a picture decoding method and apparatus for encoding a video signal . the method includes performing an encoding process on the video signal to generate a bit stream compatible with mpeg 1 moving picture video standard . the method further includes controlling the encoding process so as to generate the bit stream which includes , in a previous picture header , an extension start code indicating the beginning of extension data added when a picture header includes control data that is newly added in mpeg 2 standard format and the extension data , and does not include , in a current picture header , the extension start code and the extension data .