It's clever, but honestly I don't care how smooth it is. Scrolling should simply scroll a view up or down a page. Not invoke animation. We already have established UX patterns for playing media, slowing it down, speeding it up, randomly seeking through it.

Part of the smoothness here is that scrolling the text is 1:1 once you get down to the sections with colored headers. It demonstrates that it's possible to make a page look fancy like that without "breaking" your intuition of what scrolling "should be."

JS animations obviously don't take the place of video/audio media that you'd play/scrub through.

False. Let the web be fun again

For most websites, sure. For this website? It makes sense, it's a great demo for the product.

It's not so much about playing/slowing/speeding up an animation or video. It's about moving forward and backward through an "experience," as much as I dislike the overuse of that word. I'd suggest it's a natural evolution of the scroll behavior.

Animation isn't really "playing media".

So what would you suggest to use to move the animation forward?