Aspect ratio
Watch as an animation →The ratio of the screen's width to its height. 16:9 is for regular YouTube videos and TV, 9:16 is for Shorts and Reels, and 2.39:1 gives a cinema feel.
Decide it first of all, when you set the purpose and platform in the first stage of planning.
Make the start-frame images and the video generation in the final ratio from the beginning. If you crop a 16:9 1920×1080 into 9:16, only about 608px of width is left and the composition falls apart. If you plan to release in both ratios, make the start frame with the subject in the middle third of the frame, or generate separately for each ratio. For 2.39:1, generate in 16:9 and then make it with a letterbox (see Letterbox). YouTube classifies square and vertical videos of 3 minutes or less as Shorts, so for a contest that requires a regular video, make it in 16:9.
Vertical 9:16 two-shot sequence generated at the final ratio from the start: Shot 1, a florist arranges tulips on a wooden counter, subject centered in the middle third, 3 seconds; hard cut to Shot 2, close-up of her hands tying a ribbon, subject centered, 3 seconds. Leave the top and bottom edges calm, soft daylight.
Google — Veo 3.1 video generation docs (16:9 by default, 9:16 vertical)