1981 was the year for epic animated features pitched to adults it seems. The more successful and well known of the lot was Heavy Metal, the Canadian feature based on the magazine of the same name. American Pop, by Ralph Bakshi was a success at the time, but has flown under the radar ever since. It traces the lives of four generations of Russian Jewish immigrants as they make a place for themselves in American popular music from the 1890's through the 1970's. The characters go through many challenges ranging from clashes with the mob, to homelessness, but find their solace in music.
The process used for the majority of the animation is rotoscoping, which involves filming live actors and using the footage as a basis for the animation. It allows you to recognize character actors in the piece, including Vincent Schiavalli, who plays a theater owner early in the film. The story line tends to be a bit bleak, but it does trace American history from a series of singular points of view, which can be fascinating at times.
The film is available on DVD, and has been uploaded in full to YouTube by Stevers80. Part 1 is above. It's still largely unknown to the general public, however. The poster above is available at MoviePosterShop.com.
Obscurity factor 5 (available on DVD and YouTube, largely unknown today)