Synchronized playback on multiple devices with SLDP

Playing a live stream simultaneously on multiple devices often requires synchronized playback.

The cases look simple:

• One big screen shows something and viewers need to have the same audio on their individual devices.
• A second screen application need to be in sync with ongoing live stream on TV.
• Multiple screens in the same room show the same content with single source of sound.
• A number of surveillance cameras need to be shown on the same page.

You probably know other cases where you might have the same requirement.

With traditional delivery protocols like HLS ad MPEG-DASH it's very hard to achieve without dramatically increasing the latency.

SLDP live streaming protocol allows delivering streams real time with low latency, adaptive bitrate and small zapping time. Now it also allows synchronizing the playback among devices and browsers for all the cases which you can see above. It's supported on both server side and client side.

Web demo. You can see how this feature works on demo web page with two HTML5 SLDP players.

Mobile and web demo. Take a look at feature demonstration below with HTML5 browser, Android and iOS.

BTW, check our YouTube channel for other videos.



Now let's see how you can start using this feature.

Notice that all implementations use additional buffer to make proper synchronization which will increase latency. This buffer must be the same across all platforms. Check each player platform for parameter setup.

Enable feature in Nimble Streamer

We assume you are already familiar with Nimble Streamer setup and you have a working SLDP live stream. If not, please read SLDP setup and usage article to make it work.

On your server, edit nimble.conf to add this parameter and re-start Nimble Streamer:

sldp_add_steady_timestamps = true

You can visit Nimble Streamer parameters reference to learn more about operating that config file.

Once you re-start the server, every SLDP live stream will have a steady clock timestamps needed for playback adjustments. If the connected player doesn't request the steady clock time, Nimble Streamer will not have it in the output stream to avoid any overhead.

Playback in HTML5 SLDP player

If you want to have a synchronized playback in web browsers, use our freeware HTML5 SLDP player.

By default, the feature is turned off. To enable it, add sync_buffer parameter which specifies the buffer size in milliseconds. Recommended values are from 1000 to 5000 and it needs to be the same in all players.

Playback on iOS

Larix Player for iOS allows enabling and using synchronized playback.

1. Install Larix Player via AppStore.
2. In connection setting, enable Synchronized playback flag as shown on the screenshot below.
3. Use Buffering field to define the buffer for this feature. As mentioned above, it needs to be the same in all players.

Now save setting and start playback.

Notice that SLDP can now be played on iPhones with iOS17SLDP can now be played on iPhones with iOS17.

Playback on Android

Android Larix Player also allows enabling and using synchronized playback.

1. Install Larix Player from Google Play.
2. In connection setting, enable Synchronized playback flag.
3. Use Buffering field to define the buffer for this feature, it needs to be the same in all players.

Now save connection and start playing the stream.

You may also use this kind of custom URL

sldp://address:8081/live/stream?steady=true&buffering=2000

to set "Synchronized playback" value to "On" and "Buffering" value to "2000". This will allow passing URL among viewers with no need for additional instructions.

Once you start playback on multiple devices and browsers with that feature enabled, your playback on all devices will catch up.

DVR in SLDP HTML5 Player

HLS DVR streams can be added to SLDP HTML5 Player for rewinding low latency streams.

Read this article for details.

Let us know how it works for you and what improvements you'd like to have for it.

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Related documentation

SLDP technology overview, SLDP support in Nimble Streamer, Softvelum playback solutions, Mosaic videowall playback demo

Fallback of published RTMP, RTSP and Icecast streams

RTMP, RTSP and Icecast live protocols can be pulled by Nimble Streamer for further processing, and in order to improve robustness each pulled stream can have fallback streams. So if a primary stream cannot be pulled for some reason from the origin, an alternative stream is pulled to do a failover. The playback is not stopped so the user experience is not harmed much.

The aforementioned protocols are often used in publishing mode when the stream is pushed into Nimble Streamer for processing. In this case there is no built-in way to cover that.

Nimble Streamer provides another reliable mechanism for covering fallback of RTMP, RTSP and Icecast published streams, the Live Transcoder hot swap feature set. It allows shifting to secondary stream if the primary one is down for some reason, while maintaining the playback output  for video and audio.

The following steps allow setting this up.

1. Install Live Transcoder

Hot swap feature set requires Live Transcoder premium add-on for Nimble Streamer.

There are two main reasons for Live Transcoder usage:

• Secondary (substitution) stream needs to fit the primary (original) stream by video resolution and audio sample rate.
• The primary stream need to be decoded in order to get the substitution smoothly.

You need to obtain a license for Transcoder, then install the add-on and register a license for it.

2. Set up published inputs

You need to have both primary (original) and secondary (substitution) stream being set up and published into Nimble Streamer. In case you haven't done it yet, check the articles for RTMP, RTSP and Icecast publication setup.

3. Set up hot swap failover

Having both streams ready and Transcoder installed, you can set up failover hot swap for them. Follow the instructions and make sure you complete all steps.

4. Test the setup

As always, you need to test the setup before using it in production use cases. If you have any questions or issues, please contact our team so we could help.

Related documentation

Live streaming via Nimble Streamer, Failover hot swap, Emergency stream hot swap,

Live Transcoder control API

Nimble Streamer Live Transcoder is well known for its drag-and-drop web UI which allows setting up live stream transformation of any complexity using any browser.

However we have a number of users who need to have some automation of Transcoder operations.

Our team introduced our first approach to Transcoder API.

Visit this WMSPanel API page to see all details of API setup and usage.

The operations which you can do over Transcoder instance are as follows:

• Retrieve the list of transcoder scenarios
• Get details of particular scenario
• Pause and resume particular scenario
• Delete an existing transcoder scenario

So having a set of scenarios for your servers, you can operate them just like you can do it from scenarios list in UI.

If you need more API call, please feel free to share them using our helpdesk so we could prioritize features in our wishlist.

Related documentation

Nimble Streamer Live Transcoder, Transcoder documentation reference,

HbbTV MPEG-DASH support in Nimble Streamer

Hybrid Broadcast Broadband TV (HbbTV) has been working with MPEG-DASH for some time by now and Nimble Streamer MPEG-DASH implementation also has that support.

To enabled this support, a specific profile needs to be added to DASH outgoing streams. This can be done by adding the following parameter into nimble.conf file:

dash_live_profiles = urn:hbbtv:dash:profile:isoff-live:2012,urn:mpeg:dash:profile:isoff-live:2011

You need to re-start Nimble Streamer after changing the config. Read this page to learn more about operating config file.

Related documents

MPEG-DASH support in Nimble Streamer,