The real difference between SRT and RTMP

Does SRT use less bandwidth than RTMP?

The answer is a bit more complicated than a straight yes or no. In order to find the answer, we need to take a closer look at how these two protocols actually work.

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[trackdayguy]

Excellent explanation. I've been in IT for 30 years and haven't heard TCP, UDP and RTMP described that clearly. Wow!

[davidjoshuaford]

Great breakdown of the technical aspects - more please!

[mattwruff]

It was truly a university-quality lecture on the topic. Well Done! - I heard a lecture on this that lasted 90 minutes and you did it in 9!

[GrishTech]

One thing to note. RTMP is very useful for youtube still. I know that even if I drop frames while live, eventually my encoder / the tcp stack will send up the missing packets (if possible and successful). Youtube then in post processing re-inserts the missing frames. I know this because I once was down for almost two minutes due to an ISP issue, then when I watched the replay, nothing was missing at the drop of the outage. I was shocked.

[clearvideo]

This is exactly what I've needed to know! Thanks!

[mflotron]

Great explainer! I feel like I'm already pretty familiar with SRT and still learned a few things!

[LiveProductionTips]

You are the GOAT. Yes we need more and longer

[TVJAY]

Please do more of these...they are great to share to people.

[BensTechLab]

Well done! Good balance of technical depth without losing the audience.

[dangerismyname]

Really explantation of the benefits of SRT over RTMP - thank you.

[avtls]

Great explanation. A big YES to more like this. I think this kind off short video is very helpful for a base knowledge to allow you to go deeper into the subject. There are surely many videos out there that will go very deep, but it can be a bit overwhelming.

[frankferrer]

Thank you. Especially for that analogy.

[scottjarriel]

Great simplistic overview. Very helpful to those without a networking background. Thanks. Going into issues of how routers handle video streams without QOS tagging would be really getting into the weeds a bit, but might help people understand the differences between running video over a LAN vs through the actual internet.

[TurtleVerified]

This is an ABSOLUTELY amazing explanation. Instead of making my own video explaining this, I'm just going to recommend this video to my customers when they have questions. I may also embed it, with your permission, on website FAQs. Thank you!

[DocRock]

Good stuff AP. I knew this but was still riveted by your explanation. Now, when people do not understand my explanation, I can send them you way better Bill Nye version. #Mahalo

See you in a couple days at NAB. #Aloha 🤙🏽

[lsmith]

thank you for explaining the differences! now it would also be nice if drones and apps in general also add support for SRT.

that being said, as a YBP user I guess even if they add SRT support, it will likely not support h265. which begs the question, is there a negotiation when an SRT connection is established which codecs both sides support or does this need to be manually configured?

Edit: oh and it would be amazing to explain the differences to NDI next.

[MrGanboo]

I work as a principal engineer and this video was sent to me by a junior and genuinely feel it’s so good I’m gonna be sending it to anyone who asks me this questions at work to get them started with the concepts

[HillClimbTV]

Great description. I would describe SRT is latency aware rather than video aware - it knows nothing about the data and can be used to transport things other than video. I'm surprised there hasn't been a more video aware transport gain traction - e.g. one that knows when link is congested to prioritise audio, then 'I' frames, then other frames - ideally linked to the encoder to automatically adjust compression levels when needed. I guess there are solutions, just not open ones.

[wassagtmanndazu]

A very good summary. Thank you.

It is striking that the advertising for SRT often emphasizes that better quality would be possible. And then visual examples are used to compare it with an RTSP (!) live stream with packet loss. With RTSP (protocol from the 90s) there are many blocking artifacts and it looks bad, with SRT it looks good.

However, live streams are very rarely transmitted via RTSP these days (still a good option for IP cameras, for example). In addition, there is usually very little or no packet loss. RTMP therefore transmits absolutely smoothly in most cases and 99% of all live streams worldwide run via RTMP.

However, if you transmit via mobile network or from one continent to another, SRT has noticeable advantages. In normal everyday life, however, it makes virtually no difference.

Assuming there is only 4 mbit/s upload available and a FullHD stream is to be transmitted at 3.8 mbit/s, then there are potential problems with RTMP. And SRT can be the deciding factor. In this case, it would be far better not to think about SRT or RTMP, but to optimize the stream to 3 mbits. Or better yet, both.

But if an upload of 50 or even 100 mbit/s is normal today, and YouTube re-encodes the FullHD live stream at 5 to 8 mbit/s anyway if you deliver with a higher data rate (but with the original stream if it is transmitted at 8 mbit/s), these data rates run super smoothly through the line using RTMP.

[elsyemediagraphics]

Excellent info Aaron. Thank you for sharing! Yes, please continue to make content that explains the technical goodies! 😊