I have been poking at RealVideo 4 lately. Who knows? We might be able to make a Google Summer of Code project out of it. If the FFmpeg project is accepted for the 2007 season.
Here’s a curious artifact I found: A method called Decoder::getBackdoorOptions(). The function turns out to be a NOP, though. In the original source, I imagine the guts were protected by an “#ifdef DEBUG…#endif” pair.