"Interoperability" means a design supporting operation on multiple platforms or in multiple environments. In general, it means giving up features restricted to specific computers, operating systems or applications in favor of finding more users. Interoperability is seldom universal and is generally expensive: you have to give up a lot to increase your market.
If your CD recording is for your own use, interoperability is worth very little to you - and you are invited to skip the rest of this page. Or not. You know what computers and other devices you intend to have run your discs, so where's the issue? Simply put: do you know how you'll want to use them next week? Do you know you won't be installing a new OS, buying a new player or otherwise changing your base of operations?
The most nearly universal format for CD recording is Compact Disc - Digital Audio, CD-DA, redbook music. The standard is rigid and universal; there are extensions such as CD-Text, but adding them does not cost operation on equipment which does not support them. The problem with CD-DA is a consequence of its interoperability - inflexibility. If you want to play a CD of 1925 monaural 78s, you have to use the same audio parameters required to get year 2000 stereo. There's room on that disc for at least four times as much music without noticeable loss of quality (22.05 Ksps, monaural), but the standard will not permit it. If you write MP3s instead of CD-DA, you can put about 45 hours at 32 Kbps onto a CD-R which would hold only 74 minutes of redbook audio - but then you lose interoperability with all those audio CD players. That may be quite acceptable to you - you have an audio player which handles low-rate files without complaint. However, that won't help your neighbor whose MP3 portable demands 44.1 Ksps; or the guy down the block whose CD player only plays CDs - CD-DA recordings.
The problem shows up in many areas other than audio format. One is file naming. Your MP3 player, like your computer, displays information with which you can select what you want to do. Different players have different rules for that display, for the handling of folders and for tolerating multisession recording. Different operating systems on computers have varying rules for filenames as well. Fortunately, all common systems will handle strict ISO 9660 naming: 8.3 with a restricted character set (upper-case letters, numerals and the underscore). All MP3 players so far will handle a single-session disc without folders and eight-character names having an extension of MP3. As you stray from those rules - longer names, folders, additional characters, multisession - you lose platforms to play your discs.
If you want to include text and graphics on a disc, you have many ways to format it. Of course, TXT is the most readable. As with ISO 9660 filesystem, TXT is nearly universal, though very limiting. Other common formats are DOC (Microsoft Word) and PDF (Adobe Acrobat). If a sufficiently restricted set of capabilities for either one is used, free downloadable programs make those readable on most platforms. Another choice (my own preference in most cases) is HTML. But with any of those, you can write an elaborate version which is readable only with some versions of Word, with an advanced Acrobat reader or with a specific browser. It is your option whether to use features which enhance your product and restrict its use by others. For example, different browsers implement various features of HTML and supersets of HTML which others either treat differently or regard as errors. Most will handle mouseover (where the display changes when you pass your mouse over a target area), but some will not so you will lose the vision-impaired and others with graphics turned off or unavailable. On a simpler level, there is a small set of diacritical marks - accents and the like - which are handled easily in standard HTML, but go beyond them (to true single- and double-quotes, for example) and some browsers will give unintended results.
It is your choice when you design your project to build in interoperability. The point of this note is to induce you to think about the question at the beginning. Once the disc is designed, it is difficult or even impossible to extend its usability.
E-mail me at cdrecording@mrichter.com
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