Voice-over at Preview Time
If don't want to narrate your movie while recording, use this option to narrate your movie after you've finished editing in the Preview time
In order to record voice over narration when your movie is out of the recording phase, you need to go to the Thumbnails view. Select the speaker icon in the top panel to open the Audio editor panel.
In this panel click on the + icon and you can choose from record, text-to-speech, import or Audio collection. To record a narration, select record. A dialog box will pop up and ask if you would like to preview the movie in the background while recording, click Yes.
When you are finished recording a menu will pop up for you to put the final editing touches on your narration. Here you can select for the audio to loop, fade in or fade out.