If the audio and video are out of sync in a file that you're working on in Handbrake, you can fix the problem by adjusting a few settings. You'll know if the audio and video are out of sync in a file by watching the preview in the main Handbrake window. If you hear the audio before seeing the corresponding action on screen, you have a syncing problem. This can be fixed in seconds.
Open Handbrake via either your desktop or your "Start" menu.
Choose "Source" to select the file you've been working on in Handbrake that has an audio/video syncing issue.
Click the "Video" tab under "Output Settings." Select the "Framerate (FPS)" drop-down menu and choose a different frame rate for your video. Fixing an issue like this will require some trial-and-error work. Click "Preview" to view a preview of your file as it will be outputted using the current settings. If the audio and video syncing issue is fixed, you can proceed with the encode using Handbrake. If the issue is not fixed, select a different frame rate from the drop-down menu and try again.