Patent ID: 7747139

Claim:
A playback method for reproducing video data recorded on a medium, said video data comprising a plurality of video units which each include an intra coded I-picture, a predictive coded P-picture including a group of blocks predicted from one picture and a bidirectionally-predictive coded B-picture including a group of blocks predicted from two pictures, at least one of said video units including an access point P-picture coded by motion compensation prediction using an I-picture located at the beginning of a video unit or a selected preceding P-picture, wherein a P-picture or a B-picture following said access point P-picture is coded without referring to any picture located before said access point P-picture, said medium containing video unit structure data used for identifying said access point P-picture, said video unit structure data including picture type information specifying a type of each picture included in each of said video units; said method comprising steps of: identifying a video information unit which includes a start picture to display, in the case of starting playback from said start picture; reading said video unit structure data to identify an I-picture or a selected picture preceding P-picture used for coding a closet access point P-picture preceding said start picture; accessing said I-picture or said P picture used for coding said access point P-picture according to said picture type information of said video unit structure data; decoding said I-picture or said P-picture used for coding said access point P-picture; decoding said access point P-picture using decoded I-picture or P-picture as a reference picture; and decoding said start picture using decoded access point P-picture as a reference picture, wherein said start picture is decoded without referring to any picture located before said access point P-picture.