The owner of this Youtube channel works at VPRI with Alan Kay. I believe he mentioned he got a bunch of these tapes from Alan, which he has then been digitizing and uploading now and then.
A number of these ACM talks were recently made available on Youtube by the Computer History Museum [1], with talks/reflections by Butler Lampson, Chuck Tacker, Doug Engelbart, Larry Roberts, Gordon Bell, and many more.
The tape was from the collection of the Computer History Museum, inherited from the collection of their predecessor, the Computer History Museum in Boston. It had just never been digitized. There's a blog post on it here: http://www.computerhistory.org/atchm/the-1986-acm-conference...
A number of these ACM talks were recently made available on Youtube by the Computer History Museum [1], with talks/reflections by Butler Lampson, Chuck Tacker, Doug Engelbart, Larry Roberts, Gordon Bell, and many more.
[1] https://www.youtube.com/user/ComputerHistory/videos