From Farshid Lashkari, "In many game engines it is common to set the W component of the tangent vector to -1 if the UVs are mirrored and 1 if not. I've updated the osgUtil::TangentSpaceGenerator class to do the same."
From Wang Rui, "The osgdb_ffmpeg plugin may not work with latest ffmpeg windows sdk and will say "The procedure entry point xxx could not be located in xxx.dll" instead. The following link describes the reason (maybe a certain optimization problem of the VS compiler):
http://forum.videolan.org/viewtopic.php?f=32&t=98097

After adding the /OPT:NOREF, the problem has gone.

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