Multiple description coding has recently been proposed as a joint source and channel coding to solve the problem of robust image transmission over unreliable network, and it can offer a variety of tradeoff between signal redundancy and transmission robustness. In this letter, a novel pre-and post-processing method with flexible redundancy insertion for polyphase downsampling multiple description coding is presented. The proposed method can be implemented as pre-and post-processing to all standards for image and video communications, with obvious advantages. Simulation results show that this approach can reduce the computational complexity while provide a flexible redundancy insertion to make the system robust for any packet loss situation over different networks.