Meaning of ampersand @ in VLC

[prideaux90]

Few related questions, I am trying to understand the syntax for ampersand @, for example: rtp://@:port

So I unicast to a remote PC (192.168.1.69) using ffmpeg;

Then I can go on the remote PC and use VLC
Open Network Stream
rtp://@:1234 ** It works
rtp://192.168.1.69:1234 ** It works

But If I use the local address
rtp://127.0.0.1:1234 ** does NOT work
rtp://@127.0.0.1:1234 ** does NOT work

But using FFplay (from ffmpeg) it works !
ffplay rtp://127.0.0.1:1234

And I saw in a forum answer someone using
rtp://xxx.xxx.xxx.xxx@yyy.yyy.yyy.yyy:1234 (where x and y are just different IP addressed !
what is the meaning of this ?

[Rémi Denis-Courmont]

Ampersand separates source and destination.