[ Thanks to Jeff Cobb
for this link. ]
“Now that your video is saved, you need to add some
dialog to it. I do it like this. First plug in a headset or other
microphone (internal mics can work but sound tinny), load up your
video in a media player, the run the Sound Recorder app in
Applications->Sound and Video->Sound Recorder. Select
external mic for the input source and .WAV as the output type. Then
click Record there and play on the video player and record your
dialog. When done click stop and save it to a meaninful name with a
.WAV extension.”