Niche question, I know, but possibly someone has an idea.
Lets say a PSTN call comes in, and I answer it to find I need to transfer it to another extension. All the extensions are video enabled, so when I speak to the new extension to tell them they have a call - that transfer announcement is a video call.
When I complete the transfer, there’s no more video stream as the call is from the PSTN, so the phone displays the last frame it received, normally my face with a stupid look on it 
This seems to be because the (second) extension received a video call and then the RTP switches over to a stream without a video component. I don’t know how other video endpoints behave when this happens, but it would be interesting of someone could tell me?
Anyway, to the point - is there a way to get asterisk to tell the endpoint that it should no longer expect video? Even if there is, I don’t know if our phones would behave in the expected way but it’s a starting point.
Thanks.