Not all cameras that shoot video record the audio in sync. And no, your auto-sync software isn't going to fix it for you.
By Chris and Trish Meyer | December 03, 2013
Short Version: If you haven’t already heard, not all cameras that shoot video (for example, DSLRs like the Canon 5D mkII) record their own audio in sync with the video. This causes problems whether you’re using camera audio, dual system audio, or have a multi-camera shoot. Therefore, it’s essential to test your camera (particularly if it’s not primarily a “real” video camera) and to compensate for this potential issue. If this is news to you (or if you’ve been ignoring it), read on.