On 5/6/20 7:33 AM, Chris Howard wrote:
At my current job we were looking into delay timings of video systems.
We were doing end-to-end measurement by putting a time display in front
of a monitor
and have the camera show both the time display and the monitor.
It looks a bit like the old infinite mirror.
If you arrange things right it shows two images of the time display
one that lags the other. And the difference is the round-trip delay.
When I'm on Skype and my co-worker shares his screen, I can see my own
camera image come back to me in a similar way.
So if I were to point my camera at a rolling time display, he shares
that image back to me, I could take video (with a second camera)
of both the live time display and the delayed.
OK, but this is sort of a manual measurement.
Ditto for looping back a tone and using an oscilloscope.
What I was wondering about whether there's a way to do it in an
automated way - fire up N webex/zoom/skype "conferences" solely for the
purpose of testing.
For instance, this morning was a "very bad day" for Cisco's webex, and
it would be interesting to collect performance statistics over time.
And to explore the nature of the anomalies - are they "packet drops",
"resends", random delays, etc.
Much like the folks did in the early days of NTP development.
Some others had suggested ways of doing it "during a call" which is
interesting. I wonder if there is a way to intercept the video and
audio traffic within the OS and "tee" it off to a analyzer.
Last time I looked at doing that kind of thing, I was foiled at every
turn with Windows, because of their sensitivity to digital rights
management - you don't want someone "tee"-ing copyrighted material to
storage and redistributing. I would expect that Mac OS X is no
different. It may well be that the conferencing applications don't
bother to use the "protected content" capability. I know that folks at
work have found ways to chromakey their webcam feed before feeding it
into the Webex video input.
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