An excellent clip about Andy Warhol and the Velvet Underground's multimedia performances, from PBS's equally fantastic Andy Warhol: A Documentary Film (2006), viewable in its entirety online (Part 1 and Part 2).
Jonas Mekas, avant-garde filmmaker, on the performance: "I saw a mystical impresario, or sorcerer, structuring of temperaments, egos, and personalities who maneuvered it all into sound image and light symphonies of tremendous emotional and mental pitch…and somewhere in the shadow, totally unnoticeable but following every second and every detail of it was Andy Warhol."
