A Novel Fast Mode Decision for the H.264/AVC Based on Local Macroblock Motion Activity

The intra- and inter-prediction techniques have been effectively exploited in the H.264/AVC for significantly improving the coding efficiency. However, exhaustively searching for the optimal prediction mode vastly increases its computational complexity. To decrease the computational complexity of the mode decision process, a novel fast mode decision algorithm is proposed in this paper to speed up the encoding process by predicting the mode of the current macroblock based on the motion activity of the neighboring macroblocks. The proposed algorithm has two main stages. First, the SKIP mode is utilized as an early termination mechanism to terminate any further checking of other modes. This is quite effective for those regions with low-motion activity. If the SKIP mode is not met, the local macroblocks' motion activities will be identified in terms of motion-vector city-block length. Experimental results have shown that the proposed algorithm achieves a reduction of 56% computational complexity on average, while introducing only 0.059 dB loss in PSNR and 0.2% increment on the total bit rate compared with that of exhaustive trying out all possible modes, being set as the default in the original JM reference software.