`avformat_open_input` not found

Created by: luswangl2013

Hello, I am following the guideline in https://docs.pupil-labs.com/#windows-pupil-labs-python-libs-from-source when building pyav. I got this error as a result.

We didn't find avformat_open_input in the libraries. We look for it only as a sanity check to make sure the build process is working as expected. It is not, so we must abort.

Please open a ticket at https://github.com/mikeboers/PyAV/issues with the folowing information:

PyAV: 0.4.1.dev0 b'v0.4.1-3-gcaee136a' Python: b'3.6.3 (v3.6.3:2c5fed8, Oct 3 2017, 17:26:49) [MSC v.1900 32 bit (Intel)]' platform: Windows-10-10.0.16299-SP0 extension_extra: include_dirs: [b'include', b'D:\pupil_v1.8\ffmpeg-20180809-eb1860e-win64-dev\ffmpeg-20180809-eb1860e-win64-dev\include', b'D:\python3\include', b'D:\python3\include'] libraries: [b'avformat', b'avcodec', b'avdevice', b'avutil', b'avfilter', b'swscale', b'swresample'] library_dirs: [b'D:\pupil_v1.8\ffmpeg-20180809-eb1860e-win64-dev\ffmpeg-20180809-eb1860e-win64-dev\lib', b'D:\python3\libs', b'D:\python3\PCbuild\win32'] extra_link_args: [b'/OPT:NOREF'] config_macros: PYAV_COMMIT_STR="b'v0.4.1-3-gcaee136a'" PYAV_HAVE_AVCODEC_SEND_PACKET=0 PYAV_HAVE_AVFORMAT_ALLOC_OUTPUT_CONTEXT2=0 PYAV_HAVE_AVFORMAT_CLOSE_INPUT=0 PYAV_HAVE_AVFRAME__MB_TYPE=0 PYAV_HAVE_AV_CALLOC=0 PYAV_HAVE_AV_FRAME_GET_BEST_EFFORT_TIMESTAMP=0 PYAV_HAVE_AV_OPT_TYPE_BOOL=1 PYAV_HAVE_LIBAVRESAMPLE=0 PYAV_HAVE_LIBSWRESAMPLE=1 PYAV_VERSION=0.4.1.dev0 PYAV_VERSION_STR="0.4.1.dev0" inline=__inline