An intelligent rate control for an intrafield subband HDTV coder

An intrafield subband high-definition TV (HDTV) system has been shown to be capable of achieving high-quality coding at 130 Mbps, roughly the net payload of the proposed CCITT H4 access channel. In order to attain the maximum achievable quality within the available bit rate for a variety of video scenes, the system requires intelligent rate control. The intelligent controller regulates the coder bit rate by properly selecting prefilters and quantizers for various bands. The control decision is derived from the occupancy of the transmit buffer and the bit rate history. Using rate statistics based on test pictures, a rate model for all coding modes is established which helps in choosing the proper coding mode that leads to the desired bit rate. Programmability and flexibility to accommodate future improvement of the control are assured by implementing the rate control with a commercially available microcontroller. Computer simulations of the coding system with the rate control indicate that consistent high quality can be achieved