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. 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 do not install FFmpeg from the links below and as long as you do not specify the FFmpeg you want Audacity to use in Libraries Preferences. https://manual.audacityteam.org/man/installing_ffmpeg_for_windows.html