The best movies about rock ‘n’ roll are the ones that mock it. The worst, and there are many, are the dramas, which never get it right. Take Rock Star, which was based on an amazing true story and still managed to suck completely. But there are deep truths in both This Is Spi¬nal Tap and Eric Idle’s All You Need Is Cash, better known as The Rutles. Made in 1978 as a summer fill-in for the Saturday Night Live time slot, the faux documentary tells us everything we already know about the lives and careers of the Beatles but recasts the tale as that of the “pre-fab four”: Dirk, Stig, Ron, and Barry, four lads from Rutland. With Neil Innes’ pitch-perfect parody score and onscreen verisimilitude from Mick Jagger, Paul Simon, Ronnie Wood, and George Harrison, plus expert support from SNLers John Belushi,

Dan Aykroyd, Gilda Radner, and Bill Murray, Cash captures both the mythos and mirth of the music of our lives. It screens at 7 p.m. at the Library of Congress’ Pickford Theater, 101 Independence Ave. SE. Free. (202) 707-5677. (Dave Nuttycombe)