If the sound is 'ahead' of the video, and reaches the end before the video, you can use the Resynchronise function in FlashBack Player (Pro only) to make the sound and video end at the same point, correcting the sync.
- Find the point in the audio at which it 'ends' - this will be before the end of the movie.
- Select the sound from that point to the end of the movie.
- Delete the sound, but make sure you do not also delete the movie frames. (Only the sound should be selected and drawn in red)
- Right click on the track header and select Resynchronise.
- Select to resynchronise to the duration of the movie.
This will resample the sound track to make it the same length as the video, which should correct the sync problems.