PLEASE READ: To register, turn off your VPN (iPhone users- disable iCloud); you can re-enable the VPN after registration. You must maintain an active email address on your account: disposable email addresses cannot be used to register.
As best as I can tell, jwplayer is just media-playing software.
Where are these videos "embedded" that you want to download? YouTube?
Oh shit, you're right. They fucked it up.Google video downloader professional followed by the browser you use to get the proper version. It's simple to use and it's absolutely free. (The new version of DowloadHelper is crap.)
I guess the jwplayer videos are streamed over rtsp (I guess that's the one, there's also rtmp). Most video downloaders can't deal with it and you require software that goes a bit deeper into the whole thing.
I've used this Firefox extension to do it for a long time.
https://addons.mozilla.org/en-us/firefox/addon/video-downloadhelper/
It adds a button to your toolbar, you just go to a page with the video and start playing it, then click on the toolbar button and it will list the videos that are available to download, click on one (usually the one with the largest file size is what you want) and it will download.
Note, this works on most sites but not all. It does not work where the player is configured to simply stream the video from the server, but it does work on sites where the player is downloading and caching the video to your browser (which is most of them).
