Encoding parameters of picture and higher layers of importance to a number of applications, and encoding parameters of slice and lower layers of no importance to all applications are converted into auxiliary packets inserted respectively into a V-blanking area and an H-blanking area of a video-data signal output by a history-information-multiplexing apparatus employed in a video-decoding system. On the other hand, a video-encoding system extracts back the auxiliary packets superposed on the V-blanking area and the H-blanking area from an input base-band video signal. As a result, a technique of superposing information on data can be changed in accordance with the importance of the information and required information can be fetched with ease.