How install ffmpeg plugin to make audacity support m4a

Step1: 
RECOMMENDED Installer Package for Windows: Lame_v3.99.3_for_Windows.exe 


Step2: 
FFmpeg RECOMMENDED ZIP OPTION: ffmpeg-win-2.2.2.zip


Step 3: 
Edit->preference->Library-> locate the path for ffmpeg:
for example:
OneDrive\tools\ffmpeg-win-2.2.2\avformat-55.dll


Reference:
[1] https://lame.buanzo.org/#lamewindl
[2] https://videoconverter.wondershare.com/convert-mp3/convert-m4a-to-mp3-audacity.html