1. A device for re-encoding images according to a given preset bit rate of a video stream comprising image sequences initially coded according to at least one mode, comprising: means for extracting information associated with the re-encoding of the images, said information representing at least the complexity of re-encoding of each image, means for extracting information, in particular coding complexity information associated with the initial coding of the images, wherein it comprises: means for calculating a complexity ratio of the complexities of re-encoding of the images previously re-encoded according to said mode to the complexities of initial coding of these images, means for updating an averaged complexity ratio for said mode as a function of the complexity ratio and means for re-encoding each image according to said mode by estimating the complexity of each image to be re-encoded as being the product of the complexity of initial coding of said image times the averaged complexity ratio for said mode; means for extracting an overhead value of initial coding of each image, means for extracting an overhead value of re-encoding of each re-encoded image, means for calculating an overhead ratio of the overhead value of re-encoding of images previously re-encoded according to said mode to the overhead value of initial coding of these images, means for updating an averaged overhead ratio for said mode as a function of the overhead ratio and means for re-encoding each image according to said mode estimating the overhead value of each image to be re-encoded as being the product of the overhead value-of initial coding of said image times the averaged overhead ratio for said mode.