Microsoft is introducing animated video backgrounds for Windows 11 in the latest Insider builds, allowing users to set MP4 or M4V video files as their wallpaper. This feature can adapt videos to fit various screen resolutions without distortion and does not impose significant limitations on video size or length. To enable this feature, users must be on a Beta or Dev channel Insider build (build numbers 26220.6690 or 26120.6690 or higher) and use a command-line utility called ViVeTool to unlock it. Users can also opt for third-party applications like Lively Wallpaper to achieve animated backgrounds without joining the Insider program.