Coding method and apparatus and recorder

Abstract

A coder of the present invention is adapted to reproduce a signal of quality at a low coding rate even when a video or audio signal continuously supplied thereto should be coded in real time. The coder includes: a quantizer for quantizing the input signal; an encoder for encoding the output of the quantizer and outputting coded data; and a quantization parameter supply circuit for supplying a quantization parameter to the quantizer. If a scene change detector has detected a scene change, the supply circuit supplies a quantization parameter, which has been determined adaptively to a scene newly appearing after the scene change, to the quantizer. Otherwise, the supply circuit supplies a quantization parameter, which has been determined at such a value as to stabilize a coding rate, to the quantizer. In this manner, an average coding rate can be controlled and coding processing can be performed adaptively to individual scenes.

What is claimed is:  
     
         1 . A method for coding a signal by quantization processing, the method comprising the steps of: 
 obtaining an accumulation of errors, each representing a difference between a number of bits generated and a target number of bits;    determining a quantization parameter by a feedback control using the accumulation; and    performing the quantization processing using the quantization parameter determined,    wherein a characteristic of the feedback control is modified based on the errors.    
     
     
         2 . A coder for coding a signal, comprising: 
 a quantizer for quantizing the signal;    an encoder for encoding the output of the quantizer and outputting coded data;    a bit number calculator for calculating the number of bits of the coded data; and    means for supplying a quantization parameter to the quantizer,    wherein the supplying means obtains an accumulation of errors, each representing a difference between a number of bits calculated by the bit number calculator and a target number of bits, determines the quantization parameter by a feed-back control using the accumulation, and modifies a characteristic of the feedback control based on the errors.