Question: how to download youtube video on mac os sierra?
Answer: Free YouTube Downloader. This is a highly recommended tool to download YouTube videos on macOS 10.14. ... 
Airy. This app is one of the top free YouTube downloaders for Mojave. ... 
Any Video Converter. ... 
MacX YouTube Video Downloader. ... 
ClipGrab for Mac. ... 
WinX HD Video Converter for Mac.