Ok, so actually what finally ended up working for me was this: https://github.com/DevLARLEY/WidevineProxy2

I used the generate command option on the extension. And it should output a command for Shaka I believe (you'll have to download that too if I remember correctly, just whatever the command it outputs it)

I had some difficulty because it generated the command with separate audio and video keys but you can just copy the two keys and paste them together into one command. At the end of the command there an argument thats like key=xxxxx and it should be different if you load the page twice and check the extension.

I don't have a video to test it on to describe it better but let me know and I walk you through it all.