How is “sing along” used?

In Come from Away (2021), one line is: “Hey, hey, just sing along Nothing ventured, just prolonged”

Which movie is “sing along” from?

The clip at the top of this page is from Come from Away (2021).

to sing together with sb who is already singing or while a record, radio, or musical instrument is playing

Heard in 5 movies

Oxford100% of films
to sing together with sb who is already singing or while a record, radio, or musical instrument is playing
There's a Messiah sing-along tomorrow. Oh, no!

Definitions from the Oxford Advanced Learner's Dictionary, 9th edition

Hey, hey, just sing along Nothing ventured, just prolonged

Said in 8 films · #1