I even copied the avformat.dll along with the outer DLL files into Audacity’s directory and still could not find it. I have manually pointed Audacity to the DLL in my case C:\Program Files\FFmpeg For Audacityavformat.dll When I restart 3.1.3, it still says cannot find avformat.dll. Have reinstalled everything and still cannot find the DLL. Now Audacity is saying it cannot find the file.

I was able to get one MP4 converted to audio. I am having the same problem and am using the 64 bit version of avformat.dll.