HI I saw your useful post and thank you for taking the time to find a solution for this.
I have the same problem as you.
If I understand correctly, your method only works with the Chromium Browser but not with the standard Google Chrome Browser?
(I don't understand the first post in relation to the screenshot of the second one with the mention of the Chromium Browser...)
You mentioned that you tested this method with Windows 8.0 and 8.1, do you think it will work with 7 too?
I did a little research:
And found this solution: Chrome/Firefox extension for pen-testing to retrieve encryption keys of Widevine protected content.
See link: https://github.com/FoxRefire/wvg
What I'm wondering is it possible this can also be used to stream TV channels so that live stream videos can be played.
What I don't understand is the instructions with the CDM key pair.
I thought I'd mention it, maybe you'll take a look or try it out.