call avdevice_register_all() throw exception can't found postproc-56.dll

[Mike]

How to reproduce: Buid dynamic dll by LGPL license, call avdevice_register_all() it will throw exception : can't found postproc-56.dll

I'm trying to build ffmpeg by LGPL licese, which will not create postproc.dll, but after that I can't use avdevice_register_all() function anymore, it will always throw exception show me that: postproc-56.dll is missing. I'm not sure is that a Bug or avdevice_register_all() require some GPL licese, then why I can build it? can't we remove it when build by LGPL? Is there any alternative choice?