https://trac.ffmpeg.org/wiki/CompilationGuide/RaspberryPi

CROSSTOOL:
ct-ng menuconfig
Paths and misc options
[x] Try features marked as EXPERIMENTAL
[${HOME}/x-tools/${CT_TARGET}] Prefix directory

Target options
[hardware (FPU)] Floating point
[x] append 'hf' to the tuple (EXPERIMENTAL)

Operating system
[linux] Target OS
[4.3 mainline] Linux kernel version

Binary utilities
[2.25.1] binutils version

C compiler
[x] Show Linaro versions
[Linaro 2.20-2014.11] glibc version


ct-ng build

export PATH=$PATH:/home/user/x-tools/arm-unknown-linux-gnueabihf/bin
export CCPREFIX="/home/user/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-"



FDK-AAC:

ALSA:

## ON DEV ENV ##
cd /home/user/
git clone git://git.alsa-project.org/alsa-lib.git

cd /home/user/alsa-lib/
libtoolize --force --copy --automake
aclocal
autoheader
automake --foreign --copy --add-missing
autoconf
./configure --prefix=/home/user/alsa-lib-bin --host=arm-unknown-linux-gnueabihf --enable-static=no --enable-shared=yes
make
cd ..
scp -r alsa-lib pi@raspberrypi:/home/pi/src/alsa-lib
## PASSWORD

## ON RASPBERRY PI ##
cd /home/pi/src/alsa-lib/
./configure --host=arm-unknown-linux-gnueabihf --enable-static=no --enable-shared=yes
sudo make install

FFMPEG:

cd /home/user/
git clone git://source.ffmpeg.org/ffmpeg.git

cd /home/user/ffmpeg
./configure --enable-cross-compile --cross-prefix=${CCPREFIX} --arch=armel --target-os=linux --prefix=/home/user/ffmpeg-bin --enable-gpl --enable-nonfree --enable-libfdk-aac --extra-cflags="-I/home/user/fdk-aac-bin/include" --extra-ldflags="-L/home/user/fdk-aac-bin/lib" --extra-cfags="-I/home/user/alsa-lib-bin/include" --extra-ldflags="-L/home/user/alsa-lib-bin/lib" --extra-libs=-ldl
make
make install
cd ..
scp -r ffmpeg-bin pi@raspberrypi:/home/pi/ffmpeg-bin


RECORDING:

./ffmpeg-bin/bin/ffmpeg -f alsa -i hw:CARD=CODEC -t 30 out.wav