CNN New Video Box (scroll down while video is playing), How does this magic works?

I've just noticed CNN's new video box which have some cool effect, check this article for example.

While scrolling down reading the article, the video resizes to a small box on the right, overiding the category articles but still displayed with the title and while it keeps running perfectly when the user browsing the site.

Does anyone knows what kind of code makes this magic happens? It will be great to have some kind of thing on other sites, most of them much better than CNN.

Epic visual tool

Epson 5030UB 2D/3D 1080p 3LCD Projector Submitted September 20, 2015 at 06:58PM by omemo http://ift.tt/1KoEJH2