in my environment (kamailio - http API for retrieve destinations - rtpengine) it is used a lot parallel forking, the flow is as follows:

A -> INVITE -> Kamailio -> http API/rtjson / t_relay -> Kamailio -> client B / C / D (only one accepting the call)

Kamailio loops to itself to have a parallel forking, it involves rtpengine correctly.

Both audio and video work during call.

The issue comes with one of destinations sending 183 with SDP, the caller will send then a video preview as early media before call is established. 

I noticed that only the first one "asking" for early media is receiving this video preview (sometimes none of clients requesting it), all others are ignored by caller.  

This is a case of 1-to-many, I searched a lot about this but it seems at least not working or not supported, could you confirm that there is no configuration trick possible to make work this early media to many destinations? 

Another issue in above call flow, is that if client B is receiving correctly this early media video and client C answers the call (200OK) client C does not see any video, audio working and video is completely missing from rtp, only a reinvite makes possible to see video. Is this a client side only issue (so only solution is the reinvite) or there is something missing on my kamailio configuration? 

Thanks

Filippo