Everything You Need to Know About the SRT Protocol

SRT: Everything You Need to Know About the Secure Reliable Transport Protocol

It’s hard to believe, but the SRT open source protocol has been around for over five years. To mark this milestone, we’ve put together this comprehensive guide to everything you need to know about the video streaming protocol that’s completely disrupted the way the world streams video. In this blog post, we’ll explore the benefits of SRT, how it works, who uses it, and how it powers Haivision solutions.

What is SRT?

SRT is a video streaming transport protocol and technology stack designed to connect two endpoints for the purposes of delivering low latency video and other media streams across any network including lossy networks such as the public internet. In a nutshell, SRT brings the best quality live video over the worst networks. It accounts for packet loss, jitter, and fluctuating bandwidth all while maintaining the integrity and quality of video. With SRT, you can keep your streams secure and easily traverse firewalls.

A Brief History of SRT

Born from the need to reduce the high cost of contribution by satellite and private networks, SRT was originally developed and pioneered by Haivision. It was publicly demonstrated for the first time at IBC 2013, and, as the technology progressed, Haivision released SRT as part of its product family and customers started to enjoy the benefits of high-quality, low latency secure video over unreliable public networks.

To encourage widespread adoption so that more companies and customers could benefit from this exciting technology, Haivision released SRT on GitHub in 2017 as an open source technology stack and protocol. Since then, support for the protocol has continued to grow from strength to strength and in 2018 Haivsion was awarded an Emmy® Award by the NATAS Technology & Engineering Achievement Committee for pioneering a reliable transmission method for live contribution and distribution TV links.

“We’re excited about SRT…it’s enabling us to provide rock-solid services, you never lose a piece of video, you always get video to screen but starting to work at different price points because we’re using internet rather than traditional fixed networks as a way of carrying streams.” 
 Steve Russell, Head of OTT & Media Management Portfolios, Red Bee Media 

How Does SRT Work?

SRT solves the latency challenges of live video transport that persist despite advances in internet streaming, such as packet loss, jitter, and bandwidth limitations. SRT provides a secure and reliable solution for low latency video transport and includes:

  • End-to-end security with AES 128/256-bit encryption
  • Packet loss recovery through advanced low latency retransmission techniques
  • Video and audio stream timing recovery
  • Simplified firewall traversal
  • Network health monitoring between endpoints (packet loss, latency, jitter)

For a simple explanation of what SRT does, and how it works, watch our SRT 101 video.

Benefits of SRT

Although sometimes dubbed as “Satellite Replacement Technology”, SRT, which stands for Secure Reliable Transport, has so much to offer, including:

  • Pristine Quality
    SRT protects against jitter, packet loss, and bandwidth fluctuation, ensuring the best possible viewing experience.
  • Extremely Secure
    Using the same 128/256-bit AES encryption trusted by governments and organizations around the world, SRT ensures that valuable content is protected end-to-end from contribution to distribution so that no unauthorized parties can listen.
  • Always Reliable
    No matter how unreliable your network, SRT can recover from severe packet loss and jitter, ensuring the integrity and quality of your video streams.
  • Low Latency
    SRT’s stream error correction is configurable to accommodate a user’s deployment conditions. Leveraging real-time IP communications development to extend traditional network error recovery practices, SRT delivers media with significantly lower latency than TCP/IP, while offering the speed of unreliable UDP transmission without the disadvantage
  • Easy Firewall Traversal
    The handshaking process used by SRT supports outbound connections without the potential risks and dangers of permanent exterior ports being opened in a firewall, thereby maintaining corporate LAN security policies and minimizing the need for IT intervention.
  • Content Agnostic
    Unlike some other streaming protocols that only support specific video and audio formats, SRT is payload agnostic. Because SRT operates at the network transport level, acting as a wrapper around your content, it can transport any type of video format, codec, resolution, or frame rate.
  • Open Source
    SRT can be implemented using a free, open source code base, keeping costs low for all parties. There are no royalties, long-term contracts, or monthly subscription fees required. Being open source encourages SRT’s widespread adoption and accelerates innovation through continuous collaborative development.
  • Interoperability
    With widespread adoption comes interoperability and longevity. Users can confidently deploy SRT through their entire video and audio streaming workflows knowing that multi-vendor products will work together seamlessly.
  • Cost-Effective
    Thanks to SRT’s security and reliability, the public internet has now become a viable option for an expanded range of streaming applications. SRT offers significant operational flexibility and cost savings compared to satellite or custom network infrastructures.

“The benefits of SRT that we love to provide to our customer base include the visibility of where content is being distributed, the comfort of knowing that it’s secure, reliable, and performant, and the flexibility to ensure that we support a variety of different acquisition means.”
Peter Gibson, Executive Director of Product, Comcast Technology Solutions

 What’s New in SRT 1.5

The new features implemented in SRT 1.5 are designed to enhance the transport of live video over the public internet and improve decentralized workflows for broadcast production, remote contribution, and content distribution. New features and improvements in SRT 1.5 include:   

  • Connection Bonding brings hitless failover technology to the SRT protocol, increasing the reliability of a live video stream by routing it over more than one network path, and preventing disruption in the event of network failure.  
  • New Implementation of the Receiver Buffer for improved memory management and packet reading. The enhanced implementation also improves latency management and the handling of drop requests, providing even greater reliability when streaming over any network.  
  • Packet Pacing and Live Congestion Control Improvements for prioritizing the order of sent packets in order to help avoid congestion if there are changes to the source bitrate or significant network bandwidth fluctuations. 

How Does SRT Compare to Other Protocols?

SRT is most commonly compared to RTMP, a legacy protocol, which is still often used for video contribution. However, not only does SRT consistently outperform RTMP in terms of both latency and video quality, support for RTMP’s dated technology is dwindling. It’s a sentiment echoed by Deloitte in its recent report: Technology, Media, and Telecommunications Predictions 2020.

“Legacy protocols such as the real-time messaging protocol (RTMP), developed over a decade ago to encode video and move it across networks to clients, will likely be displaced by newer solutions such as secure reliable transport (SRT), designed to further decrease latency and meet the demands of live and on-demand streaming.”

Haivision decided to answer this frequently asked question by putting the two protocols to the test. You can read more about how they performed over public networks, how they compared in terms of both end-to-end latency and quality over long-distance streams. You can read the results in this report: RTMP vs. SRT: Comparing Latency and Maximum Bandwidth.RTMP vs SRT White Paper


What is the SRT Alliance?

As the original developer of SRT, Haivision is also a founding member of the SRT Alliance. Established in 2017, the mission of the SRT Alliance is to support the free availability of open source SRT and to foster collaborative development in order to accelerate innovation. SRT is now widely adopted and endorsed by a community of more than 550 technology vendors, working collaboratively to continually develop and evolve SRT as the defacto low latency video streaming standard in the broadcast and streaming industries.

An important goal of the SRT Alliance is to make new features available to the open source community, whether they are submitted for inclusion by community developers, or if they come directly from the Haivision development team.

With an active and engaged membership, the SRT Alliance hosts regular updates on the roadmap as well as Interop Plugfests for developers looking to test interoperability and compatibility between different technologies using the SRT protocol. In addition, the SRT Alliance hosts regular “SRT Tuesday webinars” which showcase how vendors are leveraging the power of SRT in their solutions. And, for the latest release information, visit GitHub.

“At the moment, the world is witnessing and adapting to drastic changes in the way we work and learn. Such circumstances have created a pressing demand for efficient remote communication, content production, and distance learning. By joining the SRT Alliance, we believe we can help customers to create and distribute high-quality video content with low latency in an efficient manner.”
Bruce Tanaka, General Manager of Camera System Business Division, Sony Imaging Products & Solutions Inc.

Who Uses SRT?

SRT is used by thousands of organizations globally for a wide range of applications, from IP cameras, video encoders and decoders to gateways, OTT platforms, and CDNs. SRT is being used and endorsed by major technology partners across the globe such as Avid, AWS, and Microsoft, to name a few. Not only are vendors and solutions providers embracing it, but end users like the NFL, Comcast, Al Jazeera, Fox News, Sky News, and even NASA have come to rely on SRT to power their broadcast and streaming workflows.

In fact, SRT is now so widely deployed, when we recently surveyed broadcasters and streaming professionals in our Broadcast IP Transformation Report 2021 about which video transport protocols they used in their broadcast workflows, 53% said they used SRT.

Success Stories: SRT Trailblazers

There are so many SRT success stories out there it’s hard to keep track of them all. You can check out how SRT is being leveraged in the SRT Trailblazer section of Haivision’s blog.

Hear firsthand what industry leaders are saying about the benefits of SRT.

Haivision Solutions Powered by SRT

As the original developer of the SRT open source video transport protocol, Haivision provides a portfolio of video encoding and content streaming solutions that leverage SRT to help our customers reliably stream encrypted, high quality, and low latency video across any IP network. With native support for the protocol, Haivision video solutions provide end-to-end security, resiliency, and dynamic endpoint adjustment based on real-time network conditions to deliver the best video quality at all times. Using SRT, users can optimize video streaming across unpredictable networks, like the internet, by assuring quality-of-service when faced with packet loss, jitter, latency, and fluctuating bandwidth.

Haivision Play Pro: Watch, Create, and Share Low Latency Video from Anywhere!

In addition, Haivision has created a free SRT player, Haivision Play Pro, a free app for iOS and Android that allows users to securely play or stream live SRT feeds from anywhere over the internet. Users can easily monitor multiple feeds that can be compiled and shared in customized channel lists for on-the-go access to entire SRT channel lineups. You can download it from the App Store or get it on Google Play.

Ready to learn more? 
Here are some additional useful resources: 
SRT Technical Overview 
SRT Blog Posts
Innovation Labs Blog
SRT Trailblazers 
SRT on GitHub
The SRT Protocol Internet Draft
SRT Deployment Guide 
SRT “Under the Hood” 
SRT Tuesday Webinars 
Broadcast IP Transformation Report

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