Singers Peter, Paul, and Mary and two of their mentors, Pete Seeger and Ronnie Gilbert, recall the cultural revolution of the 1960s, when music became a unifying force amid the hopeful, idealistic, and sometimes turbulent movements of social change. Performances include archival footage of "Blowin' in the Wind" from the 1963 March on Washington and "The Times They Are a-Changin'" from the Newport Folk Festival, plus clips from the trio's previous television specials and intimate rehearsal renditions of songs from the 2004 album "In These Times."