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Enhanced
Music CD
Adding a data track to a music CD allows video,
website links and other features to be added. |
CDs can be mixed mode, comprising a combination of, usually, one data track
plus up to 98 audio tracks. Such discs should only play the audio tracks
on a CD audio
player, while the data track will play on a PC allowing additional content
such as video clips, sleeve notes with graphics/photos, web access and/or
other interactive applications.
Since the Red Book was written at a time when CD-ROM was
not considered, mixed mode can cause problems when playing on audio players. In
particular, it is important to prevent audio players trying to play the data
track(s). There are several different methods of implementing a
mixed mode disc.
Data
in Track 1
In one type of mixed mode CD the first track of a CD is a CD-ROM data track.
But some early CD players will try to read the data track with possibly
disastrous consequences so this method tends not to be used except for
applications where it is unlikely to be played on a CD audio player.
CD-ROM
Ready
This is one name for mixed mode discs where the data 'track' is hidden in the pause before
track 1 (an audio track) begins. This avoids the problem of trying to play track one when
it contains data.
However, it is still possible for audio players to attempt to play the
data if the user 'rewinds' into the data and then plays it.
CD-i Ready
Another type of mixed mode disc, where the same problem has
been partly solved in a similar way, is the CD-i Ready disc. This is a CD
with the CD-i data hidden
in the pause preceding the audio tracks.
However, there are some problems with this
approach and Philips have never confirmed the current tentative specification.
CD Extra or Enhanced CD
CD audio discs can also be Enhanced CDs, which contain two sessions
so are multi-session discs. Multi-session capability was originally
defined for CD-R discs to allow data to be written in several sessions
to add or ‘modify’ data. Each session comprises lead-in, program and
lead-out areas. The first session contains up to 98 audio tracks; the
second session contains the CD-ROM track. When played on an audio
player, it only sees the first session and so does not try to play the
data session, but CD-ROM drives see both sessions and will load any
programs contained in the second session.
|
Session 1 (audio) |
Session 2 (data) |
| Lead-in |
Program Area
(up to 98 tracks) |
Lead-out |
Lead-in |
Program Area
(CD-ROM track) |
Lead-out
|
The enhanced CD specification (the Blue Book) is based on the
multi-session pressed disc specification with some application specific
additions for handling lyrics, titles, video and stills. The main
features of such discs are as follows.
- Playable on a wide range of hardware including PCs under Windows
95/98, Macintosh computers, and dedicated CD Plus players.
- Session one contains up to 98 tracks of audio data
conforming to the Red Book specification.
- Session two contains one track of CD-ROM XA (ie Mode 2)
sectors and must include certain specified files and directories and
use the ISO 9660 file system. For Macintosh compatibility, it is
possible to make the data track include HFS as well as ISO9660.
The following directories and files are required in the second
session:
- An AUTORUN.INF file in the root directory
which meets the Windows 95 Autoplay specification.
- A CDPLUS directory containing general
information, lyrics and MIDI data.
- A PICTURES directory containing pictures
encoded in both MPEG and other formats.
- An optional DATA directory containing
additional data files depending on the application.
A large proportion of CD singles now are CD EXTRA discs and normally
use Apple Quicktime videos plus text and graphic information related to
the music on the discs.
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