Having been "involved" (and I use that term loosely) with
the openH323 effort for a couple of years now, I will
second the statement that openH323 is rather well
implemented. But it is not for the faint of heart.
Alternatively, for clients running on Mac or Windows, QuickTime 4 includes a solid (or so I'm told) implementation of H.323 (and the corresponding format for video) -- both the codecs and the underlying I/O using either TCP or RTP.
�Jens
