https://arstechnica.com/gaming/2017/09/youtube-on-ios-can-now-livestream-replaykit-supported-apps/

YouTube announced some new features for its mobile apps, with one of the biggest being more livestream support. Now you can livestream content from apps on iOS that support ReplayKit, Apple's screen-casting framework. YouTube Gaming has supported ReplayKit since June, but this update brings the support to the main app and lets users livestream content other than games.