* in_ffsox-2a-0.6.1.exe is the plug-in's NSIS
(http://nsis.sourceforge.net/) based installer containing also tiny
versions of the needed third party DLLs. You should update especially
avcodec-58.dll and avformat-58.dll following the instructions
from the project's homepage at
http://in-ffsox.sourceforge.net/#installation.
* in_ffsox-2a-0.6.1.dll.7z contains the bare plug-in without any third
party DLL which you need to install yourself following the instructions
at http://in-ffsox.sourceforge.net/#installation.
* in_ffsox-2a-0.6.1-src.tar.gz contains the plug-in's sourcecode.
* in_ffsox-2a-0.6.1-src-foreign.tar.gz contains the plug-in's third party
source code especially the FFmpeg snapshot for which this plug-in
version was compiled.