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This paper describes an efficient motion estimation algorithm, the predictive line search (PLS), for real-time implementations of MPEG-4 encoder on multimedia processors. The motion-vector predictor is used as the starting point in the search process because the correlation between neighboring motion vectors is strong. The line search pattern is used in the proposed algorithm to reduce the memory access as well as to exploit the special multimedia processor instructions for sum of absolute difference calculations. Experimental results show that the performance of the PLS is very close to that of the full-search (FS) algorithm. Compared with the well-known diamond search and one-dimensional FS, the PLS shows better performance and robustness, especially for high motion sequences. A prototype MPEG-4 encoding system is implemented on a 216-MHz multimedia processor with very long instruction word architecture to verify the effectiveness of the PLS. Real-time encoding of MPEG-4 Simple Profile Level 3 (CIF, 30 fps) can be achieved with only 57% of the processor load.