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, a picture start code indicating a start point of a picture layer 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 in the previous header, the extension data in the previous header, and the picture start code in a current picture header, and does not include the extension start code in the current picture header and the extension data in the current picture header.