Go to http://en.savefrom.net/
and put ur link of youtube video you want to download
Alternatively remove www. and add ss without dot and press go
e.g., in my case link is
https://www.youtube.com/watch?v=TieiJWTG2zU
I have to remove www. or if u r using mobile then u have to remove m. as follows
https://ssyoutube.com/watch?v=TieiJWTG2zU