I've installed Yeastar S20 and cant make video call by my Panasonic KH-HDV430.
Codec H.264 is installed on S20
Panasonic KH-HDV430 uses H.264 too.
Other device is Beward DS03MP intercom and it uses H.264 too.
Grandstream and Yeastar phones make videocalls correctly.
Panasonic makes only audio call, showing black screen.