export FFBUILD_FLAGS="--enable-ffnvcodec --enable-dxva2 --enable-amf --enable-libmfx"
export FFBUILD_PLATFORM="win"
export MFX_HOST=x86_64-w64-mingw32

FFMPEG_OS=mingw32 OPENH264_ARCH=x86_64 OPENH264_OS=mingw_nt CC=x86_64-w64-mingw32-gcc CXX=x86_64-w64-mingw32-g++ AR=x86_64-w64-mingw32-gcc-ar bash build.sh --arch x86_64