RTSP Port Forwarding

RTSP forwarding.md

RTSP forwarding using UDP transport

This is based on https://gist.github.com/corenel/db98113b346717e114864538996134a8, however, adapted to work over UDP transport, rather than TCP, which makes it a bit more complicated, and requires the client to fix the UDP ports used.

Assume we have the following network environments:

• Forwarder device:
  • eth0 (192.168.144.25): for camera access
  • wlan0 (192.168.1.54): for PC access
• IP Camera：192.168.144.25
• PC：192.168.1.51

On forwarder device, we want to forward the 8554 port (used for RTSP) of the IP camera (192.168.144.25) to the same port in 192.168.1.54.

1. Run rtsp-forwarding.sh

2. You can use the following command to play forwarded RTSP stream on PC:

gst-launch-1.0 rtspsrc location=rtsp://192.168.1.54:8554/main.264 latency=0 protocols=udp port-range=25004-25005 ! rtph264depay ! avdec_h264 ! xvimagesink

The port range needs to be fixed, in order for UDP to be routed back to the client.

rtsp-forwarding.sh

#!/usr/bin/env bash
#
# This script is based on:
# https://gist.github.com/corenel/db98113b346717e114864538996134a8
#
# The original script only supported forwarding using TCP transport but not
# UDP transport.
#
# The issue is that UDP traffic is set up from the client in the RTSP SETUP
# call. In there, it sets the UDP port on which it wants to receive the RTP
# traffic. Most RTSP clients choose this port randomly, and so the forwarder
# doesn't know which ports to forward from RTSP server to the client.
# We can work around this by fixing the UDP port on the client side, e.g.:
#
# gst-launch-1.0 rtspsrc location=rtsp://192.168.1.54:8554/main.264 latency=0 protocols=udp port-range=25004-25005 \
#   ! rtph264depay ! avdec_h264 ! xvimagesink

set -e

enable_forwarding () {
  ip=$1
  port=$2
  nic=$3

  # Forward traffic from interface nic and port to the IP of the camera.
  sudo iptables -t nat -A PREROUTING -p tcp -i ${nic} --dport ${port} -j DNAT --to-destination ${ip}:${port}
  sudo iptables -t nat -A PREROUTING -p udp -i ${nic} --dport ${port} -j DNAT --to-destination ${ip}:${port}

  # Accept traffic from camera.
  sudo iptables -A FORWARD -p tcp -d ${ip} --dport ${port} -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
  sudo iptables -A FORWARD -p udp -d ${ip} --dport ${port} -m state --state NEW,ESTABLISHED,RELATED -j ACCEPT
}

# Parameters
CAMERA_IP=192.168.144.25
CAMERA_NIC=eth0

CLIENT_IP=192.168.1.51
CLIENT_NIC=wlan0


# Enable ipv4 forwarding in system side
sudo sysctl net.ipv4.ip_forward=1

# Flush existed rules of iptables
sudo iptables -F
sudo iptables -t nat -F
sudo iptables -X

# Enable port forwarding
enable_forwarding ${CAMERA_IP} 8554 ${CLIENT_NIC}
enable_forwarding ${CLIENT_IP} 25004 ${CAMERA_NIC}
enable_forwarding ${CLIENT_IP} 25005 ${CAMERA_NIC}

# Enable routing
sudo iptables -t nat -A POSTROUTING -j MASQUERADE