Penelope Spheeris’s writhing and raucous portrait of the L.A. punk scene circa 1979/80 is about the surface tension, the appearance of decline. And on the surface there is a certain decrepitude as Darby Crash, lead singer of the Germs, slogs around his house issuing an inventory of his addictions, or Lee Ving, the chilling frontman for Fear, spews off-color jokes meant to raise the heckles. But onstage, the music is propulsive, and despite its tear-it-down tenacity it’s about liberation through pure velocity. At 300 bpm, even the skinheads pogoing in the pit can leave this earth and its grim politic behind. X’s ode to orgasmic excess, “Johnny Hit and Run Paulene”; Black Flag’s inverted cry of injustice, “White Minority”; Fear’s cure for our carbon footprint, “Let’s Have a War”: in these grimy songs and more, the exuberance always trumps the decline.