Efficient Motion Re-Estimation With Rate-Distortion Optimization for MPEG-2 to H.264/AVC Transcoding
One objective in MPEG-2 to H.264/advanced video coding transcoding is to improve the H.264/AVC compression ratio by using more advanced macroblock encoding modes. The motion re-estimation process is by far the most time-consuming process in this type of video transcoding. In this paper, we present an efficient H.264/AVC block size partitioning prediction algorithm for MPEG-2 to H.264/AVC transcoding applications. Our algorithm uses rate-distortion optimization techniques and predicted initial motion vectors to estimate block size partitioning. It is also shown that using block size partitioning smaller than 8 × 8 (i.e., 8 × 4, 4 × 8, and 4 × 4) results in negligible compression improvements, and thus these sizes should be avoided in transcoding. Experimental results show that, compared to the state-of-the-art transcoding scheme, our transcoder yields similar rate-distortion performance, while the computational complexity is significantly reduced, requiring an average of 29% of the computations. Compared to the full-search scheme, our proposed algorithm reduces the computational complexity by about 99.47% for standard-definition television sequences and 98.66% for common intermediate format sequences. Compared to UMHexagonS, the fast motion estimation algorithm used in H.264/AVC, the experimental results show that our proposed algorithm is a better trade-off between computational complexity and picture quality.