Need Help for a Video-phone

Kahan, Joseph M. (JKAHAN@ssf4.jsc.nasa.gov)
Wed, 15 Feb 1995 13:44:00 -0500


First, I want to complement everyone on the CU-SeeMe staff. This tool is
fantastic and has enabled me to start work developing a Mac based Video-
phone.

I have been using your tool for about 6 months now and have reached a stage
where I need some specific help.

Test Equipment:

(2) 28.8 Kbps Modems
(2) QuickCams
(1) Quadra 610 (Medium frame rate testing)
(1) Perform 405 (Low frame rate testing)

Just to let your staff know, video transmission using CU-SeeMe over a couple
of 28.8 Kbps modems works pretty good. But, the bottom-line is, "It can be
done..."

Test notes:

If I could, I would like to correct a statement published by your team about
"not" being able to transmit audio plus video over a pair of 14.4 Kbps
modem. With just a few minor changes on the configuration, audio at the 16K
format is possible over a 14.4 Kbps modem. It is choppy, but it is
recognizable.

Issue - I notice that the frame rate transmission will decrease if the
contrast and lighting is turned up or down for a camera. I thought this
might be a factor of the Connectix QuickCam, but it seems to be a problem
even when the picture is solid black. Also, Frame rates seem to decrease
over time from the original saved filed, varying from 10-12 frame per second
down to 3-4 frames per second. Could you please explain how these two
setting are used in your program so I can understand how to work around this
effect.

Development Comments:

In order to send data at lower rates (i.e. 4-14 Kbps per end point), a few
changes in your code would be greatly appreciated. These changes would also
help network data throughput issues for subscribed users.

1) Change the present lowest transmission rate to be 0 and variable in
stages of 2 Kbps instead increments of 10 Kbps. This change
would help for selecting suitable modem rates.
2) Change the present highest transmission rate to be 0 and
variable in stages of 2 Kbps instead increments of 10 Kbps. This
change would help for selecting suitable modem rates.
3) Provide a lower Audio compression such as a 4800 or 9600 standard. I
can supply some of these if you want them.
4) Throw away video packets that exceed the maximum
throughput allocation for a combined A/V transmission while
audio data is being compressed. This should prevent freeze-
framing while audio data is being transmitted and should
provide the user with smoother graphics imaging.

Future Request - In recent publications of CU-SeeMe, I noticed a statement
concerning incorporation of a better audio compression scheme. The
publication went on to state that it will only be good for PPC's and fast
PC's. Could you please try to develop something for the 68K side of the
house. It would greatly be appreciated...

Please feel free to contact me at JKahan@SSF4.jsc.nasa.gov. Again, thank you
for your time. "See" you later.

J Kahan