Cross-Compiling for Ubuntu ARM by ffmpeg Example

In ARM Linux, Ubuntu on 5 November 2012 with 8 comments 7702 views

This has been a delayed post since I only figure out how to solve configure error just now. It wasn’t really necessary to cross-compile last year because compiling ffmpeg directly on the ARM-board finished overnight (despite the low CPU). Anyway, in this post I’m still using the board to easily retrieve package dependencies from Ubuntu ARM repository. Toolchain used is arm-linux-gnueabi-gcc-. The following steps will apply in general:

1. download source file (that is ffmpeg in this example)
2. retrieve development library/build dependecies
3. place header files and dependency libraries into toolchain path
4. configure with toolchain
5. make and create .deb installer package with checkinstall

cross-compile: Illustration of what's done on ARM-board and what's done on desktop

Prior to anything, install Linaro toolchain by adding their repo first:

$ sudo add-apt-repository ppa:linaro-maintainers/toolchain
$ sudo apt-get install gcc-arm-linux-gnueabi

A complete guide on how to compile ffmpeg can be found in their wiki. It applies generally. So, I’ll just skip to following configure:

[ubuntu-desktop]$ ./configure --cross-prefix=arm-linux-gnueabi- --enable-cross-compile --target-os=linux --arch=arm  --cpu=cortex-a8 --extra-cflags='-march=armv7-a -mfpu=neon -mfloat-abi=softfp' --enable-libtheora

As an example, the above configure requires Theora libraries. libtheora-dev itself requires libogg-dev. Use apt-get on the board to get them from Ubuntu ARM repository. Get the .deb files from /var/cache/apt/archives/ of the ARM-board to your desktop and extract them as root:

[root@ubuntu-desktop]$ dpkg -x libogg-dev_1.2.2~dfsg-1ubuntu1_armel.deb /usr/local/cross-compile
[root@ubuntu-desktop]$ dpkg -x libtheora-dev_1.1.1+dfsg.1-3_armel.deb /usr/local/cross-compile

The above /usr/local/cross-compile is just a temporary directory. The toolchain needs header files and dependency libraries to be placed inside /usr/arm-linux-gnueabi/include/ and /usr/arm-linux-gnueabi/lib/ consecutively. In my case I created the following link for header’s include:

[root@ubuntu-desktop]$ cd /usr/arm-linux-gnueabi/include
[root@ubuntu-desktop]$ ln -s /usr/local/cross-compile/usr/include/theora
[root@ubuntu-desktop]$ ln -s /usr/local/cross-compile/usr/include/ogg

and copied these from /usr/local/cross-compile/usr/lib:

libogg.a
libogg.so
libtheora.a
libtheoradec.a
libtheoradec.la
libtheoradec.so
libtheoraenc.a
libtheoraenc.la
libtheoraenc.so
libtheora.la
libtheora.so

After successful configure, run make (this will take some time), and then pack the whole working directory to the ARM-board. Instead of doing make install in the ARM-board, use checkinstall to install and create the .deb package. This way we can make use of dpkg to uninstall or re-install in the manner of package manager.

[root@beagleboard]$ sudo checkinstall --pkgname=ffmpeg --pkgversion="5:$(./version.sh)" \
     --backup=no --deldoc=yes --default

Please mind that even if we put “--install=no“, the above checkinstall will overwrite all ffmpeg binaries in /usr/local/bin/. This is the reason why I move the process to the ARM-board: to keep other running version on my desktop stays as it is.

Check the test of streaming from our cross-compiled ffmpeg in previous post.

A Little History

When first attempt to configure exited with ERROR: libtheora not found, I found the following test failed in the output log:

$ arm-linux-gnueabi-gcc -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_POSIX_C_SOURCE=200112 -D_XOPEN_SOURCE=600 -march=armv7-a -mfpu=neon -mfloat-abi=softfp -mcpu=cortex-a8 -std=c99 -fomit-frame-pointer -marm -pthread -E -o /tmp/ffconf.UdYctJgq.o /tmp/ffconf.mwXpf9Tl.c
...
/usr/lib/gcc/arm-linux-gnueabi/4.6.1/../../../../arm-linux-gnueabi/bin/ld: cannot find -ltheoraenc
/usr/lib/gcc/arm-linux-gnueabi/4.6.1/../../../../arm-linux-gnueabi/bin/ld: cannot find -ltheoradec
/usr/lib/gcc/arm-linux-gnueabi/4.6.1/../../../../arm-linux-gnueabi/bin/ld: cannot find -logg

What was inside the above temporary file (/tmp/ffconf.mwXpf9Tl.c):

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#include <theora/theoraenc.h>
int x;

You can run that test to check whether all dependencies are met.

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