SRT Protocol: The Complete Guide to Secure Reliable Transport Protocol

Phil Henken
Phil Henken
Updated April 24 2022
SRT Protocol
Phil Henken
Phil Henken
Updated April 24 2022

SRT Protocol: The Complete Guide to Secure Reliable Transport Protocol

If you follow video streaming technology, you might be hearing about SRT protocol, that is, the “Secure Reliable Transport” protocol, or even the SRT Alliance. You might not have heard too much though, because at around 4 years old, SRT protocol is still brand new, at least as internet protocols go. If you’re wondering what SRT protocol and the SRT Alliance are and what they do, allow us to give you a fuller picture.



What is Secure Reliable Transport (SRT) Protocol?

SRT protocol, in short, is a new open-source transport protocol that’s designed to optimize streaming transport from one endpoint to another across unpredictable networks. What that means is that it can deliver high-quality video at low latency, and the phrase “unpredictable networks” refers to noisy, public networks …such as the Internet. When transmitting over networks like these, there are inevitably obstacles, such as bandwidth fluctuation and data packet loss, that may result in a lower-quality video at the receiving end.


SRT is a reliable protocol that adapts to network conditions, minimizes data packet loss, and delivers a better final product. It uses UDP (User Datagram Protocol) as a transport at the application layer (i.e. where software and interfaces operate) and bills itself as being able to provide “best quality video over the worst networks.” The “secure” part of SRT means that the protocol supports end-to-end AES encryption, better protecting the stream data.




How Does SRT Improve the Video Industry?

SRT protocol was designed to support mission-critical real-time video streaming at a global scale–it enables content encoding and streaming solutions that reliably stream encrypted, low latency, and high-quality video across any IP network. Additionally, its technology stack is open source and therefore free to all market participants–hundreds of solution and service providers have signed on to support it within just a few years. As such, the availability of SRT brings a few improvements:


  • Optimization of streaming performance.
  • Improvements in workflows and production environments.
  • Security is right there in the protocol’s name; SRT helps ensure content is better protected from contribution to distribution.


These features will be extremely important for both the present and in the future, as the consumption of high-performance video by businesses, governments, and schools has made a sharp rise. The open-source nature of the SRT protocol also has provided a rapidly growing community who are contributing to the protocol and hardware and software solutions that support it. For a closer look into SRT’s specific benefits and uses, continue below!




SRT Protocol’s Main Benefits & Implementations

SRT is primarily a transport protocol based on UDP however it adds error-checking similar to the well-known TCP/IP protocol to increase reliability. However, it’s intended for high-performance video specifically!


Use cases so far include encoders, decoders, gateways, IP cameras, and more, and it’s been acknowledged as a reliable transmission method for live contribution and distribution TV links–in other words, it’s proved highly invaluable to the film, broadcast and video industry.


Specific benefits of the SRT protocol include:


High Quality: The protocol protects against packet loss, jitter, and bandwidth fluctuation guaranteeing a high-performance viewing experience.


Reliable and Low Latency: SRT protocol can ensure quality and integrity of video streams no matter how unreliable the network. It does this by implementing stream error correction at lower latency than traditional protocols like TCP/IP that allows it to recover from packet loss and other networking obstacles.


Open Source: SRT is implemented with a free, open-source code base keeping costs low with no royalties, long-term contracts, or monthly subscriptions. This has also made it widely adopted by a variety of professional-grade solutions. Further widely-used free tools such as OBS Studio and VLC player also now support SRT protocol.


Interoperable and Content Agnostic: Wide adoption means you can deploy SRT through an entire video and audio streaming workflow, knowing multi-vendor products can work together. Similarly, SRT is not like other protocols that only support specific formats–it acts as a wrapper around content at the network transport level, and can take any type of video format, codec, resolution, or frame rate.


Highly Secure: SRT uses the 128/256-bit AES encryption trusted by organizations and governments. Content is protected end-to-end so no unauthorized parties can’t listen in.

  • Easy Firewall Traversal: In addition to quality encryption, SRT protocol uses a “handshake” process supporting outbound connection without the risks of opening permanent exterior ports in a firewall. IT and corporate LAN security can be assured it will work alongside their policies.




Who Invented SRT Open-Source Protocol?

SRT Protocol was originally developed by Haivision but more recently has been taken up by a consortium of video tech companies who improve and advocate for it. Marc Cymontkowski of Haivision is frequently cited as the lead technologist behind, and architect of, the SRT protocol though undoubtedly others have contributed both in early development and as the protocol has evolved into a collectively used technology.


Interestingly, SRT’s open-source approach has given the protocol quite a bit of industry credibility, as well as created an energetic community around the protocol. The open-source licensing allows anyone to take the protocol and include it in a piece of hardware, and over recent years there have been numerous contributors providing steady feedback and development of the protocol.




What is the SRT Alliance?

The SRT Alliance promotes itself as a “collaborative community of industry leaders … continuously improving SRT.” Haivision is a founding member as are other luminaries in the audio-visual, IT, and streaming fields including companies such as Avid, Microsoft, Brightcove, and Panasonic (and Kaltura!). Members develop, use, and promote SRT protocol as well as software and products based on it.




SRT Supported Services & Devices

Products and services incorporating SRT protocol are an expanding roster, encompassing thousands of organizations across the globe and a wide range of industry applications that include IP cameras, video encoders and decoders, gateways, OTT platforms, and content delivery networks (CDNs).


Here are a few prime examples.


Encoding appliances: Many hardware encoders are bundled with SRT support alongside other protocols, and it’s an added advantage when delivering capture, streaming, and recording in 4K/UHD.


Capture cards: Likewise, SRT-enabled capture cards can provide an array of additional options for high-def, high-density video like 4K, especially in a control room environment.


Decode and display cards: Multiviewer cards can take in SRT-compliant streams from any device and any location in the world. These devices are a great benefit for real-world, “non-entertainment” use cases, such as security and crisis-management applications.


Encoder/decoders: Professional grade encoder/decoder pairs support many streaming protocols, including SRT, and can transmit live camera streams in 4K or quad HD over networks, and feeds can be optimized for integration into studio environments.


How about a more specific example of a service supporting SRT protocol?


Kaltura: As previously mentioned, Kaltura is a member of the SRT Alliance, and the protocol is a great fit for our flexible and protocol-agnostic platform–an open-source protocol addressing issues of secure, low latency, reliable video over the internet allows Kaltura to provide our customers a better viewing experience at a lower cost!



In summary, the SRT protocol is poised to be a key technological component for streaming in the future. Keep a lookout for compatible products and services for inclusion in your workflow as the protocol continues to evolve!

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