Device for generating multiple quality level bit-rates in a video encoder

Device for generating multiple quality level bit-rates in a video encoder having a motion estimator providing a predicted block for each predefined block based upon estimating the motion between the predefined block of the current image and the corresponding block in the previous image, a transformer for transforming a prediction error resulting from the difference between the predicted block and the predefined block into the frequency domain, and a quantizer for quantizing the coefficients of the prediction error and providing the quantized coefficients to a video multiplex coding unit. Such a device includes a number n of stages, each corresponding to a quality level i=1 to n, and each stage having a computer for reducing the prediction error in accordance with the quality level i and providing a corresponding quantized prediction error residual QDi, and an adder for obtaining a cumulative prediction error:corresponding to quality level iwherein QDj is the de-quantized value of the quantized prediction error residual QDj. Such a device is well suited to the current H.263 bitstream structure of the ITU recommendation H.324/H.323 by using the sub-bitstream feature without the need to change the bitstream structure.