I don't know the answer however I suggest you review the X264 encoder source to see how it is done.
 
Here is the answer to the reason why the x264 does not return an NAL less than 1.4kb and a patch to fix it.
http://mailman.videolan.org/pipermail/x264-devel/2009-July/005989.html
Simon
 
From: h323plus-bounces@lists.packetizer.com [mailto:h323plus-bounces@lists.packetizer.com] On Behalf Of ooi khai chin
Sent: Wednesday, 25 November 2009 1:02 AM
To: h323plus@lists.packetizer.com
Subject: [h323plus] H264 Plugin in H323Plus

Hi All,

regarding the H.241 documentation, it mention that H.264 plugin in H.323 only support single NAL mode. Then, I refer the RFC 3984, it state that single NAL mode only support type 1-23 NAL unit, no FU-A, no FU-B, ...

Currently, I am using H.264 hardware encoder which used baseline profile, not libx264.

My H.264 encoder(hardware) will only return the whole encoded data and it's total length, not each  NAL and it's length.

So, how can I make it comply to H.323 if no fragmentation is allowed in H.323?

Thanks.