Sweet and Low-Down (movie, 1944)

After their annual free concert at Chicago's Dearborn Settlement, Benny Goodman and his band are packing up to go to their next engagement when a kid steals Goodman's clarinet. Goodman and Popsie pursue him to a tenement flat where he has led them to hear his brother play the trombone. Shenanigans ensue following Goodman's offering the brother a job with the band.