Patent Publication Number: US-8526491-B2

Title: Image encoding device, and image decoding device

Description:
This application is a divisional of U.S. application Ser. No. 11/660,335 now U.S Pat. No. 7680182 which is the National Stage of International Application No. PCT/JP2005/014593, filed Aug. 9, 2005. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image encoding device, an image decoding device, and the like, and particularly to encoding and decoding of a stream that includes a moving image and a still image. The present invention also relates to a packaged medium that ensures random accessibility at the time of reproduction. 
     BACKGROUND ART 
     The following describes a DVD-Video disc (hereinafter simply referred to as a “DVD”) of a conventional technology. 
       FIG. 1  is a diagram showing the structure of a DVD. As shown in the bottom of  FIG. 1 , the DVD disc includes a logical address space in between the lead-in area and the lead-out area. In the logical address space, volume information of the file system is stored at the top, and application data such as video and audio is stored in the subsequent areas. 
     The file system, which is a file system compliant with ISO9660 and the Universal Disc Format (UDF), is a mechanism for representing data on a disc by units called directories and files. Even in a personal computer (PC) for everyday use, data stored in the hard disk in the form of directories and files are represented on the computer via a file system called FAT or NTFS, as a result of which usability is enhanced. 
     Both UDF and ISO9660 (which are sometimes referred to collectively as “UDF Bridge”) are used in DVDs, and data can be read out by the file system driver of any of UDF and ISO9660. In the case of DVD-RAM/R/RW, which are rewritable DVD discs, data reading, writing, and deletion are physically possible via these file systems. 
     Data stored on a DVD can be viewed, via the UDF bridge, as directories or files as shown in the upper left of  FIG. 1 . Immediately below the root directory (“ROOT” in  FIG. 1 ), a directory called “VIDEO_TS” is placed, where application data of the DVD is stored. The application data is stored as plural files. The following are some of the major files:
         VIDEO_TS. IFO disc reproduction control information file   VTS — 01 — 0. IFO video title set#1 reproduction control information file   VTS — 01 — 0. VOB video title set#1 stream file       

     There are two types of extensions specified. “IFO” indicates that the corresponding file stores reproduction control information. “VOB” indicates that the corresponding file stores an MPEG stream being AV data. The reproduction control information is information that includes information for realizing interactivity (technique for dynamically changing the state of reproduction according to a user operation) employed for the DVD as well as information, such as meta data, which is attached to a title or an AV stream. The reproduction control information of the DVD is called navigation information in general. 
     The reproduction control information files include “VIDEO_TS. IFO” intended for the management of the entire disc, and “VTS — 01 — 0. IFO” being the reproduction control information of an individual video title set (a single DVD disc can store plural titles, that is, different movies and movies with different versions). “01” in the body of the filename indicates the number of the video title set. In the case where the number of a video title set is #2, for example, the filename is “VTS — 02 — 0. IFO”. 
     The upper right of  FIG. 1  shows a DVD navigation space in the application layer of the DVD, i.e., a logical structure space where the above-described reproduction control information is shown. Information in “VIDEO_TS. IFO” is shown in the DVD navigation space as Video Manager Information (VMGI). 
     Reproduction control information which exists for each “VTS — 01 — 0. IFO” or for each video title set, is shown in the DVD navigation space as Video Title Set Information (VTSI). 
     VTSI describes Program Chain Information (PGCI) which is information about a reproduction sequence called a Program Chain (PGC). The PGCI is made up of a group of cells and a kind of programming information called a command. Each cell represents a part or the whole segments in a VOB (which is an abbreviation of Video Object and which includes an MPEG stream). The reproduction of a cell means to reproduce segments in the VOB that are specified by such cell. 
     A command, which is processed by a DVD-capable virtual machine, is similar to Java (registered trademark) Script executed on a browser. However, a DVD command is different from a Java (registered trademark) Script in that, while Java Script performs window and browser controls (e.g., opens a new browser window) in addition to logical operations, a DVD command performs only the reproduction control of AV titles, such as the specification of a chapter to be reproduced, in addition to logical operations. 
     Each cell includes, as its internal information, the start address and end address (logical storage address on the disc) of a VOB stored on the disc. A player reads out data using such information described in the cell about the start address and end address of the VOB, and reproduces the read data. 
       FIG. 2  is a schematic diagram for describing the navigation information embedded in the AV stream. Interactivity, which is characteristics to a DVD, is not realized only by the navigation information stored in the above-described “VIDEO_TS. IFO” and “VTS — 01 — 0. IFO”; several pieces of important information are multiplexed in the VOB together with video data and audio data, using dedicated carriers called navigation packs (hereinafter referred to as navi pack(s) or NV_PCK). 
     Here, a description is given of a menu as a simple example of interactivity. Several buttons appear on the menu screen. For each of such buttons, a process to be performed when such button is selected and activated, is defined. One button is selected on the menu (the fact that the button is selected is indicated to the user by a semitransparent color overlaid on such button in a highlighted manner). The user can shift to any of the buttons located above, below, right or left of the currently selected button, using the Up/Down/Right/Left key on the remote control. Using the Up/Down/Right/Left key on the remote control, the user moves the highlight to a button such user wishes to select and activate, and then determines (presses the Determination key). Accordingly, a program of the corresponding command is activated. In general, the reproduction of the corresponding title or chapter is activated by the command. 
     The upper left of  FIG. 2  shows an overview of the control information stored in NV_PCK. NV_PCK includes highlight color information and button information of each button. The highlight color information describes color palette information, which specifies a semitransparent color of a highlight to be overlaid. Each button information describes: rectangular area information that is information about the position of each button; shift information indicating a move from one button to another button (specification of a destination button corresponding to a user selection of the Up/Down/Right/Left key); and button command information (a command to be executed when such button is selected). 
     As shown in the upper right center of  FIG. 2 , a highlight on the menu is generated as an overlay image. The overlay image is an image generated by giving a color specified by the color palette information to the rectangular area information in the button information. Such overlay image is displayed on the screen, superimposed on the background image shown in the right of  FIG. 2 . 
     The menu of the DVD is realized in the above-described manner. The reason that a part of the navigation data is embedded in the stream using NV_PCK is to allow the menu information to be dynamically updated in synchronization with the stream (e.g., to allow the menu to be displayed only for five to ten minutes in the middle of movie reproduction), and to realize the menu of the DVD without any problems even for an application which is likely to have a problem of synchronization timing. Another major reason is to improve user operability by, for example, storing, in NV_PCK, information for supporting special reproduction, so as to smoothly decode and reproduce AV data even when a DVD is reproduced in a special manner such as fast-forward reproduction and rewind reproduction. 
       FIG. 3  is a conceptual diagram showing a VOB being a DVD stream. As shown in the drawing, data such as video, audio, and subtitles (as shown in A) are each packetized and packed (as shown in B), based on the MPEG system standard (ISO/IEC13818-1), and multiplexed to be a single MPEG program stream (as shown in C). NV_PCK including a button command for realizing interactivity as described above is multiplexed together. 
     Multiplexing in the MPEG system is characterized in that, while each data to be multiplexed forms a bit string based on its decoding order, data to be multiplexed, i.e., video data, audio data, and subtitle data do not necessarily form a bit string in order of reproduction. This is attributable to the fact that a decoder model for a multiplexed MPEG system stream (generally referred to as a System Target Decoder or an STD (shown in D in  FIG. 3 ) has decoder buffers corresponding to the respective elementary streams obtained by demultiplexing the multiplexed data, and such demultiplexed data are temporarily stored in the respective decoder buffers until the time of decoding. The size of decoder buffers specified by the DVD-Video standard differs on an elementary stream basis. The size of the buffer for video data is 232 KB, the size of the buffer for audio data is 4 KB, and the size of the buffer for subtitle data is 52 KB. 
     In other words, the subtitle data that is multiplexed together with the video data is not necessarily decoded or reproduced at the same timing. 
     Meanwhile, there is the Blu-ray Disc (BD) standard as a next-generation DVD standard. 
     While a DVD is intended for the package distribution of video with standard image quality (standard-definition image quality) as well as the recording of analog broadcasting (the DVD Video Recording format), a BD is capable of recording digital broadcasting with high-definition image quality as it is (the Blu-ray Disc Rewritable format; hereinafter referred to as the BD-RE). 
     However, since the BD-RE format widely supports the recording of digital broadcasting, information that supports special reproduction or the like is not optimized. Considering that high-definition video will be distributed in the future by means of package distribution at the rate higher than that for digital broadcasting (the BD-ROM format), there will be the need for a mechanism that stresses out a user even at the time of special reproduction. 
     The special reproduction support information (time map) of the BD-RE format is disclosed in Patent document 1.
         Patent Document 1: Japanese Laid-Open Patent Application No. 2000-228656.       

     DISCLOSURE OF INVENTION 
     Problems that Invention is to Solve 
     The conventional information storage medium has a problem that a still image cannot be encoded into a high-quality image since both a moving image and a still image has the same upper limit value for the amount of code per picture. 
     For example, MPEG-4 AVC specifies the maximum value for the amount of code per picture. An application specification such as that for BD uses, as the upper limit value of the amount of code per picture, the value specified by MPEG-4 AVC or the value uniquely set in the application. It is possible to control the upper limit value using a parameter known as a Minimum Compression. Ratio (MinCR) specified by the MPEG-4 AVC standard. MinCR is a parameter which indicates the lower limit of a compression ratio of an encoded picture with respect to the original image. For example, when MinCR is 2, it indicates that the amount of code per encoded picture is half the data size of the original image or smaller. 
     In the conventional information storage medium, the same MinCR values are used for both a moving image application and a still image application. The amount of processing to be performed at the time of decoding encoded data is large in the case of a moving image. Therefore, MinCR is determined so that an operation is ensured particularly in the worst case scenario where the amount of operations to be performed at the time of decoding one picture becomes the upper limit value specified by a standard. In the case of still images, on the other hand, image quality is of more importance than the amount of processing performed at the time of decoding since a display interval of still images is longer than that of a moving image. However, due to the fact that the amount of code increases as a result of encoding a still image into a high-quality image, there has been a problem with the conventional information storage medium, which uses the same MinCR values for still images and a moving image, the problem being that a sufficient amount of code cannot be assigned to a picture especially at the time of intra encoding. 
     An object of the present invention is to provide an image encoding device and an image decoding device that are capable of encoding and decoding a still image into an image with higher image quality than that of a moving image in the case where there is a mixture of a moving image and still images. 
     Means to Solve the Problems 
     In order to achieve the above object, the image encoding device of the present invention is an image encoding device that encodes a still image and a moving image, the device including: a determination unit that determines a first upper limit and a second upper limit, the first upper limit indicating an upper limit of the amount of code per picture of still images, and the second upper limit indicating an upper limit of the amount of code per picture in a moving image; an encoding unit that encodes each of the still images and the moving image in such a manner that the first and second upper limits are satisfied; a multiplexing unit that generates a stream by multiplexing the encoded still images and the encoded moving image; a generation unit that generates management information that identifies the first and second upper limits; and an output unit that outputs the stream and the management information. Here, the first upper limit may be higher than the second upper limit. 
     With the above structure, it is possible to set a higher upper limit as the upper limit of the amount of code per still image (the first upper limit) than the upper limit of the amount of code per moving image (the second upper limit). This makes it possible for the reproduction device, in the case where there is a mixture of a moving image and a still image, to suppress the amount of decoding processing performed on the moving image and to encode the still image into an image with higher quality than that of the moving image. 
     Here, the management information may include a flag that corresponds to each predetermined unit in the stream, and the flag may indicate whether or not the corresponding predetermined unit is a moving image or a still image. 
     With this structure, it is possible to determine, for each predetermined unit in the stream, whether the amount of code per picture corresponds to the first upper limit or the second upper limit. Furthermore, by previously fixing the first and second upper limits between the image encoding device and the image decoding device, it becomes not necessary for the management information to explicitly indicate the first and second upper limits, and it suffices to simply indicate whether each predetermined unit is a moving image or a still image. This results in a further reduction in the data amount of the management information. 
     Here, the first and second upper limits may each indicate how much the amount of code per picture is compressed with respect to the amount of original image data. 
     Here, each of the encoded still images may include a first unit and a second unit, the first unit storing initialization information that is referred to when the still image is decoded, and the second unit storing pixel data of the still image, the first unit may store: information indicating a frame rate at which the still image is repeatedly displayed; and an identification flag indicating whether or not the information indicating the frame rate is included in the first unit, and the identification flag may be set in the case where the first unit is included in data of the still image. 
     With this structure, it is possible to set the display time and the display duration of a still image based on a frame rate. 
     Here, the management information may include information regarding addresses of all the still images in the stream. 
     The image decoding device of the present invention is image decoding device, including: an obtainment unit that obtains a stream which includes an encoded moving image and an encoded still image; a demultiplexing unit that demultiplexes the encoded still image and the encoded moving image from the stream; and a decoding unit that decodes the encoded moving image and the encoded still image demultiplexed from each other, wherein the decoding unit may add a margin to a decoding period between a decoding time stamp and a presentation time stamp of the encoded still image, and start decoding or outputting the encoded still image according to the decoding period added with the margin. 
     With this structure, it is possible to decode, in an easy and reliable manner, a still image whose image quality is higher than that of a moving image, in the case where the amount of code per still image is larger than the amount of code per picture in the moving image. 
     Here, wherein the decoding unit may: start the decoding at a time indicated by the decoding time stamp of the encoded still image; add a margin to the presentation time stamp in the case where the decoding of the still image has not completed by a time indicated by the presentation time stamp; and output the decoded still image at a time indicated by the presentation time stamp added with the margin. 
     With the above structure, it is possible to dynamically and flexibly change the time at which a still image is outputted according to the amount of code and the amount of processing performed at the time of decoding, since the actual time of output is delayed only in the case where the decoding of the still image is delayed. 
     Here, the decoding unit may add the margin to the decoding time stamp, and start the decoding of the still image at a time indicated by the decoding time stamp added with the margin. 
     With the above structure, it is possible to reproduce a still image appropriately at the time indicated by the presentation time stamp without delaying the output of the still image, since the time to start decoding is set earlier than the time indicated by decoding time stamp. 
     Here, each of the encoded still images may include a first unit and a second unit, the first unit storing initialization information that is referred to when the still image is decoded, and the second unit storing pixel data of the still image, the first unit may store: information indicating a frame rate at which the still image is repeatedly displayed; and an identification flag indicating whether or not the information indicating the frame rate is included in the first unit, the identification flag may be set in the case where the first unit is included in data of the still image, and the decoding unit may output a still image which has been decoded according to the frame rate during a period of time from a presentation time stamp of the still image which has been decoded to a presentation time stamp of a next still image in decoding order. 
     Note that the image encoding method, image decoding method, semiconductor device, and encoded stream of the present invention have the same structure as described above, and thus they are not described here. 
     Effects of the Invention 
     As described above, the image encoding device, the image decoding device, and the like of the present invention produce an advantage of being able to reproduce still images with high image quality at the time of still image reproduction, while suppressing the amount of processing performed by the reproduction device at the time of moving image reproduction, by setting a higher upper limit to the amount of code per still image than that of the moving image. Therefore, the present invention has a high practical value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a structure of a DVD. 
         FIG. 2  is a diagram showing a structure of highlight. 
         FIG. 3  is a diagram showing an example of multiplexing in a DVD. 
         FIG. 4  is a diagram for describing a flag indicating that a specified MinCR value is applied to a clip as well as describing a data structure in a first embodiment. 
         FIG. 5  is a flowchart illustrating operations performed in a multiplexing method. 
         FIG. 6  is block diagram showing a structure of a multiplexing device. 
         FIG. 7A  is a diagram for describing a first reproduction method of reproducing a still image. 
         FIG. 7B  is a diagram for describing a second reproduction method of reproducing a still image. 
         FIG. 8  is a flowchart showing the first reproduction method of reproduction a still image. 
         FIG. 9  is a flowchart showing the second reproduction method of reproduction a still image. 
         FIG. 10  is a hierarchy chart showing data on an HD-DVD. 
         FIG. 11  is a diagram showing a structure of a logical space on the HD-DVD. 
         FIG. 12  is a block diagram showing an overview of an HD-DVD player. 
         FIG. 13  is a block diagram showing a structure of the HD-DVD player. 
         FIG. 14  is a diagram for describing an application space on the HD-DVD. 
         FIG. 15  is a diagram showing a structure of an MPEG stream (VOB). 
         FIG. 16  is a diagram showing a structure of each pack. 
         FIG. 17  is a diagram for describing a relationship between an AV stream and a player structure. 
         FIG. 18  is a model diagram showing a continuous supply of AV data to a track buffer. 
         FIG. 19  is a diagram showing a structure of a VOB information file. 
         FIG. 20  is a diagram for describing a time map. 
         FIG. 21  is a diagram showing a structure of a playlist file. 
         FIG. 22  is a diagram showing a structure of a program file corresponding to a playlist. 
         FIG. 23  is a diagram showing a structure of a management information file related to the entire BD disc. 
         FIG. 24  is a diagram showing a structure of a file for recording a global event handler. 
         FIG. 25  is a diagram showing an example of a time event. 
         FIG. 26  is a diagram showing an example of a user event. 
         FIG. 27  is a diagram for describing an example of a global event handler. 
         FIG. 28  is a diagram showing a structure of a virtual machine. 
         FIG. 29  is a diagram showing a table of player variables. 
         FIG. 30  is a diagram showing an example of an event handler (for a time event). 
         FIG. 31  is a diagram showing an example of an event handler (for a user event). 
         FIG. 32  is a flowchart showing basic player processes. 
         FIG. 33  is a flowchart showing playlist reproduction processes. 
         FIG. 34  is a flowchart showing event processes. 
         FIG. 35  is a flowchart showing subtitle processes. 
         FIG. 36  is a diagram for describing a relationship between the time map and still images. 
         FIG. 37  is a diagram for describing a flag indicating whether or not a picture to be referred to is decodable. 
         FIG. 38  is a diagram for describing a flag indicating that all entries refer to I pictures. 
         FIG. 39  is a diagram for describing a difference between a moving image application and a slideshow. 
         FIG. 40  is a diagram for describing a flag that guarantees that all I pictures are referred to. 
         FIG. 41  is a diagram showing a data structure of a still image in compliance with MPEG-4 AVC. 
         FIG. 42  is a diagram for describing a reproduction method for still images in compliance with MPEG-4 AVC. 
         FIG. 43A  shows an example physical format of a flexible disk as a storage medium itself. 
         FIG. 43B  shows an external view of the flexible disk viewed from the front, its schematic cross-sectional view, and the flexible disk itself. 
         FIG. 43C  shows a structure required for storing and reading out the program on and from the flexible disk FD. 
     
    
    
     NUMERICAL REFERENCES 
     
         
         
           
               201  BD disc 
               202  Optical pick-up 
               203  Program storage memory 
               204  Management information storage memory 
               205  AV storage memory 
               206  Program processing unit 
               207  Management information processing unit 
               208  Presentation processing unit 
               209  Image plane 
               210  Video plane 
               211  Composition processing unit 
               301  Program storage memory 
               302  Program processor 
               303  UOP manager 
               304  Management information storage memory 
               305  Scenario processor 
               306  Presentation controller 
               307  Clock 
               308  Image memory 
               309  Track buffer 
               310  Demultiplexer 
               311  Image processor 
               312  Video processor 
               313  Sound processor 
               314  Image plane 
               315  Video plane 
               316  Composition processing unit 
               317  Drive controller 
               1001  Encoding unit 
               1002  System multiplexing unit 
               1003  Combination unit 
               2000  Multiplexing device 
               2001  MinCR information determination unit 
               2002  MinCR information generation unit 
               2003  Management information creation unit 
               3207  Moving image down-converter 
               3215  Subtitle down-converter 
               3223  Still image down-converter 
               3228  Audio down-converter 
             S 101  Disc insertion step 
             S 102  BD.INFO reading step 
             S 103  BD.PROG reading step 
             S 104  First event generation step 
             S 105  Event handler execution step 
             S 201  UOP acceptance step 
             S 202  UOP event generation step 
             S 203  Menu call determination step 
             S 204  Event generation step 
             S 205  Event handler execution step 
             S 301  Playlist reproduction start step 
             S 302  Playlist information (XXX. PL) reading step 
             S 303  Play program (XXX.PROG) reading step 
             S 304  Cell reproduction start step 
             S 305  AV reproduction start step 
             S 401  AV reproduction start step 
             S 402  VOB information (YYY.VOBI) reading step 
             S 403  VOB (YYY.VOB) reading step 
             S 404  VOB reproduction start step 
             S 405  VOB reproduction end step 
             S 406  Next cell existence determination step 
             S 501  Playlist reproduction start step 
             S 502  Playlist reproduction end determination step 
             S 503  Time event time determination step 
             S 504  Event generation step 
             S 505  Event handler execution step 
             S 601  Playlist reproduction start step 
             S 602  Playlist reproduction end determination step 
             S 603  UOP acceptance determination step 
             S 604  UOP event generation step 
             S 605  Menu call determination step 
             S 606  User event validity period determination step 
             S 607  Event generation step 
             S 608  Event handler execution step 
             S 701  Playlist reproduction start step 
             S 702  Playlist reproduction end determination step 
             S 703  Subtitle rendering start determination step 
             S 704  Subtitle rendering step 
             S 705  Subtitle display end determination step 
             S 706  Subtitle deletion step 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The following describes embodiments of the present invention with reference to the drawings. 
     (First Embodiment) 
     The present embodiment describes an information storage medium and a reproduction device therefor which are capable of encoding a still image into a high-quality image while reducing the amount of processing to be performed at the time of reproducing a moving image in a package medium such as a BD-ROM. 
     The information storage medium of the present embodiment applies different MinCR values to a moving image and still images; a larger MinCR value is set for a moving image in consideration of the amount of processing performed at the time of decoding, and a MinCR value smaller than that for the moving image is set for still images in order to ensure that an encoded picture has the picture size which is sufficient as a high-quality picture. 
       FIG. 4  shows an example data structure of the information storage medium of the present embodiment. In the stream management information in the BD management information, attribute information of a clip is indicated in a data object known as ClipInfo. Note that a clip refers to an AV data file. For example, one file storing an MPEG-4 AVC still image stream is one clip. In order to indicate that different MinCR values are applied to a moving image and still images, information indicating the MinCR value of each clip is required. Therefore, information indicating the MinCR value to be applied to a clip to be referred to, is added to ClipInfo. Here, the MinCR value to be applied to a clip is indicated by storing flag information that indicates whether a clip to be referred to is a moving image clip or a still image clip, on the assumption that MinCR values to be applied to a still image clip and a moving image clip are determined in advance. Referring to an example in  FIG. 4 , at least a still image clip and a moving image clip are stored on the disc, and these clips are referred to from ClipInfo# 1  and ClipInfo# 2 , respectively. Here, flag information indicating that the clip is a still image clip is stored in ClipInfo# 1  and flag information indicating that the clip is a moving image clip is stored in ClipInfo# 2 . By referring to such flag information, it is possible to obtain the MinCR value of pictures making up a clip. In an example shown in  FIG. 4 , it is possible to achieve both the improvement in the quality of still images and the reduction in the amount of processing performed at the time of decoding a moving image, by setting 2 as MinCR of the still image clip and setting 4 as MinCR of the moving image clip. Note that the MinCR values used here are only examples, and thus a combination of other values may be used. In an application which allows the reproduction device to spend additional processing amount, the same MinCR value may be used for still images and a moving image. Furthermore, MinCR values may also be indicated by preparing plural combinations of MinCR values for still images and a moving image and by employing a parameter that indicates a specified one of the combinations. Furthermore, a clip may be an MPEG-2 system transport stream or a stream which is obtained by packetizing program stream AV data. 
     Note that there exists in ClipInfo a field known as application 13  type, which indicates the type of an application for reproducing a clip. This field can indicate whether the application is for a moving image or still images, and when the application is for still images, this field can indicate whether the application is a time-based application or a browsable application. Here, “time-based” indicates that still images are displayed at a predetermined interval, and “browsable” indicates that the user can determine the timing for displaying still images through this application. Therefore, in the case where the field value of application_type indicates time-based or browsable still image application, a MinCR value for still images may be applied, whereas in the case where the field value indicates a moving image application, a MinCR value for a moving image may be applied. 
     Note that MinCR values may be switched not only between a moving image and still images, but also between clips of different moving images. For example, in the case where main video and sub video are included, it is possible to set a smaller MinCR value for the main video so as to encode it into high-quality video, and to set a larger MinCR value for the sub video in consideration of the amount of processing. In this case, information indicating the MinCR values of the respective clips is used as information indicating the respective MinCR values, rather than using flag information indicating whether images are still images or a moving image. 
     Note that the parameter that indicates the upper limit of the amount of code of a moving image or a still image is not limited to MinCR, and thus an other parameter may be used such as by directly indicating the upper limit value for the amount of code as data size. 
     Also note that the information indicating the upper limit value of the amount of code per picture in a clip may either be stored in BD management information other than ClipInfo or may be stored in encoded data. In the case of storing the information in encoded data, such information can be stored for each random access unit such as a Group Of Picture (GOP). In the case of MPEG-4 AVC, for example, it is possible to utilize a data unit of storing user data. The data unit for user data storage includes: a Network Abstraction Layer (NAL) unit with a specific type; a Supplemental Enhancement Information (SEI) message for storing user data; and the like. Furthermore, the upper limit value of the amount of code per picture may be switchable in a unit other than a clip, such as a random access unit. 
     Also note that when it is determined, at the time of decoding a moving image, that the time required to decode the encoded data of one picture exceeds a predetermined length of time or a picture display interval, some data reproduction devices skip the decoding of such picture and start decoding the next picture. Alternatively, even in the case where it is possible to support the worst case scenario at the time of decoding, the decoding of a still image is consequently skipped in some cases at the time of reproducing still images stored in the information storage medium of the present embodiment. This is because the upper limit of the amount of code of a still image becomes larger than that of a moving image and the time required for decoding increases in relation to an increase in the amount of code. The display interval of still images is usually longer than that of a moving image. Therefore, even when decoding has not completed until a predetermined display start time, degradation in reproduction quality can be limited to small by displaying still images after the decoding thereof completes. Thus, at the time of decoding still images, even in the case where decoding thereof has not completed by a predetermined display start time, they only have to be displayed after decoding thereof completes, without skipping decoding thereof. 
     Note that although the above description is given for the BD, the same method can be used for an information storage medium as long as such information storage medium is capable of storing still images and moving images. Also, the encoding scheme is not limited to MPEG-4 AVC, and thus the present invention is applicable also to MPEG-2 Video as well as to VC-1 which is currently standardized by the Society of Motion Picture Television Engineers (SMPTE). 
       FIG. 5  is a flowchart showing a multiplexing method for creating data stored in the information storage medium of the present embodiment. The multiplexing method of the present embodiment is different from a conventional multiplexing method in that the multiplexing method of the present embodiment includes a step of switching between MinCR values depending on the type of a clip (Step S 2001 , Step S 2002  and Step S 2003 ) and a step of preparing flag information that identifies a MinCR value and incorporating it into management information (Step S 2004  and Step S 2005 ). 
     First, in Step S 2001 , it is determined whether a clip to be generated is a moving image clip or a still image clip. In the case where the clip is a still image clip, the process proceeds to Step S 2002  so as to set a predetermined MinCR value for still image clip, whereas in the case where the clip is a moving image clip, the process proceeds to Step S 2003 , and a predetermined MinCR value for moving image clip is set. Next, in Step S 1001 , pictures making up the clip are encoded in a manner that the MinCR value set in Step S 2002  or in Step S 2003  is satisfied, and the process proceeds to Step S 1002 . In Step S 1002 , the data encoded in Step S 1001  is system-multiplexed. In the BD, an MPEG-2 transport stream is used as a system multiplexing scheme. Next, in Step S 2004 , flag information is generated that identifies the MinCR value applied to the pictures making up the clip, and in Step S 2005 , management information is generated that includes the flag information generated in Step S 2004 . Finally, in Step S 1003 , the management information and the system-multiplexed encoded data are combined and the resultant data is outputted. Here, when the management information and the system-multiplexed encoded data are combined, they may be stored in separate files or may be stored collectively in the same file. When stored in separate files, the management information and the system-multiplexed encoded data may be stored in the same directory. Note that the MinCR value for still images only has to be set in Step S 2001  based on the bit rate, level, and profile of the stream. Here, the level is a parameter that indicates the upper limit value indicated by an encoding parameter such as bit rate, frame rate, and image size, whereas the profile is a parameter that specifies a combination of tools that can be used at the time of encoding. For example, in the case where the bit rate of a stream is relatively low, the same MinCR value may be assigned both for still images and a moving image, since the frame rate of the moving image is enough to complete decoding, even when a small MinCR value is set (when the upper limit amount of code is set high). On the contrary, in the case where the bit rate is relatively high, it is possible to give high image quality to still images by setting a smaller MinCR value for still images than for a moving image (setting a high upper limit amount of code). The information that identifies the MinCR value may be other than the flag information, and thus it is possible to directly store the upper limit value of the amount of code per picture. Meanwhile, in the case of handling plural clips, the processes from Step S 2001  to Step S 2005  are repeated, and the management information and the system-multiplexed encoded data may be combined and outputted in Step S 1003  after the system multiplexing and the generation of the management information for all clips completes. 
     Furthermore, unlike a moving image, it is desirable to take a relatively long time to appreciate each image of still images, and thus a display interval may be set to be equal to or greater than a predetermined value. In this case, the encoding in Step S 1001  may be performed so that the display times of contiguous still images in decoding order are equal to or greater than a predetermined value. Note that since decoding time and display time are set in Step S 1002 , only the display times of contiguous still images in decoding order may be set in Step S 1002  to be equal to or greater than a predetermined value. When this is done, it is not necessary in Step S 1001  to take into consideration intervals between display times at the time of encoding an input image. 
     Note that it is possible to multiplex data such as audio and graphics with a moving image or still images, but a description for it is not given here. 
       FIG. 6  is block diagram showing the structure of a multiplexing device  2000  that realizes the multiplexing method of the present embodiment. The multiplexing device  2000  includes a MinCR determination unit  2001 , a MinCR information generation unit  2002 , an encoding unit  1001 , a system multiplexing unit  1002 , a management information creation unit  2003 , and a combination unit  1003 . The multiplexing device  2000  is different from a conventional multiplexing device in that the multiplexing device  2000  includes the MinCR determination unit  2001  and the MinCR information creation  2002 , and in that the management information creation unit  2003  creates management information that includes flag information for identifying a MinCR value. 
     Next, a description is given of an operation of each of the units. The MinCR determination unit determines a MinCR value to be applied to pictures making up a clip, based on a clip attribute ClipChar indicating whether the clip is a moving image clip or a still image clip, and inputs the determined MinCR value cr into the encoding unit  1001  and the MinCR information generation unit  2002 . The encoding unit  1001  encodes an input moving image or image data Vin based on the MinCR value cr determined by the MinCR determination unit, and inputs the encoded data Cdata into the system multiplexing unit  1002 . The system multiplexing unit  1002  system-multiplexes the encoded data Cdata and inputs the resulting multiplexed data Mdata into the combination unit  1003 . Meanwhile, the MinCR information creation unit creates MinCR information crInf, which is flag information for identifying the MinCR value applied to the pictures making up the clip, based on the MinCR value, and inputs the resulting information into the management information creation unit  2003 . The management information creation unit obtains, from the system multiplexing unit  1002 , stream information StrInf used to generate management information of the multiplexed data Mdata, creates the management information CtrInf that includes the MinCR information crInf, and outputs the created management information CtrInf to the combination unit  1003 . The combination unit  1003  combines the management information CtrInf and the multiplexed data Mdata, and outputs the resulting data as record data Dout. Note that the stream information StrInf may be inputted from the encoding unit  1001  to the management information creation unit  2003 . 
     The generation of encoded data, and the system multiplexing or the creation of management information are performed by separate devices in the case of creating data by use of an authoring tool. Even in this case, however, the operations of the respective devices may be designed to be the same as the respective units in the multiplexing device  2000 . 
     Next, a description is given of the reproduction method. In the case where the amount of code of a still image is larger than that of a moving image, it can happen that the decoding of the still images cannot complete within the decoding period between Decoding Time Stamp (DTS) and Presentation Time Stamp (PTS), although it depends on processing capability of a reproduction device. In order that still images can be normally reproduced and outputted even in such a case, still images are reproduced in the present embodiment using a first or a second reproduction method described below. 
       FIG. 7A  is a diagram for describing the first reproduction method for reproducing still images. In this drawing, DTS 1  denotes the time indicated by a decoding time stamp included in the header of a packet (called PES packet) that carries codes of a still image pic 1 , and indicates the time at which the decoding of the still image pic  1  should be started. PTS 1  denotes the time indicated by a presentation time stamp included in the header of the packet that carries the codes of the still image pic 1 , and indicates the time at which the presentation (output or display) of the still image pic  1  should be started. The same applies to DTS 2  and DTS 3 , as well as to PTS 2 , and PTS 3 . 
     In the drawing, it is illustrated that the decoding of a still image pic 2  starts at the time indicated by DTS 2  and completes after the time indicated by PTS 2 . In the first reproduction method, in the case where the decoding of a still image has not completed before the time indicated by its PTS, the presentation of such still image is started at the time of the frame grid that comes immediately after the time at which the decoding has completed. 
     As described above, in the first reproduction method, in the case where the decoding of a still image is started at the time indicated by the decoding time stamp included in the encoded still image and the decoding of the still image has not completed by the time indicated by the presentation time stamp, a margin is added to the presentation time stamp so that the decoded still image is outputted at the time indicated by the presentation time stamp added with the margin. 
       FIG. 7B  is a diagram for describing the second reproduction method for reproducing still images. In the second reproduction method: a margin is added to DTS; the decoding of a still image is started at the time added with the margin; and the decoded still image is outputted at the time indicated by PTS. 
       FIG. 8  is a flowchart showing the first reproduction method for reproducing a still image stream. As shown in this drawing, the following are performed in the first reproduction method: the decoding of a still image picture (pic_N) is started at the time indicated by DTS of the pic_N (S 3001 ); it is determined whether or not the decoding of the still image picture (pic_N) has completed at its PTS (PTS_N) (S 3002 ); in the case where the decoding has completed, the decoded still image picture (pic_N) is outputted at the time indicted by PTS (PTS_N) (S 3003 ); and in the case where the decoding has not completed, the decoded still image picture (pic_N) is outputted at the time of the frame grid that comes immediately after the completion of the decoding (S 3004 ). 
     As described above, the first reproduction method enables to flexibly and dynamically change the time at which a still image should be outputted depending on the amount of code of the still image, since the actual time of output is delayed only in the case where the decoding of the still image is delayed. 
       FIG. 9  is a flowchart showing the second reproduction method for reproducing a still image stream. As shown in the drawing, the following are performed in the second reproduction method: it is determined whether or not a stream is a still image stream (S 4001 ); in the case where the stream is a still image stream, the decoding of a picture (pic_N) is started at the time which is earlier than the time indicated by DTS only by a predetermined amount of time T (S 4002 ); and in the case where the stream is not a still image stream (i.e., the stream is a moving image stream), the decoding of the picture is started at the time indicated by DTS ( 43003 ). Here, the predetermined amount of time T is a margin added to DTS. The predetermined amount of time T is defined so that the time from the time indicated by DTS added with the margin to the time indicted by PTS is longer than the time required to decode a still image with the maximum amount of code. 
     The second reproduction method enables to reproduce a still image appropriately at the time indicated by PTS without delaying the output of the still image, since the time to start decoding is set earlier than the time indicated by DTS. 
     Note that although the time to start decoding of all still images is set earlier in  FIG. 9 , the time to start decoding may be set earlier only in the case where the amount of code of a still image exceeds a threshold value. For example, in the case where the amount of code of pic  1  and pic  3  in  FIG. 7B  is equal to or smaller than a threshold value, and the amount of code of pic  2  exceeds the threshold value, the times to start decoding the pic  1  and pic  3  are the times indicated by DTS 1  and DTS 3 , respectively. Meanwhile, the time to start decoding pic 2  is (DTS 2 -T). Furthermore, the process of Step S 4002  may be performed only in the case where a parameter such as image size, bit rate, and level, exceeds a predetermined threshold value. 
     Note that the first and second reproduction methods shown in  FIG. 8  and  FIG. 9  are performed by a presentation management unit  208  in  FIG. 12 , a video processor in  FIG. 13  and  FIG. 17 , or a combination processing unit in  FIG. 13 , and are included in Step S 404  in  FIG. 33 . 
     &lt;Logical Data Structure on Disc&gt; 
       FIG. 10  is a diagram showing the structure of a BD-ROM, and more particularly showing a BD disc ( 104 ) being a disc medium, as well as the structure of data ( 101 ,  102 , and  103 ) stored on the disc. Stored on the BD disc ( 104 ) are: AV data ( 103 ); BD management information ( 102 ) including AV data management information, an AV reproduction sequence, and the like; and a BD reproduction program ( 101 ) for realizing interactivity. For the sake of illustrations, the present embodiment describes the BD disc by focusing on an AV application for reproducing the AV contents of a movie, but the same is applied to the case where the BD disc is used for other purposes. 
       FIG. 11  is a diagram showing the structures of directories and files of the logical data stored on the above-described BD disc. As in the case of other optical discs such as DVDs and CDs, the BD disc has storage areas that are spirally formed in a direction from the inner radius toward the outer radius, as well as a logical address space for storing logical data in between the lead-in area at the inner radius and the lead-out area at the outer radius. At the innermost area of the lead-in area, there is a special area called a Burst Cutting Area (BCA), from which data can be read out only by a drive. Since this area cannot be read by the application, it is sometimes used, for example, for copyright protection technology or the like. 
     In the logical address space, file system information (volume) is stored at the top of the space, and application data such as video data is stored in the subsequent areas. The file system, which is a file system compliant with UDF and ISO9660 as described in “Background Art”, is a system for reading the stored logical data using directory and file structures, as is done in ordinary PCs. 
     According to the structures of the directories and files on the BD disc of the present embodiment, a BDVIDEO directory is located immediately below the root directory (ROOT). This directory is a directory storing data such as AV contents and management information ( 101 ,  102 , and  103  shown in  FIG. 10 ) stored on the BD. 
     Seven types of files described below are stored under the BDVIDEO directory. 
     BD. INFO file (this filename is fixed) 
     This file forms a part of the “BD management information”, and stores information related to the entire BD disc. This is the first file to be read out by a BD player. 
     BD. PROG (this filename is fixed) 
     This file forms a part of the “BD reproduction program”, and stores reproduction control information related to the entire BD disc. 
     XXX. PL (where “XXX” is variable, and the extension “PL” is fixed) 
     This file forms a part of the “BD management information”, and stores playlist information being a scenario (reproduction sequence). There exists one file for each playlist. 
     XXX. PROG (where “XXX” is variable, and the extension “PL” is fixed) 
     This file forms a part of the “BD reproduction program”, and stores reproduction control information for each playlist as described above. The corresponding playlist is identified by a file body name (identified by a matching “XXX”). 
     YYY. VOB (where “YYY” is variable, and the extension “VOB” is fixed) 
     This file forms a part of the “AV data”, and stores a VOB (such a VOB as described in “Background Art”). There exists one file for each VOB. 
     YYY. VOBI (where “YYY” is variable, and the extension “VOBI” is fixed) 
     This file forms a part of the “BD management information”, and stores stream management information related to a VOB being AV data. The corresponding VOB is identified by the file body name (identified by the matching “YYY”). 
     ZZZ. PNG (where “ZZZ” is variable, and the extension “PNG” is fixed) 
     This file forms a part of the “AV data”, and stores image data PNG (which is an image format standardized by W3C, and is pronounced “ping”) for constructing subtitles and a menu. There exists one file for each PNG image. 
     &lt;Structure of Player&gt; 
     Next, referring to  FIG. 12  and  FIG. 13 , a description is given of a player that reproduces the above-descried BD disc. 
       FIG. 12  is a block diagram showing an overall function of the player. 
     Data stored on a BD disc ( 201 ) is read out via an optical pick-up ( 202 ). Each data read out is transferred to a dedicated memory, which depends on the type of such data. The BD reproduction program (the file contents of “BD.PROG” or “XXX.PROG”), is transferred to the program storage memory ( 203 ), the BD management information (“BD.INFO”, “XXX.PL” or “YYY.VOBI”) is transferred to the management information storage memory ( 204 ), and the AV data (“YYY.VOB” or “ZZZ.PNG”) is transferred to the AV storage memory ( 205 ), respectively. 
     The BD reproduction program stored in the program storage memory ( 203 ) is processed by the program processing unit ( 206 ), the BD management information stored in the management information storage memory ( 204 ) is processed by the management information processing unit ( 207 ), and the AV data stored in the AV storage memory ( 205 ) is processed by the presentation processing unit ( 208 ), respectively. 
     The program processing unit ( 206 ) receives, from the management information processing unit ( 207 ), information about a playlist to be reproduced and event information such as timing for executing a program, and then executes the program. In the program, it is possible to dynamically change the playlist by sending, to the management information processing unit ( 207 ), an instruction to reproduce a playlist. The program processing unit ( 206 ) receives an event from the user, i.e., a request from a remote control key, and executes a program corresponding to the user event, if there is any. 
     The management information processing unit ( 207 ), in response to an instruction from the program processing unit ( 206 ), analyzes the corresponding playlist and management information of a VOB corresponding to the playlist, and instructs the presentation processing unit ( 208 ) to reproduce the target AV data. Furthermore, the management information processing unit ( 207 ) receives reference time information from the presentation processing unit ( 208 ), and instructs the presentation processing unit ( 208 ) to end the reproduction of the AV data based on such time information, as well as generating an event, for the program processing unit ( 206 ), indicating the timing for executing the program. 
     The presentation processing unit ( 208 ), which has decoders corresponding respectively to video, audio, and subtitles/images (still images), decodes and outputs the AV data according to an instruction from the management information processing unit ( 207 ). In the case of video data, and subtitles/images, they are rendered onto the respective dedicated planes, that is, the video plane ( 210 ) and image plane ( 209 ) after being decoded and composed by a composition processing unit ( 211 ), and the composed images are outputted to a display device such as a television. 
     The BD player, as is shown in  FIG. 12 , has a device structure which is based on the respective structures of the data stored on the BD disc shown in  FIG. 10 . 
       FIG. 13  is a block diagram showing a detailed structure of the above-described player. In  FIG. 13 , the AV storage memory ( 205 ) corresponds to an image memory ( 308 ) and a track buffer ( 309 ), the program processing unit ( 206 ) corresponds to a program processor ( 302 ) and an UOP manager ( 303 ), the management information processing unit ( 207 ) corresponds to a scenario processor ( 305 ) and a presentation controller ( 306 ), and the presentation processing unit ( 208 ) corresponds to a clock ( 307 ), a demultiplexer ( 310 ), an image processor ( 311 ), a video processor ( 312 ) and a sound processor ( 313 ), respectively. 
     The VOB data (MPEG stream) and image data (PNG) read from the BD disc ( 201 ) are stored respectively into the track buffer ( 309 ) and the image memory ( 308 ). The demultiplexer ( 310 ) demultiplexes the VOB data stored in the track buffer ( 309 ) based on the time indicated by the clock ( 307 ), and sends the video data to the video processor ( 312 ) and the audio data to the sound processor ( 313 ), respectively. The video processor ( 312 ) and the sound processor ( 313 ) are each made up of a decoder buffer and a decoder, as specified by the MPEG system standard. In other words, the video data and audio data inputted from the demultiplexer ( 310 ) are temporarily stored in the respective decoder buffers and decoded by the respective corresponding decoders according to the clock ( 307 ). 
     The PNG stored in the image memory ( 308 ) is processed using two methods described below. First, in the case where the image data is subtitle data, the presentation controller ( 306 ) gives an instruction about decoding timing. Upon receipt of time information from the clock ( 307 ), the scenario processor ( 305 ) instructs, when it is the time to display the subtitles (when it is the time to start/end the display), the presentation controller ( 306 ) to display or not to display the subtitles so that the subtitles are displayed in an appropriate manner. The image processor ( 311 ), upon receipt of an instruction from the presentation controller ( 306 ) to decode/display the image data, reads out the corresponding PNG data from the image memory ( 308 ), decodes it, and renders the decoded data onto the image plane ( 314 ). 
     Second, in the case where the image data is menu data, the program processor ( 302 ) gives an instruction about decoding timing. Timing at which the program processor ( 302 ) gives an instruction to decode the image data all depends on BD program processed by the program processor ( 302 ), and therefore it is not simply determined. 
     As has been described with reference to  FIG. 12 , the image data and video data are outputted respectively onto the image plane ( 314 ) and the video plane ( 315 ) after being decoded, and are outputted after being composed by the composition processing unit ( 316 ). 
     While the management information (scenario information and AV management information) read from the BD disc ( 201 ) is stored into the management information storage memory ( 304 ), the scenario information (“BD. INFO” and “XXX. PL”) is read out and processed by the scenario processor  305 . Furthermore, the AV management information (“YYY. VOBI”) is read out and processed by the presentation controller ( 306 ). 
     The scenario processor ( 305 ) analyzes the information in the playlist, and notifies the presentation controller ( 306 ) of a VOB referred to by the corresponding playlist and the reproduction position of such VOB. The presentation controller ( 306 ) analyzes the management information (“YYY. VOBI”) of such target VOB, and instructs the drive controller ( 317 ) to read out the target VOB. 
     According to the instruction from the presentation controller ( 306 ), the drive controller ( 317 ) reads out the target AV data by moving the optical pick-up. The AV data read out is stored into the image memory ( 308 ) or the track buffer ( 309 ), as described above. 
     The scenario processor ( 305 ) monitors the time indicated by the clock ( 307 ), and outputs, to the program processor ( 302 ), an event at the timing set in the management information. 
     The BD program (“BD. PROG” or “XXX. PROG”) stored on the program storage memory ( 301 ) is executed by the program processor ( 302 ). The program processor ( 302 ) processes the BD program in the case where an event is sent from the scenario processor ( 305 ) or where an event is sent from the UOP manager ( 303 ). The UOP manager ( 303 ) generates an event for the program processor ( 302 ) in the case where a request is sent from the user using a remote control key. 
     &lt;Application Space&gt; 
       FIG. 14  is a diagram showing an application space on the BD. 
     In the application space on the BD, a playlist (PlayList) serves as a unit of reproduction. Each playlist, which is a concatenation of cells (Cell), includes a static scenario being a reproduction sequence determined by the order of cell concatenation and a dynamic scenario described by the program. Unless the program makes a dynamic change in a scenario, the cells in the playlist are reproduced in order of concatenation, and the completion of the reproduction of all the cells marks the completion of the reproduction of such playlist. Furthermore, the program can change reproduction targets when reproduction and description is carried out beyond the playlist, as well as depending on user selection or player status. A typical example of this is menu. In the BD, a menu can be defined as a scenario to be reproduced according to a user selection, and the playlist can be dynamically selected by the program. 
     The program here refers to an event handler that is executed by a time event or a user event. 
     Time events are events that are generated based on time information embedded in a playlist. An example of time events is an event sent from the scenario processor ( 305 ) to the program processor ( 302 ), which has been described with reference to  FIG. 13 . When a time event is issued, the program processor ( 302 ) executes an event handler associated with the corresponding ID. As has been described above, it is possible, for a program to be executed, to give an instruction to reproduce another playlist. In this case, the program stops the reproduction of the current playlist to reproduce another playlist. 
     User events are events that are generated by remote key operations by the user, and are categorized roughly into two types. User events of a first type are menu selection events that are generated by operating cursor keys (the Up/Down/Right/Left key or the “Determination” key). Event handlers corresponding to menu selection events are effective only during a limited period indicated in a playlist (the validity period of each event handler is set as one of the information in the playlist). When the Up/Down/Right/Left key or the “Determination” key on the remote control is pressed, a search is made for an effective event handler. In the case where there is an effective event handler, such event handler is executed, whereas in the case where there is no effective event handler, this menu selection event is ignored. 
     User events of a second type are menu call events that are generated by operating the “Menu” key. When a menu call event is generated, a global event handler is called. The global event handler is an event handler that is always effective without depending on any playlists. Using this function, it is possible to implement a DVD menu call (e.g., a function of calling audio (data) or a subtitle menu during the reproduction of a title, and resuming the reproduction of the title at the point of suspension after a change is made in the audio (data) or subtitle (data)). 
     A cell (Cell), which is a unit constituting a static scenario in a playlist, represents the whole or a part of reproduction segments in a VOB (MPEG stream). Each cell includes the reproduction segments in a VOB as information about reproduction start time and reproduction end time. VOB management information (VOBI), which is paired with an individual VOB, includes a time map (TimeMap or TMAP), which is table information indicating storage addresses corresponding to data reproduction times. The use of a time map makes it possible to derive the read-start address and the read-end address within a VOB (i.e., the target “YYY. VOB”) based on the above-described reproduction start time and reproduction end time of the VOB. Time map is described in detail later. 
     &lt;Details about VOB&gt; 
       FIG. 15  is a diagram showing the structure of an MPEG stream (VOB) used in the present embodiment. 
     As shown in  FIG. 15 , a VOB is made up of plural Video Object Units (VOBUs). A VOBU serves as one unit of reproduction in a multiplexed stream that additionally includes audio data in a Group of Pictures (GOP) in an MPEG video stream. The reproduction duration of a VOBU is 1.0 seconds or less, and normally about 0.5 seconds. 
     The TS packet (MPEG-2 Transport Stream Packet) at the head of a VOBU stores a sequence header, which is followed by a GOP header and an I picture (Intra-coded), so that decoding can be started from this I picture. Furthermore, managed in the time map are: the address of a TS packet that includes the head part of the first I picture in the VOBU (start address); the address of a TS packet that includes the last part of the I picture, starting with the start address (end address); and the reproduction start time of this picture (PTS). Thus, an entry of the time map is provided for each TS packet at the head of a VOBU. 
     Each VOBU includes video packets (V_PTK) and audio packets (A_PTK). Each packet is 188 bytes. While not illustrated in  FIG. 15 , an Arrival Time Stamp (ATS) is provided immediately before each TS packet. The ATS indicates a relative time at which such TS packet is provided to the decoder. 
     An ATS is assigned for each TS packet because the system rate of this TS stream is not a fixed rate but a variable rate. In general, in the case where a fixed system rate is used, a dummy TS packet called a NULL packet is inserted. However, a variable rate is suitable in order to store high-quality images in a limited storage capacity, and a TS stream with an ATS is stored on the BD. 
       FIG. 16  is a diagram showing the structure of each TS packet. 
     As shown in  FIG. 16 , a TS packet is made up of a TS packet header, an adaptation field, and a payload. A Packet Identifier (PID) is stored in the TS packet header, thereby the type of information stored in the TS packet is identified. A Program Clock Reference (PCR) is stored in the adaptation field. The PCR is a reference value of a reference clock (referred to as a System Time Clock; STC) of a device which decodes the stream. Typically, the device demultiplexes the system stream at the timing indicated by the PCR, and reconstructs various streams such as a video stream. A PES packet is stored in the payload. 
     Stored in the PES packet header is a Decoding Time Stamp (DTS) and a Presentation Time Stamp (PTS). The DTS indicates the timing of decoding a picture/an audio frame stored in the PES packet, and the PTS indicates presentation timing such as the timing of outputting video/audio. Each elementary data, such as video data and audio data, is stored into a data storage area called a PES Packet Payload in a PES Packet sequentially from the top. Also stored in the PES packet header is an ID (stream_id) that identifies the type of the stream to which the data stored in the payload corresponds. 
     The details of a TS stream is specified by ISO/IEC13818-1. What is characteristic about the BD is that an ATS is assigned for each TS packet. 
     &lt;Interleaved Storage of VOB&gt; 
     Next, referring to  FIG. 17  and  FIG. 18 , a description is given of interleaved storage of a VOB file. 
     The upper part of  FIG. 17  shows a part of the structure of the above-described player. As shown in the drawing, data on the BD disc is inputted, through the optical pick-up, to the track buffer in the case where it is a VOB, i.e., an MPEG stream, whereas it is inputted to the image memory in the case where it is PNG, i.e., image data. 
     The track buffer is a FIFO buffer, and each VOB data inputted thereto is sent to the demultiplexer in order of input. At this time, each TS packet is extracted from the track buffer according to the ATS described above, and then sent to the video processor or the sound processor via the demultiplexer. Meanwhile, regarding the image data, which image to be rendered is instructed by the presentation controller. In the case where image data used for rendering is subtitle image data, such image data is deleted from the image memory upon being used. On the other hand, in the case where image data used for rendering is menu image data, such image data remains stored in the image memory while the rendering of the menu is taking place. Menu rendering depends on user operation, and therefore when a part of the menu is displayed again or replaced by another image according to a user operation, the decoding of the image data to be displayed again is facilitated by allowing the menu image data to remain stored in the image memory while the rendering of the menu is taking place. 
     The bottom part of  FIG. 17  shows the interleaved storage Of a VOB file and PNG files on the BD disc. In general, on a ROM such as a CD-ROM and a DVD-ROM, AV data made up of a series of continuous reproduction units to be sequentially reproduced, are stored contiguously. As long as the data are stored contiguously, the drive simply has to read out the data sequentially and deliver the read data to the respective decoders. However, in the case where such contiguous data are stored on the disc in a discrete manner, the drive needs to seek individual continuous units, and thus there is a possibility that data supply stops since data reading stops while the seek is taking place. It is preferable that data in a VOB file are stored in contiguous areas on the BD. Such data as subtitle data, which is reproduced in synchronization with video data stored in a VOB, needs to be read from the BD disc by some method, as in the case of a VOB file. 
     The methods of reading out subtitle data include a method of collectively reading out the whole subtitle image data (PNG files) before starting the reproduction of a VOB. However, it is not realistic to use this method, since a large capacity memory is required. 
     In view of this, the present embodiment employs a method in which a VOB file is divided into several blocks and stored by being interleaved with image data. The bottom part of  FIG. 17  illustrates such interleaved storage. 
     By appropriately placing a divided VOB file and image data in an interleaved manner, it becomes possible to store image data into the image memory at the required timing without having to use a large capacity temporary memory as described above. 
     However, the reading of VOB data is suspended during the reading of image data. 
       FIG. 18  is a diagram for describing a model, which solves this problem, for continuous supply of VOB data using the track buffer. 
     As has been described above, VOB data is accumulated into the track buffer once. Taking that the rate at which data is inputted to the track buffer is Va, and the rate at which data is outputted from the track buffer is Vb, the amount of data accumulated in the track buffer keeps increasing, when the difference between Va and Vb is Va&gt;Vb, as long as data is continuously read from the BD disc. 
     Suppose, as shown in the upper part of  FIG. 18 , that a contiguous VOB storage area starts with the logical address “a1” and ends with the logical address “a2”. Also suppose that image data is stored in an area between “a2” and “a3”, and that VOB data cannot be read out in such area. 
     The bottom part of  FIG. 18  shows the inside of the track buffer. The lateral axis indicates time, and the vertical axis indicates the amount of data accumulated in the track buffer. Time “t1” indicates the time at which the reading of data starts, the data being stored in “a1”, which is the start point of the contiguous VOB storage area. At such time and thereafter, data is to be stored into the track buffer at the rate of Va−Vb. Needless to say, this rate equals to a difference between the rates at which data is inputted to and outputted from the track buffer. Time “t2” indicates the time at which data is read out, the data being stored in “a2”, which is the end point of the contiguous VOB storage area. In other words, during the period from the time “t1” and the time “t2”, the amount of data accumulated in the track buffer increases at the rate of Va−Vb. The amount of accumulated data at the time “t2” (B(t2)) is determined by the following Equation 1:
 
 B ( t 2)=( Va−Vb )×( t 2 −t 1)  (Equation 1).
 
     After this, since image data is stored until the addresses “a3” on the BD disc, there is no input of data into the track buffer, and thus the amount of data in the track buffer decreases at an output rate of “−Vb”. This continues until the read-out point “a3” is reached, which corresponds to “t3” in time. 
     What is important here is that there is a possibility that the reproduction of the VOB stops if the amount of data accumulated in the track buffer becomes 0 before the time “t3”, since it means that there is no VOB data to be supplied to the decoders. However, when there remains data in the track buffer at the time “t3”, this means that the reproduction of VOB continues without stopping. 
     A condition for this is represented by the following Equation 2:
 
 B ( t 2)≧− Vb ×( t 3 −t 2)  (Equation 2).
 
     In other words, the position of each image data (non-VOB data) should be determined so that Equation 2 is satisfied. 
     &lt;Structure of Navigation Data&gt; 
     Referring to  FIG. 19  to  FIG. 25 , a description is given of the structure of the navigation data (BD management information) on the BD. 
       FIG. 19  is a diagram showing an internal structure of a VOB management information file (“YYY. VOBI”). 
     The VOB management information includes stream attribute information (Attribute) of the VOB, and a time map. Each stream attribute includes a video attribute (Video) and audio attributes (Audio# 0  to Audio#m). Since a VOB can include plural audio streams, there is an indication of the number of audio streams (Number). 
     The following lists fields included in the video attribute (Video) and possible values included in the respective fields: 
     Compression mode (Coding): 
     MPEG1 
     MPEG2 
     MPEG4 
     MPEG-4 AVC (Advanced Video Coding) 
     Resolution (Resolution): 
     1920×1080 
     1440×1080 
     1280×720 
     720×480 
     720×565 
     Aspect ratio (Aspect) 
     4:3 
     16:9 
     Frame rate (Framerate) 
     60 
     59.94 (60/1.001) 
     50 
     30 
     29.97 (30/1.001) 
     25 
     24 
     23.976 (24/1.001) 
     The following lists fields included in each of the Audio attributes (Audio) and possible values included in the respective fields: 
     Compression mode (Coding): 
     AC3 
     MPEG1 
     MPEG2 
     LPCM 
     Channel number (Ch.): 
     1 to 8 
     Linguistic attribute (Language): The time map (TMAP), which is a table holding information for each VOBU, includes the number of VOBUs (Number) in the VOB, and VOBU information of each of such VOBUs (VOBU# 1  to VOBU#n). 
     Each VOBU information is made up of: the address I_start of the first TS packet in the VOBU (the start of an I picture; the offset address indicating the end of such I picture (I_end); and the reproduction start time of such I picture (PTS). 
     The actual end address of the I picture may be used as the value of I_end, rather than using the offset value, that is, the size of the I picture. 
       FIG. 20  is a diagram for describing the details of each VOBU information. 
     As is widely known, MPEG video streams are compressed, in some cases, at a variable bit rate for storing them with high image quality, and therefore there is no simple correlation between their reproduction duration and data size. In contrast, since AC3, which is a compression standard for audio, performs compression at a fixed bit rate, a relationship between duration and each address can be represented by a linear expression. The display duration of each frame in MPEG video data is fixed. For example, the display duration of one frame in the case of NTSC is 1/29.97 seconds, but the data size of each frame after compression greatly differs from frame to frame depending on the pictorial feature and the picture type used for compression, i.e., whether a frame is an I picture, a P picture or a B picture. Thus, in the case of MPEG video, it is impossible to represent a relationship between duration and each address by a linear expression. 
     As a matter of fact, it is impossible to represent duration and each data size by a linear expression in the case of an MPEG system stream, i.e., a VOB, in which MPEG video data is multiplexed. For this reason, in a VOB, duration and each address are associated with each other in a time map (TMAP). 
     As described above, the following is performed when certain time information is provided: first detecting which one of the VOBUs such time belongs to (checks the PTS of each VOBU); jumping to the VOBU whose TMAP includes the PTS immediately previous to such time (address specified by I_start); performing decoding starting from the first I picture in the VOBU; and displaying pictures starting with the picture corresponding to such time. 
     Next, referring to  FIG. 21 , a description is given of an internal structure of playlist information (“XXX. PL”). 
     The playlist information is made up of a cell list (CellList) and an event list (EventList). 
     The cell list (CellList) is a sequence of cells to be reproduced in the playlist, wherein the cells are reproduced in order of description in this list. The cell list (CellList) is made up of the number of cells (Number) and cell information of each of such cells (Cell# 1  to Cell#n). 
     Cell information (Cell#) includes a VOB filename (VOBName), start time (In) and end time (Out) in the VOB, and a subtitle table (SubtitleTable). The start time (In) and the end time (Out) are each represented by a frame number in the VOB, and it is possible to obtain the address of VOB data necessary for reproduction, using the above-described time map. 
     The subtitle table (SubtitleTable) is a table holding information about subtitles to be reproduced in synchronization with the VOB. Subtitles can be in plural languages as in the case of audio, and the subtitle table (SubtitleTable) includes the number of languages (Number), which is the first information therein and is followed by tables for the respective languages (Language# 1  to Language#k). 
     The table for each language (Language#) is made up of language information (Lang), the number of subtitle information to be individually displayed (Number), and subtitle information to be individually displayed (Speech# 1  to Speech#j). Each subtitle information (Speech#) is made up of: the filename of corresponding image data (Name); display start time (In) of the subtitles and display end time (Out) of the subtitles; and a display position of the subtitles (Position). 
     The event list (EventList) is a table that defines events that occur in the playlist. The event list includes the number of events (Number), which is followed by individual events (Evnet# 1  to Evnet#m). Each event (Event#) is made up of the type of the event (Type), the ID of the event (ID), and the time at which the event occurs (Time), and the validity period (Duration). 
       FIG. 22  is a diagram showing an event handler table (“XXX. PROG”) that holds event handlers (for time event and user event for menu selection) of each playlist. 
     The event handler table holds the number of event handlers/programs defined (Number), and individual event handlers/programs (Program# 1  to Program#n). Each event handler/program (Program#) includes the definition of the start of the event handler (&lt;event_handler&gt; tag) and the ID of the event handler (ID) that is paired with the ID of the event as described above. The program is described in the brackets { } that follows Function. The events (Event# 1  to Evnet#m) stored in the above-described event list (EventList) in “XXX. PL” are identified using the ID (IDs) of the corresponding event handlers in “XXX. PROG”. 
     Next, referring to  FIG. 23 , a description is given of an internal structure of information related to the entire BD disc (“BD. INFO”). 
     The information related to the entire BD disc is made up of a title list (TitleList) and an event table (EventList) for global events. 
     The title list (TitleList) includes the number of titles in the disc (Number), which is followed by title information of each of such titles (Title# 1  to Title#n). Each title information (Title#) includes a playlist table (PLTable) holding playlists in the title and a chapter list (Chapterlist) holding chapters in the title. The playlist table (PLTable) includes the number of playlists in the title (Number) and the playlist names (Name), i.e., the filenames of the respective playlists. 
     The chapter list (Chapterlist) is made up of the number of chapters included in the title (Number) and chapter information of each of such chapters (Chapter# 1  to Chapter#n). Each chapter information (Chapter#) includes a cell table (CellTable) holding cells included in the chapter. The cell table (CellTable) is made up of the number of cells (Number) and cell entry information of each of such cells (CellEntry# 1  to CellEntry#k). Each cell entry information (CellEntry#) is made up of the name of the playlist including the cell, and the cell number in the playlist. 
     The event list (EventList) includes the number of global events (Number), and information about each of such global events. What should be noted here is that the first defined global event is referred to as a first event (FirstEvent), and such event is first read out when the BD disc is inserted into the player. Event information for a global event includes only the type of the event (Type), and the ID of the event (ID). 
       FIG. 24  is a diagram showing a table holding programs of global event handlers (“BD. PROG”). 
     The contents of this table are the same as the contents of the event handler table described with reference to  FIG. 22 . 
     &lt;Mechanism of Event Occurrence&gt; 
     Referring to  FIG. 25  to  FIG. 27 , a description is given of a mechanism of event occurrence. 
       FIG. 25  is a diagram showing an example of a time event. 
     As has been described, a time event is defined in the event list (EventList) in playlist information (“XXX. PL”). In the case where an event is defined as a time event, i.e., an event whose event type (Type) is “TimeEvent”, a time event with the ID “Ex1” is outputted to the program processor from the scenario processor at the event generation time (“t1”). The program processor searches for an event handler with the event ID “EX1”, and executes such target event handler. For example, an event such as the rendering or the like of two button images is executed in the present embodiment. 
       FIG. 26  is a diagram showing an example of a user event for menu operation. As has been described above, a user event for menu operation is also defined in the event list (EventList) in playlist information (“XXX. PL”). In the case where an event is defined as a user event, i.e., an event whose event type (Type) is “UserEvent”, such user event becomes ready at the event generation time (“t1”). At this time, the event itself has not been generated yet. This event is in the ready state during the period indicated by its validity period information (Duration). 
     As shown in  FIG. 26 , when the user presses the Up/Down/Right/Left key or the “Determination” key on the remote control, the UOP manager first generates an UOP event, and outputs it to the program processor. The program processor outputs such UOP event to the scenario processor. The scenario processor checks whether or not there exists any user event that is effective at the time of receiving the UOP event. In the case where there exists an effective user event, the scenario processor generates a user event, and outputs it to the program processor. The program processor searches for an event handler with the event ID “Ev1”, and executes such target event handler. For example, the reproduction of the playlist # 2  is started in the present embodiment. 
     The generated user event does not include information for identifying which one of the remote control keys the user has pressed. Information about the selected remote control key is notified to the program processor by the UOP event, and stored into the register SPRM ( 8 ) of the virtual player. By checking the value of such register, it is possible to perform branch processing on the program of the event handler. 
       FIG. 27  is a diagram showing an example of a global event. 
     As has been described above, a global event is defined in the event list (EventList) in information related to the entire BD disc (“BD. INFO”). In the case where an event is defined as a global event, i.e., an event whose event type (Type) is “GlobalEvent”, such event is generated only when the user has performed a remote control key operation. 
     When the user presses the “Menu” key, the UOP manager first generates a UOP event, and outputs it to the program processor. The program processor outputs such UOP event to the scenario processor. Then, the scenario processor generates a global event corresponding to such UOP event, and sends it to the program processor. The program processor searches for an event handler with the event ID “menu”, and executes such target event handler. For example, the reproduction of the playlist# 3  is started in the present embodiment. 
     Note that the number of “Menu” keys is assumed to be one in the present embodiment, but there may be plural menu keys as in the case of a DVD recorder. It is possible to support such case by defining an ID corresponding to each menu key. 
     &lt;Virtual Player Machine&gt; 
     Referring to  FIG. 28 , a description is given of the functional structure of the program processor. 
     The program processor is a processing module having a virtual player machine therein. Such virtual player machine has the function of supporting BDs, and does not depend on the implementation of a BD player. In other words, the virtual player machine is guaranteed to realize the same function regardless of BD player. 
     The virtual player machine roughly has two functions: programming functions and player variables (registers). In the programming functions, two properties described below are defined as BD eigen functions based on Java Script: 
     Link function: stopping the current reproduction, and starting the reproduction starting from a specified playlist, cell, or time. 
     Link (PL#, Cell#, time)
         PL#: Playlist name   Cell#: Cell number   time: Reproduction start time in the cell       

     PNG rendering function: render specified PNG data onto the image plane 
     Draw (File, X, Y)
         File: PNG filename   X: Position on the X coordinate   Y: Position on the Y coordinate       

     Image plane clear function: clear a specified area on the image plane 
     Clear (X, Y, W, H)
         X: Position on the X coordinate   Y: Position on the Y coordinate   W: Width in the X direction       

     H: Width in the Y direction 
     Player variables include system parameters (SPRMs) indicating the status of the player, and general parameters (GPRMs) that can be used for general purposes. 
       FIG. 29  shows a list of system parameters (SPRMs). 
     SPRM ( 0 ): Language code 
     SPRM ( 1 ): Audio stream number 
     SPRM ( 2 ): Subtitle stream number 
     SPRM ( 3 ): Angle number 
     SPRM ( 4 ): Title number 
     SPRM ( 5 ): Chapter number 
     SPRM ( 6 ): Program number 
     SPRM ( 7 ): Cell number 
     SPRM ( 8 ): Key name 
     SPRM ( 9 ): Navigation timer 
     SPRM ( 10 ): Current playback time 
     SPRM ( 11 ): Player audio mixing mode for Karaoke 
     SPRM ( 12 ): Country code for parental management 
     SPRM ( 13 ): Parental level 
     SPRM ( 14 ): Player configuration (video) 
     SPRM ( 15 ): Player configuration (audio) 
     SPRM ( 16 ): Language code for audio stream 
     SPRM ( 17 ): Language code for audio stream (extension) 
     SPRM ( 18 ): Language code for subtitle stream 
     SPRM ( 19 ): Language code for subtitle stream (extension) 
     SPRM ( 20 ): Player region code 
     SPRM ( 21 ): reserved 
     SPRM ( 22 ): reserved 
     SPRM ( 23 ): Player status 
     SPRM ( 24 ): reserved 
     SPRM ( 25 ): reserved 
     SPRM ( 26 ): reserved 
     SPRM ( 27 ): reserved 
     SPRM ( 28 ): reserved 
     SPRM ( 29 ): reserved 
     SPRM ( 30 ): reserved 
     SPRM ( 31 ): reserved 
     Note that the programming functions are defined in the present embodiment based on Java Script, but these programming functions may be defined based on other programming functions such as B-Shell and Perl Script used in such OS as a UNIX (registered trademark) OS, rather than being defined based on Java Script. In other words, the present invention is not limited to the use of Java Script for their definitions. 
     &lt;Example of Program&gt; 
       FIG. 30  and  FIG. 31  are diagrams showing examples of programs as event handlers. 
       FIG. 30  is a diagram showing an example of a menu having two selection buttons. 
     The program illustrated on the left of  FIG. 30  is executed based on the top time event of the cell (PlayList# 1 . Cell# 1 ). Here, “1” is set to one of the general parameters GPRM ( 0 ) by default. GPRM( 0 ) is used in the program to identify the selected button. In the initial state, it is an initial value indicating that the button  1  located on the left is selected. 
     Next, using a rendering function Draw, PNG of each of the button  1  and button  2  is rendered. The button  1  is formed by rendering the PNG image “1black. png” that extends from the coordinates ( 10 ,  200 ) as the starting point (upper left corner). The button  2  is formed by rendering the PNG image “2white. png” that extends from the coordinates ( 330 ,  200 ) as the starting point (upper left corner). 
     Then, the program illustrated on the right of  FIG. 30  is executed based on the last time event of the current cell. In this program, it is specified, using Link function, that the cell should be reproduced from the top again. 
       FIG. 31  is a diagram showing an example of an event handler for a user event for menu selection. Programs corresponding to each of the remote control keys, in the case where any of the “Left” key, “Right” key, and “Determination” key is pressed, is described in the event handler. As has been described with reference to  FIG. 26 , when the user presses a remote control key, a user event is generated, and then the event handler shown in  FIG. 31  is invoked. In this event handler, branch processing is performed using the value of GPRM ( 0 ) for identifying the selected button and using SPRM ( 8 ) for identifying the selected remote control key. 
     Condition 1) in the case where the button  1  is selected, and the “Right” key is selected GPRM( 0 ) is reset to 2 so as to change the currently selected button to the button  2  on the right. 
     The images of the respective button  1  and button  2  are re-rendered. 
     Condition 2) in the case where the “Determination (OK)” key is selected, and the button  1  is selected 
     The reproduction of the playlist# 2  is started. 
     Condition 3) in the case where the “Determination (OK)” key is selected, and the button  2  is selected 
     The reproduction of the playlist# 3  is started. 
     The execution is carried out in this manner. 
     Flow of Player Processes&gt; 
     Next, referring to  FIG. 32  to  FIG. 35 , a description is given of the flow of processes performed by the player. 
       FIG. 32  is a diagram showing the flow of basic processes until the reproduction of AV data. 
     When the BD disc is inserted (S 101 ), the BD player loads and analyzes the BD. INFO file (S 102 ), and then loads the BD. PROG (S 103 ). The BD. INFO and BD. PROG are both stored into the management information storage memory once, and analyzed by the scenario processor. 
     Next, the scenario processor generates the first event based on the first event (FirstEvent) information in the BD. INFO file (S 104 ). The program processor receives the generated first event, and executes an event handler corresponding to such event (S 105 ). 
     It is expected that the playlist information that should be reproduced first is stored in the event handler corresponding to the first event. If there is no instruction to reproduce a playlist, the player keeps waiting for a user event without reproducing anything (S 201 ). When the BD player receives a remote control operation from the user, the UOP manager causes the program manager to start the execution of the UOP event (S 202 ). 
     The program manager determines whether or not such UOP event is a menu key event (S 203 ). In the case where the UOP event is a menu key event, the program manager outputs the UOP event to the scenario processor, and the scenario processor then generates a user event (S 204 ). The program processor executes an event handler corresponding to such generated user event (S 205 ). 
       FIG. 33  shows the flow of processes from the reproduction of a PL to the reproduction of a VOB. 
     As has been described above, the reproduction of the playlist is started by a first event handler or a global event handler (S 301 ). The scenario processor loads and analyzes the playlist information “XXX. PL” as information required to reproduce the playlist to be reproduced (S 302 ), and loads the program information “XXX. PROG” corresponding to such playlist (S 303 ). Then, the scenario processor instructs the reproduction of a cell based on the cell information registered in the playlist (S 304 ). Since the reproduction of the cell means that there is a request from the scenario processor to the presentation controller, the presentation controller starts the reproduction of the AV data (S 305 ). 
     When the reproduction of the AV data starts (S 401 ), the presentation controller loads and analyzes the information file (XXX. VOBI) of the VOB corresponding to the cell to be reproduced (S 402 ). Referring to the time map, the presentation controller identifies the first VOBU to be reproduced and the address of such VOBU, and notifies such address to the drive controller, and the drive controller then reads out the target VOB data (S 403 ). Accordingly, the VOB data is sent to the decoders, and the reproduction of such data starts (S 404 ). 
     The reproduction of the VOB continues until the end of the reproduction segments of such VOB is reached (S 405 ), which is followed by the reproduction of the next cell S 304 . If there is no cell that follows, the reproduction stops (S 406 ). 
       FIG. 34  shows the flow of event processes after the reproduction of the AV data starts. 
     The BD player is an event-driven player. When the reproduction of a playlist starts, event processes for time event, user event, and subtitle display are respectively invoked, and event processes are executed in parallel with them. 
     Processes in S 500 &#39;s are a flow of time event processes. 
     After the reproduction of the playlist starts (S 501 ) and a step of checking whether or not the reproduction of the playlist has ended is performed (S 502 ), the scenario processor checks whether or not it is the time for time event occurrence (S 503 ). In the case where it is the time for time event occurrence, the scenario processor generates a time event (S 504 ), and the program processor receives such time event and executes the corresponding event handler (S 505 ). 
     The processes returns to Step S 502  again in the following cases, and the above-described processes are repeated: it is not the time for time event occurrence in Step S 503 ; and after the event handler is executed in Step S 504 . Meanwhile, in the case where the result of the check in Step S 502  is that the reproduction of the playlist has ended, the time event processes are forcefully terminated. 
     Processes in S 600 &#39;s are a flow of user event processes. 
     After the reproduction of the playlist starts (S 601 ) and a step of checking whether or not the reproduction of the playlist has ended is performed (S 602 ), the process proceeds to a step of checking whether or not there is any UOP accepted (S 603 ). In the case where there is a UOP accepted, the UOP manager generates a UOP event (S 604 ), and the program processor receives such UOP event and checks whether or not the received UOP event is a menu call (S 605 ). In the case where the UOP event is a menu call, the program processor causes the scenario processor to generate an event (S 607 ), and the program processor executes the corresponding event handler (S 608 ). 
     In the case where the result of the check in Step S 605  is that the UOP event is not a menu call, it indicates that the UOP event is an event that is generated by operating a cursor key or the “Determination” key. In this case, the scenario processor determines whether or not the current time is within the user event validity period (S 606 ). In the case where the current time is within the user event validity period, the scenario processor generates a user event (S 607 ), and the program processor executes the corresponding event handler (S 608 ). 
     The process returns to Step S 602  again in the following cases and the above-described processes are repeated: the result of the check in Step S 603  is that there is no UOP accepted; it is determined in Step S 606  that the current time is not within the user event validity period; and after the event handler is executed in Step S 608 . Meanwhile, in the case where the result of the check in Step S 602  is that the reproduction of the playlist has ended, the user event processes are forcefully terminated. 
       FIG. 35  shows the flow of subtitle processes. 
     After the reproduction of the playlist starts (S 701 ) and a step of checking whether or not the reproduction of the playlist has ended is performed (S 702 ), the process proceeds to a step of checking whether or not the current time is the time to start the rendering of subtitles (S 703 ). In the case where the current time is the time to start the rendering of subtitles, the scenario processor instructs the presentation controller to render subtitles, and the presentation controller instructs the image processor to render subtitles (S 704 ). In the case where the result of the check in Step S 703  is that the current time is not the time to start the rendering of subtitles, it is then checked whether or not the current time is the time to end the display of the subtitles (S 705 ). In the case where the result of the check is that the current time is the time to end the display of the subtitles, the presentation controller instructs the image processor to delete the subtitles, and the image processor deletes the subtitles rendered on the image plane (S 706 ). 
     The process returns to Step S 702  in the following cases and the above-described processes are repeated: after the subtitle rendering performed in Step S 704 ; after the subtitle deletion performed in Step S 706 ; and the result of the check in Step S 705  is that the current time is not the time to end the display of the subtitles. Meanwhile, in the case where the result of the check in Step S 702  is that the reproduction of the playlist has ended, the subtitle processes are forcefully terminated. 
     (Second Embodiment) 
     Next, a description is given of the second embodiment of the present invention. 
     The second embodiment is a description for realizing a slideshow of still images by using the above-described application. Basically, the details of the second embodiment are based on the first embodiment. Thus, the second embodiment focuses on extended parts or differences. 
     &lt;Reference to I Picture&gt; 
       FIG. 36  shows a relationship between a slideshow (still image application) and a time map. A slideshow is usually composed only of still images (I pictures). The time map includes the position and size information of still image data. When a certain still image is chosen, such single still image is to be displayed after extracting necessary data and sending it to the decoder. Usually, a slideshow is not necessarily displayed in order of images as in the case of a moving image, since their display order differs depending on a user interaction. In order to ensure that image display is performed from any images, I pictures, which are intra coded and can be decoded by themselves, are used. 
     However, in order to reduce the amount of data, it is also possible to realize a slideshow using P pictures, which are compressed with reference to I pictures, and using B pictures, which are compressed with reference to two or more forward/backward pictures. 
     However, P pictures and B pictures cannot be decoded without pictures they refer to. For this reason, a P picture or a B picture positioned in the middle cannot be decoded even when the reproduction is wished to be started from these pictures in response to a user interaction. In view of this, as shown in  FIG. 37  a flag is provided indicating that a picture indicated in the time map is an I picture and that does not refer to any pictures. The reference to this flag makes it possible to know: that, in the case where a certain image does not require any reference images, or in other words, such image can be decoded by itself, it is possible to perform decoding and display, starting from such image regardless of its forward and backward images that are displayed; and that, in the case where a certain image requires a reference image, such image may not be displayed depending on its display order, since the image cannot be displayed unless its related images have been decoded prior to such image. 
     Note that all through the time map, flags indicating that pictures referred to from the time map are always I pictures, or in other words, that any picture can be decoded by itself, may be stored in the time map as shown in  FIG. 38  or in a part of the related navigation information. In the case where such a flag is not set, an entry of the time map does not necessarily indicate an I picture, and thus there is no guarantee that the picture referred to is decodable. 
     Note that although the above description has been given using an I picture based on an MPEG-2 video stream, an Instantaneous Decoder refresh (IDR) picture may be used in the case of MPEG-4 AVC (also referred to as H.264 orJVT). 
     &lt;Guarantee for Reference of all I Pictures&gt; 
       FIG. 39  shows a difference between a moving image application and a still image application (a slideshow). As shown in (a) in  FIG. 39 , in the case of the moving image application, once the reproduction starts, the subsequent pictures are to be sequentially decoded. Therefore, it is not necessary to set reference made from the time map to all I pictures and it suffices if an entry of the time map is set only at least at a point from which the reproduction is wished to be started. 
     (b) in  FIG. 39  shows an example of a slideshow. In the case of the slideshow, it is necessary to display still images without displaying the forward and backward video independently of their order, in response to a user operation such as a skip operation. For this reason, data of I pictures to be displayed cannot be outputted to the decoder without actually analyzing the whole stream, unless entries are registered in the time map for all I pictures. This results in poor efficiency. If there is an entry in the time map for each I picture, it is possible to make a direct access only to the data of necessary I pictures so as to read such data and output it to the decoder. This results in a favorable access efficiency as well as in a favorable efficiency since a shorter length of time is required before the pictures are displayed. 
     If it can be identified that entries exist for all I pictures, it is possible to know the scope of data to be read out by referring to the corresponding entry in the time map when making an access to any I picture. Accordingly, there is no need for making unnecessary analysis of the forward and backward pictures. 
     In the case where it is not guaranteed that entries exist for all I pictures and where an I picture not registered in the time map is specified to be displayed, it is necessary to extract necessary data while analyzing its forward and backward pictures in the stream. This results in poor access efficiency and poor efficiency since it takes time until pictures are displayed. 
     In view of this, by providing a flag indicating whether or not there is a guarantee that all I pictures are referred to from the time map as shown in  FIG. 40 , it becomes possible to identify whether or not the analysis of the forward and backward pictures in the stream is necessary by analyzing the static data, and thus such a flag is effective. 
     Note that such a flag is effective not only for a still image application such as a slideshow but also for a moving image application and that such a flag can serve to guarantee that reproduction can be started from any I picture. 
     (Third Embodiment) 
     The second embodiment has described that MPEG-4 AVC can be used as an encoding scheme to implement a still image application. Still images in compliance with the MPEG-4 AVC are specified as AVC Still Pictures not in MPEG-4 AVC standard itself but in an extension standard for MPEG-4 AVC in the MPEG-2 system (ISO/IEC13818-1Amendment3). However, the MPEG-2 system specification does not specify a method of reproducing still images. Due to this, it is not possible to determine the timing to display MPEG-4 AVC still images at the time of reproducing them and thus a reproduction device displays these still images at an arbitrary timing. As a result, there has been a problem that compatibility of reproduction operations cannot be ensured between devices. The present embodiment describes a data structure of still images and a display method therefor for applying MPEG-4 AVC to a still image application. 
     It is specified that AVC Still Pictures in the MPEG-2 system standard include: an IDR picture; a Sequence Parameter Set (SPS) referred to by the IDR picture; and a Picture Parameter Set.  FIG. 41  shows a data structure of a still image in compliance with MPEG-4 AVC (hereinafter referred to as an AVC still image) according to the present embodiment. Each box in the drawing shows a Network Abstraction Unit (NAL unit). The AVC still image shall include a NAL unit of END of Sequence without fail. Since End of Sequence is identification information which indicates the end of a sequence in MPEG-4 AVC, it is possible to define a unique display method for AVC still images, which is not defied by the MPEG-4 AVC standard, by placing a NAL Unit of End of Sequence that marks the end of the sequence. Here, it is assumed that the order in which each NAL unit appears is specified by the order defined by the MPEG-4 AVC standard. Note that an end of stream NAL unit may be placed at the end of an AVC still image instead of placing an end of sequence. 
     Next, referring to  FIG. 42 , a method for displaying AVC still images is described. In a still image application, it is necessary to specify the display time of a still image and the display duration of a still image. The display time (Presentation Time Stamp: PTS) of an AVC still image is obtained from a time map or from the header of a Packetized Elementary Stream (PES) packet. Here, in the case where the display times of all still images are indicated in the time map, it is possible to obtain display times by reference only to the time map. During a period of time from the display time of the Nth AVC still image to the display time of the N+1th AVC still image, the display of the Nth AVC still image is frozen, or in other words, the Nth AVC still image is repeatedly displayed. 
     When AVC still images are reproduced, it is desirable to be able to obtain the frame rate from the data of the AVC still images. According to MPEG-4 AVC, it is possible to indicate the display rate of a moving image stream as Video Usability Information (VUI) in an SPS. More specifically, reference is made to the following three fields: num_units_in_tick, time_scale, and fixed_frame_rate_flag. Here, time_scale indicates a time scale. time_scale of a clock that operates at 30000 Hz can be represented, for example, as 30000. num_units_in_tick is a basic unit that indicates the time at which a clock operates. For example, assuming that num_units_in_tick of a clock whose time_scale is 30000 is 1001, it is possible to show that the fundamental period at which the clock operates is 29.97 Hz. Furthermore, by setting fixed_frame_rate_flag, it is possible to show that the frame rate is fixed. In MPEG-4 AVC, the use of these fields makes it possible to show a difference value between the display times of consecutive two pictures. In the present embodiment, these fields are used to show the frame rate at which an AVC still image is repeatedly displayed. First, by setting 1 to fixed_frame_rate_flag, that the frame rate is fixed is shown. Next, in the case of setting the frame rate to 23.976 Hz, num_units_in_tick is set to 1001, and time_scale is set to 24000, for example. In other words, both of these fields are set so that the frame rate=time_scale/num_units_in_tick. Furthermore, in order to ensure the existence of a VUI and the above three fields in the VUI, both vui_parameters_present_flag in the SPS and timing_info_present_flag in the VUI are set to 1. In the case where the Nth AVC still image is the last AVC still image, the display thereof shall be frozen until there is a user operation or the next operation or the like predetermined by a program starts. Note that a method for setting the frame rate is not limited to the use of time_scale/num_units in_tick. In the case of a moving image stream in compliance with MPEG-4 AVC, for example, time_scale/num_units_in_tick indicates a field rate (parameter indicating intervals at which fields are displayed), and thus the frame rate is indicated by time_scale/num_units_in_tick/2. Thus, the frame rate of still images may be set as time_scale/num_units_in_tic/2. 
     The frame rate that is indicated according to the above method shall match the frame rate value indicated in the BD management information. More specifically, the frame rate shall match the value indicated by the frame_rate field in SteamCodingInfo. 
     Note that it is possible to obtain the display period at which an AVC still image is repeatedly displayed from the frame rate that is indicated according to the above method. Such display period may be set as an integral multiple of a frame grid or a field grid. Here, “gird” refers to the timing at which a frame or a field can be displayed. This ensures synchronized reproduction with an other video source such as video and graphics. Here, the frame grid or field grid is generated based on the frame rate of a specified stream such as video. Furthermore, the difference value between the display times of the Nth AVC still image and the N+1th AVC still image may be set as an integral multiple of a frame grid or a field grid. 
     The time map of the second embodiment is used as a time map to be referred to at the time of reproducing AVC still images. 
     In addition, in the BD-ROM format and the like, these fields may be omitted by specifying the default values of num_units_in_tick, time_scale, and fixed_frame_rate_flag. 
     It is prohibited to change the resolution within a stream in the case of a video stream. However, in the case of a still image stream, it may be allowed to change the resolution within a stream since buffer management can be carried out in a decoding operation without any problems even if the resolution is changed. Here, the resolution is indicated in a field within the SPS. 
     Note that the data structure and the reproduction method of the present embodiment are applicable also to an encoding scheme other than that of MPEG-4 AVC in the case such encoding scheme employs a similar data structure. 
     (Fourth Embodiment) 
     Furthermore, if a program for realizing the information storage medium, its encoding method, decoding method, and multiplexing method as presented in each of the aforementioned embodiments is stored on a storage medium such as a flexible disk, it becomes possible to easily perform the processes presented in the respective embodiments in an independent computer system. 
       FIG. 43A  to  FIG. 43C  are diagrams illustrating the case where the encoding method and decoding method of each of the above embodiments are performed in a computer system, using a program stored on a storage medium such as a flexible disk. 
       FIG. 43B  shows an external view of the flexible disk viewed from the front, its schematic cross-sectional view, and the flexible disk itself, while  FIG. 43A  illustrates an example physical format of the flexible disk as a storage medium itself. The flexible disk FD is contained in a case F, and a plurality of tracks Tr are formed concentrically on the surface of the flexible disk in the radius direction from the periphery, each track being divided into 16 sectors Se in the angular direction. Therefore, in the flexible disk storing the above-mentioned program, the above program is stored in an area allocated for it on the flexible disk FD. 
     Meanwhile,  FIG. 43C  shows the structure required for storing and reading out the program on and from the flexible disk FD. When the program realizing the encoding method and decoding method is to be stored onto the flexible disk FD, such program shall be written by the use of the computer system Cs via a flexible disk drive. Meanwhile, when the reproduction method and storage method realizing the encoding method and decoding method through the program stored in the flexible disk, is to be constructed in the computer system through the program in the flexible disk, the program shall be read out from the flexible disk via the flexible disk drive and then transferred to the computer system. 
     The above description has been given on the assumption that a storage medium is the flexible disk, but an optical disc may also be used. In addition, the storage medium is not limited to this, and any other media such as an IC card and a ROM cassette capable of storing a program may also be used. 
     The functional blocks shown in the block diagrams of  FIG. 6 ,  FIG. 12 ,  FIG. 13 , and the like are typically achieved in the form of integrated circuit or LSI. Each of these parts can be in plural chips, or also can be in one chip (for example, the functional blocks other than memory may be in one chip). The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI in accordance with the degree of integration. 
     The method of incorporating the functional blocks into an integrated circuit is not limited to the LSI, and it may be realized with a private line or a general processor. After manufacturing of LSI, a Field Programmable Gate Array (FPGA) that is programmable or a reconfigurable processor whose LSI allows reconfiguration of connection and setting of a circuit cell, may be utilized. 
     Furthermore, along with the arrival of technique for incorporating the functional blocks into an integrated circuit that replaces the LSI owing to a progress in semiconductor technology or another technique that has deviated from it, integration of the functional blocks may be carried out using the newly-arrived technology. Bio-technology may be cited as one of the examples. 
     Out of the functional blocks, only a unit which stores data may be constructed separately without being incorporated in a chip form, as in the case of the storage medium  115  of the embodiments. 
     Note that in each functional block in the block diagrams such as those shown in  FIGS. 6 ,  12 , and  13  as well as in the flowcharts such as those shown in  FIGS. 5 ,  7  to  9 ,  32 , and  33 , major parts may be implemented also as a processor or a program. 
     As described above, it is possible to use the image encoding method and image decoding method presented in the above-described embodiments in any of the devices/systems described above, thereby achieving the effects described in the above-described embodiments. 
     INDUSTRIAL APPLICABILITY 
     The present invention is suited as an encoding device and a decoding device which encode or decode an image, and suited as a web server which distributes a moving image, a network terminal which receives the distributed moving image, a digital camera capable of recording and reproducing a moving image, a camera-equipped mobile phone, a device for recording/reproducing an optical disc such as a BD, a PDA, a personal computer, and the like.