Digital transmission systems for broadcast program materials have been studied in Association of Radio Industries and Businesses (ARIB). MPEG-2 Video has been adopted as a video coding method for HDTV codec. It was necessary to examine required bit rates in order to determine appropriate bandwidths and modulation methods for wireless transmission media used for FPU and SNG. Coding experiments and subjective evaluation of the picture quality were thus carried out at different bit rates and coding configurations including cascading of codec. The results show that the video bit rate of 52 Mbit/s is required to satisfy the user requirements on the program material transmission specified in the ITU-R Recommendations.
In the digital broadcasting, various data programs are expected as potential attractive services in addition to video and audio. It will become possible to offer the additional services without increasing the total transmission capacity, if the bit rate for video programs can be reduced without deterioration in the picture quality. Some video scenes may not require a full bit rate allocated for a program to obtain sufficient picture quality. By setting up a minimum quantizer scale according to targeted picture quality, which results in VBR coding, some considerable amounts of bit expenses can be saved for additional opportunistic data services while maintaining the required picture quality. Temporal characteristics of the bit savings are also shown, which can be used as fundamental data when considering the additional services.