Check this clip from the 1981 Film 'Downtown 81' that starred Jean-Michel Basquiat. This is apparently the first time Hip-hop was featured in a movie (unconfirmed) and features a track by Melle Mel from Grandmaster Flash & The Furios 5 although there is some debate as to whether that is actually him you see in the club performing the rap. DJ Sinbad is DJing (unconfirmed). Basquait himself can be seen getting down to the track in the club and is named checked by the Rappper.
Debbie Harry also appears in the movie and you can see the clip featuring her below too although she does not have a singing part. Interestingly the original audio for the movie was destroyed and the sound you hear in the clips is the over dub which was re-recorded for the re-issue of the film. However Basquiat unfortunately died in 1998 so his voice part was played by Saul Williams (unconfirmed).