Background fixed/scroll effect

Hi all,

On this website there’s a background video at the top of the page which then makes way for a fixed background image - however the background image only stays fixed until the next section comes along and then it begins to scroll up. Then this repeats on the next section…

So, it’s kind of a mix of fixed background elements, and parallax scrolling, or something?

How would I go about achieving this?

Many thanks in advance.