You can save a YouTube video as a Zotero item via the address bar icon, but you can't save the video itself with Zotero alone. There are third-party programs that let you do that, however, and you can then attach those files to the Zotero items.
Zotero used to save videos from YouTube automatically, but they've made it considerably more difficult to do. (I think all of the current tools require Java or a native program, though I'm not sure of the technical reasons for that.)
just as Zotero doesn't work on pdf-only pages, it doesn't work on pop-up videos from youtube. If you go to the actual youtube page of that video: http://www.youtube.com/watch?v=E8nJhG1xE5o#t=21 you'll be able to save it to Zotero.
you get to the regular page when you click on the video title. It's also the page that you'd get to from searching youtube or by clicking on "watch on youtube" if someone has a video embedded. I don't know how you got to the popup view.
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Zotero used to save videos from YouTube automatically, but they've made it considerably more difficult to do. (I think all of the current tools require Java or a native program, though I'm not sure of the technical reasons for that.)
Can you ?
http://www.youtube.com/watch_popup?v=E8nJhG1xE5o
http://www.youtube.com/watch?v=E8nJhG1xE5o#t=21
you'll be able to save it to Zotero.
where is that popup coming from ?