Journal of Zhejiang University-SCIENCE A

, Volume 7, Supplement 1, pp 70–75

Fast mode decision algorithm for spatial resolutions down-scaling transcoding to H.264


  • Bu Jia-jun 
    • School of Computer ScienceZhejiang University
  • Mo Lin-jian 
    • School of Computer ScienceZhejiang University
  • Chen Chun 
    • School of Computer ScienceZhejiang University
  • Yang Zhi 
    • School of Computer ScienceZhejiang University

DOI: 10.1631/jzus.2006.AS0070

Cite this article as:
Bu, J., Mo, L., Chen, C. et al. J. Zhejiang Univ. - Sci. A (2006) 7: 70. doi:10.1631/jzus.2006.AS0070


A fast mode decision algorithm is proposed in this paper to accelerate the process of transcoding videos into H.264 with arbitrary rate spatial resolution down-scaling. The proposed algorithm consists of three steps. First, an early-stop technique is introduced to determine the 16×16-mode blocks, which take up about 70% of all the macroblocks; then, a bottom-up merging process is performed to determine the mode of rest non-early-stopped blocks; and then, we adopt half-pixel motion estimation to further refine the acquired predictive motion vectors. In order to obtain the predictive motion vectors for early-stop and merging processes, we propose a motion vector composition scheme, which can reuse the information in the input pre-encoded videos to handle the spatial resolution down-scaling. Experimental results showed that our algorithm is about four times faster than the Cascaded-Decoder-Encoder method and has negligible PSNR drop and little bit rate increase.

Key words

TranscodingH.264Mode decisionMotion composition

CLC number


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© Zhejiang University 2006