HDR stands for High Dynamic Range. HDR videos provide a broader range of colors and luminance compared to sub-HDR content, and the format also supports quality video playback on a wide variety of screen sizes.
Logged-in subscribers of the BT Sport app on an iPhone X, XS, XS Max, Apple TV 4K, or iPad Pro (2nd and 3rd generation) will be served with a tile on the homepage so they know the Champions League soccer final is available to them. Users without a HDR-capable device or logged-out users will see the normal tile on the homepage without any reference to HDR.
To AirPlay the match, users will need a capable TV to watch in HDR. The vast majority of 4K TVs sold in the last few years also support HDR. The app will detect HDR compatibility and serve the appropriate stream.
The Champions League final will also be available to non-BT Sport subscribers for free, though not in HDR. It will be shown on the mobile and large-screen apps, on BTSport.com and on YouTube. BT Sport's live coverage begins at 7pm on BT Sport 2 and BT Sport 4K UHD.
Apple debuted HDR support with the "Super Retina" display in the 2017 iPhone X, which became the first HDR OLED display incorporated into one of Apple's smartphones.
Apple also lists the iPhone 8, iPhone 8 Plus, and iPhone XR as supporting HDR, but the displays for these devices are not the same as the Super Retina display on Apple's OLED iPhones, so any HDR content played on the 8 or 8 Plus isn't true HDR.
BT Sport claims its live HDR coverage of the Champions League Final on a mobile device is a "world first," and says that going forward it plans to show up to 70 live sporting events in High Dynamic Range per season.