A fast downsizing video transcoder for H.264/AVC with rate-distortion optimal mode decision

This paper focuses on the mode decision and motion selection problem when H.264/AVC video streams are transcoded in spatial resolution. A fast downsizing transcoding scheme is developed in which a new ratedistortion (R-D) optimal mode decision mechanism is presented for high speed transcoding as well as high coding efficiency. A model for estimating relative prediction errors is applied in this paper, which is free from computation of interpolation and SAD/SSD computation. Based on the selected model, a motion refinement within a distance of 1 pixel is performed after mode decision. Experimental results demonstrate that our method can significantly speed up the spatial resolution reduction process, while achieving high coding efficiency.