Variable bit-rate encoder

Process for coding digital data of a video image sequence effecting image compression of this data and regulation of the bit rate at the output of the coder by way of a regulating loop acting on a quantization interval for the data to be coded, storage in a buffer of the data output by the coder for its transmission over a channel at a variable bit rate to a buffer of a decoder, a tagging of this data so as to guarantee a constant time τ between the instant of storage of an image in the buffer of the coder and the instant of output of this image from the buffer of the decoder, characterized in that the bit rate regulation in respect of the image at the instant n is performed as a function of a bit rate prediction in respect of the transmission channel for the instant n+τ, and in that the regulation is performed within the limits of a virtual buffer defined by a top address and a bottom address in the buffer of the coder, the top address or offset of the virtual buffer changing with respect to the top address of the buffer of the coder, starting from a time τ before the variation of the transmission bit rate at the output of the buffer of the coder, depending on a value corresponding to the bit rate variation multiplied by the time τ.