Face Blurring, with the Track Matte Key

I took a video blog that I had saved on the desktop and opened it in premier. I had to use two copies of the video, double layering it. At this point I had to use a third layer of black video. On the black video (which I made transparent) I had to apply a Mosaic blur which pixelated the video. I used a circle to focus in on my face. Once I had done that, I animated the circle to follow my face through out the video I blurred the edges of the circle to make it softer and applied the track matte key, which pixelated everything outside of the circle. I inverted it, and so it only pixelated what was in the circle, providing me with the finished product.

http://library.creativecow.net/articles/devis_andrew/Premiere-Pro-CS6-Basics_97/video-tutorial