http://en.wikipedia.org/wiki/MPEG4MPEG-4 is patented proprietary technology. This means that, although the software to create and play back MPEG-4 videos may be readily available, a licence is needed to use it legally. Patents covering MPEG-4 are claimed by over two dozen companies. There is no simple way to license MPEG-4, but the MPEG Licensing Authority can license patents required for MPEG-4 visual techniques from a wide range of companies (audio is licensed separately). A one stop shop is currently not possible; this article claims that AT&T is suing companies such as Apple over alleged MPEG-4 patent infringement. This AT&T action against Apple illustrates that it is hard to know which companies have patents covering MPEG-4.
(Sorry for being off-topic again...)