This short video does an excellent job explaining how autofocus systems work, without over-complicating the subject matter. It touches on the various types of autofocus systems in Canon cameras as well as specific features like subject tracking and Dual Pixel AF.

It starts with the dawn of autofocus and moves on to modern day from there. And though it is marketing material from Canon USA, it's still worth a watch. In fact, it got us thinking about how incredibly far AF technologies have come in just about 30 years. Imagine where we'll be in another 30.