How much great music has been lost, overlooked or never even written because of the cataclysmic events of history? That’s the question explored by fascinating Canadian documentary Exit: Music, screening in this year’s Jewish International Film Festival.

Directed by James Murdoch (no, not that one), the film takes as its focus five mainly Jewish composers of the mid-20th century whose careers were severely disrupted by Nazism.All somehow managed to survive – albeit usually at great personal cost – and continued to write music after gaining asylum overseas or in one case hiding.

The most famous is Austrian-born former child prodigy Erich Korngold, best known for his Violin Concerto and his scores for Hollywood movies, written following his relocation to California in the 1930s.

Of the four lesser known composers, three were born in Germany – Paul Ben-Haim, who resettled in Israel; the non-Jewish but anti-Nazi violinist and quartet leader Adolf Busch, who escaped to live in Vermont before returning home after the war; and Walter Braunfels, who astonishingly stayed alive by living quietly on the edge of Lake Constance, just across the water from Switzerland.

Meanwhile Poland’s Mieczysław Weinberg fled to the Soviet Union to escape the Nazis and...