userbinator points at https://meta.m.wikimedia.org/wiki/Have_the_patents_for_H.264..., but most of the patents there have a precedence date after the h.264 standard was finalized, and therefore can't be necessary to implement h.264 itself (unless the argument is that, at the time it was standardized, it was not known to be implementable, a rather implausible argument)
what's surprising is that the last 20 years have produced a few things that are arguably a little better, but nothing that's much better, at least according to my tests of the implementations in ffmpeg
it seems likely that its guaranteed patent-free status will entrench it as the standard codec for the foreseeable future, for better or worse. av1 has slightly better visual quality at the same bandwidth, but is much slower (possibly this is fixable by a darktangent), but it's vulnerable to patents filed by criminals as late as 02018