Sorry to sound like a broken, well, record.
I am trying to import an M4a file into Audacity 2.3.2, and have downloaded the requisite FFmpeg-win-2.2.2-exe as per the Audacity instructions. After installing it and re-opening Audacity, it is still stating ‘library not found’.
However, it evidently has found the library as when I click on ‘locate’ it automatically finds C:\Program Files (x86)\FFmpeg for Audacity\avformat-55.dll. When I hit open and ok and ok, it still says ‘library not found’.
I’m running Windows 10 64 bit os so it should be compatible with my os and my version of Audacity.