IMO the best way to block ads in YouTube is by avoiding it completely 
I suggest using https://invidio.us/ instead. Invidious is an open-source front-end for YouTube. It works without javascript enabled (unless you want to see the comments for each video) and you won't see any ads.
By default, you'll see network requests to googlevideo.com. However, even this can be avoided by checking the "Proxy videos?" option in the settings in the upper right corner.
Note that there are several Invidious instances available which might be more performant than invidio.us.
The best way to use it, IMO, is by installing the Invidition add-on for Firefox which redirects all requests to YouTube (even in embedded videos on other sites) to invidio.us (or, alternatively, to one of the other instances). You can check the option "Force proxy" to avoid googlevideo.com.
Result: a Google-free YouTube 
Note: If you're using uMatrix or Noscript you might want to add the appropriate rulesets for those add-ons available on the Invidition homepage.