Fitting content onto audio CDs

Q: I’m trying to burn some playlists to an audio CD, and some them will not burn the entire playlist.  For instance, I have one playlist which contains 18 songs in MP3 format at various bit-rates totaling 89MB which burns a complete CD with no problems.  On the other hand, I have another playlist with only 15 MP3 tracks at various bit-rates totaling 79MB and iTunes will not burn this entire playlist, insisting that I remove at least 3-5 tracks before it will burn properly. I have tried deleting and recreating the playlist with the same tracks and I’m still having the same problem, even on different user accounts and different machines.  Any help would be appreciated.

– Laurie

A: The key point to consider when burning tracks to an Audio CD is not the size of the selected tracks, but rather the total duration of the playlist.

Tracks that are burned to an audio CD are converted back to a standard uncompressed WAV format, and are therefore constrained by the length of a standard audio CD.  The problem with basing this on the file size, particularly when working with files at different bit-rates, is that the relationship between the size and length (or duration) of a given track is entirely dependent upon it’s bit-rate.  For example, if you were burning a playlist composed entirely of 128kbps files, you would be able to fit approximately 73MB worth of MP3 files.  On the other hand, the same tracks at 192kbps would take up approximately 108MB.  Conversely, 73MB of 96kbps tracks would run at 106 minutes in duration—far too much to fit on any standard audio CD.

Since the file size-to-duration ratio can vary widely with different bit-rates, the only reliable way to get a determination as to whether your tracks will fit on an audio CD is to look at the “total time” shown at the bottom of the playlist, rather than the total size:

Modern CD-Rs generally offer 80 minutes of recording time, although some media still uses the older 74-minute standard.  You can check the CD-R packaging to confirm which type you’re using.  You also need to keep in mind that if you’re placing a two-second gap between tracks (which is the default in iTunes), this extra time needs to be factored into your calculations.  Therefore, your total time shown at the bottom of the playlist should be 1:20:00 minus the number of tracks in your playlist multiplied by the “Gap Between Songs” setting in iTunes’ “Burning” preferences.  Since the gap between tracks generally only accounts for a few seconds, it’s seldom particularly relevant unless you’re burning tracks very close to the maximum capacity, or unless you have a very large number of tracks.


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