If you go here (link: https://yle.fi/uutiset/3-11555155) and scroll down this news article, you will see there is a rather long background video that plays as you scroll showcasing some nodes and boxes. However the initial page load is very fast and I don't see it loading a video from anywhere at all.
As I try to understand how this website is put together, I'm not able to see where the video comes from, nor do I know if it's an .mp4 or some other format. When I try to hunt it down in my network tab and monitor if it loads, I just cannot see it and there is no resource that seems to be more than a couple of hundred kilobytes.
How is this possible from a web-design standpoint? Is it some sort of a proprietary solution that stealthily streams the video as it is loaded? If I would like to build a background video that plays on scroll like this in such a performant manner, how could I do it?
Such videos that play on scroll can often be seen for example on the apple.com website, but at least there I can easily also see the original source videos and materials of how the page is put together. Here this is not the case.
I would greatly appreciate if you could answer this super basic question I have. Thank you!