[Freeswitch-users] Ring Group with Video Preview

Hey there.... Does anyone have experience with ring groups that show a preview (on all video capable phones) of a door phone? I have Fanvil (V67/I53W) and Grandstream video phones (GXV3480/GXV3240) connected to Fanvil(I64) and Axis(A8207) door phones. the door phones are able to send preview and the phones are able to receive previdw but the screens only show a black image - no live video. Jerry