Failing to get SRTP to work

[Ben Rush]

I've looked at the following:

https://lists.freedesktop.org/archives/gstreamer-bugs/2017-August/204646.html

https://stackoverflow.com/questions/7669240/webcam-streaming-using-gstreamer-over-udp

https://stackoverflow.com/questions/44458012/gstreamer-srtp-for-full-hd-h-264-video
http://gstreamer-devel.966125.n4.nabble.com/SRTP-audio-encryption-problems-td4686501.html

...but for whatever reason, I still cannot get SRTP to work at the command
line (Windows).  What I mean by that is running both a "server" and a
"client" and having them communicate with each other over SRTP. The most
insightful comment was:

 "You have to connect to the "request-key" signal and return appropriate
caps there, or make sure to set complete caps on the stream via udpsrc.
Your caps are missing the "roc" field at least."

...in the last link above. But, I'm doing what's suggested there (I
believe, anyway). Here are my commands:

 Server == gst-launch-1.0 videotestsrc ! videoconvert ! openh264enc !
rtph264pay ! application/x-rtp, payload=(int)96 ! srtpenc
key=987654321001234567890123456789012345678901234567890123456789
rtp-cipher=aes-128-icm rtp-auth=hmac-sha1-80 rtcp-cipher=aes-128-icm
rtcp-auth=hmac-sha1-80 ! udpsink host=127.0.0.1 port=5000

Client == gst-launch-1.0 udpsrc port=5000 caps="application/x-srtp,
payload=(int)96,
srtp-key=(buffer)987654321001234567890123456789012345678901234567890123456789,
srtp-cipher=(string)aes-128-icm, srtp-auth=(string)hmac-sha1-80,
srtcp-cipher=(string)aes-128-icm, srtcp-auth=(string)hmac-sha1-80,
roc=(uint)0" ! srtpdec ! rtph264depay ! h264parse ! openh264dec !
videoconvert ! autovideosink

To test, I fire up the "server" first and it spins up and waits. That part
appears to be correct. However, when running the "client", I get a spew of:

0:00:02.197235000 23116 000001FF981D7040 WARN                 srtpdec
gstsrtpdec.c:992:request_key_with_signal:<srtpdec0> Could not get caps for
stream with SSRC 1451949075

Ok. So, to do some digging. The code is here:
https://github.com/agx/gst-plugins-bad/blob/master/ext/srtp/gstsrtpdec.c.
The comment here:
https://github.com/agx/gst-plugins-bad/blob/74bcc835aa7d74e83e69eafe83869c1be72195a5/ext/srtp/gstsrtpdec.c#L286
seems to indicate maybe the plugin is unable to determine the keys and
cipher information it needs. This seems to jive with the comment I
mentioned earlier (that I need to then put them as caps on the udpsrc,
therefore) ... but I'm doing that. Do you spot anything wrong with my caps?
I assume the mechanism is srtpdec is signaling to the pipeline to give to
it the parameters it needs, but it's not getting a response or getting
something invalid.

Thanks in advance.
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