iMovie Sound Issue

When using the facetime camera to import/record a video in iMovie, the sound will sometimes stop recording about 30 seconds before the video ends. I cannot figure out why this has started to happen, it never used to but in the last couple months it seems to be happening more often.

The sound and video are great for almost the entire video, until the last 20-30 seconds. Then, although the video still plays/records, with people moving their lips and all, the sound just ends prematurely. If the visual is still recording, I do not understand why the audio would stop since they should be tied together? Does anyone know why this may be happening or what I can do to fix it?

If I view the sound waves in the video, you can see the abrupt end. Any help is appreciated!