Okay, so there is a bug in omcproxy that causes the segmentation fault. It has been fixed in this PR https://github.com/openwrt/omcproxy/pull/10
I tried it and it works. But seems the project seems dead, I instead use smcroute.
I follow the instructions here [How To] Cast to a LG TV in another VLAN with fw4 (ssdp and a bit of mdns)
The only change between smcroute and mcproxy is that I had to add a rule in firewall to increase the ttl of the broadcast packages.
Hope this help