Yet in one of the 20th century’s most extreme examples of the effects of politics on popular culture, Cambodia’s pop scene — along with virtually every other manifestation of modern society there — was brutally stamped out with the 1975 arrival of the Khmer Rouge, whose nearly four-year reign led to the deaths of 1.7 million people.

Since then, pre-Khmer Rouge pop has survived in fragments, but the history behind it has remained frustratingly incomplete. Now, after a decade of research by an American filmmaker, John Pirozzi, that history has been told thoroughly in “Don’t Think I’ve Forgotten: Cambodia’s Lost Rock and Roll” (2014, 105 min).