ffmpeg - building opencv, got undefined reference to avformat_network_init error -

i using centos6.5, downloaded opencv-2.4.9, made build directory, , under there, ran 'cmake ..' , 'make'. during make run, got error message.

i found avformat_network_init in ffmpeg source, installed ffmpeg once in home , /usr/lib. don't know how tell cmake ffmpeg installed (include header , library).
see *.so files ffmpeg under /usr/lib64. why can't cmake find ffmpeg location? in advance.

i succeeded in building opencv. anyone's reference post answer here.
have had installed ffmpeg in 3 different places before (/usr/local/lib, /usr/local/lib64 , /usr/local). removed of them (i ran make uninstall @ build directories used install ffmpeg had been configured different prefix values).
removed ffmpeg installed yum install running 'rpm -e ffmpeg'. started fresh installing ffmpeg (to /usr/local). time ok until last part, make couldn't find javac compiler.
figured java_home env varailbe pointing wrong place set java_home directory right place(in case, /usr/lib/jvm/java-1.6.0-openjdk-1.6.0.0.x86_64). 'make' completed! ran 'make install'