In Canadian-born John Cook’s restless documentary of an Austrian couple, I JUST CAN’T GO ON, the husband Petrus, channeling “Cassius Marcellus Clay,” takes up boxing to supplement the income from his day-job burnishing frames. His companion, the much older Gisi, works as a janitor. They are an odd couple, scavenging at the bottom of the Viennese social ladder. But there is nothing patronizing or exploitative in Cook’s treatment of the couple and their eccentricities as they try to make ends meet. In one of the film’s key aesthetic choices, Cook eschews synched sound in favor of a stream-of-consciousness soundtrack pitting Petrus and Gisi’s unfiltered remarks in relief against the harsh material world.