I’m only going by what I’ve read in a few places on the Internet. Here are a few examples. I thought this could be the solution, but you may be right in that plugins are not mentioned in these posts:
“The optional FFmpeg library allows Audacity to import and export a much larger range of audio formats including M4A (AAC), AC3, AMR (narrow band) and WMA and also to import audio from most video files.
Because of software patents, Audacity cannot include the FFmpeg software or distribute it from its own websites. Instead, use the following instructions to download and install the free and recommended FFmpeg third-party library”.
Also: https://www.youtube.com/watch?v=_1rcvBerl9k
And ffmpeg for Audicity for windows: http://ffmpeg-for-audacity-on-windows.software.informer.com
And:
"The optional FFmpeg library allows Audacity to import and export a much larger range of audio formats including M4A (AAC), AC3, AMR (narrow band) and WMA and also to import audio from most video files.
Because of software patents, Audacity cannot include the FFmpeg software or distribute it from its own websites. Instead, use the following instructions to download and install the free and recommended FFmpeg third-party library.
Warning icon FFmpeg 2.2.2 for Windows and Mac from the links below should be used with the latest version of Audacity.
The previous FFmpeg 0.6.2 for Audacity will not be recognized by Audacity 2.0.6 and later, and FFmpeg 2.2.2 will not be recognized by Audacity versions before 2.0.6.
FFmpeg 2.3.x shared libraries should also be recognized by Audacity 2.0.6 and later. FFmpeg 2.4.x and later is not supported, except for exports using Audacity’s command-line encoder.
Advanced usage: If you already have Audacity-compatible FFmpeg 2.2.x or 2.3.x shared libraries in the system PATH, Audacity will use those as long as you don’t install FFmpeg from the links below and as long as you don’t specify the FFmpeg you want Audacity to use in Libraries Preferences".
There are many more sites that describe the relationship between Audacity and ffmpeg. I’m not an expert, but I thought I’d give ffmpeg a try based on these readings.
Beats me.