To further improve the performance of H.263' s encoder in the real time H.324 system

a motion search algorithm using zero block detection technology

is proposed in this paper. This algorithm exploits the fact that many residual blocks become all zero blocks after DCT and coarse quantization in very low bit rate video coding. To further speed up the encoder implementation

this zero detection technology is combined with motion estimation. In the motion search process

if an all zero macro-block is detected using the distortion value of the macro-block

the search process is stopped. The choice of the threshold for zero detection is critical. Simulation results show that the algorithm can dramatically decrease the motion search points. And also many blocks' quantization

DCT and other reconstruction steps are skipped. Under typical quantization parameter of 12

the average search points decrease is 30%~50%

and 25%~30% blocks' DCT and quantization is skipped due to the zero detection in the motion search. With the gain of encoder speed

the algorithm does not suffer the coding efficiency of the H.263 baseline. The algorithm does not affect the reconstructed image quality either. After the algorithm is combined into a real~time H.324 system

the performance of the whole system is improved a lot.