In this paper, we adopt a linear relative formula of a logarithmic function between bitrate and quantization step-size for homogeneous transcoding. Also we propose a novel transcoding method to convert the bitrates between H.264 coded bitstreams. The proposed transcoding method updates the model parameters given for the previous picture or slice by using an approximated relationship between bitrate and quantization step-size. In order to meet a lower target bitrate, it finds a target quantization step-size, and then generates a bitstream by a simple re-quantization process. From the simulation, this paper illustrates that the designated lower target bitrate can be obtained by the re-quantization process after finding the proper quantization step-size with simple implementation only without a complex bitrate control, for the four test sequences with different scene characteristics.

Transcoding, Bitstream conversion, Bitrate control, Quantization step-size