Recently, within development team we was discussing how it would be possible to build ffmpeg libraries for iOS.
We have found, that there was already a project which was doing this: ffmpeg4ios.org

Unfortunately, because it provided only dynamically linked libraries (which wasn’t so useful for our case), I had to dig deep into how ffmpeg was compiled for arm platform.
Fortunately, it provided build scripts, which was possible to use as a draft for our own build.

Few words about using 3d party libraries in iOS project.
Even though it is not possible to use dynamically linked binaries (*.dylib), it is completely legal to use static ones (*.a).

To have full set of build for all platforms and cpu (armv7,armv7s and iOS simulator) code had to be compiled 3 times and then single fat binary had to be created using lipo tool.

Important note: ffmpeg requires gas-preprocessor to be installed. It can be found here.

In order to compile native code for armv7/armv7s build scripts from ffmpeg4ios.org had to be changed to generate static libraries, i.e. config parameters had to be changed to “–enable-static –disable-shared”.

iOS simulator code was more complex to figure out, but in the end I was able to come up with stable working build script:

#!/bin/bash

SRC_PREFIX=$HOME/src
INST_PREFIX=$HOME/build

cd $SRC_PREFIX/ffmpeg

./configure \
--disable-doc \
--disable-ffmpeg \
--disable-ffplay \
--disable-ffserver \
--disable-ffprobe \
--arch=i386 \
--target-os=darwin \
--cpu=i386 \
--cc=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/gcc \
--sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk \
--extra-cflags='-arch i386' \
--extra-ldflags="-arch i386 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator6.1.sdk" \
--disable-logging \
--disable-debug \
--enable-static \
--disable-shared \
--enable-pic \
--disable-asm \
--prefix=$INST_PREFIX/iossim

make
make install

This would produce ffmpeg static libraries for iOS simulator in “$HOME/build/iossim”

Finally, all three build has to be used to create single fat binary suitable for both iOS native platform and iOS simulator.

#!/bin/bash

#
# This build file will create universal binaries for multiple platforms:
# 
# - iOS armv7 cpu
# - iOS armv7s cpu (newer)
# - iOS simulator

INST_PREFIX=$HOME/build
ARMV7_PREFIX="${INST_PREFIX}/armv7/lib"
ARMV7S_PREFIX="${INST_PREFIX}/armv7s/lib"
IOSSIM_PREFIX="${INST_PREFIX}/iossim/lib"
UNIVERSAL_PREFIX="${INST_PREFIX}/universal"

cd $INST_PREFIX
[[ ! -d "${INST_PREFIX}/universal" ]] && mkdir "${INST_PREFIX}/universal"

LIBS=( libavcodec.a libavdevice.a libavfilter.a libavformat.a libavutil.a libswresample.a libswscale.a )

for i in ${LIBS[@]}; do
        LIBNAME=`basename $i .a`
        xcrun -sdk iphoneos lipo -output $UNIVERSAL_PREFIX/$LIBNAME -create -arch armv7 $ARMV7_PREFIX/$i \
        -create -arch armv7s $ARMV7S_PREFIX/$i \
        -create -arch i386 $IOSSIM_PREFIX/$i
done

Finally, it is important to add header files together with library files, otherwise it won’t be possible to build project with those libraries.