Bluegrass musician Tim O’Brien ’76 rallies audiences with his spirited tunes on CDs like his latest, “Traveler.” Now he takes his talent from the stage to the big screen, in Bluegrass Journey, a documentary that’s touring the country and recently played at the Maine International Film Festival. Dubbed by Variety as “a genuine crowd-pleaser,” the film explores the culture around the music featuring top musicians, O’Brien prominent among them.