The Betamax case predates the DMCA, which created the “anti-circumvention” laws the RIAA is relying on here. It was also a 5:4 decision that depended on “a significant likelihood that substantial numbers of copyright holders who license their works for broadcast on free television would not object to having their broadcasts time-shifted,” and the copyright holders’ failure “to demonstrate that time-shifting would cause any likelihood of non-minimal harm to the potential market for, or the value of, their copyrighted works.” The opinion explicitly did not cover pay TV, and the court also noted that the cost of Betamax tapes made it difficult to build your own library of tapes for repeated viewing, in concluding that there was no likelihood of harm. I think it’s an interesting and open question whether the typical use of youtube-dl falls under fair use.
