

Vertical videos are videos that are shot in portrait mode on smartphones. Previously, viewing a vertical video in the YouTube app added two black bars to the sides of the video, shrinking the actual image and making it difficult to view. Now, vertical videos play in full screen the same way they were filmed, allowing users to have a better experience on mobile devices.
YouTube is a universal app available for free on the App Store. [Direct Link]
Article Link: YouTube App Updated With Fullscreen Playback for Vertical Videos