Be sure to update the FFmpeg library if you use it.
FFmpeg 2.2.2 should be used with the latest version of Audacity.
FFmpeg 0.6.2 for Audacity -> versions lower than 2.0.6
FFmpeg 2.2.2 for Audacity -> versions 2.0.6 and higher
FFmpeg 2.3.x -> versions 2.0.6 and higher
FFmpeg 2.4.x and later is not supported, except for exports using Audacity's command-line encoder.
Audacity Manual FAQ: Installation, Startup and Plug-ins
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.