I installed libavcodec-extra module.  Still does not work. Now get:

2015-11-07 22:24:34.697659 [WARNING] mod_local_stream.c:658 Unknown source stereo, trying 'default'
2015-11-07 22:24:34.697659 [ERR] mod_local_stream.c:667 Unknown source default
2015-11-07 22:24:34.697659 [DEBUG] mod_conference.c:379 Auto recording file: /var/lib/freeswitch/recordings/CONFER_NAME_2015-11-07-22-24-34.mp4
2015-11-07 22:24:34.697659 [ERR] switch_core_file.c:240 Invalid file format [mp4] for [/var/lib/freeswitch/recordings/CONFER_NAME_2015-11-07-22-24-34.mp4]!
2015-11-07 22:24:34.697659 [ERR] conference_record.c:241 Error Opening File [{channels=2,samplerate=8000,vw=640,vh=480,fps=15.00}/var/lib/freeswitch/recordings/CONFER_NAME_2015-11-07-22-24-34.mp4]

I tried same settings with FSV format and it records something, but doubt I can find a video player to test it anything is actually recorded.

FYI, I had mod_local_stream errors before, but I assume they are unrelated to mp4 recording.

From: Calvin Walton <calvin.walton@kepstin.ca>
To: FreeSWITCH Users Help <freeswitch-users@lists.freeswitch.org>
Sent: Friday, November 6, 2015 3:39 PM
Subject: Re: [Freeswitch-users] writing to mp4 file not work

On Fri, 2015-11-06 at 10:23 -0600, Bradley Jokinen wrote:
> > [ERR] avformat.c:411 Could not open audio codec: Experimental feature
> It looks like it's trying to use the native AAC encoder instead of
> the
> VisualOn encoder. Install the libavcodec-extra package and see if it
> works after that.

One thing to note is that the native AAC encoder in ffmpeg is actually
significantly better than the VisualOn encoder in quality - see 
https://trac.ffmpeg.org/wiki/Encode/AAC
which describes the encoders the ffmpeg can use.

The issue is that enabling the native AAC encoder requires passing an
additional flag to allow the "experimental" codec. I suspect that
adding this flag would be a fairly simple patch to FreeSWITCH.

--
Calvin Walton <calvin.walton@kepstin.ca>