Encoder/decoder buffer control for variable bit-rate channel

DETAILED DESCRIPTION Shown in FIG.
1, in simplified block diagram form, are multiplexer unit 100, variable bit-rate channel 101 and demultiplexer unit 102, incorporating aspects of the invention.
An original video input signal, VIDIN, that includes frames which contain at least one image representation, is supplied as an input of multiplexer 100.
Such video signals are well known in the art.
Also supplied to multiplexer unit 100 are a corresponding audio signal and J.
sub.
dec.
As described below, J.
sub.
dec is representative of the cell delay variation at a video decoder in demultiplexer unit 102 and is employed by a video encoder in multiplexer 100 to adjust its parameters to avoid encoder/decoder buffer overflow and underflow.
Multiplexer 100 supplies as an output bit-stream CODETR which is transmitted across variable bit-rate channel 101 to demultiplexer unit 102.
As described below, the bit-stream supplied as an output from multiplexer 100 also includes audio and other information necessary to properly decode the video and corresponding audio signals at demultiplexer unit 102.
However, in the discussion below CODETR is assumed to be an encoded version of VIDIN.
It is assumed that the variable bit-rate channel 101 will be able to transmit at a desired bit-rate R.
sub.
i.
In many applications, however, the variable bit-rate channel 101 will be unaware whether or not it can transmit at the desired bit-rate R.
sub.
i, as in an ethernet network or on an asynchronous transfer mode (ATM) network.
In an ATM network, there may be a policing function or usage parameter control (UPC) function that is used to constrain the number of bits entering variable bit-rate channel 101.
An aspect of this invention, is to mimic the UPC function at the channel rate control device 208 (FIG.
2) so as to prevent the UPC function in variable bit rate channel 101 from reducing the transmitted bit-rate below the desired bit-rate R.
sub.
i.
If the variable bit-rate channel 101 is capable of providing a determination as to whether or not it can transmit at the desired bit-rate R