Before it's even out of your mouth, there are plenty of videos which are perfectly legal and legitimate to download, which probably forces me to make a list even though that's NOT the subject.
Big buck bunny
Elephant's dream
Sintel
Caminandes <- this one is funny
Tears of Steel
Sita Sings the Blues <- a one lady project, quite interesting
Hak5 episodes and videos, there's more than a thousand, all ok to download and copy and give away ! what ! all of these are ! what !
....and everything else that is creative commons or PD licensed.
(Edit: Every episode of Hak5 has the creative commons license in it's credits at the end of the video. )
Of course any large site wants to make it next to impossible to download video, they just want to make the most money they can by hosting OTHER people's work without the owner's permission AND make money out of you, by watching you watching videos and selling the results. They also want to elbow you out of your seat and stop you watching lots of videos as well, for whatever reason. This is why tracking devices like all smartphones don't let you download for free if they can possibly stop you.
Generally I've used videodownloadhelper but I want to know what to do when it goes on it's regular holiday from downloading, which is what it is doing at the moment.
What other free software/ add-ons or easy command line stuff, especially Linux, is there for downloading video ?
No I can't watch online as the internet SUCKS here and always will. Many millions have the same problem with their internet.