Downloading video from YouTube

Question

I wish to download a video from YouTube and then extract its audio.

Can anyone point me to some C# code to download a video?

For clarification purposes, I

Answer 1

To all interested:

The "Coding for fun" book's chapter 4 "InnerTube: Download, Convert, and Sync YouTube Videos" deals with the topic. The code and discussion are at http://www.c4fbook.com/InnerTube.

[PLEASE BEWARE] While the overall concepts are valid some years after the publication, non-documented details of the youtube internals the project relies on can have changed (see the comment at the bottom of the page behind the second link).