In order to compile C plugins, media-videp/mpv should install headers when USE=cplugins is enabled. In the case of https://github.com/hoyon/mpv-mpris which I tried, at the very least these headers are required: libmpv/{client.h,stream_cb.h} misc/{bstr.h,mpv_talloc.h} mpv/client.h osdep/compiler.h ta/{ta.h,ta_alloc.h} Additionally a pkgconfig (mpv.pc) should be installed. The aforementioned plugin's Makefile calls it, which fails: Package mpv was not found in the pkg-config search path. Perhaps you should add the directory containing `mpv.pc' to the PKG_CONFIG_PATH environment variable No package 'mpv' found It's compilable without it, but header locatios need to be defined manually. Thanks!
Created attachment 642782 [details] mpv-mpris-0.4.ebuild This is an upstream issue: the headers are only installed if you activate "libmpv". See attached an ebuild for the mpris plugin.
It has nothing to do with gentoo. Rely on the build system, if it does not work properly - report upstream.
https://github.com/mpv-player/mpv/issues/7918