Many multimedia applications involve real-time video communication over distributed systems, in which there is no centralized controller. Examples of such distributed systems are peer-to-peer (P2P) networks, wireless ad hoc networks, and wireless sensor networks. In this paper, we provide a review of recent advances on optimal resource allocation for video communication over some major distributed systems including P2P streaming systems, wireless ad hoc networks, and wireless visual sensor networks. In P2P streaming systems, we review the scheduling optimization problem, streaming capacity problem, routing optimization problem, and the prefetching optimization problem. In wireless ad hoc networks, we present the routing optimization problem, joint optimization of the source rate and the routing scheme, joint optimization of sender selection and the routing scheme, and joint optimization of the source rate, the routing scheme and the power. In wireless visual sensor networks, we discuss the network lifetime maximization problem, optimal power allocation, maximization of accumulative visual information (AVI). Illustrative simulation results are provided to demonstrate the performance improvement brought by the optimal resource allocation in the distributed systems. Finally, we give our vision on the future work in the area of video communication over distributed systems.