Hmmmmm... interesting question regarding the use of YouTube videos to assist map editing.
Personally I think YouTube is indeed one of the many Alphabet's tentacles.
I would simply ask the original uploader for an original copy instead*, rather than, you know, traversing the grey area of copyright.
*Not really feasible yet in my country (big file size!), unless the video owner would be willing to do their part, reuploading as an email attachment
There's this one case where a mapper simply did it when the uploader themself said their videos are copyright controlled...