Yes, and it needs to be set in the dialplan, because once the call is going out a trunk, even if you have “videosupport=no” on your trunk settings, Asterisk has already negotiated video with your video phone.
Here’s how I solved it. In /etc/asterisk/extensions_custom.conf, in [from-internal-custom], I added extensions that match my PSTN calling patterns, and explicitly set the codecs. (By not including video codecs, video is not negotiated on the first call leg.)
; prevent black video screen on PSTN calls (outbound) exten => _1NXXNXXXXXX,1,Set(__SIP_CODEC=ulaw) exten => _1NXXNXXXXXX,n,Goto(outbound-allroutes,${EXTEN},1) exten => _NXXNXXXXXX,1,Set(__SIP_CODEC=ulaw) exten => _NXXNXXXXXX,n,Goto(outbound-allroutes,${EXTEN},1) exten => _011.,1,Set(__SIP_CODEC=ulaw) exten => _011.,n,Goto(outbound-allroutes,${EXTEN},1)
Similarly, I removed video on calls coming in from the PSTN trunk:
; prevent black video on calls coming in from PROVIDER [from-trunk-PROVIDER-custom] exten => _.,1,Set(__SIP_CODEC_OUTBOUND=ulaw) exten => _.,n,Goto(from-trunk-sip-PROVIDER,${EXTEN},1)
and set the context in your trunk setting, context=from-trunk-PROVIDER-custom
replace PROVIDER
with your Outgoing PEER Details name.