Interframe-coded output data amount control system.

摘要

A video signal having a group of frames of successive dependent frames and an independent frame following the frames is coded per group of frames, by interframe and intraframe coding, and a data amount of the group is controlled by feedback and feed forward control. A quantization step number for the dependent frames is changed based on a rate of a total data amount of the group and a data amount of the dependent frames for the feedback control. A temporary quantization number of the independent frame is determined for the feed forward control. A data amount predictive value for each blocks in the independent frame is determined by an activity of an image in each blocks and the temporary number of quantization steps. The predictive value is subtracted form the total data amount. A subtraction result for each blocks is accumulated to output a positive compensation amount if the result is a positive amount and a negative compensation amount is a negative amount. The compensation amount is then added to the temporary number of quantization steps to obtain a number of quantization steps for the independent frame. The data amount of the group is thus controlled by quantizing the dependent and independent frames by the numbers of quantization steps of the dependent and independent frames, respectively.