Suing end-users would be dependent on the particular domestic law. In the US, my understanding (IANAL) is that practicing a patent does not require a license, only importing or distributing. Certainly, if I were to write my own H.264 decoder, I am not infringing. Now, if I were to distribute a software decoder, that would require a license under current case law. Surprisingly, there has been no effort as of yet to stop US-based mirrors of distributions containing FFMPEG. Of course, this case law is under review by the US Supreme Court, so this uncertainty could be inhibiting bringing of lawsuits, as they could make such lawsuits easier or harder. This leaves the typical method of getting H.264 software, importing it into the US. The International Trade Commission can block import of products containing patented technology, although how that would play out against multiple, independent importers could be interesting.