thank you very much for your answer. I will try to use rtpengine module.

As I can see from logs, kamailio is sending correctly data to rtpengine but rtp engine

failed to parse IPv6 address from SDP body.

I'm sending flags to rtpengine according to the howto from link I've posted in the original post.

This is the part of the config:

if (!(isflagset(FLT_NATS) || isbflagset(FLB_NATB)
			|| isbflagset(FLB_V4V6)))
		return;
 
	if(isbflagset(FLB_V4V6)) {
		if(af==INET6) {
			rtpproxy_manage("FAEI");
		} else {
			rtpproxy_manage("FAIE");
		}
	} else {
		if(af==INET6) {
			rtpproxy_manage("FAEE");
		} else {
			rtpproxy_manage("FAII");

I'm not sure if I need to inform rtpengine that in SDP body will be IPv6 address.