I always thought The Blues Brothers was the first SNL-based movie (June 1980), but there's an earlier one. Rack your brain for the answer, then see below for the reveal.

From March 1980, featuring all of Gilda's iconic SNL characters, most of the SNL writers (including Lorne Michaels), and Father Guido Sarducci.

Rated R

I was going to say How to Beat the High Cost of Living.

1942 or that frat boy movie?

1941, I meant, from 1979. and Animal House, 1978

Ya, but I don't think the presence of a performer makes it an SNL movie. Gilda Live and The Blues Brothers share characters with the TV show and build upon SNL sketches.

Animal House would have been my guess. The soundtrack was our group's album that would get played for any party we hosted.