Date: Thu, 23 Oct 1997 11:14:12 -0700 (PDT) From: lamaster@george.arc.nasa.gov To: multimedia@FreeBSD.ORG Subject: Re: [murali@vsofti.stph.net: Videoconf. solution req.] Message-ID: <199710231814.LAA27295@george.arc.nasa.gov>
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On Mon, 20 Oct 1997, Wolfram Schneider wrote: > Is there any Video Conferencing solution you know of on freeBSD. > It should work both on Ethernet LAN and SLIP or PPP WAN at 28.8K. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^ I assume that you realize that you can't satisfy both requirements within the same session. [At the present time - there is research going on with layered codecs, etc., but, for the moment, you have to choose your settings to match the lowest-bitrate.] The standard Mbone tools (sdr; vic; vat or rat; wb or nte) work fine over Ethernet, and even passably well over ISDN with some care used in choosing codecs (e.g. DVI4 or GSM audio) and parameters (keeping video bitrate down). Over 28.8, however, you have very limited options. One option is to use proprietary hardware and software, rather than FreeBSD. Even then, quality is limited. The other option is to go ahead and use vat/rat, with the lpc4 codec. I have used it before under vat, (on an SGI Irix system - I haven't tested it on FreeBSD or rat) and it worked OK for me. LPC4 sounds tolerable for speech, like a moderate-quality AM radio signal listened to over a portable radio speaker - in other words, it is clear enough, but is obviously a little unnatural. Music sounds absolutely terrible. GSM sounds better, but, given SLIP/PPP overhead, I doubt if there would be enough bandwidth left over for much video. You have no option but to severely limit your video bandwidth. Using vat with either H.261 or nv (at very low bitrates, I prefer using nv or H.261 at a quality 4 setting, using "small picture", setting the bitrate limit to 1 fps and 10 kbits/sec, use "sending slides" mode. In other words, forget about trying to capture facial movement, and just get a sequence of stills. (Others may differ with this choice.) With your video bitrate set this low - that is, to 10 kbits/sec, you *might* barely have enough audio bandwidth left over to use rat with lpc+lpc redundancy, which would likely be a good thing using SLIP/PPP over 28.8 modem. Experiment. The "rat" audio tool is not quite as solid/debugged as vat, but, the redundancy feature should make a big difference in low bitrate-lossy situations. This is unavoidably an experimental situation in which you will have to actively choose settings which are, at best, usable. In other words, if you already have the systems at either end, it is worthwhile to try, although, since this is experimental, you certainly wouldn't want to "sell" a solution to an end-user. If you were thinking about one of the new, very-low-bitrate video codecs, AFAIK, no support is expected any time soon, because, even though there are standards, they involve patented, proprietary technology that has to be licensed. Corrections welcome. -Hugh LaMaster Hugh LaMaster, M/S 258-5, ASCII Email: hlamaster@mail.arc.nasa.gov NASA Ames Research Center Or: lamaster@nas.nasa.gov Moffett Field, CA 94035-1000 No Junkmail: USC 18 section 2701 Phone: 415/604-1056 Disclaimer: Unofficial, personal *opinion*.
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