What is the SRT Protocol?

SRT (Secure Reliable Transport) is a royalty-free, open-source video streaming transport protocol that delivers secure low-latency streaming performance over noisy or unpredictable (lossy) networks such as the public internet. SRT uses an intelligent packet retransmit mechanism called ARQ (Automatic Repeat reQuest) on top of a UDP data flow to protect against packet loss and fluctuating bandwidth, as well as to ensure the quality of your live video.

The use of video in businesses, governments, schools, and defense is on a sharp rise. Many protocols have addressed compatibility distribution of streaming video to very large volume of viewers consuming content from disparate devices and appliances. However, one of the best ways to leverage the assets already on premises at various organizations, as well as the considerable investment by service providers in the cloud, is to feed streaming distribution tools with very low-latency video and do so reliably.  

SRT takes some of the best aspects of User Datagram Protocol (UDP), such as low latency, but adds error-checking to match the reliability of Transmission Control Protocol/Internet Protocol (TCP/IP). While TCP/IP handles all data profiles and is optimal for its job, SRT can address high-performance video specifically. 

IT thought leaders among enterprise and government end-users are especially excited about SRT because it’s a viable replacement for the Real-Time Messaging Protocol (RTMP). RTMP is a TCP-based streaming protocol originally developed to work with Adobe Flash players and still in use today as a protocol for live streaming video.  

RTMP’s primary function is to deliver content from an encoder to an online video host. Known for its low-latency streaming and minimal buffering capabilities, RTMP was often used by broadcasters for streaming live events in real time. However, because RTMP cannot stream HEVC video content, it’s not ideal for new applications. SRT, unlike RTMP, is codec agnostic and can stream any type of video content.  

• Pristine quality video – SRT is designed to protect against jitter, packet loss, and bandwidth fluctuations due to congestion over noisy networks for the best viewing experience possible. This is done through advanced low latency retransmission techniques that compensate for and manage the packet loss. SRT can withstand up to 10% packet loss with no visual degradation to the stream. 
• Low latency – In spite of dealing with network challenges, video and audio is delivered with low latency. It has the combined advantages of the reliability of TCP/IP delivery and the speed of UDP. 
• Secure end-to-end transmission – Industry-standard AES 128/256-bit encryption ensures protection of content over the internet. SRT provides simplified firewall traversal. 
• Leveraging the internet – Because SRT ensures security and reliability, the public internet is now viable for an expanded range of streaming applications—like streaming to cloud sites (for example, LiveScale omnicast multi-cloud platform’s concurrent distribution to multiple social media such as Facebook Live, YouTube, Twitch, and Periscope from one live video feed), streaming or remoting an entire video wall content, or regions of interest of a video wall, and more. 
• Interoperability – Users can confidently deploy SRT through their entire video and audio streaming workflows knowing that multi-vendor products will work together seamlessly. 
• Open source – Royalty-free, next-generation open-source protocol leads to cost-effective, interoperable, and future-proofed solutions. 

SRT also addresses security concerns and focuses on performance video – even through public internet infrastructure. Common applications of SRT include: 

• Remote broadcasting 
• Online video platforms 
• Content delivery networks 
• Enterprise video content management systems 
• Hardware, software, and services internet streaming infrastructure companies 

Established in 2017, the SRT Alliance is a community of industry leaders and developers that aims to support the free availability and collaborative development of the SRT protocol.

Matrox Video is a member of the SRT Alliance and endorses the use of SRT.