Buffer management in variable bit-rate compression systems

Abstract

A method of compression is provided for transmission of digital video signals between an encoder buffer and a decoder buffer. A tunable delay is provided at the encoder, suitably in the form of a portion of encoder buffer memory, with data being read out to a communications channel at a rate determined by the input bit rate of signals received a predetermined number of frame periods later. Use of the tunable delay improves efficiency of decoder buffering by maintaining a relatively constant level of decoder buffer fullness irrespective of signal bit rates.

1 - 8 . (canceled)  
   
   
       9 . A video signal decoding apparatus for decoding a received digital video signal for transmission, the apparatus comprising: 
 an decoder stage for decoding a received video signal according to a predetermined coding algorithm and producing the decoded video signal as a variable bit-rate data stream at an output of said decoder stage;    a buffer coupled to receive said variable bit-rate data stream from the decoder stage and arranged to output a data signal corresponding thereto for transmission; and    a detector coupled to said decoder stage to detect the bit-rate of said variable bit-rate data stream,    a processor to derive a second bit rate as a percentage of the detected bit-rate, which percentage changes in inverse relation to changes in the detected bit rate,    a buffer control to control said buffer to produce said output data signal at second bit rate, and transmit the output data signal to a decoder buffer at the second bit rate; wherein the detected bit rate and said second bit rate are variable.    
   
   
       10 . An apparatus according to  claim 9 , wherein the decoder stage is configured to decode the received video signal in accordance with the MPEG standard.  
   
   
       11 . An apparatus according to  claim 9 , wherein said means for detecting a bit rate stores a plurality of contiguous ranges of bit rate values and, on first detecting a dencoder output bit rate falling within a first of said ranges, maintains the derived second bit rate substantially constant until a detected encoder output bit rate falls with another of said ranges.