. what has been missing here is the "reason" (some of) the devel packages aren't being released.
This question was answered earlier in this thread (by me even), so I'm a bit confused why you say the reason is missing.
In the case of libbluray-devel, it's because Red Hat only uses a very small piece of that library, and doesn't want to have to support the whole library, including being liable for CVEs and other bugs in the parts of the library it doesn't use.
I don't know why libXvMC-devel wasn't released originally. As they appear to have decided to go ahead and release it, apparently wasn't for the same reason as libbluray-devel.
the src.rpm is available. Build it for yourself if Red Hat and CentOS aren't providing what you want. As a maintainer of packages in the CentOS Storage SIG, even I have to build and provide packages in the SIG that Red Hat and CentOS don't provide, e.g. userspace-rcu.. (They're in EPEL, but currently CBS doesn't/can't use EPEL.) I don't understand why people have so much trouble with this.
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Kaleb