Bit rate control for video data compression

In MPEG2 encoding, the quantiser is controlled to manage the occupancy of a video buffer. A dynamically varying working range is determined by forecasting from recent coding history the number of bits required in coding of future pictures, and deriving upper and lower ends of the working range which correspond respectively with attainment within the forecast period of predetermined maximum and minimum buffer occupancies. The quantiser scale is then controlled through the position of the actual buffer occupancy within that working range.