CIF-to-QCIF video bitstream down-conversion in the DCT domain

Many advanced video applications require converting a compressed video bitstream from the Common Intermediate Format (CIF) to the Quarter Common Intermediate Format (QCIF). This task could be performed in the pixel domain or in the discrete cosine transform (DCT) domain. In this paper, we propose a DCT-domain approach, which requires lower complexity than that in the pixel domain. We also propose a scheme for selecting a coding mode and a motion vector for a macroblock (MB) in a QCIF video sequence from those of the corresponding CIF video without motion estimation (ME), which is computationally very expensive. Simulation results show that our DCT-domain approach reduces computational complexity by about 40% compared to the pixel-domain approach while providing comparable picture quality with about 0.4 dB degradation.