Forwarding RTSP port to multiple IP Cams

[Rover <rover@xxxxxxxxxxxxxxxx>]

I would like to hear from those of you who operate several IP cameras
behind a router's firewall which all require forwarding the same RTSP
port 554. How do you configure your router for that so you can watch the
live video stream from outside (the WAN side?)

Most cams allow the use of not just the default port 80 for their HTTP
interface, so the different HTTP ports can easily be forwarded to the
right LAN IP of each cam, but as far as I know, they don't allow
different RTSP ports to forward to each cam. Yet, I know such cameras do
operate out there so I wonder how. I would appreciate any help in this
issue.