Thumbnails are used to represent your experience on its details page and can be used to help it stand out while also showing new players what they can expect when they join. You can use thumbnail and icon features to help your places/experiences get noticed and stand out.
Please be aware that videos can be up to 30 seconds long. If your video is longer than that, you will receive an error message and it will not upload. For a full list of other video restrictions and acknowledgments, please click here.
Check out the Game Icons and Thumbnails Creator Documentation for assistance with this process as well as some tips on how to create a promotional thumbnails, videos, icons.
Note: Thumbnails, Videos, Icons, and images must meet Roblox Community Standards.
Additional Help
Video Advertisement Policy
Creator Documentation
Thumbnails And Videos