How is the SVCD disc structure?

The Disc format is compliant with CD-ROM XA, and can be a pre-mastered disc or a CD-Recordable disc. All tracks of the Program Area are encoded as CD-ROM XA data tracks. The first track on the disc is a special DATA track with data retrieval information and interactive playback MPEG sequences. The MPEG-2 streams on disc are recorded in MPEG tracks, and are intended to be played sequentially starting from Track #2 . A Karaoke / Music application has normally one track per song. This means that song number 1 is recorded in Track #2, and song number 2 in Track #3, and so on. A Movie could have different coded parts of INTRO, COPYRIGHT, FILM, CREDITS, each stored in a separate track. The film itself can be stored in one track with the possibility to be subdivided into chapters within the one track.

DATA track format
The DATA track contains Special Information Areas, and a Segment Play Item Area intended for menus or interactive use, and other optional program data files. Data files use Mode2, Form1 ( 2048 byte ) DATA sectors, and MPEG files use Mode2, Form2 (2324 byte ) MPEG sectors.

Karaoke Basic Information Area
A Super Video CD disc can contain the Karaoke Basic Information Area as an option. The data in the Karaoke Basic Information Area provides basic information to produce a quick reference table of the Karaoke music programs on the disc.

Information Area
The Super Video CD Information Area contains the files "INFO.VCD" and "ENTRIES.VCD", "TRACKS.SVD" and "SEARCH.DAT". As an option it may contain the files "LOT.VCD" and "PSD.VCD".

Segment Play Item Area
A Segment Play Item consists of a MPEG-2 Program Stream (PS) stored in MPEG sectors. It may contain video, audio and still pictures conform to MPEG 2 Program Stream coding. The Segment Play Item Area address is indicated in "INFO.VCD". Segment Play Items may occupy one or more segments. Segment Play Items are not accessed directly by the normal track playing mechanism, but indirectly by interpretation of the Play Sequence Descriptor file.

MPEG track format
All Tracks except the first Track should be MPEG tracks. Each MPEG track must contain only one MPEG-2 Program Stream, stored in MPEG sectors, using Mode2 Form2 with 2324 user bytes.

File system structure
A Super Video CD disc contains two different Data Retrieval Structures; The first is the File System structure conform to CD-ROM XA, and ISO 9660, and a second Data Retrieval Structure is based on absolute sector addresses to the specific SVCD files.

Directory structure
The required directories for a Super Video CD disc are: Root directory 0, "SVCD", "MPEG-2", and "EXT" directories. If Karaoke Basic Information is available on a disc, then these files must be located in the directory "KARAOKE". The SVCD Information files must be located in the directory "SVCD". If the Segment Play Items are available on the disc then these files must be located in the directory "SEGMENT".

All files that represent the MPEG Audio/Video Tracks must be located in the directory "MPEG2". The "SCANDATA.DAT" file must be located in the "EXT" directory. Other files or directories may exist outside the required Super Video CD directory. The figure below gives an example of the file structure for a Super VideoCD disc. Additional files can exist within the directories shown.

SVCD directory
This directory contains the files from the Super Video CD Information Area.  The required mandatory files in the SVCD directory are "INFO.VCD" , "ENTRIES.VCD", SEARCH.DAT and TRACKS.SVD. Optional files in the SVCD directory are "PSD.VCD" and "LOT.VCD".

INFO.VCD file
This file of one sector contains the Super Video CD system identification and a provision to identify the discs belonging to one Album.  An Album is a series of discs which contain related Audio/Video programs. It also contains information associated with the Play Sequence Descriptor ( PSD ).

ENTRIES.VCD file
This file of one Sector contains the list of start positions of Entries in the MPEG-2 Audio/Video Tracks on the disc. The Entry address values are used by the PSD playlist to access Play segments in the MPEG tracks. It's also used at linear playback for NEXT / PREVIOUS chapter.

SEARCH.DAT file
Due to VBR coding and the nature of the buffering used in MPEG-2 video coding the relation between playing time and sector address is not fixed. This file contains a list of Access Point sector addresses of the nearest Intra pictures on a regular time interval for the MPEG tracks. This is usefull for features such as time search.

TRARKS.SVD file
This file contains content related information as the Playing time, Video system type, and number of audio streams for each MPEG track on the disc.

PSD.VCD file
This file contains the data for the Play Sequence Descriptor (PSD). The size of the PSD may be variable, up to a maximum of 256 sectors or 512 KB.

LOT.VCD file
This 32 sectors file contains the List ID Offset Table (LOT). The LOT associates List ID numbers with the corresponding List Offset values.

MPEG-2 directory
This directory contains the files that represent the MPEG-2 encoded Audio/Video Tracks. Each MPEG-2 Track is represented by a file with the name "AVSEQnn.MPG", where "nn" is the Sequence Number. The Sequence Numbers (nn) starts with number = 01, and are incremented sequentially for each recorded MPEG track. The file with the name "AVSEQ01.MPG" corresponds to Sequence Number 1 and is the only file in Track number 2.

SEGMENT directory
This directory is optional and contains the files that represent the Segment Play Items. Each Segment Play Item is represented by a file with the name "ITEMnnnn.MPG", where "nnnn" is the Segment Play Item Number.

EXT directory
This directory contains:

SCANDATA.DAT file
Used for playing time related access. This file contains a list of Access Point sector addresses. For playing time access into a MPEG stream the sector address can be found in the list by looking up the sector address for the corresponding time. There is a sector address list for each MPEG track and for each motion picture Segment Play item.

CAPTnn.DAT file.
For each track containing user data with Closed Caption information a file shall be present Other (CD-ROM) files may be included in this directory, usually intended for computer based systems.