Disk-type recording media in which optical reading is applied, such as DVD (Digital Versatile Disk) and CD (Compact Disk) (hereinafter referred to as “optical disk”), are rapidly coming to be used commonly for the purpose of saving computer files or movie streams. Optical disks have large storage capacities, and allow random access.
Recording/playing apparatuses that use optical disks are already in common use, for example, as external recording media and external storage devices for computers. Recently, in accordance with the increase in the recording capacities of disk-type recording media, video cameras of the type that saves movies on a disk instead of on a conventional recording tape (e.g., refer to Patent Document 1) have appeared.
Disk-type recording media allow random access, so that it is possible to efficiently find desired scenes, and since data is accessed in a contactless manner, the recording media can be used without being degraded. For example, DVD video cameras, since their release in the year 2000, are coming to be used by an increasing number of users year by year due to favorable image quality and usability such as support for editing.
For example, the AVCHD standard, while inheriting contents of existing disk format standards as appropriate, defines specification regarding a data format and so forth for High Definition (HD) video cameras by adding recording compatibility and additional recording compatibility functions. The AVCHD standard employs the MPEG-4 AVC/H.264 scheme, having a high compression rate, and its main object is to allow recording of HD images on a low-capacity low-speed recording medium. Although recording on DVD disks is assumed, it is possible to perform recording on various recording media, such as memory cards or HDDs, according to the AVCHD standard format (e.g., refer to Non-Patent Document 1 and Non-Patent Document 2).
In the AVCHD standard, MPEG (Moving Picture Experts Group)-2 System has already been determined as the movie stream file format. Note that a complex file structure is provided in which in addition to saving a stream file alone on a recording medium, a plurality of accompanying management information files for playing or editing the movie files are saved. That is, in the case of movie content encoded as an MPEG2-TS stream, a set of data forming a unit that needs to be played in such a manner that continuous synchronous playing, i.e., real-time playing, is ensured is recorded as one clip (Clip), i.e., a clip AV stream (ClipAVStream) file. Furthermore, when this clip AV stream file is recorded on a recording medium, management information files of the types called a playlist (PlayList) file and a clip information (ClipInformation) file are recorded in accompany therewith.
The clip information file is a file that exists as a pair with a clip AV stream file and in which information regarding a stream, needed to play an actual stream, is described. A playlist can specify play segments and play order of movie data by registering play items (PlayItem) describing play segments formed of play start points (IN points) and play end points (OUT points) for clips and arranging a plurality of play items in order of time. Furthermore, in the playlist, it is possible to put a playlist mark (EntryMark) that serves as an entry point for access to the stream by a user. A segment defined by adjacent entry marks constitutes a minimum editing unit visible to the user, i.e., a “chapter”. Furthermore, a recording editing function can be realized suitably by using management information files such as clip information and playlists.
Furthermore, in the AVCHD standard, as attributes of a playlist, in addition to real playlists (Real PlayList) having bodies of content (i.e., clip AV streams), virtual playlists (Virtual PlayList) not having bodies of content are defined. Editing of a real playlist is editing of the body of content, i.e., destructive editing involving change in components themselves on a recording medium. In contrast, editing of a virtual playlist only redefines play start points and play end points for a clip AV file, so that non-destructive editing is allowed, which does not alter the body of content itself.
In non-destructive editing, it is readily possible to perform rearrangement of the positions or deletion of components that are referred to on a playlist visible to the user by operations on management information files, and the original form of stream data on a recording medium can be maintained. On the other hand, in a recording application, there are cases where the convenience for the user is improved if division editing of content that has been picked up is allowed. That is, management of content, such as backup, is facilitated if, in addition to inserting a playlist mark at a desired entry point in a playlist to provide a new chapter, a stream file is divided at a chapter boundary so that one-to-one corresponding relationship between chapters and stream files is maintained.
In a movie stream encoding scheme such as MPEG, a GOP (Group of Picture) structure, in which several frames are collected into one set, is employed. In a GOP, frames of different types, namely, an I/IDR picture obtained through intra-frame encoding, a P picture obtained through inter-frame forward predictive encoding, and a B picture obtained through bilateral predictive encoding, are arranged according to a predetermined rule, and random access to individual GOPs is allowed in the movie stream. In such a case, since it is possible to divide the stream only at the position of a GOP boundary, in a case where a specified division point does not coincide with a GOP boundary, a problem arises as to how to divide the stream.
For example, according to a proposed file dividing and joining method (e.g., refer to Patent Document 2), padding packets are provided in an empty portion from the file beginning of the latter portion of a divided file (cluster boundary) to the first GOP boundary, a padding portion provided at the time of division of a file is formed of one or more private stream packets, information of the padding portion provided at the time of division is provided in the same packets, and the padding portion is deleted efficiently at predetermined timing on the basis of the information in the padding portion, so that the capacity in the recording medium is used efficiently.
Furthermore, according to a proposed method of editing a stream (e.g., refer to Patent Document 3), in consideration that audio data becomes incomplete in the proximity of a division position when an MPEG-2 transport stream is divided, in a stream ahead of the division position, a TS packet in which video information TS packet is replaced with dummy data not including either video signals or audio signals so that audio frame data crossing the division position is formed completely, and in a stream after the division position is overwritten with a TS packet in which audio information is replaced with dummy data until occurrence of audio information packet data that coincides with play timing of video information at the division position. According to this editing method, it is possible to remove audio data that could cause such an abnormal sound or silent state that the user would feel a sense of unnaturalness when the two streams generated by the division are decoded and played.
Furthermore, according to a proposed video and audio signal editing method (e.g., refer to Patent Document 4), when division editing is performed at a boundary of video signal data constituting a GOP, in a case where a transport packet of audio signal data that does not satisfy the data structure of a decoding unit exits in divided video signal data, the transport packet is replaced with a transport packet not including video information and audio information, and an overwrite recording is performed on a recording medium.
However, in a case where a restriction on management size defined for each file system or physical type of recording medium exits, division is not allowed even at a GOP boundary in a stream. For example, in a DVD-like recording medium, 2K byte constitutes one sector, and an ECC (Error Collection Code) block composed of 16 sectors, i.e., 32 Kbytes, is used as an access block, i.e., a unit of management in a file system (refer to FIG. 13), and it is not allowed to divide an ECC block.
Furthermore, in the AVCHD standard described above, a length alignment restriction dictating that the stream file length be a multiple of 6K bytes is defined (refer to FIG. 14), and there are cases where it is not possible to comply with this restriction simply by dividing a stream at GOP boundaries.
Note that, in a case where a stream at the time of recording is a non-closed GOP of AVC, even if the stream is divided at a GOP boundary, it is not possible to decode and play a frame preceding the first I or IDR picture at the beginning of the subsequent portion. Furthermore, even in a closed GOP, a similar problem arises if division at a non GOP boundary is desired.
Patent Document 1:
    Japanese Unexamined Patent Application Publication No. 2004-120364Patent Document 2:    Japanese Unexamined Patent Application Publication No. 2005-286366Patent Document 3:    Japanese Unexamined Patent Application Publication No. 2005-117556Patent Document 4:    Japanese Unexamined Patent Application Publication No. 2004-336128Non-Patent Document 1:    http://www.avchd-info.org/Non-Patent Document 2:    http://support.d-imaging.sony.co.jp/www/handycam/products/be nri/avchd/index.html