there's actually a TON of cool stuff you can do with audio CDs, including putting stuff before the first song even starts--- you have to start the CD, then rewind backwards to get to it. very cool way to hide stuff. You can also make integrated CDs with movies, pictures, etc and audio that will play on any regular CD player. Here's the how to I saved from god knows where.
There are two ways to do this. The first is to put the data on track 1 of the CD, and audio on the next several tracks (discs created this way are referred to as "mixed-mode" CDs). The CD-ROM drive will automatically look at track 1 and ignore all other tracks, so you'll be able to get at the data and -- depending on the operating system -- will be able to play the audio tracks. Remember that all of the tracks, both audio and data, need to be recorded in a single session.
The down side of this is that audio CD players may attempt to play track 1, which can be obnoxious or downright harmful to audio equipment. Most modern CD players are smart enough to ignore data tracks, so this won't usually be a problem.
The other approach is to create a multisession disc with the audio tracks in the first session and the data track in the second. This is how CD Extra (the format formerly known as CD Plus) works. Audio CD players only look at the first session, and CD-ROM drives are (supposed to) start with the last session, so it all works out. Sony Music has some pages at
http://www.cdextra.com/.
(NOTE: it appears that in some situations a Macintosh will not handle multi-session audio/data CD-R discs correctly. For example, a G3 with a DVD-ROM drive running Mac OS 8.6 works fine, but a G4 or iMac running Mac OS 9 will reject the disc as unreadable. The same system will handle pressed discs correctly -- only CD-Rs fail. The reason for this is uncertain, but it may be possible to work around it by disabling the system's audio CD extension when you want to read the data portion.)
A common question is how to write the audio in the first session without gaps between tracks, because you can't use disc-at-once recording. (If you did use DAO recording, the disc would be closed, and you wouldn't be able to write the data track). With the right hardware and software, you can do "session-at-once" recording to write the audio without gaps. For example, if you're recording with Nero and SAO-capable hardware, you just select disc-at-once mode but don't select "finalize CD".
What happens when you try to play one of these as audio in your CD-ROM drive? As with most things multisession, it depends on your drive. (The player that comes with Plextor CD-ROM drives does the right thing. If you're using a different drive, you're on your own.)
There's actually a third way to do this that involves putting the data track into the extended pregap of the first audio track. Instead of the audio starting at minute:second:block 00:02:00, the data starts there, and the audio is written after. The pregap is adjusted accordingly. This method never gained popularity because some drives started playing at 00:02:00 regardless. There doesn't seem to be a way to do this on CD-R.
Some CDs perversely put audio in the pregap. You can play it by starting to play track 1, then holding the "reverse" button until it seeks all the way to the start of the disc. Some older digital audio extraction programs would just ignore the "hidden" audio, but most newer ones will extract the entire track.
For example, _Factory Showroom_ by "They Might Be Giants" looks like this:
TRACK 01 AUDIO
INDEX 00 00:00:00
INDEX 01 01:01:00
TRACK 02 AUDIO
INDEX 00 04:52:10
INDEX 01 04:52:10
TRACK 03 AUDIO
[...]
Index 01 on track 01 is usually 00:02:00. Holding down the reverse button backs the time up to -1:03. This disc actually causes one of my Windows machines (Win98SE with a Plextor 12/20 CD-ROM) to read the disc incessantly, making it impossible to play the disc or extract audio tracks.
See section (3-36) for more information on "hiding" audio tracks.
