Optimization of requantization parameter for MPEG transcoding
Shinya Kadono, Minoru Etoh, Naokazu Yokoya · Systems and Computers in Japan · 2002
Abstract This paper considers transcoding in which an MPEG stream is converted to a low‐bit‐rate MPEG stream, and proposes a method in which the transcoding error can be reduced by optimally selecting the quantization parameter for each macroblock. In transcoding with a low compression ratio, it is crucial to prohibit transcoding with a requantization parameter which is 1 to 2 times the quantization parameter of the input stream. Consequently, as the first step, an optimization method for the requantization parameter is proposed which cares for the error propagation effect by interframe prediction. Then, the proposed optimization method is extended so that the method can also be applied to the case of a high compression ratio in which the rate—distortion curve is approximated for each macroblock in the range of requantization parameters larger than 2 times the quantization parameter. It is verified by a simulation experiment that the PSNR is improved by 0.5 to 0.8 dB compared to the case in which a 6 Mbit/s MPEG stream is not optimized by twofold recompression. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(9): 21–30, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/scj.10096