In the summer of 1970, a collection of rootsy musicians — The Band, the Grateful Dead, and others — spent a week traveling across Canada by train to do a series of concerts. Festival Express, which is basically a performance doc, features footage of the journey as well as interviews with the participants, who recall what transpired on that train as if it were the ultimate cosmic effusion of brother-and-sister good vibes. All we really see, however, is a bunch of skinny young musicians jamming in a jovial backstage way that wouldn’t be worth a second thought if it weren’t offered up as some sort of privileged end-of-the-’60s be-in. ”Festival Express” is a likable time capsule inflated with counterculture hot air. The best reason to see the movie is Janis Joplin, whose volcanic stage presence erupts right out of her dazed instability.