GIVE [dive into mark] is a Gentle Introduction to Video Encoding by Mark Pilgrim.  It’s an on-going, really well-written set of articles on all parts of video and audio encoding.  Considering these topics took up a large part of my livelihood in the past, the articles definitely grabbed my attention.  So far they’ve all been really informative, and they’ve been great in catching me up on things that I’ve lost track of in the past few years.  Even if you’re not interested in backing up your movies on a computer, I found the article on container formats and especially the one on lossy audio encoding incredibly informative.