alt Hacker NewsSpeaking from firsthand experience: codec and other media processing libraries are some of the easiest software to find address leaks in.
(There are a number of reasons for this, not least being that C makes it very easy to ship partially initialized memory over the wire.)
Speed and security are not good bedfellows. Combine that with really shitty standards and dozens of years of development...
Oh, and licensing. Licensing is the real killer. I could just write my own mp3 decoder easily (the format not the file type) but I'm not gonna risk my company getting sued into the ground by doing that.