Just a wild guess that it could be a difference in sampling rate. Audio for CDs is recorded at 44.1 kHz. Audio for video is typically recorded at 48kHz. I once made the mistake of recording separate audio onto a recorder that was set for 44.1. When I dropped it into a sequence that was set for 48, there was a time discrepency between the video clip and the audio clip. I made it work through trial and error by using the rate stretch tool on the video until it matched. I might have been able to resample the audio to 48kHz, but I thought I'd waste less time using rate stretch because the clips were over an hour each.
Check to see if your Audition output is set for 44.1. If so, change it to 48.
Thanks, Stan. That took care of it. I don't understand what's going on since I only work at 44.1 kHz at all stages of production, but making the sample rate adjustment takes care of the duration discrepency. Thanks! (I've got my fingers crossed that my client won't balk at receiving a different sample rate from the spec).
Good deal! Ya know, sometimes clients have to be educated as to best practices, too.