SRT 101

What is SRT? SRT stands for Secure Reliable Transport and is a protocol for streaming pristine quality live video over the internet. As a low latency point-to-point streaming protocol, SRT is ideal for first model applications, such as video contribution, backhaul, bi-directional interviews, and broadcast return feeds.

When sending live video from one location to another, satellite and fiber are not always viable options due to cost and deployment time. The internet, however, is ubiquitous and cost effective. But as a unmanaged network, it can be unpredictable.

SRT delivers great looking video over the internet by combining low latency UDP streaming with ARQ packet loss recovery. Let’s take a look at how SRT works. To recover lost packets and prevent jitter, the SRT protocol includes a latency buffer on both the sender and receiver side.

The SRT receiver buffer reconstructs the sender stream packets and sequences before passing them on to a decoder. If a packet gets lost along the way, a negative acknowledgment, or NAK, is sent back to the sender. The sender then re-sends the packet from its buffer back to the receiver.

The SRT latency buffer can be configured as a multiple of RTT depending on network conditions and distance to allow for packet retransmission. SRT can stream any type of content, including H.264 and HEVC video. The SRT protocol includes AES-128 and 256-bit encryption to ensure the secure delivery of high value content.

When sharing streams between networks, SRT includes caller and listener modes for establishing secure bi-directional data flows from behind a firewall. SRT has been widely adopted by over 250 technology vendors, and it continues to evolve as the industry standard for video streaming. Best of all, SRT is open source. It can be downloaded on GitHub. If you are interested in high vision solutions that support SRT, then please get in touch.