SRT – Secure Reliable Transport

Contents:

• What is SRT protocol
• How SRT works
• Quick Guide to Setting Up SRT

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SRT: Secure Reliable Transport

SRT – a data transmission protocol based on UDP. It is an open-source project developed by Haivision.

SRT Alliance has over 500 members, including Haivision, Sony, Microsoft, Wowza, Panasonic, AVID, AJA, Matrox, BirdDog, Magewell, and Telestream.

Advantages:

• Low latency
• Original quality
• Stream security
• Firewall transparency
• Route redundancy
• Support for any codec

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Unlike other protocols, SRT checks for lost packets and retransmits them.

The protocol developers compared SRT and RTMP under real conditions:

• In latency tests, SRT was 2.5 to 3.2 times faster (depending on the distance between the sender and receiver).
• When using SRT, the maximum speed of 20 Mbps was maintained when transmitting data to any region in the world. With RTMP, the speed decreased with distance. For example, transmission from Europe to Australia showed a speed of no more than 2 Mbps.

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Quick Guide to Setting Up SRT

1. Install the Required Software

• Ensure you have installed and properly configured software that supports the SRT protocol, such as OBS Studio with the SRT plugin, VLC, or media servers like Wowza Streaming Engine.

2. Determine Connection Parameters

• IP Address and Port: Identify the IP address and port that will be used for data transmission. For example, 192.168.1.100:5000.
• Mode of Operation: Choose the SRT mode of operation:
  • Caller: Initiates the connection to another device.
  • Listener: Waits for an incoming connection from another device.
  • Rendezvous: Both devices simultaneously initiate a connection to each other.

3. Configure SRT on the Sending Side

• Enter the IP address and port of the receiver.
• Choose the “Caller” mode.
• Configure encryption settings if required (AES 128/256 bit).
• Set buffering and latency parameters according to the network quality.

4. Configure SRT on the Receiving Side

• Specify the IP address and port where the stream will be received.
• Choose the “Listener” mode.
• Configure encryption settings to match those on the sending side.
• Ensure that the firewall and router are configured to allow traffic through the specified port.

5. Check the Connection

• Start streaming on the sending side.
• Ensure that the stream is successfully received on the receiving side.

6. Monitoring and Optimization

• Use built-in monitoring tools in the software to check the quality of the stream, delays, and packet loss.
• Adjust buffering and latency settings as necessary to optimize transmission quality.

Example Configuration in OBS Studio:

On the Sending Side (Caller):

1. Open OBS Studio.
2. Go to “Settings” -> “Stream”.
3. Select “Custom” under the “Service” section.
4. Enter srt://:?mode=caller (e.g., srt://192.168.1.100:5000?mode=caller).
5. Configure encryption and buffering parameters if necessary.
6. Click “OK” and start streaming.

On the Receiving Side (Listener):

1. Open OBS Studio.
2. Go to “Settings” -> “Stream”.
3. Select “Custom” under the “Service” section.
4. Enter srt://:?mode=listener (e.g., srt://0.0.0.0:5000?mode=listener).
5. Configure encryption and buffering parameters if necessary.
6. Click “OK” and start receiving the stream.

This way, you can set up and use SRT for reliable and secure video streaming with low latency.