SRT for mobile streaming on Android and iOS

SRT (Secure Reliable Transport) is a UDP-based protocol that optimizes streaming performance on unreliable networks to deliver the best quality and lowest latency video at all times. The initial version was created by Haivision and now it's available as open source and it's maintained and promoted by SRT Alliance.

Softvelum products have full support for SRT technology. Nimble Streamer was the first software media server to support SRT protocol in all of its modes. Our customers actively use SRT for heavy duty projects which need media transmission across large networks across continents. Recent blog post called Reliable Low Latency Delivery with SRT+SLDP demonstrates SRT capabilities in action using the great combination of Haivision encoders and Nimble Streamer media server. Softvelum and Haivision partner to offer you reliable, low latency video streaming over the public internet with SRT.

Mobile SRT streaming

Having SRT working perfectly on server side, we now introduce SRT streaming for

Larix Broadcaster now allows streaming via SRT in Push (Caller) mode. It supports all of its features including compensating for jitter by errors correction, AES encryption and more.
This is now available in addition to existing features such as

• RTMP and RTSP streaming support.
• Multiple simultaneous destinations for the same stream.
• Full support for YouTube, Facebook Live, Twitch, Limelight CDN, Periscope and other services.

So you may have your own CDN taking SRT input stream and also send content to Limelight and Facebook - this all can be done simultaneously using the same application.

You can try that in action using Larix Broadcaster freeware app which demonstrates all features of our streaming library. App sources are included in the SDK package so you can easily create your own apps.

Check these links:

• Larix Broadcaster for Android and its setup instruction.
• Larix Broadcaster for iOS and its instructions.

You can also refer to these screenshots as example of SRT setup in Larix, it's very simple.

Go to Setting dialog (the gear icon) then click on Connections and create new connection to see this dialog.

First you define your destination URL - it will start with "srt://" and will include the server address and the port which was set up to receive SRT.
If you use encryption, you can fill in SRT passphrase field.

If you need to set more options for your SRT connection, you need to save settings, then go to Manage connections menu and click on its details to see more.

We highly recommend you to set up "maxbw" and "latency" SRT parameters for your connection. This will allow optimizing the packets re-transmission and reducing bandwidth consumption. Read this article for details.

When you have your connections ready to go, check those which you'd like to send your streams to as shown below.

Once you start transmission, you will have your stream being sent to multiple locations.

Also take a look at this video demonstrating some example of SRT streaming.

Glass-to-glass SRT delivery setup article describes how to deliver live stream via SRT using Nimble Streamer, Larix Broadcaster and SLDP Player.

You can also watch How to connect your phone to a live video production with SRT and Larix Broadcaster video by vMix team which demonstrates how you can steam from Larix to vMix via SRT. Our YouTube channel has other useful setup videos.


That's it. With those capabilities you can now have full power of SRT being applied to mobile streaming use cases.

Nimble Streamer SRT setup

Nimble Streamer media servers supports SRT protocol in all modes.
To use SRT with Nimble Streamer, you need to do the following:

• Install Nimble Streamer or upgrade it to latest version if you already have it.
• Install SRT package for Nimble Streamer to add respective functionality.
• Follow this article to see how to set up Nimble Streamer to receiving SRT.
• Read Haivision blog article as a how-to for setting up SRT reception and further transmuxing to SLDP low latency protocol.
• Set up OBS Studio SRT streaming with Larix Broadcaster and Nimble Streamer

This will allow you using full power of SRT in your mobile streaming scenarios.

If you have any issues with setting up SRT, please contact our helpdesk so we could help you.


Also please visit our Larix documentation reference page for more setup information.

Please also take a look at Phone Takeover: Replacing Pro Cameras in Live Streaming article which shows how a modern phone can be used instead of low- and mid-tier cameras for live production.

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/)

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Related documentation

Nimble Streamer, Nimble Streamer SRT protocol support, Larix mobile streaming SDK,  Larix SDK FAQ, Larix Broadcaster, Larix documentation reference, SRT in other Softvelum products

FAQ: Larix mobile broadcasting SDK

The content of this article has been permanently moved to Larix FAQ page on Softvelum website.

SRT, RTMP, WebRTC and RTSP publish control framework overview

For the past few years, mobile devices were showing significant improvements for video creation capabilities hence the popularity of video live streaming solutions - from mobile broadcasting applications to complex all-in-one solutions. If you create a streaming solution yourself, you need to be able to control the publication process for the protocol which you choose to work with, e.g. for RTSP or RTMP.

SRT, RTSP, RTMP and WebRTC WHIP incoming streams were supported in Nimble Streamer for a while already among other protocols. Nimble supports SRT, RTSP, RTMP and WebRTC streaming authentication server-wise as well as for specific applications. So if a customer needed to separate publishing permissions between his users, he needed to create separate application for each individual publisher. But when you broadcast from mobile devices, you probably will need some better way to make sure each publisher has separate permission to publish.

Our customers have been using WMSAuth Paywall functionality to secure the outgoing streaming for a long time. Now to secure the incoming streams, we introduce the Publish control framework which allows performing multi-level authorization.

So now Nimble Streamer allows controlling the publication for RTSP, RTMP and SRT in Listen mode receiver both when establishing connection time and during the streaming process. It has various options so let's see what we have, step by step.

The following scenarios authentication are available.

"Zero option" is if you don't need any protection for incoming streams, then you can just specify only port number for RTMP and RTSP, and define SRT listener. Any publishers can push any streams to your server through the specified port so we do not recommend it. WebRTC requires authentication though.

1. Use publishing credentials

The first scenario is to create a separate application in Nimble Streamer settings for each user with unique username and password to get authorized streams from different authorized users. This mechanism is unsuitable for the large number of users and does not allow to block users during streaming process because the authorization takes place only at the time of connection of the user.

2. Use per-stream publish signature.

In order to allow multiple users to publish streams to the media server and to have the flexibility to control streams, you need to use our Publish control framework.

At this step we add a publish signature, which is based on the following parameters:

• user identifier (ID);
• stream name;
• password which was specified in application;
• publisher IP address (this one is optional).

You need to specify an application in WMSPanel control UI to operate the incoming streams. Publishing users will be grouped in. The application name should be the same as specified on step 2. The password which is used in this signature should be specified in the publish control application settings via the UI.

To publish to Nimble Streamer, the publisher will use the URL like this:

rtsp://192.168.5.5:554/live/stream?publishsign=aWQ9SURfMSZzaWduPW95Zi9YVHBLM0c3QkQ4SmpwVnF1VHc9PSZpcD0xMjcuMC4wLjE=

For RTMP this will be

rtmp://192.168.5.5:1935/live?publishsign=aWQ9SURfMSZzaWduPW95Zi9YVHBLM0c3QkQ4SmpwVnF1VHc9PSZpcD0xMjcuMC4wLjE=/stream

For SRT receiver in Listen mode you will define streamid as shown in the following example, read Setting SRT user and password authentication with SRT PASSet article for setup details of proper streamid.

ffmpeg -re -i video.mp4 -codec copy -f mpegts pipe:1 | ./srt-live-transmit -v file://con "srt://127.0.0.1:2020?streamid=/live/srtstream?publishsign=aWQ9SURfMSZzaWduPVQ3SzVlMkMySlRxRExmSTdybVdibVE9PSZpcD0xMjcuMC4wLjE="

For WebRTC the WHIP signaling URL will be

https://your_host/live/whip?publishsign=aWQ9SURfMSZzaWduPW95Zi9YVHBLM0c3QkQ4SmpwVnF1VHc9PSZpcD0xMjcuMC4wLjE=

Here, a publishsign is the signature for incoming stream.

When the user is going to publish RTSP or RTMP stream, the media server will check publish signature and if this signature does not match the calculated signature, then the user stream will not pass. At this step the publish control is very similar to the hotlinking protection.

Notice that you may skip the signature in case you handle your authorization in some other way. The "Signature-free mode" is defined to make this way during app publish control setup, see detailed documentation for more on that.

3. Use connection handler to manage connection process.

To get full control for the incoming streams, you need to create a handler application and specify its URL in the control UI.

The handler is an HTTP application which is able to process POST requests and return the response according to the business logic of the customer. If you don't specify the handler URL then Publish control framework will not try to call the handler. This is done to allow debugging the signature-checking mechanism.
Besides handler URL, you can set up the grouping interval for the incoming streams. The handler is called with some timeout to aggregate several requests in one. This allows avoiding the resources waste in case of frequent calls.

Publish control passes the client publisher IP, ID and stream to the handler. As a response to the request, the handler must return the status and Nimble Streamer acts accordingly to allow or deny the connection, based on the status received from the handler.

4. Use publication controller during streaming

With publish control framework you can manipulate SRT, RTSP and RTMP streams not only at connection time, but also during the streaming process as well when the user is already connected and streaming. To perform this, each streaming session is assigned with its own key. You can create publish controller app which can request Nimble with any frequency to identify which users still publish their streams.
If you need to stop certain streaming session then your controller calls Nimble, specifies the session ID and this stream will be blocked immediately.


Using publish control framework you can implement any level of incoming streams security from basic level authorization to advanced business logic solution.

If you need to change the incoming streams' content parameters, like change the bitrate, use our Live Transcoder for Nimble Streamer to transform. It has high performance and low resource usage.

Next step is the setup

The next article describes step-by-step publish control set up with examples of source code, requests and responses.




Also check playback authorization feature set which allows controlling playback connections via external handler similar to what is used in publish control.

Related documentation

RTSP streaming via Nimble Streamer, RTMP feature set in Nimble, Nimble Streamer paywall feature set, Larix Broadcaster, SRT Publisher Assistance Security Set, WebRTC support in Nimble