1. An MPEG-4 video streaming system for providing video streaming over error-prone environment, said MPEG-4 streaming system comprising: an encoder, having a rate-distortion optimization intra-refreshment functional unit, for encoding a series of video images into an encoded bit stream; and a decoder including a decoding module, an error resilience functional unit and an error concealment functional unit, said decoding module decoding said encoded bit stream into decoded video images, said error concealment functional unit receiving said decoded video image and performing a hybrid error concealment method to form error concealed decoded video images, said hybrid error concealment method including an intra surrounding check and a fast motion check based on temporal activity, spatial activity, and boundary similarity in said decoded video images to determine if spatial concealment or temporal concealment should be applied to conceal said decoded video images, said hybrid error concealment method dividing a macro-block of said decoded video images to be concealed into 4 sub-blocks and determining a concealment order for the sub-blocks based on validation of four surrounding macro-blocks of said decoded video images and locations of the sub-blocks, said four surrounding macro-blocks including right, left, top and bottom neighboring macro-blocks of said macro-block to be concealed; wherein 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 functional unit of said decoder is used to enhance quality of said decoded video images with said hybrid error concealment method.