Safe zone

Thumbnails are never shown clean. YouTube draws the video duration over the bottom-right corner, and progress bars, watch-later buttons and channel avatars cover other edges depending on the surface. The safe zone is whatever survives all that. Keep faces and any text away from the bottom-right in particular, since a duration stamp landing across a word makes it unreadable at the size most people see it. Shorts have their own version of the problem: the frame is 9:16, but the area shown consistently across devices and surfaces is closer to a 3:2 crop, so anything important should sit well away from the top and bottom edges.