The deal with students recording the session is that the recordings are for personal use only. Noone has broken that understanding as yet so far as I am aware...
EDIT: s/wild/public/ I was originally looking for 'viral', but I just remember some of my smaller college classes sometimes getting into intimate discussions that wouldn't have happened if there was a chance that the class would have been public.
Perhaps the solution is to cut them off at the pass, as it were. Record your lectures yourself and make them available online, so students won't even be thinking about making bootlegs.
The point though is then it's not the same teaching--- if I'm recording something For Official Broadcast, it's a different kind of thing than if I'm having an informal seminar with 20 people in a room where we all (at least sort of) know each other. I'll be more formal and less chatty, students will be less free with their discussion too, etc.
I don't think there's anything wrong with a more formal, archival-intended lecture from the podium, like a keynote speech or a big auditorium lecture. But I don't think it should be the only kind of thing to exist, either. I think it should be possible for people to discuss and learn in smaller groups without anyone (teachers or students) worrying that every single thing they say is on-camera, 1984-style. I mean, apart from me; do my students want every single question they ask in class, some smarter-sounding than others, to end up on the internet?
I do support making the materials more widely (and ideally, freely) available--- course notes, slides, papers, tutorials, textbooks, etc. It's just actually recording people against their will in a setting where they should be able to feel free to discuss & ask questions that has the weird 1984-ish vibe.
I have only ever taught lab classes, and even in those groups of 10-14 people, getting people comfortable enough to ask their questions took a skill (I don't know if I ever got the hang of it) and constant attention toward not shutting people down. The times that the class was split into lab-partner teams of 2 people, and I roamed between those teams, the questions were far more free-flowing, and about basic/fundamental concepts. Letting me know I probably wasn't covering those kinds of concepts well enough other times, but I wasn't getting feedback on it because no one had wanted to ask.
In my possibly biased and very limited experience, it was usually students with more "in-your-face gruffness" that would speak-up in larger groups to ask about basic things I wasn't explaining as well as they needed. It made me appreciate that personality type more.
With, say, conference keynotes it's different because those are consciously supposed to be public performances, and arguably the big Physics 101 lectures in a 300-person auditorium are pretty similar as well, especially if they're by a prof who's given the lecture several times, so has a sort of "standard" rehearsed performance of it.