<p>I need an encoder that can convert mp3 files to he-aac (aka aac+).
So far the best one I have found is <a href="http://www.nero.com/eng/down-ndaudio.php" rel="nofollow noreferrer">nero aac encoder</a> . 
I have two problemes with it :
  - Only one input format : wav . It is a little bit slow to transform mp3 files to wav and then to he-aac.
  - a free license for <strong>non commercial</strong> use.</p>

<p>Too bad ffmpeg does not support he-aac ...
There is a commercial solution, <a href="https://flix.on2.com/" rel="nofollow noreferrer">on2 flix</a>, but it seems to be a golden hammer for the simple task I need to do.</p>

Nero AAC is the only one as far as I know.  Even if FAAC supported HE-AAC it would be useless, since as an encoder its pretty awfully designed and its quality is not even competitive with LAME, let alone a good AAC encoder.
Kostya on the FFMPEG team is currently working on an AAC encoder but it has a long way to go--its not ready for primetime with LC-AAC, let alone HE-AAC (its not even committed to the repository yet).  The first step before anything will be to get the ffmpeg decoder to support HE-AAC; currently it can only be decoded through FAAD.
I don't believe there is
any
HE-AAC encoder on any platform with a more permissive license than Nero's at this point in time.