This is actually really interesting to me. I can imagine the complexities of building a programming language (it was a undergrad course in my school!) but how is building a new multimedia codec that much more difficult?

Does it have anything to do with most multimedia techniques being patent encumbered?

I took an undergrad Compilers course at my school. We wrote a compiler from scratch in one semester. Our compiler parsed and compiled a useful subset of Pascal, but changing it to a novel programming language would have been trivial. It doesn't have to be a GOOD programming language, just a new one.

For a multimedia codec, though, there's no low-hanging fruit. H.264 is already VERY good, so beating it is hard.