This topic was discussed many months ago, probably archived. If I knew where to look. I'd direct you there. Earl, Sonny, Bill emerson, JD, Saburo Watanabe Inoue, Kid?, Jimmy Arnold, Don Stover, Al Munde, ?, Rick Riman?, JD, Earl & Randy.
I probably have some wrong, like the long-haired guy(who might be Rick Riman or John McKuen but not John Hartford) and the guy with glasses and the kid and a couple of others in the background who didn't pick.
I don't remember all the names, but the clip is from a movie call "Bluegrass: Country Soul". I rented it from Netflix a couple of months ago. If you listen to the commentary they name off all of the players except for the younger boy whom they couldn't remember. The movie was pretty good it has live performances by a lot of the greats, well worth checking out.