1. An MPEG-4 video streaming system for providing video streaming over error-prone environment suffering video bitstreams corruption or packet loss during transmission, said MPEG-4 streaming system comprising: an encoder, having a rate-distortion optimization intra-refreshment functional unit, for encoding a series of video images; and a decoder, having an error resilience functional unit and an error concealment functional unit, for decoding said video images encoded by said encoder; where said rate-distortion optimization intra-refreshment functional unit of said encoder computes an intra-coding cost and an inter-coding cost to determine whether intra-coding or inter-coding should be applied in encoding said video images, and said error resilience functional unit of said decoder is used against error occurrence and said error concealment function unit of said decoder is used to enhance said video image quality with a hybrid error concealment method.