Rainbrow Bridge trailer (1972)
I have the soundtrack but have never seen the movie – gonna have to check it out.
(via the always-excellent South Willard)

Everyone in the country has seen pictures of the crowd. Was it bigger than it looked? Whoever saw so many people in the same spot with the same idea? Well, Hitler did, and General MacArthur, and Mao, but this was a somewhat better occasion. They came to hear the music and they stayed to dig the scene and the people and the countryside, and at any time, no matter who was playing, one could see thousands moving in every direction and more camped on every hill and all through the woods. The music became something that was going on there, and it was terrific, but it was by no means the whole show. The magnificent sound system was clear and audible long past the point at which one could no longer see the bands, and some were discussing the bass player in Janis' band even though they hadn't the slightest idea of what he looked like.Right on.