Bollywood actor Ranbir Kapoor and film director Imtiaz Ali promoted their upcoming film 'Rockstar' in Mumbai on Sunday. Kapoor, who plays the lead role, described the film as a musical journey and a love story of a local Delhi boy who transforms into a famous rockstar.The director of the film, Imtiaz Ali, informed that the music of the film, will be launched on September 20.For regular updates on the latest happenings in Bollywood kindly subscribe www.youtube.com/thebollywoodshow