I didn't use MacPorts
but I solve this and other similar problem, at least on my Mac OS Lion
10.7.4 + FFmpeg0.11 + OpenCV2.4.0
I install FFmpeg(with other 3rd libraries) and OpenCV from sources
downloaded from official sites
"SOME" of the libraries used by ffmpeg such as faac and faad are configure
with --build=i386-XXX or --build=i686-XXX by a wrong guess
watch the dump message carefully after you ./configure
especially the "build system type" and "host system type"
"checking build system type ... i386-apple-XXXX"
"checking build system type ...i686-apple-XXXX"
Both are need to fix. Only x86_64 or x86_64-XXX-XXX are OK
You should let the ./configure guess first. If it guess incorrectly, then
After rebuild all libraries with ./configure --build=x86_64 or something
There is no error "Undefined symbols for architecture x86_64" while
ALL libraries such as FFmpeg (--arch=x86_64) or the libraries used by
FFmpeg SHOULD be checked and reinstall
Libraries (other than FFmpeg) used by OpenCV also need to check.
Set the architecture of OpenCV in CMake to be x86_64 is recommended but