Techical Specification: Tracks on VCD - Page 10

Source ( VideoPack 4 Manual)

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The structure of CDs is defined by a lead-in area followed by the program area containing user data, and CDs are finished by the lead-out area. Lead-in and lead-out area of Video CDs contain series of empty of CD-ROM/XA Mode 2 Form 2 sectors. Although the Lead-in area contains empty sectors there are so called subchannels (P, Q, R, S, T, U, V, W) in addition to every sector containing information about the disc.

The main subchannels are P and Q containing control information, the disc's time code and a Table of Contents (TOC) giving the starting time of the tracks on the CD and allowing direct access by this way. In the program area of the Video CD there can be different kinds of tracks. Tracks are data units built from one unique sector format defined by the specification books. An Audio CD for example contains sectors conforming to the specification of the Red Book. On an Audio CD each track contains the data of one song, and track-jumping enables the access to the songs.

Data tracks of CD-ROMs conform to the Yellow Book. Access to the disc's data is done by a file system conforming to ISO 9660 standard. Green Book (CD-i) sectors, Form 1 and Form 2, have the same physical structure as CD-ROM/XA tracks. Form 1 sectors size is 2048 Bytes user data and used to store computer data. An additional error correction scheme increases data integrity. Form 2 sectors size is 2324 Bytes and used to store video and audio sequences, where only the mandatory CD error correction scheme and no additional one is sufficient. Bridge Discs combine green tracks with red or yellow ones.

How are tracks organized into VCD?

Video CD conforms to the Bridge Disc concept. The first track is a data track containing an ISO 9660 file structure and special information for CD-i players. The next tracks are MPEG-Audio-Video-Tracks each containing sequences with MPEG video and audio data.Behind the MPEG-Audio-Video-Tracks Red-Book-Tracks can follow. The maximum track number of a video CD is 99 including the Video CD data track (track 1). If the last tracks of the discs are Red-Book-Tracks, the Lead-out area may as well be encoded as an audio track.