Based on the characteristics of quality scalable video coding

a fast inter encoding algorithm was proposed on the enhancement layer for the medium-grain quality scalability（MGS）.Firstly

based on the base layer macroblock mode and rate-distortion

the order of the coding mode for the current macro block was proposed.Then based on the encode structure

the correlation between layers

and the spatial correlation

desicions for the Direct coding mode

layer mode

and adjacent mode were proposed

respectively.Finally

the macroblocks were encoded in the order predicted

with the proposed three decisions to improve on the coding speed by early termination.The experimental results show that the computational complexity of the algorithm is reduced by 68% on the average compared to that of the standard method

with only negligible coding loss and bit-rate increase.