I pretty much gave up on all those vid-downloaders, they work for a while until youtube (and others) changes things, or they're loaded with adware.
Now I use VideoCacheView. Now I don't have to download the same video twice, first time watching it, second time downloading it. With VideoCacheView, you watch all the movies you want, then run VideoCacheView, select the vids that you want to keep, and it copies them to the folder you choose.