, allows customers to stream video in HDR quality if they have a supported TV, and there are rumors it will add support for mobile HDR content in the future.
You'll be able to spot HDR-enabled content in the app by looking for an [HDR] tag in the video's title.
Just because you select an HDR-enabled movie however, that doesn't necessarily mean it'll look better on your current setup. However, unlike Chromecast Ultra, Google has not made it clear whether Play Movies & TV service would support both the HDR formats. The results are pretty spectacular, even on small screens, and assuming there's a good library of content, Google's support should go a long way toward making it more of a mainstream format.
Among those films compatible with the new standard are Kong Skull Island, The Lego Batman Movie, Fantastic Beasts and Where To Find Them and Mad Max Fury Road. This includes TVs with Google Cast built in, including some sets from Vizio, Sony, Toshiba, Philips, and others, as well as Google's own Chromecast Ultra. You'll need a TV or monitor with HDR support in order to enjoy the upgrade.