The job of an above the fold video is to answer one question fast: does this product actually do the thing the headline just claimed. A visitor who has not even scrolled yet is not committed to anything. They are deciding whether to keep reading, and a video that proves the claim in a few seconds does more work than another paragraph of copy underneath it. Every second the video takes to get to that proof is a second in which the visitor could decide the page is not worth their attention.
Bubble apps complicate this slightly, in a useful way. Because a Bubble build is frequently a real product with a database and user accounts from day one, the interesting workflow the landing page wants to prove is often the same workflow that lives behind a login. That means the landing page video has to bridge a gap other tools do not always have: showing the logged in product convincingly, on a page whose whole job is to convert a visitor who is not logged in yet. Getting that bridge right is most of the work in this format, since the rest of the recording is comparatively straightforward once a believable logged in state exists to record from.
