Download youtube videos with Tampermonkey
Tampermonkey extension allow user to run custom scripts, and saveform.net provider a script to download from youtube.
First, install Tampermonkey
Open https://tampermonkey.net/ and install the extension for your browser.
Second, install saveform.net helper
Open https://en.savefrom.net/userjs-setup.php and install the script.
Now you can download any youtube videos as you like.