Re: Audio & Video over phone lines with 28K modems

Jason Williams (streak@ccwf.cc.utexas.edu)
Sat, 30 Aug 1997 06:30:50 -0500 (CDT)


On Thu, 28 Aug 1997, Richard Ashley wrote:
> I want to transmit good audio and half-decent (could be B&W) video to a
> bunch of students over phone lines using 28K modems.

Define "bunch of".. 20? 50? 200?
With CU-SeeMe, it's hard to do both audio and video at the same time on
28K modems. It's my understanding that the audio takes precedence, so
technically when you speak, and someone doesn't have enough bandwidth, it
should pause the video itself. The idea is that high packet loss with
audio can prevent you from understanding what's being said whereas high
packet loss in video just slows the video down a bit. That's how I
understand it anyway.

> I'm thinking of using
> the White Pine CUSM, because the whiteboarding sounds useful

I don't know much about other people, but I've never had much success with
whiteboarding on a modem.

> I've heard that it does a better job with compression than the Cornell
> version. I would set it to B&W video (I assume I can do that), and (if
> possible) allocate most of the bandwidth to audio.

As far as I know, it doesn't do any better job with compression of the
grayscale codec than Cornell does. It does allow compressed color..but
that's another story. The Mac version I believe does let you set the min,
max, and max without audio so you can regulate the bandwidth used for
audio.

> 1. Must I have the students buy the WP client also? Since they also have
> to buy a textbook, that makes this course really expensive for them. Some
> posts I have seen here seem to indicate that the WP codecs primarily help
> with the color video.

If you use the lower-bandwidth audio codecs or the whiteboard, everyone
will need the WP client. I'd just go with the Cornell client and move
from audio to video with a verbal phrase "Ill stop talking and cut the
video on now" or something. Modems just don't have the bandwidth CU
needs.

> 2. Is this feasible at all? The video doesn't have to be as good as the
> audio, but I don't want to have to freeze it altogether whenever I am
> talking.

you could try the low bandwidth audio codecs of the WP client so you don't
have to freeze. That works out ok but then it also requires everyone have
a somewhat modern computer and also the WP client. I do audio all the
time on my modem with Cornell but I also pause the video.

> 3. If it does work, can I expect to be able to use White Pine's
> whiteboarding feature also?

I'd say no...whiteboarding on a modem is just way too slow..and an email I
got from White Pine mentioned the fact that whiteboarding was meant for
higher bandwidth connections.

> 4. Lastly, is there anything about my plans that really requires the WP
> reflector, or will I be better off using Brian Goddette's reflector?

You'll need some sort of reflector. I'm not sure how well Brian Godette's
reflector handles the whiteboard and the lower bandwidth audio codecs. It
should be ok but I haven't played with that part of it. If you have
around 40-50 people, I know the White Pine 2.1 reflector has special
"observer" and "observer broadcast" modes that allow everyone on the
reflector just to watch one participant. That reduces the overhead of
interaction between everyone else if you wanted that. I'm not sure what
the Enhanced Reflector has in that respect except the monitor conferences.

If you didn't HAVE to do both audio and video at the same time, I'd go
with Cornell and pause the image when you speak. With that requirement,
the only way I can see doing it with CU is with the lower quality audio
codecs..forcing everyone to buy the WP client.

--
streak@ccwf.cc.utexas.edu    * Jason Williams -- Austin, Tx.  |     |
streak@mail.utexas.edu       * University of Texas at Austin  | ___ |
streak@cs.utexas.edu         * BS Computer Science             \_|_/
*************** http://ccwf.cc.utexas.edu/~streak/ **************|