The last time Cameron Crowe, onetime wunderkind Rolling Stone reporter, fully devoted a movie to rock-and-roll music, the end result was the classic Almost Famous. (The clumsy headline above is, of course, a reference to the “I Am a Golden God” scene from Almost Famous, in which Billy Crudup as Russell Hammond switches his would-be last words from “I’m on drugs” to “I dig music” and back again.) Well, Crowe’s back on the beat with the documentary Pearl Jam Twenty (premiering October 21 on PBS), and while the scope might be more limited this time out, the end result is still quite promising. If you need convincing that this thing’s not just for the diehards, take ten seconds to watch the beginning of the trailer, in which David Lynch — in endearingly halting fashion — asks Eddie Vedder when he first got into music. Vedder takes a breath, and before he starts to answer, the trailer swings back to the early days, with vintage footage of the lithe Pearl Jam dudes flinging their guitars and flying off balconies. And then the voice-over, from Eddie: “When you’re sitting in your room playing guitar, you don’t have to worry about being successful … it’s not gonna happen. [Chuckle.] It’s just not gonna happen.” Awww.