I saw many videos that do not have sound on it because the Quicktime needs to install the add-on program to capture the computer audio. It is called, “Soundflower”. For those who need to record the computer audio as well, I uploaded my dropbox. The password is 1111 when you download it.

Download from dropbox: https://www.dropbox.com/sh/f8tbojjt9a5nx74/AAAeeITe1nA-6LPX1o62nJOta?dl=0

Tutorial to install the soundflower: https://www.youtube.com/watch?v=HHW2gMjvUHw

Reference: https://rogueamoeba.com/freebies/soundflower/