Now that you have mastered recording data and audio separately, you are ready to tackle those great interactive discs which mix the two - and maybe other stuff as well. There seem to be many ways to do it, but what are they? how are they used? how are they written? Unfortunately, with one exception they are complicated, used with difficulty and written in various ways. Since this is a primer, not a comprehensive treatise, it will cover the easy way and give some clues to the others which you are free to research if you wish.
Before getting into that, it's important to keep in mind some properties of CD readers. First, almost all CD-ROM drives are multisession so will see the last session on a disc and all that link up to it. Second, audio-only players are single-session so will see only the first session on a disc. A player which handles multiple formats, such as a standalone DVD player, should be single-session at least for audio and will probably be single-session for everything. However, one which also handles MP3s may be mutlisession, UDF-compatible and just about anything the manufacturer makes it.
In these modes, an audio session is written first with as many tracks as you wish. That session is closed but the disc is left open so that it can be followed by a data session. The two sessions are not linked; they are in separate volumes. When placed in a single-session reader such as an audio player only the first session (audio) is seen and the disc plays as a conventional CD-DA. The same disc in a multisession CD-ROM shows up as data and can Autorun and otherwise operate as though a pure data disc. In fact, to get to the audio session, you must use a tool such as Session Selector or ISOBuster to make the unlinked CD-DA visible to the computer.
If we stop at that point, we have an undefined but fully usable combination mode - which is what most people want to create and most drives accept without complaint. However, there are standards for two specific formats: CD Extra and Enhanced CD. Those contain specific folders and specific types of files which most users do not need or want. In early versions of ECDC, CD Extra was supported explicitly. In 5.x, the menu item for a new CD Extra generates a format close to Enhanced CD, but not quite on target. Nevertheless, it's an easy way to create the combination mode with only a small waste of disc for the unnecessary folders and files.
What if you want to access the audio from the data side? Simply put, you cannot. There is no link between the two volumes, so neither knows that the other is there, let alone what's in it. Even if you had the link, you would have no way to address the tracks from the data side. One solution is to include MP3 versions of the audio tracks on the data side; then the sound can be played as though there were a link without spending a great deal of space on it.
There are many of these and only a few will even be discussed here. Further information is available in the CD-R FAQ at http://www.cdrfaq.org/ and in the excellent Technical Library of PDF files at http://www.cinram.com/ Compared with the authoritative sources in the colored books, both are easy reading - but that is only relative.
In Mixed Mode, a single session is written with a data track followed by audio tracks. Because it is a single session, the audio can be accessed from the data side with appropriate software - but that software is not generally available and involves information not accessible to the casual user. This mode is out of favor because the data track comes first. Most modern audio players will skip a data track, but some may not and the resulting sound can be catastrophic. Mixed Mode is still used for some interactive programs written by experts and intended for restricted players, not for a Discman. The data track is accessible from a CD-ROM and at least some systems will play the audio as audio in the CD-ROM drive since the data track is skipped for audio play.
A VCD is similar to a CD Extra disc except that the audio tracks are replaced by video files (DAT) in Mode 2 Form 2. Because the folders, files and pointers are explicit in this mode, a specialized program is needed. General-purpose mastering programs such as ECDC, WinOnCD and Nero provide VCD capability; some also provide enhanced versions such as SVCD.
The standard requires that an audio disc begin with a two-second "pregap" before the first track. The location of that first track is specified in the TOC, so it can be made longer than two seconds - the equivalent of 300 KB - without confusing most players. By setting a larger pregap, information can be stored and hidden from 'normal' operations. Conventional mastering programs do not give you access to the pregap and do not provide ways to use it if you get there.
E-mail me at cdrecording@mrichter.com
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