It’s an mp4 video. Use your browser’s inspector to find it. It takes a small amount of digging. Tip: If you do something like this you don’t want to have the sound on by default, that’s considered rude.
Agreed. When I’m bothered with audio that I didn’t ask for, that’s an instant rage-close. I think it’s not even possible anymore to auto-play videos with audio on page load (without some trickery), browsers have become very strict in this regard. They only allow autoplay if the tag includes either the muted or the controls attribute to allow the user to stop the video. @Dobs If you really want audio to play automatically (I think some subtle water sounds are within the range of “acceptable”), you can’t use a video, it’ll have to be a HTML audio element.