Rationality of restricted re-quantization for efficient MPEG transcoding

A macroblock-based optimization method is described for selecting quantization parameters so as to reduce the re-quantization errors in MPEG transcoding. Analysis has shown that re-quantization using a parameter larger than the original input quantization parameter but smaller than twice the original causes significant information loss in transcoding. This problem can be avoided by using a parameter larger than twice the original. The optimization method was thus extended based on a rate-distortion model to enable the re-quantization parameter to be selected from ones larger than twice the original input quantization range. This improved method outperformed a typical non-optimized transcoding scheme, improving the PSNR by about 1 dB