A fixed camera. No clips. Just conversation. The link below takes you to a miraculous project involving television luminaries. There are over 1,900 videos. There are a lot of theatre folks interviewed (those that had a television career).
I should also add that part of the charm of this series is the bits of raw footage. Not much was edited out. Here's an example. Angela Lansbury yawning at the beginning of one of her segments. Angela Lansbury
Well its not exactly the same thing, but the American Theatre Wing's "Working in the Theatre" series is awfully similar, except that it focuses on roundtable discussions.