How to enable VP9 codec on Google Stadia in Chromium

This is a DRAFT. I put it together as the original post on Reddit about this was removed. The solution and most Reasoning I needed to run Stadia on a Libreboot laptop which runs entirely free software. This includes Chromium, which meeans, that I have to use VP9 codec in Stadia to even make it work. Otherwisee it would not work. Introduction First we have to understand what is going on.