If you have iTunes installed (free), then you have access to iTunes U, which is a very large collection of university teaching videos. If your browser and iTunes software are communicating with each other properly (which is not guaranteed), then you can bookmark your favourite iTunes pages, and loading the URL in your browser will (or should) cause iTunes to load the correct page.
The iTunes U Mathematics page has URL
http://itunes.apple.com/gb/genre/itunes-u-mathematics/id40000077?mt=10
Under Mathematics, they include a “New and Noteworthy” section with URL
Here I am pleased to see my Definitions, Proofs and Examples album is currently top of the bill. (I’m not sure how long these things last!)
Explaining mathematics 