Got a CD from a firm today. They said the CD would not play on their Windows computers at work. I put it in the mac here at home and it came up with an MP3 and a CDA as the contents. I am not sure if those are the same recordings in different formats or if they are separate. Nevertheless, I can't listen to the CDA of course, but after google searches I can't find a program on a mac that will convert it.
let me know
Where did that disc come from? Who made it? How? For what purpose?
A disk with both "CDA" and MP3 files is not a legal Red-Book audio CD. It may be some sort of semi-standard hybrid that probably won't play everywhere.
Note that (at least in the PC world) "CDA" is not really a file type, it is a placeholder for the Red-Book audio CD track. Standard audio CDs can be "ripped" with a "ripping" program that will convert the audio CD track (which is called a "CDA file") into an actual computer file (like WAV or MP3, etc.)
Note that the epic conversion search engine at http://www.videohelp.com has more information about converting one file type to another (both audio and video) than you would probably ever want to know.
Yes, there are valid hybrid CD formats, but you never know how people are trying to play them on the other end. I don't think that technology is necessarily the problem. User Error plays a big part. The more simple you can make something, the better chance you have of success at the far (uncontrollable) end.