Motion estimation for high performance transcoding

Traditionally, the re-use of motion vectors extracted from incoming video bit-stream during transcoding has been widely accepted. However, this simple re-use scheme introduces significant quality degradation in many applications including the situation when the frame-rate conversion is needed. In this paper, we analyzed the quantization errors that cause the extracted motion vectors to be non-optimal and we performed simulations to show the quality degradation due to the inaccurate motion vectors during transcoding. To improve the video quality, we proposed an adaptive motion vector refinement. With a highly reduced computational complexity, the proposed adaptive motion vector refinement achieves significant quality improvement in comparison to the conventional motion vector re-use scheme. In addition, the adaptive motion vector refinement is almost as good as performing a new full-scale motion estimation.