在安裝完 opencv 後， 回頭來裝ffmpeg 支持 openv，有如下問題
ERROR: opencv not found using pkg-config
在沒有安裝 opencv的情況下，出現這個問題不奇怪，但是已經安裝完成 opencv後，依舊有這個問題。
執行命令:
./configure --enable-libopencv
解決:
vi ~/.bashrc
添加
PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/lib/pkgconfig
export PKG_CONFIG_PATH重新執行:
./configure --enable-libopencv
linux-vdso.so.1 => (0x00007fff115ff000)
libavdevice.so.56 => /usr/local/lib/libavdevice.so.56 (0x00007fb615e61000)
libavfilter.so.5 => /usr/local/lib/libavfilter.so.5 (0x00007fb615b0c000)
libavformat.so.56 => /usr/local/lib/libavformat.so.56 (0x00007fb61573c000)
libavcodec.so.56 => /usr/local/lib/libavcodec.so.56 (0x00007fb61429a000)
libavresample.so.2 => /usr/local/lib/libavresample.so.2 (0x00007fb61407c000)
libpostproc.so.53 => /usr/local/lib/libpostproc.so.53 (0x00007fb613e2e000)
libswresample.so.1 => /usr/local/lib/libswresample.so.1 (0x00007fb613c13000)
libswscale.so.3 => /usr/local/lib/libswscale.so.3 (0x00007fb613992000)
libavutil.so.54 => /usr/local/lib/libavutil.so.54 (0x00007fb61372e000)
libm.so.6 => /lib64/libm.so.6 (0x0000003664000000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003663800000)
libc.so.6 => /lib64/libc.so.6 (0x0000003663400000)
libdc1394.so.22 => /usr/lib64/libdc1394.so.22 (0x00007fb6134b8000)
libopencv_imgproc.so.3.0 => /usr/local/lib/libopencv_imgproc.so.3.0 (0x00007fb612588000)
libopencv_core.so.3.0 => /usr/local/lib/libopencv_core.so.3.0 (0x00007fb611965000)
libz.so.1 => /lib64/libz.so.1 (0x0000003664800000)
libx264.so.148 => /usr/local/lib/libx264.so.148 (0x00007fb6115ac000)
libwavpack.so.1 => /usr/lib64/libwavpack.so.1 (0x0000003663000000)
libvpx.so.1 => /usr/local/lib/libvpx.so.1 (0x00007fb61130b000)
libvorbisenc.so.2 => /usr/local/lib/libvorbisenc.so.2 (0x00007fb610f31000)
libvorbis.so.0 => /usr/local/lib/libvorbis.so.0 (0x00007fb610d00000)
libtheoraenc.so.1 => /usr/local/lib/libtheoraenc.so.1 (0x00007fb610abc000)
libtheoradec.so.1 => /usr/local/lib/libtheoradec.so.1 (0x00007fb6108a4000)
libspeex.so.1 => /usr/lib64/libspeex.so.1 (0x0000003665000000)
libopenjpeg.so.2 => /usr/lib64/libopenjpeg.so.2 (0x00007fb610684000)
libmp3lame.so.0 => /usr/local/lib/libmp3lame.so.0 (0x00007fb6103fc000)
libgsm.so.1 => /usr/lib64/libgsm.so.1 (0x00007fb6101f0000)
libfdk-aac.so.1 => /usr/local/lib/libfdk-aac.so.1 (0x00007fb60ff3f000)
libfaac.so.0 => /usr/local/lib/libfaac.so.0 (0x00007fb60fd2d000)
librt.so.1 => /lib64/librt.so.1 (0x0000003663c00000)
/lib64/ld-linux-x86-64.so.2 (0x0000003662c00000)
libraw1394.so.11 => /usr/lib64/libraw1394.so.11 (0x00007fb60fb1e000)
libusb-1.0.so.0 => /usr/lib64/libusb-1.0.so.0 (0x0000003666c00000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007fb60f919000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x000000361fc00000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x000000361f800000)
libogg.so.0 => /usr/lib64/libogg.so.0 (0x0000003673800000)
