on a Mac, you can record your screen + mic audio by following these two sets of instructions:
install the Soundflower Kernel Extension https://github.com/mattingalls/Soundflower/releases
follow the steps from the "The Holy Grail (Adding Audio from your Microphone and your Computer while being able to hear the audio as it records)" section here: https://publish.illinois.edu/ahovious/help-stuff/screen-recording-with-audio-on-mac-osx/
This is great for a screen-sharing session where you are talking to someone and walking through an application over the computer. This was the exact thing I needed to do when I figured this out, thought I would write it up to remember in the future. NOTE: If you do not want to include your microphone audio and only include the audio from your computer in your screen recording, just take out the steps related to the “Aggregate Device” and choose SoundFlower 2ch in QuickTime for your screen recording. Download and install Soundflower http://cycling74.com/products/soundflower/ Go to Applications – Utilities — Open Audio Midi Setup Click the (+) Plus sign in bottom left corner Choose “Create Aggregate Device” Place a checkmark next to Soundflower 2ch and Built-in Microphone Click the (+) Plus sign again Choose “Create Multi-Output Device” Place a checkmark next to SoundFlower 2ch and Built-in Output Go into System Preferences – Sound – Output — choose Multi-Output Device Now, when you open up QuickTime – Start New Screen Recording and select “Aggregate Device” from drop down arrow on the right. Voila!
updated 2019/11/21, testing working with MacOS Mojave 10.14.6