I'm using mig's DownloadHelper for a couple of years now.

http://www.downloadhelper.net/

So far it never stopped working longer as maybe a day at most.

I either download as .vfl or as .mp4.

Have you updated it to the latest version ?

It works on a ton of other streaming sites, too, and so far it never dissapointed me.

If everything else fails, you could use a screen recording software that catches the actual video stream.