SRT Protocol: What is it and how does it work?

If you're looking to stream audio and video over a secure, reliable, open-source protocol with top-notch quality, high affordability, and low-latency, Secure Reliable Transport (SRT) will meet your needs. SRT streaming is a popular and increasingly compatible standard that delivers clear live audio and video to viewers, no matter their network conditions. 

What is Secure Reliable Transport Protocol (SRT)?

SRT is a protocol designed to deliver low-latency audio and video streams across public and private networks.

The protocol combines the best aspects of User Datagram Protocol (UDP), like low latency, with 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 focus on delivering a high-performance stream.

Essentially, SRT brings the best quality live video over the worst networks while maintaining the integrity and quality of the video. It also supports end-to-end AES encryption, keeping your streams secure.

Technical Overview of SRT

The technical information below is SRT at a glance: 

  • Audio Codecs: Codec-agnostic
  • Video Codecs: Codec-agnostic
  • Playback Compatibility: Includes VLC Media Player, FFPlay, Haivision Play Pro, Haivision Play, Larix Player, and Brightcove
  • Benefits: High-quality, low-latency video streams over suboptimal and public networks
  • Drawbacks: Not widely supported for video playback
  • Latency: 3 seconds or less, varies depending on how much latency the streamer is willing to trade for packet loss

How Does the SRT Protocol Work?

The SRT protocol can solve the typical latency challenges associated with live video transport, like packet loss, bandwidth limitations, and jitter. But how does SRT provide such a secure and reliable solution? It relies on these characteristics:

  • 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 

The Top 9 Benefits of SRT Streaming

As the name indicates, SRT's primary advantages are its security and reliability. However, it has many others that have earned it a spot among the top choice of live streamers. Here are the top nine benefits: 

1. Quality

SRT protects against jitter, packet loss, and bandwidth fluctuation, ensuring the best possible viewing experience.

2. Security

Using 128/256-bit AES encryption, SRT ensures that valuable content is protected end-to-end from contribution to distribution so that streams stay secure.

3. Reliability

No matter how unreliable your network is, SRT can recover from severe packet loss and jitter, ensuring the integrity and quality of your video streams.

4. 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.

5. Easy Firewall Traversal

SRT streaming 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.

6. 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.

7. Open-Source

SRT streaming can be implemented using a free, open-source code base, keeping costs low for all parties.

8. 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.

9. Affordability

SRT's security and reliability make the public internet 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.

What is the SRT Alliance?

The SRT Alliance is 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. Members develop, use, and promote SRT protocol and software and products based on it.

SRT Compatible Devices and Services

The number of products and services that support the SRT protocol is increasing to over 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 some of the compatible devices and services SRT users can leverage: 

  • 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: SRT-enabled capture cards can provide an array of additional options for a high-definition, 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 "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.

Frequently Asked Questions

Is SRT UDP or TCP?

The SRT video streaming protocol relies on UDP. 

Is SRT better than RTMP?

SRT delivers video streams much faster than RTMP and with lower latency, making it a preferable option. 

Is SRT better than NDI?

Network Device Interface (NDI) and SRT leverage UDP to transmit live audio and video over the Internet. SRT focuses more on delivering video over unpredictable network conditions, while NDI focuses on maintaining high quality and low latency; determining which is "better" depends on the broadcaster's needs. 

How reliable is the SRT protocol?

SRT is not only extremely reliable but secure as well. It is a great choice for streamers who wish to have a quality, clear, and encrypted video and audio transmission.

SRT is a widely supported and highly performant video and audio streaming protocol suitable for multiple use cases and industries.

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