Most European carriers (including KLM, Lufthansa, Air France, Transavia, and Ryanair) explicitly state in their conditions of carriage or safety announcements that capturing other passengers or crew members on video without consent is forbidden. One instance they actually used the PA system to say to not record other passengers. As far as I've seen, it's not heavily enforced as long as you're doing holiday pics but the moment somebody starts harassing someone else with recording they turn on the harasser.

It's a bit of a grey area. Filming in public places is generally allowed, but an airplane isn't really a public space in the same sense, since you need a ticket to enter. I guess it would also depend on the airline's terms and conditions.