How do I diagnose why a .so file won't load when executing a .mex file in MATLAB?

I'm trying to use a video library called VideoIO with MATLAB for a machine learning project. When I try to invoke the library in MATLAB, I get an error saying that it can't find libavutil.so.50, one of the ffmpeg libraries that VideoIO depends on. I've checked a few different things but can't find anything that looks wrong, other than the fact that it doesn't run. Can anyone suggest anything else to check to help me debug?

Here is the error:

error while loading shared libraries: libavutil.so.50: cannot open shared object file: No such file or directory 
??? Error using ==> videoReader_ffmpegPopen2 EOF found while trying to read the communication tag.
The server process probably died.
String so far: "" Function: int VideoIO::readMessageHeader(FILE*)
File : pipecomm.h Line : 306
Error in ==> videoReader.videoReader at 152 vr.handle = feval(vr.plugin, 'open',vr.handle, ...

Trying to figure out what went wrong, I found where vr is allocated:

 vr = struct('plugin',pvtVideoIO_mexName(mfilename, plugin), ... 'handle',int32(-1));

I printed out mfilename, then ran ldd on the file it points to:

$ ldd videoReader_ffmpegPopen2Server
linux-vdso.so.1 => (0x00007fff41dff000)
libavutil.so.50 => /u/goodfeli/ffmpeg/libavutil/libavutil.so.50 (0x00007fd5f2895000)
libavdevice.so.52 => /u/goodfeli/ffmpeg/libavdevice/libavdevice.so.52 (0x00007fd5f268c000)
libavformat.so.52 => /u/goodfeli/ffmpeg/libavformat/libavformat.so.52 (0x00007fd5f23bf000)
libavcodec.so.52 => /u/goodfeli/ffmpeg/libavcodec/libavcodec.so.52 (0x00007fd5f1792000)
libavfilter.so.1 => /u/goodfeli/ffmpeg/libavfilter/libavfilter.so.1 (0x00007fd5f1584000)
libswscale.so.0 => /u/goodfeli/ffmpeg/libswscale/libswscale.so.0 (0x00007fd5f1351000)
libstdc++.so.6 => /usr/lib64/libstdc开发者_如何学Go++.so.6 (0x000000378ea00000)
libm.so.6 => /lib64/libm.so.6 (0x0000003788a00000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x000000378c600000)
libc.so.6 => /lib64/libc.so.6 (0x0000003788600000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003789200000)
libasound.so.2 => /lib64/libasound.so.2 (0x000000379a200000)
libbz2.so.1 => /lib64/libbz2.so.1 (0x0000003b0b400000)
libz.so.1 => /lib64/libz.so.1 (0x0000003789600000)
/lib64/ld-linux-x86-64.so.2 (0x0000003787400000)
libdl.so.2 => /lib64/libdl.so.2 (0x0000003788e00000)
librt.so.1 => /lib64/librt.so.1 (0x000000378b200000)

Now, by copy-pasting the path for libavutil, I verify that it is correct:

$ ls /u/goodfeli/ffmpeg/libavutil/libavutil.so.50
/u/goodfeli/ffmpeg/libavutil/libavutil.so.50

So that file exists. Now in MATLAB I check MATLAB's LD_LIBRARY_PATH variable:

 >> getenv('LD_LIBRARY_PATH')
ans = /soft/diro/share/matlabr2009b/sys/os/glnxa64:/soft/diro/share/matlabr2009b/bin/glnxa64:/soft/diro/share/matlabr2009b/extern/lib/glnxa64:/soft/diro/share/matlabr2009b/runtime/glnxa64:/soft/diro/share/matlabr2009b/sys/java/jre/glnxa64/jre/lib/amd64/native_threads:/soft/diro/share/matlabr2009b/sys/java/jre/glnxa64/jre/lib/amd64/server:/soft/diro/share/matlabr2009b/sys/java/jre/glnxa64/jre/lib/amd64:/u/goodfeli/ffmpeg/libavfilter:/u/goodfeli/ffmpeg/libswscale:/u/goodfeli/ffmpeg/libavdevice:/u/goodfeli/ffmpeg/libavformat:/u/goodfeli/ffmpeg/libavcodec:/u/goodfeli/ffmpeg/libavutil:/opt/lisa/os/cuda/lib64:/opt/lisa/os/cuda/lib:/opt/lisa/byhost/lib:/opt/lisa/os/lib/vtk:/opt/lisa/os/lib/intelmkl/lib/32:/opt/lisa/os/lib:/opt/lisa/os/lib64:/usr/local/lib:/usr/lib64/atlas/::/opt/lisa/os/panda/lib:/opt/lisa/os/lib32:/opt/lisa/byhost/lib32

This seems to be correct, it includes /u/goodfeli/ffmpeg/libavutil/ and by copy-pasting it I can verify there is no typo:

 $ ls /u/goodfeli/ffmpeg/libavutil/ | grep "\.so"

Any suggestions for what to check next? Thanks in advance.

Setting export LD_DEBUG=libs before invoking Matlab may provide clues.