My understanding is that IPMP was not precisely builtin to MPEG-2 or -4.  The fact that it could be backported to MPEG2 is partly indicative of this.<p>IPMP does not in any meaningful way alter the H.263 or H.264 compression algorithims, even though it does alter the bitstream in ways that require modifications of the encode&#x2F;decode pipeline<p>There is nothing stopping a third-party from similarly making a pipeline-invasive DRM for any open codec.  As a matter of fact, if the open codec is patent free, then there would be no legal way to stop them.