The libX11-devel package contains libraries and header files for libX11.
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development files and header files for libXext
The libXext-devel package contains libraries and header files for developing applications that use libXext.
XvMC is an extension of the X video extension (Xv) for the X Window System. The XvMC API allows video programs to offload portions of the video decoding process to the GPU video-hardware.