video file out of sync after 20 minutes

[snafubaby]

What could cause this? It's fine at the beginning, maybe 20 minutes, and then it goes out of sync. Could a virus cause it? Also, if i were to use a program that defrags files, could that fix the problem?

thanks!

[redwudz]

I doubt defragging would have any effect, and a virus is very unlikely unless it's causing a playback problem.

Check the length of the audio VS the video. That sort of sync problem is usually caused by different lengths of the two files. It shows as a sync error that increases linearly as the file plays. Converting VBR audio improperly to CBR can cause that problem also. If it's not off too far, you can stretch or shrink the length of the audio stream to match to match the video. Audacity is one way to do this.

If the file itself is badly damaged, the sync error may unevenly vary for the length of the video. That is much harder to correct.