The mention of the copyrighted work eg. "Taylor Swift" does not lay out a case of infringement. Merely possessing a copy does not indicate infringement, you could be in pursuit of your fair use rights, with no intention to share. Given the cost of bandwidth and predilection of media conglomerates to meter and limit it, I would argue that there is actually no likelihood of facilitating any substantially infringing use.
The person who took a copy has no substantial reason to share it with anyone, as it is freely available through the content providers. Anyone with a copy of youtube-dl can get it, (does youtube-dl enable the download of any paywalled content? If so, that might be a fact that changes the game. But if so, does the RIAA claimant have standing to make that argument?)
Merely possessing a copy does not indicate infringement, you could be in pursuit of your fair use rights, with no intention to share.
Right, but you're looking at the wrong thing. The use of youtube-dl by you to download Taylor Swift is not what the courts are looking at (and note, that would generally not be fair use if your intent was just to watch it later as the time-shifting defense from the Betamax case is generally not applicable to content available on-demand, though using the video in a derivative work like non-profit educational content would probably still be fine).
It's the fact that youtube-dl holds itself out as being the tool to use so that you can download Taylor Swift that is at issue.
The person who took a copy has no substantial reason to share it with anyone, as it is freely available through the content providers. Anyone with a copy of youtube-dl can get it, (does youtube-dl enable the download of any paywalled content? If so, that might be a fact that changes the game. But if so, does the RIAA claimant have standing to make that argument?)
It doesn't matter if they intend to share the video further. The copyright violation act is the downloading of a permanent copy of video content provided on a streaming/on-demand basis. The downloader sharing the video with others would be a separate copyright violation.
This case is going to be really interesting if it goes to court, but right now it's not in court.
The letter makes two claims, "copyright infringement" which might be substantiated by the readme, (but not against youtube-dl authors, perhaps against their users) and "anticircumvention [sic]" which is the meat of their real issue.
The making of a copy is not outside of fair use unless it fails the balance test, aka "four factors."
Sony Betamax disagrees with you, if we can agree that youtube is similar to a broadcast medium and that youtube-dl is similar to a "VTR" from that case, aka VCR, unless there are other substantial differences that I'm missing.
Making a copy is only infringing if it isn't for fair use, and Betamax ruled that time shifting could be fair use.
One of the four factors is market impact, so how is the market for this content impacted by this taking a permanent copy? It would be impacted if the purpose and character of the copy was inconsistent with fair use, but remember youtube-dl hasn't taken or shared any permanent copies.
So unless you think that youtube-dl has made a copyright violation (which I think we've established they haven't) then youtube-dl is Sony Betamax, permitted to sell VTRs as long as there are substantial non-infringing uses, and the copyright claim will have to be brought against the infringing users.
That does not mean the courts won't find this is an "anticircumvention device" or will find that the takedown is improperly executed. They may very well rule it is an illegal anticircumvention device, Betamax happened before DMCA, and didn't decide anticircumvention.
But to my knowledge, in Sony one of the opinions spoke about "jamming" with hypothetical language, stating that it could be possible for Sony to build a box that jams unauthorized copying and I'm not aware of landmark cases that would have solidified those concepts.
If RIAA has accurately characterized the key rotation mechanism in YouTube then youtube-dl may well be ruled a circumvention device and that could be the end of it, fair use or no.
The person who took a copy has no substantial reason to share it with anyone, as it is freely available through the content providers. Anyone with a copy of youtube-dl can get it, (does youtube-dl enable the download of any paywalled content? If so, that might be a fact that changes the game. But if so, does the RIAA claimant have standing to make that argument?)