How is an algorithm proprietary if I can go online to the website of the ITU, a division of the United Nations, and download a copy of the standard and go write my own implementation?<p>ffmpeg's reverse-engineered Real Video decoder is an open-source implementation of a proprietary specification.  <i>Depending on the country and legal interpretation, the mere existence of this is illegal.</i><p>ffmpeg's H.264 decoder is an open-source implementation of a patented, but not proprietary, specification.<p>ffmpeg's Theora decoder is an open-source implementation of a probably-not-patented specification.<p>If a definition doesn't distinguish between something freely available for all to view/implement and something which <i>cannot even be implemented</i> without potentially falling afoul of copyright laws and the DMCA, it isn't a very good definition.