@mux/ai

Video Education: What is SRT?

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SRT is an open source

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contribution protocol

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for moving video

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between two points.

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It's a protocol designed for

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reliability and high quality

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video delivery, even when the

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network is less than perfect.

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I know what you're

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all thinking.

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Isn't that a subtitles format?

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We're talking about

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Secure Reliable Transport.

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Confusing that there's two video

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related acronyms for SRT?

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Yeah, really annoying.

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Believe it or not, SRT has

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been around about a decade

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at this point, originally

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demoed by Haivision at

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IBC back in 2013, and then

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open sourced a couple of

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years later on GitHub.

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If you're already

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live streaming, then

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you're probably live

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streaming over RTMP.

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RTMP is ultimately connection

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oriented, it works over TCP.

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It's really easy for a TCP

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connection to get dropped,

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or a bit of packet loss, or

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a bit of jitter, and to cause

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a live stream to run into

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network connectivity problems.

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And that means you're

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kind of only one dropped

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TCP connection away

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from an interruption

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to your live stream.

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Under the hood SRT is working

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at a different network layer,

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running over UDP rather than

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TCP, so you don't have that

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connection oriented component

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of the communication.

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All of the reliability

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features are implemented at

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the protocol level instead.

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Obviously, if some packets

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go missing, some packets

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do occasionally go missing,

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SRT holds a buffer on both

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ends of the connections.

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And the size of this buffer

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is configurable when you

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connect to an SRT endpoint.

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And so, for example, you

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have a second of frames on

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either end of the connection.

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And then if some packets get

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lost or reordered, You can

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resend those lost frames to

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fill that gap in the buffer.

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Obviously, interestingly,

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what this means is you

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can trade off latency for

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reliability within SRT.

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So if you increase your buffer

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size, there's more opportunity

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to recover if you do encounter

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those horrible internet

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connectivity problems.

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And SRT is a great option

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for all of those social,

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user generated video apps

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that you've been building

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on mobile recently.

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Because, hey, you're more

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likely to be connected

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over WiFi or a cellular

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network where SRT can shine.

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So that's SRT, a modern,

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reliable ingest protocol,

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much better than RTMP, that

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lets you improve reliability

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of your live streams.

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It's now GA on Mux.

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That's where I work.