Overview: The series' 40th anniversary is celebrated with clips of classic performances; and collaborations between such artists as Willie Nelson and Emmylou Harris. Among the performers: Alabama Shakes, Sheryl Crow, Foo Fighters, Buddy Guy and Bonnie Raitt. Also: Doyle Bramhall II; Double Trouble; Joe Ely; Mike Farris; Grupo Fantasma; Robert Earl Keen; Kris Kristofferson; Lyle Lovett; Robert Randolph, Kenny Wayne Shepherd and Jimmie Vaughan. Jeff Bridges, Crow and Matthew McConaughey host.