A fascinating documentary portrait of this nascent musical revolution, “Underground Chinese Hip Hop” follows pioneering rapper, MC Weber, as he spearheads the creation of rap music in China. This form of creative self-expression has spread like wildfire amongst those struggling the most — young working-class students and migrants left out of the country’s meteoric rise. Through rap, these post-Mao millennials have found a voice and vehicle for expressing the frustration, anger, hopes and dreams of a generation grappling with their place in the new China, yet the movement is challenged by two distinct parties. The strain of social commentary and opposition that is a hallmark of underground hip hop makes it a threat in the eyes of the state censors, and state-backed pop stars also seek to co-opt the genre for their own gain. Will this musical movement survive?