It's simple. when you use the rtmp parameters from html server sends a 302 redirect AMF packet which contains the new url.
Code:
Property: <Name: level, STRING: error>
Property: <Name: code, STRING: NetConnection.Connect.Rejected>
Property: <Name: description, STRING: Connection failed: Application rejected connection.>
Property: <Name: ex, OBJECT>
Property: <Name: redirect, STRING: rtmp://live4.seeon.tv:1935/edge>
Property: <Name: code, NUMBER: 302.00>
Use this URL instead of original URL to download successfully with
rtmpdump. rtmpdump doesn't handle redirects automatically.