The new mac OS Sierra update has many fixes in it, especially for audio video issues. You will be very glad you updated! Here's how:
Please go to the App Store -> Featured-> macOS Sierra (righthand column, 5th item down)
The button will say either Download or if you have already done this it will say Open.
If you have not downloaded it, please do so - you can keep using your computer.
Clicking on Open will begin the install process. It will take about an hour so please have your laptop plugged in. You will not be able to use your laptop during this process.