Can I stream from multicast to one client with ffmpeg?

I'm trying to do streaming from a source (tv box transmitting in multicast in this source rtp://@X.X.X.X:Y) to Internet (to my mobile phone as example or another device inside of my LAN) but I can not achieve it. The command I'm using is something like this ffmpeg -i rtp://@X.X.X.X:Y -vcodec copy -f mpegts udp://127.0.0.1:1234 But it does not work as I expected, I mean, I'm able to open vlc and play the streaming in the same machine I'm running ffmpeg but not in another machine in the same LAN. Somebody can help me? Thank you! EDIT: Finally I solved installing a software called "udpxy" that forwards multicast content to the clients. I installed in a raspberry and it works perfect for this purpose. Thank you for all your explanations. It helped me to understand what I want to do and the limitations I have using a transcoder. I guess I can do the same with udpxy with ffmpeg but I can publish directly the TV Box IPs.