This can be a film where someone known primarily for music plays a musician or an actor who really plays the instrument in the film plays a musician. To clarify, the actor must really be able to play the instrument and singing alone does not count.
I posted a video of her song the other day. She was only singing, and not playing a musical instrument. So this does not meet the criteria. However, the movie itself DOES have real musicians playing in their own song, being sung by the Blues Brothers.
"Landis remembers Aretha’s re-recording of the extended film version of the song:
So, we laid down the tracks for “Think.” She came in, a couple days before she was to be shot. She listened to the track once and said, “OK, but I would like to replace the piano.” We said, great, what do you want to do? She said, “I’ll play.”
So we got a piano, she sat in a recording studio, and it was Universal Studios’ recording studios in Chicago, a very old, funky studio we were delighted to be in because it was where Chess Records did all their recordings. We had a piano for her. She sat with her back to us, at the keys, and the piano and her voice was mic’d. She did it once, listened to the playback. She said, “I’d like to do it again.” She played piano as she sang, and the second take is the one in the movie. She was just wonderful. She didn’t like doing so many takes and she had issues with lip-syncing."
Per IMDB's Trivia section, several of the Blues Brothers singers did not want to lip sync:
Some performers were not used to lip-syncing to pre-recorded songs, standard procedure for movie musicals. James Brown ended up singing his number live with a recorded backing (the rest of his choir was lip-syncing). John Lee Hooker's performance of "Boom Boom" was recorded live at Chicago's Maxwell Street Market. Aretha Franklin's performance is cut together from many, many takes, using the parts where her lip-syncing was actually in sync.
I really get sick of parades and things like the Super Bowl, where for years the "live" performances were actually lip syncing. If you are not going to sing live, then do NOT show up at all!
1. Joan Jett - Light of Day (1987)
2. Prince - Purple Rain (1984)
3. Steve Cropper and Donald Dunn - The Blues Brothers (1980)
4. Rick Springfield - Ricki And The Flash (2015)
5. Keith Moon - Tommy (1975)
6. The Beatles - A Hard Day's Night (1964)
1. Joan Jett - Light of Day (1987)
2. Prince - Purple Rain (1984)
3. Steve Cropper and Donald Dunn - The Blues Brothers (1980)
4. Rick Springfield - Ricki And The Flash (2015)
5. Keith Moon - Tommy (1975)
6. The Beatles - A Hard Day's Night (1964)
7. Nick Cave - The assassination of Jesse James by the coward Robert Ford. (2007)
1. Joan Jett - Light of Day (1987)
2. Prince - Purple Rain (1984)
3. Steve Cropper and Donald Dunn - The Blues Brothers (1980)
4. Rick Springfield - Ricki And The Flash (2015)
5. Keith Moon - Tommy (1975)
6. The Beatles - A Hard Day's Night (1964)
7. Nick Cave - The assassination of Jesse James by the coward Robert Ford. (2007)
8. Paul Simon - One-Trick Pony (1980)