iTube Grabber for Mac OS X enables you to capture almost any audio and/or video stream!
(Software Santa's note: discontinued by the developer/no longer available even though it IS working on Mavericks Mac OS X 10.9.2 !
In addition: it lets you download from certain sites that 4K Downloader can not handle.)Publisher's Description
From iTubeGrabber:
iTube Grabber enables you to capture almost any audio and/or video stream. Most video streams are in Flash Video format and cannot be played by with QuickTime by default. If wanted iTube Grabber can automatically convert to several formats and presets (iPod, iPhone, MP4, MPEG) With the very intuitive user interface you can browse and capture with ease.
What's new in this version: Fixed issue when quiting.
http://download.cnet.com/iTube-Grabber/3000-2381_4-10972178.html