In this paper, we investigate the problem of cooperative relay in CR networks for further enhanced network performance. In particular, we focus on the two representative cooperative relay strategies, and develop optimal spectrum sensing and $p$-Persistent CSMA for spectrum access. Then, we study the problem of cooperative relay in CR networks for video streaming. We incorporate interference alignment to allow transmitters collaboratively send encoded signals to all CR users. In the cases of a single licensed channel and multiple licensed channels with channel bonding, we develop an optimal distributed algorithm with proven convergence and convergence speed. In the case of multiple channels without channel bonding, we develop a greedy algorithm with bounded performance.