I'm posting this so you folks won't have to go through the 8-hour search I just did through Reddits, video and audio forums, and trial-and-error with video and audio editors and converters to resolve a baffling out-of-sync audio/video problem with audio extracted from a video.
I recorded audio and video on-camera so I wouldn't have to sync audio later. However, I did want to extract the audio and fix some noise issues in Audacity, then recombine. This seemed easy until I saw that now, the audio and video were not in sync.
I tried extracting in Camtasia, in Audacity, and with various video-to-audio converters, and what I found was that the audio file was slightly different in length for each extraction.
At first, the Internet mind led me to believe this was because of a frame rate discrepancy (29.97 vs 30fps), so I re-created my videos at 30fps. Alas, this didn't solve the problem.
Finally, I saw that both Camtasia and Audacity (and the converters I'd tried) all padded the beginning and end of the extracted audio file.
I could fix that by trimming the extracted audio, but there had to be a better way!
There is, and two hours later I found Pazera Free Audio Extractor (http://www.pazera-software.com/products/audio-extractor/), which is capable of extracting the audio from video files without altering it in any way.
Now the extracted audio and video are in sync. And, if you are encountering this frustrating problem, yours can be, too!
David