The YouTube app for Android gets an update to play vertically recorded videos in full screen. Many users create vertical videos with the camera on their phone, so there are many vertical YouTube videos.
Until version 10.25.xx, users get, when they play a vertically recorded video in fullscreen, a horizontal screen on which the video is often shown only slightly less than a third of the screen. From version 10.28.xx YouTube shows videos vertically and on the entire surface of the screen, Android Police reports.
The version is not yet available to all users in the Play Store, but you can already find the APK file on APKMirror. Vertical recorded videos this year also gained popularity trough apps such as Periscope, Twitters live streaming app that works only in portrait mode.
The function is currently only available in the Android version of YouTube. It’s not known when the iOS version get’s the same update.