Found this during package testing and worked out a minimal set of USE-flags. Building fails with USE="X chromium v4l". Builing succeeds with USE="X -chromium v4l". [...] powerpc64-unknown-linux-gnu-gcc -shared -Wl,-soname,libffmpeg.so -Wl,-Bsymbolic -Wl,-z,now -Wl,-z,relro -Wl,-z,defs -Wl,--gc-sections -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavresample -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,-O1 -Wl,--as-needed -Wl,--hash-style=gnu -Wl,--as-needed -Wl,-z,noexecstack -Wl,--warn-common -Wl,-rpath-link=libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil:libavresample -o libffmpeg.so -Wl,--whole-archive libavcodec/libavcodec.a libavformat/libavformat.a libavutil/libavutil.a libswresample/libswresample.a -Wl,--no-whole-archive -lXv -lX11 -lXext -ljack -lasound -lm -ldl libavcodec/libavcodec.a(v4l2_buffers.o): In function `v4l2_free_buffer': v4l2_buffers.c:(.text+0xc64): undefined reference to `sem_post' libavcodec/libavcodec.a(v4l2_m2m.o): In function `v4l2_prepare_contexts': v4l2_m2m.c:(.text+0x58): undefined reference to `sem_init' libavcodec/libavcodec.a(v4l2_m2m.o): In function `ff_v4l2_m2m_codec_reinit': v4l2_m2m.c:(.text+0x230): undefined reference to `sem_wait' v4l2_m2m.c:(.text+0x27c): undefined reference to `sem_destroy' v4l2_m2m.c:(.text+0x290): undefined reference to `sem_init' libavcodec/libavcodec.a(v4l2_m2m.o): In function `ff_v4l2_m2m_codec_end': v4l2_m2m.c:(.text+0x3fc): undefined reference to `sem_destroy' v4l2_m2m.c:(.text+0x500): undefined reference to `sem_destroy' libavcodec/libavcodec.a(v4l2_m2m.o): In function `ff_v4l2_m2m_codec_full_reinit': v4l2_m2m.c:(.text+0x62c): undefined reference to `sem_wait' collect2: error: ld returned 1 exit status make: *** [/var/tmp/portage/media-video/ffmpeg-3.4.5/work/ffmpeg-3.4.5/ffbuild/libffmpeg.mak:5: libffmpeg-] Error 1
Created attachment 566406 [details] build.log.xz
Created attachment 566408 [details] emerge --info
media-video/ffmpeg-4.2.2 builds fine with USE="X chromium v4l".