TeCh-CoSmOs

Here's a really simple way to do that. 

Open the video on your browser. Go to the url and add a "ss" (without quotes) at the beginning of the url and hit Enter. Click the download button now and there you go! The browser will download the video for you. Cool, eh? :D

Here's where you add the "ss" :

if the video url is: https://www.youtube.com/watch?v=KPmoDYayoLE
you have to edit it to: https://www.ssyoutube.com/watch?v=KPmoDYayoLE


and hit enter!

This works for a couple of other websites too. Check which ones HERE.