You can add a background video to your forms by following these steps:
In the form editor, click on Theme (waterdrop icon) → UI Elements → Background.
Paste your video URL into the field below "Background Video". You can also add URL parameters from the video hosting site that change the behavior of your video, such as autoplay.
(Optional) Choose whether you want to cover the entire form background with the video, or if you prefer the entire video to be visible instead.
(Optional) Choose the amount of blur and an overlay color for the background video.