How to convert/export WAV to AC3?

I think this should be fairly simple.
I have tried to load into Audacity (still using 2.0.3) my 2 channel PCM WAV 16bit/44.1 audio, and export as 16bit 48000 AC3 as I plan to mux the audio with video to make a DVD, however when I go to export and try to select AC3 it says I need to download ?FFMPEG libraries? or something like that?, sorry I’m not at my PC and can’t think of exactly what it said but I’m sure it’s a common default and people will understand my question.
I never usually work with ‘video’ so although have done a lot of audio editing I haven’t worked with AC3 before.
Could somebody please give some advice/help on what and where do I download from and how do I install?
Thanks in advance for any help!

Many common formats are encumbered by patent and/or other licensing issues that prevent us from including encoders/decoders by default… However, Audacity is able to use appropriate versions of “FFmpeg” to greatly increase the number of supported formats. See here for more information:

Thank Steve.
Will converting the WAV to AC3 sound any better than converting the same WAV to 384kbps MP2?, there probably wouldn’t be any audible difference between the AC3 and 384kbps MP2 would there?

Probably not,