Abstract: In view of the compatibility with the standard and the prospect for application's extending, this paper introduced ways of hierarchical coding based on the International standard MPEG-2. We selected the SNR based hierarchical way as the main emulation mode from the four hierarchical ways which are mentioned by MPEG-2. The SNR based hierarchical way produces two videolayers from one source video. These two layers have different image quality butthe same resolving power in space and time. When decoding , the low layer will be decoded by itself to provide a video with basal quality while the enhanced layer will be used to improve the quality of the video that produced by the low layer. Through experiment, the enhanced effect on the quality of the base layer video is showed to be evident and promising.

Key words: hierarchical coding, MPEG-2, enhanced layer