CODEWITHSUNDEEP
ffmpeglinker
Danny
Danny

Reputation: 2673

Undefined FFMPEG references in my shared library when linking main program

I've built a shared library which references the FFMPEG libraries. I've having a tough time to link the final application. I've fiddled for hours with library order but no joy.

g++ -o testVideoTranscode testVideoTranscode.o /usr/lib/libstdc++.so.6 -L../../../lib3p -lavutil  -lswresample -lavcodec -L../../../lib -ldvsutils -ldvscfg -ldvstc -lstdc++ -lmch264dec -lfreeimage -lpthread

../../../lib/libdvstc.so: undefined reference to `sws_getContext(int, int, AVPixelFormat, int, int, AVPixelFormat, int, SwsFilter*, SwsFilter*, double const*)'
../../../lib/libdvstc.so: undefined reference to `av_frame_alloc()'
../../../lib/libdvstc.so: undefined reference to `avcodec_close(AVCodecContext*)'
etc etc

For example, one missing symbol, av_frame_alloc(), is correctly in the ibavutil.so library (albeit in a non-standard location):

nm -D ../../../lib3p/libavutil.so | grep av_frame_alloc
00021360 T av_frame_alloc

My library, libdvstc.so, correctly shows the reference to the symbol and the file:

nm -D --demangle ../../../lib/libdvstc.so | grep av_frame_alloc
         U av_frame_alloc()

ldd ../../../lib/libdvstc.so
    linux-gate.so.1 =>  (0xb77c3000)
    libavutil.so.55 => /mnt/swdevel/DVStor/source_build/lib3p/libavutil.so.55 (0xb772f000)
    libswresample.so.2 => /mnt/swdevel/DVStor/source_build/lib3p/libswresample.so.2 (0xb7714000)
    libavcodec.so.57 => /mnt/swdevel/DVStor/source_build/lib3p/libavcodec.so.57 (0xb623f000)
    libstdc++.so.5 => /usr/local/dvstor/lib/libstdc++.so.5 (0xb616f000)
    libm.so.6 => /lib/libm.so.6 (0xb6144000)
    libgcc_s.so.1 => /lib/libgcc_s.so.1 (0xb6126000)
    libc.so.6 => /lib/libc.so.6 (0xb5f8f000)
    libpthread.so.0 => /lib/libpthread.so.0 (0xb5f74000)
    librt.so.1 => /lib/librt.so.1 (0xb5f6b000)
    libdl.so.2 => /lib/libdl.so.2 (0xb5f65000)
    libz.so.1 => /lib/libz.so.1 (0xb5f51000)
    /lib/ld-linux.so.2 (0x00871000)

Its all there. I'm stuck...

Upvotes: 1

Views: 1364

Answers (2)

proxima
proxima

Reputation: 313

Alternate method (http://soledadpenades.com/2009/11/24/linking-with-ffmpegs-libav/) is to compile by linking to ffmpeg libraries in following format:

gcc -o main.o main.c `pkg-config --cflags --libs libavformat libavutil`

Upvotes: 0

Ronald S. Bultje
Ronald S. Bultje

Reputation: 11174

Use extern "C" around the include statements of the FFmpeg headers:

extern "C" {
#include <libavutil/avutil.h>
#include <libswscale/swscale.h>
[etc]
}

Most libraries do that for you, but FFmpeg doesn't, for some philosophical reason.

Upvotes: 4

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