I know this post is old but i have the same problem in april 2021 other users had from 2015
so i simply think that also newer versions of videopad don't solve the no-audio issue.
tried all tricks listed before. none working. using latest version of april 2021 on win 7 64bit
the only way is to extract the audio from video as a mp3 file and then attach it to the video.
ia lot of work to fix a unsolved bug.
i would i have red these posts before paying the license....
very disappointed