It is a long-cherished dream for movie manufacturers to realize an interactive control, in which buttons appear on a screen in the course of reproduction of a motion picture made of a plurality of pictures, and the course of reproduction changes according to an operation directed to the buttons. DVD is an epoch-making product in a sense of having realized such an interactive control. The synchronous reproduction between a motion picture made of a plurality of pictures and buttons is realized by setting a time stamp so that buttons appear at an arbitrary time on a reproduction time axis of the motion picture.
However, so as to realize the interactivity, it is not sufficient only to record graphics data constituting buttons in the recording medium; control is also required such as to change the state of a plurality of buttons arranged on a screen in response to a user operation, and to change the state of the buttons in the course of the reproduction of the motion picture data. So as to realize such state control for a DVD, in the stream (video object) generated by multiplexing audio/videos, state control information is provided in a NAVI pack positioned at the beginning of each VOBU. Each VOBU includes one GOP of the video stream, audio data to be read from the DVD together with the GOP, and sub-picture data. The state control information is information to change the state of each button arranged on a screen, and a NAVI pack is information indicating a transfer rate, a buffer size, and the like, for GOP for each stream. By setting such state control information in a NAVI pack, a DVD realizes the state transition of a button with a time accuracy of GOP. FIG. 1 shows the above-described interactive control. In this drawing, data allocation in a DVD is shown at the bottom, and state control information is stored in the NAVI pack. Furthermore, the state control information is valid during the duration of the GOP to which the NAVI pack belongs. In addition, a graphics object is stored in a PES packet, and is displayed at a same display time as picture data to be synchronously displayed. One prior art disclosing such a technology is the following patent reference 1.
(Patent Reference 1 )
Japanese Patent Publication No. 2813245
However, movie manufacturers today are not satisfied with a current level of interactive control, and require further contrivance of the makers of recording media and reproduction apparatuses. Such contrivance includes realization of the state transition of a button by means of animation. Realization of such animation increases the number of graphics to be decoded, and decoding load. Accordingly, there are cases where a reproduction apparatus cannot immediately respond to a user operation. For example, assume that an interactive display has four buttons, each of which has three states: normal state; selected state; and active state. Also assume that each state of button is presented in 2-3 seconds of animation display. Even if one page of graphics data is displayed at intervals of 5 frames in an image signal, about 30 pages of graphics data are required to realize 2-3 seconds of animation. Not only that, since there are three states for a button (normal state, selected state, and active state), there will be total of 90 pages (3*30) of graphics data. So as to dispose four buttons on an interactive display, it requires decoding of 360 pages (4*90), which is an enormous amount of graphics data. Decoding load for one page of graphics data is light. However, it takes about dozens of seconds so as to decode several hundreds of pages of graphics data. If a reproduction apparatus cannot receive any user operation during the dozens of seconds, the user cannot help feeling a sense of response debasement.