Despite following the instructions and multiple tries, I cannot get Audacity to recognise the avformat.dll file under Edit>Preferences>Libraries or in the Export Audio dialog. See the attached report of a session where I tried to load the dll under Edit>Preferences>Library.
I am having the same problem and am using the 64 bit version of avformat.dll. Didn’t have the issue Audacity 3.1.2. I was able to get one MP4 converted to audio. Now Audacity is saying it cannot find the file. Have reinstalled everything and still cannot find the DLL. 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. I even copied the avformat.dll along with the outer DLL files into Audacity’s directory and still could not find it.
I reinstalled 3.1.2 and discovered this:
Launched Audacity 3.1.2
Looked at the preferences and Audacity had found avformat.dll in C:\Program Files\FFmpeg For Audacity
Right Click on an MP4 file
Left Click on Open With
Audacity gives error that it cannot find the avformat.dll
After a manual search for it. Audacity still cannot find it.
Click on File
Click on Open
Find an MP4
The MP4 Opens
If Audacity is already Open, I can right click on a MP4 file chose Open With → Audacity, and it will open properly.
Conclusion with 3.1.2, Audacity is trying the read the MP4 before it loads the avformat.dll.
I decided to reinstall 3.1.3. My conclusion remains the same as for 3.1.3. When one does the above Audacity operates the same way when I follow the above steps.
I believe that Audacity needs to wait for everything to load before it tries to load a file.
The log file contains (among other things) the following entry:
Error: Failed to load avformat-55.dll (error 193: %1 is not a valid Win32 application.)
After trying various things without success, I downloaded the FFmpeg zip file from the LAME website (https://lame.buanzo.org/#lamewindl > FFmpeg for Windows and latest Audacity versions > FFmpeg RECOMMENDED ZIP OPTION: ffmpeg-win-2.2.2.zip), which contains the 32-bit version of avformat-55.dll. After selecting this dll version in Preferences > Libraries, Audacity works as it should.
‘W32’ in the error message refers to Windows 32-bit. Audacity 3.1.3 is 64-bit (at least that what is claimed) and the recommended avformat.dll is 64-bit, but apparently the code actually expects a 32-bit version.