Can we download all video tutorials from unity website to learn ??
Physically yes. They are all hosted on YouTube, so any service that can download videos from YouTube should work.
I haven’t looked to see if that’s within the terms of service of Unity or YouTube.
Is there (free) services that allow to sniff out video based on playlist 
?
I thought all these bitty internet things were in the virtual realms of men.
Damn I’ve been wrong all these years 