Variable block size selection for a transcoder based on MB movement information

To improve coding performance, the new video compression standard H.264 employs seven variable block sizes for one Macro Block (MB) to conduct motion estimation and compensation. MPEG-2 only has one size 16times16. This paper presents a novel fast variable block size selection method for an inter-MB in a video transcoder from MPEG-2 to H.264 with downscaling by a factor two in each dimension based on the MB motion information. Without conducting motion re-estimation, an optimal block size is decided. Experiment results show that this method saves the transcoder complexity dramatically with little compression performance degradation.