MPEG-2 one-pass variable bit rate control algorithm and its LSI implementation

MPEG-2, the international standard of the ISO/IEC, is a key technology for video coding and is widely used in digital television etc. Its most frequently used coding rate control is the constant bit rate (CBR) mode. CBR's bandwidth requirement is relatively low, but it needs further improvement in terms of the coding efficiency. On the other hand, the variable bit rate (VBR) mode may be able to enhance the picture quality in situations that are rich in bandwidth or in storage media such as DVD. We have already developed a one-chip MPEG-2 video encoder LSI (SuperENC) to cope with the broader range of digital image communication applications. This paper discusses a new one-pass VBR coding control algorithm based on mathematical relations among coding parameters such as quantization parameter, bit rate and decoded image distortion. Our aim is to solve the problems of conventional techniques and verify the algorithm's effectiveness through hardware implementation. A one-pass VBR control function was implemented in the chip's firmware. Not being a very complex algorithm, it is robust with respect to abrupt scene changes. The SNR gain in a TM-5-based CBR mode was 1.5 to 1.8 dB, and the bit rate reduction under the same subjective quality was 10-30 %.