Helping people with computers... one answer at a time.
Audio CDs are different from data CDs. Typically, your burning software needs to know how to create audio CDs, and you need to explicitly tell it to do so.
When I download music and then burn it to a CD, it comes out just fine. But, I cannot play the CD in my car's CD player. The music is almost always MP3. Is there a way I can convert the MP3 to play in my car? And what format are store-bought CDs?
The CDs that you play on your computer and those that you listen to in a standard CD player, such as the one in your car, are formatted quite differently. And while you can play store-bought audio CDs in your computer, the CDs that you burn on your computer will usually not work in your car stereo or other audio CD player.
Why? Simply put, your car stereo is not a computer.
Let's look at the two different formats first. Audio CDs are designed for one purpose: audio. They contain raw, uncompressed data, in a very fixed format: 44,000 samples per second, with each sample consisting of a 16-bit (2-byte) number for each of the right and left channels.
If you do the math, that's 176,000 bytes per second, or 633,600,000 bytes for an entire hour of audio.
If you've ever seen blank, 70-minute CDs, these hold roughly 740 megabytes of data - enough for about 70 minutes of sound in audio CD format.
Data CDs, on the other hand, hold anything. They're just another media on which you can store files from your computer. The format of a data CD is even similar to the format of your computer's hard disk. It has a file system, directories, folders and files.
But your car stereo knows nothing about file systems, folders and the like. All it knows is how to stream that raw audio data off of an audio format CD. While your computer can do that it too, it's also a general-purpose device that understands the format of a data CD.
But that's not the only difference. Remember that I said that an audio CD is uncompressed. Every second takes up 176,000 bytes, regardless of whether that's a second of a symphony, someone speaking, or just silence.
MP3 is a compressed format, like almost every other common audio format available for internet downloads and computer use. It uses compression technology to make the file much smaller. A second of silence, for example, is going to require less data than a second of complex sounds. When you play an MP3 file, the software you use decompresses the sound as it's played. The problem is your car stereo probably doesn't have a clue about compression or decompression.
So what do you do? If you want to create an audio CD that will work in regular CD players, you'll need to use audio CD burning software. I happen to use Roxio's Easy CD Creator. This automatically decompresses my MP3 files to the correct format for audio CDs. The trick is simply to select Roxio's "Music Disc Creator" program and click the Audio CD option as the type of CD you want to create. Other CD burning software will have similar options.
The catch is that the audio CD is uncompressed. While you might have been able to put seven or eight hours of MP3s onto a single data CD before, you're out of luck with an audio CD. These contain only about 70 minutes or so. It may take several audio CDs to hold what you might currently have on a single data CD.
The good news is that CD players are catching up. The ability to play MP3 files from data CDs has already appeared in car and home stereo CD players. And like a computer, these can play both audio and data CDs. Unfortunately, unless that functionality is built in, it's not something that can be added later.
Personally, what I want is a "Line In" port on my car stereo so I can hook up my portable media player (any portable media player, not just the iPod) and listen to my music without ever having to burn a CD at all. Maybe some day.