How do you control the playback of a video with scroll?

How do you do this: https://www.squarespace.com/refresh

The first section has a background video that is controlled by scrolling. It appears the video plays back and forth on its own, then when you scroll, it plays forward or backwards with your scroll wheel. When the end of the video is reached, the page scrolls as normal.

Would also be very curious how to implement parallax json or ideally mp4 scroll animations like this. Have been trying to track down native options for squarespace, but it seems a json code implementation is the only present option.