Meloclassic just put a wonderful video about chamber music in America on Facebook.
In this 17-minute segment from the 1991 French video Les Musiciens du Quatuor - Reprise, Dernier Mouvement, we can see footage of Louis Kransner, Eugene Lehner, and Joel Krosnick coaching string quartets at Tanglewood. There is a generous interview with Eugene Lehner, one with Leonard Stein (who was a student of Schoenberg), and one with Eleanor Aller talking about the genesis of the Hollywood Quartet and their performance for Schoenberg of his Verklärte Nacht at his home. There are short film clips of Bruno Walter, Jascha Heifetz, Pierre Monteux, Igor Stravinsky, Ossip Gabrilowitch, and Gregor Piatigorsky, and there are filmed performances of the Budapest Quartet playing some of the last movement of Beethoven Op. 59, no. 3 and the Hollywood Quartet playing some of the Wolf Italian Serenade with an unconventional quartet set-up that allowed all the musicians to be filmed by a single still camera.