ffmpeg on iOS 5.1 Undefined Symbols Error - iphone

Question

So I've spent several hours now working through the scant amount of information available online about building ffmpeg for iOS. The building process seems to work well and I end up with fat files for armv6 and armv7 which I drag over into my project.
However, whenever I try to use the "avcodec_init()" command I get the following error:
Undefined symbols for architecture armv7:
"_avcodec_init", referenced from:
-[FirstViewController viewDidLoad] in FirstViewController.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)
The library files are included in the 'Link Binary with Libraries' of the project settings, so they are definitely compiled into the app. I just can't for the life of me work out why I'm getting an error on this.
I've tried several different projects, and downloaded some existing project files from the web and get the same error.
This is the build script I used:
export PLATFORM="iPhoneOS" export MIN_VERSION="4.0" export
MAX_VERSION="5.1" export
DEVROOT=/Volumes/Lion/Applications/Xcode.app/Contents/Developer/Platforms/${PLATFORM}.platform/Developer
export SDKROOT=$DEVROOT/SDKs/${PLATFORM}${MAX_VERSION}.sdk export
CC=$DEVROOT/usr/bin/llvm-gcc export LD=$DEVROOT/usr/bin/ld export
CPP=$DEVROOT/usr/bin/cpp export CXX=$DEVROOT/usr/bin/llvm-g++ export
AR=$DEVROOT/usr/bin/ar export LIBTOOL=$DEVROOT/usr/bin/libtool export
NM=$DEVROOT/usr/bin/nm export CXXCPP=$DEVROOT/usr/bin/cpp export
RANLIB=$DEVROOT/usr/bin/ranlib
COMMONFLAGS="-pipe -gdwarf-2 -no-cpp-precomp -isysroot ${SDKROOT}
-marm -fPIC" export LDFLAGS="${COMMONFLAGS} -fPIC" export CFLAGS="${COMMONFLAGS} -fvisibility=hidden" export
CXXFLAGS="${COMMONFLAGS} -fvisibility=hidden
-fvisibility-inlines-hidden"
FFMPEG_LIBS="libavcodec libavdevice libavformat libavutil libswscale"
echo "Building armv6..."
make clean ./configure \
--cpu=arm1176jzf-s \
--extra-cflags='-arch armv6 -miphoneos-version-min=${MIN_VERSION} -mthumb' \
--extra-ldflags='-arch armv6 -miphoneos-version-min=${MIN_VERSION}' \
--enable-cross-compile \
--arch=arm \
--target-os=darwin \
--cc=${CC} \
--sysroot=${SDKROOT} \
--prefix=installed \
--disable-network \
--disable-decoders \
--disable-muxers \
--disable-demuxers \
--disable-devices \
--disable-parsers \
--disable-encoders \
--disable-protocols \
--disable-filters \
--disable-bsfs \
--enable-decoder=h264 \
--enable-decoder=svq3 \
--enable-gpl \
--enable-pic \
--disable-doc perl -pi -e 's/HAVE_INLINE_ASM 1/HAVE_INLINE_ASM 0/' config.h make -j3
mkdir -p build.armv6 for i in ${FFMPEG_LIBS}; do cp ./$i/$i.a
./build.armv6/; done
echo "Building armv7..."
make clean ./configure \
--cpu=cortex-a8 \
--extra-cflags='-arch armv7 -miphoneos-version-min=${MIN_VERSION} -mthumb' \
--extra-ldflags='-arch armv7 -miphoneos-version-min=${MIN_VERSION}' \
--enable-cross-compile \
--arch=arm \
--target-os=darwin \
--cc=${CC} \
--sysroot=${SDKROOT} \
--prefix=installed \
--disable-network \
--disable-decoders \
--disable-muxers \
--disable-demuxers \
--disable-devices \
--disable-parsers \
--disable-encoders \
--disable-protocols \
--disable-filters \
--disable-bsfs \
--enable-decoder=h264 \
--enable-decoder=svq3 \
--enable-gpl \
--enable-pic \
--disable-doc perl -pi -e 's/HAVE_INLINE_ASM 1/HAVE_INLINE_ASM 0/' config.h make -j3
mkdir -p build.armv7 for i in ${FFMPEG_LIBS}; do cp ./$i/$i.a
./build.armv7/; done
mkdir -p build.universal for i in ${FFMPEG_LIBS}; do lipo -create
./build.armv7/$i.a ./build.armv6/$i.a -output ./build.universal/$i.a;
done
for i in ${FFMPEG_LIBS}; do cp ./build.universal/$i.a ./$i/$i.a; done
make install

Answer 1

I haven't used ffmpeg yet (even though a number of my bosses have had me thinking about using it), but lemme suggest a couple things that could be happening here.
1)
Let's see if the symbol really exists in your compiled library.
Go to Terminal and "cd" to the directory where your .a library lives.
Then type in "nm -arch armv7 ffmpeg.a | egrep avcodec_init" (where you can replace ffmpeg.a in my sample command with the actual name of the .a library) all on one line. That dumps out the symbols in the library for the armv7 architecture and pipes it into grep, which should show you if avcodec_init really does exist in your library.
If it doesn't appear, then it didn't get compiled into your library.
2)
If the symbol does exist in your library, then make sure the path to your .a file is correct in your project. You may be accidentally only including a simulator-only (i386 architecture) version of ffmpeg.