I use this extension for downloading music videos to change to .mp3 so that I have accurate examples to practice singing covers by. Ever since I began using it the developer has been quick to catch up with YouTube's evasive maneuvers and to update the extension to continue working.
Please don't rate the extension badly if it doesn't work for you! It's always simply a matter of YouTube moving the goalposts yet again, and it takes time to compensate for that.
EXCELLENT EXTENSION!