With the development of video encoder and decoder technology

H. 264 has become one of the most important standards. In this paper

we proposed novel moving object detection based on spatial-temporal method in compressed domain

which mainly depended on the motion vector field and efficiently segmented the object. Firstly

a spatially median filter was applied to the motion vector to alleviate the error vector due to difference between the motion vector obtained from motion estimation and the real motion information. Secondly

we built the spatial and temporal coherence model with the entropy based method. We obtain the threshold with these models. The effectiveness of our method was demonstrated with its performance on experiment results.