Efficient requantization method for INTRA MB in heterogeneous transcoding In this paper, we propose an efficient requantization method for INTRA Macroblocks (MB) in heterogeneous transcoding MPEG1 to MPEG4 simple profile. The quantizer for MPEG1 INTRA MB usually uses a quantization matrix while the quantizer for MPEG4 simple profile doesnu0027t. As a result, the quantization step sizes of the two quantizers may not be the same even for the same quantization parameter. Due to this mismatch in the quantization step size, the transcoded MPEG4 sequence suffers serious quality degradation and the number of bits produced by transcoding increases from the original MPEG1 video sequence. To solve these problems, we propose an efficient method to find a nearoptimum reconstruction level in the transcoder. We also present a PDF (probability distribution function) estimation model for the original DCT coefficients of MPEG1 video sequence, which is required for the proposed requantization. Experimental results show that the proposed method gives 0.3xe2x88xbc0.7dB improvement in PSNR over the conventional method, even at the reduced bitrate about 5xe2x88xbc7% from the conventional method.

Highdefinition video coding with supermacroblocks A high definition video coding technique using supermacroblocks is investigated in this work. Our research is motivated by the observation that the macroblockbased partition in H.264AVC may not be efficient for high definition video since the maximum macroblock size of 16 x 16 is relatively small against the whole image size. In the proposed supermacboblock based video coding scheme, the original block size M x N in H.264 is scaled to 2M x 2N. Along with the supermacroblock prediction framework, a lowcomplexity 16 x 16 discrete cosine transform (DCT) is proposed. As compared with the ID 8 x 8 DCT, only 16 additions are added for a ID 16 points 16 x 16 DCT. Furthermore, an adaptive scheme is proposed for the selection the best coding mode and best transform size. It is shown by experimental results that the supermacroblock coding scheme can achieve a higher coding gain.