If you get my build of RtmpSrv, you can use the "--printonly" option.
Code:
$ rtmpsrv --help
This is just a stub for an RTMP server. It doesn't do anything beyond
obtaining the connection parameters from the client.
-h, --help Prints this help screen.
-c, --port port Overrides the port in the rtmp url
-i, --printonly Print RtmpDump command and exit
-z, --debug Debug level command output.
-N, --version Print version information and exit
github.com/svnpenn/rtmpdump/downloads