Start with Roman’s tutorial.
Following changes apply to Windows: you should use the NDK make.exe, not the one from cygwin. So, I simply wrote d:/dev/Android/ndk/prebuilt/windows-x86_64/bin/make.exe in my build_android.sh. For some weird reason, I could not run make clean – but I simply chose to ignore this problem for now.
Following the tutorial, don’t forget to set
TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.8/prebuilt/windows-x86_64
Also, use mixed-style paths, i.e. d:/dev/whatever and not cygwin style /cygdrive/d/dev/whatever. Be careful not to use paths with spaces – neither for ndk installation, nor for ffmpeg git clone.
With ffmpeg 2.2, you can use --target-os=android for ./configure, instead of mangling ./configure file as described in step 2.
On my machine, I did not have pr and od commands. I chose simply to fake them, writing
echo 'cat $3' > ./pr
echo 'echo od' > ./od
These do not spoil the build.
So, my build process is as follows:
git clean -d -f -x
./configure --enable-shared --disable-static --disable-doc --disable-ffmpeg --disable-ffplay --disable-ffprobe --disable-ffserver --disable-avdevice --disable-doc --disable-symver --cross-prefix=d:/android-ndk-r9c/toolchains/arm-linux-androideabi-4.8/prebuilt/windows-x86_64/bin/arm-linux-androideabi- --target-os=android --arch=arm --enable-cross-compile --sysroot=d:/android-ndk-r9c/platforms/android-9/arch-arm/ --extra-cflags="-Os -fpic"
Compilation does display some warnings, but the .so files are all produced.
To enable NEON, I used
--extra-cflags="-Os -fpic -marm -march=armv7-a -mfloat-abi=softfp -mfpu=neon"
--extra-ldflags="-Wl,--fix-cortex-a8"
Now, libavcodec.so could not be built anymore: too many files on the linker list. So, after it crashed, I launched the linker manually:
$ d:/Dev/Android/ndk/toolchains/arm-linux-androideabi-4.8/prebuilt/windows-x86_64//bin/arm-linux-androideabi-gcc -shared -Wl,-Bsymbolic -Wl,--version-script,libavcodec/libavcodec.ver -Llibavcodec -Llibavdevice -Llibavfilter -Llibavformat -Llibavresample -Llibavutil -Llibpostproc -Llibswscale -Llibswresample -Wl,--fix-cortex-a8 --sysroot=d:/Dev/Android/ndk/platforms/android-9/arch-arm/ -isysroot d:/Dev/Android/ndk/platforms/android-9/arch-arm/ -Wl,--as-needed -Wl,--warn-common -Wl,-rpath-link=libpostproc:libswresample:libswscale:libavfilter:libavdevice:libavformat:libavcodec:libavutil:libavresample @libavcodec/libavcodec.list -lswresample -lavutil -lm -lz -pthread -o libavcodec/libavcodec.so.55
I patch the library.mak file as follows: for $(SUBDIR)$(SLIBNAME_WITH_MAJOR), replace
$$(LD) $(SHFLAGS) $(LDFLAGS) $$(LD_O) $$(filter %.o,$$^) $(FFEXTRALIBS)
with
$(Q)echo >$(SUBDIR)lib$(NAME).list $(wordlist 1,400,$(filter %.o,$$<))
$(Q)echo >>$(SUBDIR)lib$(NAME).list $(wordlist 401,999,$(filter %.o,$$<))
$$(LD) $(SHFLAGS) $(LDFLAGS) $$(LD_O) @$(SUBDIR)lib$(NAME).list $(FFEXTRALIBS)
.. and from there, make proceeded smoothly.
PS: I used make -n libavcodec/libavcodec.so.55 to prepare the response file libavcodec/libavcodec.list.
PPS: Here is another article that helps to build and use ffmpeg for Android.