If while attempting to record your webcam, you receive a "System Denied" error then you might have accidentally clicked "Block" while you were starting a recording.
To remedy the situation so you can continue recording, select the camera icon next to the address bar in the tab you wish to record and select "Always Allow":
If this was not the case, you may need to grant Chrome access to your Camera in your Mac System Preferences.
To do so, open your System Preferences by clicking the Apple icon in the upper left of your screen and select System Preferences:
Next, open Security and Privacy and click on the Privacy tab. Scroll down on the left hand pane to where it says Camera:
Make sure that the box next to Google Chrome is checked. You will need to restart Chrome after making this change but you should be all set to record a video!