vcdimager: Anatomy of Video CDs
1.2 Anatomy of Video CD's
=========================
Basically a Video CD is made up of CD-ROM XA sectors, i.e. CD-ROM mode
2 form 1 & 2 sectors. Non-MPEG data is stored in mode 2 form 1 sectors
with a user data area of 2048 byte, which have a similiar L2 error
correction and detection (ECC/EDC) to CD-ROM mode 1 sectors. While
realtime MPEG streams is stored in CD-ROM mode 2 form 2 sectors, which
by have no L2 ECC, yield a ~14% greater user data area consisting of
2324 bytes(1)
*Warning:* Realtime MPEG streams on Video CD's are only protected by
L2 error detection (but no correction!), EDC, and CIRC encoding. Thus
Video CD's are more easily affected by scratches and alike on the CD-ROM
media surface.
In general, a Video CD is made up of several mode 2 (and optionally
CD-DA) tracks. The layout of a Video CD is as follows:
* lead-in area containing the TOC.
* Mandatory pre-gap consisting of 150 sectors ('00:00:00' -
'00:01:74').
* ISO-9660 data track. The beginning of this track is defined to
have the LSN '0'. 
The ISO-9660 Track.
* ISO-9660 structure at '00:02:00' consisting of 16 empty
sectors, primary volume descriptor ("PVD") and directory
records with file pointers to information area structures
(described below) and external pointers to MPEG/CD-DA tracks
following the ISO-9660 data track.
* Optional karaoke area at '00:03:00'. (not supported yet by
vcdimager)
* Video CD information area at '00:04:00'.
* Optional segment play item area with MPEG items aligned in 150
sector segments. There can be up to 1980 segments on a disc.
* Optional program and data file area, for additional files
added to the ISO-9660 track.
* Up to 98 MPEG mode 2 form 2 tracks wrapped in front and rear
margin(2) empty sectors and preceded by (at least) 150 empty sector
pre-gaps.
* 150 sector post-gap after the last mpeg track, as required by the
ECMA-130 standard.
* Up to 97(3) CD-DA tracks. (not supported yet by vcdimager)
* Lead-out area.
---------- Footnotes ----------
(1) actually raw mode 2 sectors have a 2336 byte user data area, but
parts of it are used for error codes and headers when using the mode 2
form 1 or form 2 configurations.
(2) Margins seem to be used, in order to compensate for inaccurate
sector addressing issues on CD-ROM media. Interestingly, they have been
abandoned for the Super Video CD.
(3) the maximum number of tracks on a Video CD must not exceed 99
tracks
Info Catalog
vcdimager: Overview
vcdimager: Video CD Concepts
vcdimager: Known Video CD Flavors