You can dock a pre-recorded video or broadcast from your X for iOS and X for Android app. With video docking, it’s easy to watch while continuing to use X––like scrolling through your timeline or sending a Direct Message.
How to dock and undock a video (iOS and Android):
To dock a video, simply tap on the docking icon  in the top right of a video in full-screen mode.
To return to full-screen view from a docked video, tap on the video.
To dismiss a docked video, use your finger to slide the docked video towards the edge of your screen until it disappears. Alternatively, if you tap on a different video, the currently-docked video will automatically disappear.