[Libav-user] FFMPEG: undefined reference to `avcodec_register_all' does not link

Alexander Botev botevmg at gmail.com
Mon Jun 30 12:36:58 CEST 2014

So I have a very sample code for trying to decode a FFMPEG video stream. My
problem is avcodec does not want to link, to do so I made a clean
installation of Ubuntu 13.04. I have build ffmpeg from source following the
guide here: https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu

I just want to compile my file. Note that my ubuntu does not have any
implementations or header files for avcodec. The command line I use is:

gcc -I/home/USER/ffmpeg_build/include -L/home/USER/ffmpeg_build/lib
-lavcodec -o test.exe Downloads/auv/src/dronerosvideo/src/ar2.cpp

/tmp/ccKTprFq.o: In function `fetch_and_decode(int, int, bool)':

ar2.cpp:(.text+0x36e): undefined reference to `avcodec_register_all'

ar2.cpp:(.text+0x378): undefined reference to `av_log_set_level'

ar2.cpp:(.text+0x382): undefined reference to `avcodec_find_decoder'

ar2.cpp:(.text+0x3b1): undefined reference to `avcodec_alloc_context3'

ar2.cpp:(.text+0x3d6): undefined reference to `avcodec_open2'

ar2.cpp:(.text+0x46d): undefined reference to `av_init_packet'

ar2.cpp:(.text+0x50a): undefined reference to `avcodec_decode_video2'

ar2.cpp:(.text+0x534): undefined reference to `av_free_packet'

/tmp/ccKTprFq.o:(.eh_frame+0x13): undefined reference to

collect2: error: ld returned 1 exit status

Just for a sane test if I remove the -L argument compiler says:

/usr/bin/ld: cannot find -lavcodec

Which means that the linker finds the library in
*/home/USER/ffmpeg_build/lib*. Also if we check the library for
implementation it exists:

nm ffmpeg_build/lib/libavcodec.a | grep "register_all"0000000000000000
T avcodec_register_all

Also as advised since it is C++ I have exten "C" around the include of the

At this point I'm falling out of any ideas at all, why exactly compilation
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