Transformative use

Courts weighing fair use ask what the new work is doing, and transformative use is the label for adding something: commentary, criticism, parody, a different purpose, a new meaning. Commentary and review channels lean on it heavily.

Three things get missed. Fair use is United States law, and other countries have narrower rules under different names. It is decided by a court after the fact, so nobody can promise you in advance that a video qualifies. And Content ID does not assess it at all, being a matching system, so a video with a strong fair use argument still gets claimed and the argument has to be made afterwards through the dispute process.