Casey Affleck AffleckPhoenix.jpgCasey Affleck is set to document Joaquin Phoenix's attempt to reinvent himself as a rapper.

Affleck is directing a feature-length documentary about his friend's transition from life as an actor to that of a musician, according to The Hollywood Reporter.

Phoenix, who shocked Hollywood with the news he was giving up acting, is working on an album with Sean Combs. His first performance is scheduled for tonight in Las Vegas.

Affleck has previously directed several short films that have aired on the Sundance Channel.