A new requantization method for MPEG-1 to MPEG-4 transcoder

In this paper, we propose a new requantization method for the transcoder from MPEG-1 to MPEG-4 in DCT-domain. For rate control of heterogeneous transcoder, we use the requantization method. Conventional requantization methods for the homogeneous transcoder cannot be used directly for the heterogeneous transcoder due to the mismatch in quantization parameters between MPEG-1 and MPEG-4 syntax and the difference of compression efficiency between MPEG-1 and MPEG-4. In order to solve these problems, we propose a new requantization method for MPEG-1 to MPEG-4 transcoder. It consists of the conventional R-Q model with a simple feedback and an adjustment of quantization parameters with which the output rate of MPEG-4 follows the target rate of MPEG-1. By a simulation of transcoding, it is shown that the proposed requantization can generate output rate much closer to the target rate than the conventional requantization and it gives the superior image quality to the conventional requantization.