How do you download national geographic videos?

I know there are many apps are able to download videos off nationalgeographic.com. Firefox browser extension that the video download browser plug-in

Or some video download website-videograbber.net. Specific say, you just copy and paste video URL to let it download video for you.

While, if you want to download a big size documentary from Nat Geo, or watch downloaded video with iphone, HTC, ipad and suchlike stuff, you'd better use a dedicated video download software. Below I attach the detailed instructions of it.