In several places in this article, they say things like:

libopenh264 code is open source but due to the H.264 patents, no vendor is legally allowed to distribute their own binaries.

I don’t know anything about Flatpack, but it I were involved in doing something with containers, I’d be sorely tempted to build an image that contains the source code, dependencies, and clang. The first time it’s run by the user, it’d compile the library and that’s what would be in the container. First run’s slow, and the base image would be bigger (clang is, what, 123MB?), but… no license issues. Or, maybe it only pulls clang if gcc or clang aren’t already installed.

Anyway, is the license issue really only about shipping binaries? Would a concoction that builds it the first time on the user’s machine be legal?