Softvelum Low Delay Protocol

Low latency is an important issue for live streaming industry. Many use cases need lowest possible delay in delivery, such as security, online chats, gaming, bidding and more.

For a long time, RTMP was the leading technology for providing low latency playback. However, Adobe stopped support for Flash technology which caused the RTMP playback decline. With Flash and RTMP being declined by the industry, there is a need for real-time delivery protocol supported on multiple platforms.

Softvelum introduces SLDP - a last-mile delivery protocol to provide sub-second delay between media server output and user playback.

  • SLDP is based on WebSockets for transmission over HTTP/HTTPS.
  • Up to one second delay between origin and player.
  • Codec-agnostic. you can stream H.264, H.265/HEVC, VP8, VP9 video and AAC, MP3, Opus audio to the platforms which support the playback.
  • Real-time adaptive bitrate (ABR) is supported to allow switching channels nearly instantly. It takes just a GOP time to start new rendition playback.
  • Simultaneous synchronized playback among multiple browsers and mobile devices.
  • CEA-608/708 closed captions are supported with HTML5 Player SDK.

SLDP ads insertion live demo

Here you can play SLDP live stream with ads insertion in our free HTML5 player.

Find out more on Nimble Advertizer Live Demo page.

Transmuxing and transcoding for SLDP

Nimble Streamer takes most popular protocols as input for further processing. They are RTMP, SRT, RTSP, NDI, WebRTC, MPEG-TS, HLS, Icecast and SHOUTcast. Once the data is received it can be transmuxed into all supported live streaming protocols which include SLDP among others.
Server passes though the content without changes in case of transmuxing, so whatever the original protocol carries, it will be brought via SLDP to a client.

Live Transcoder can be used in this pipeline in cases when some content transformation is needed. This might be downscaling for ABR, filtering, re-sampling, changing profile or whatever else is needed. Transcoder produces H.264 or H.265 (HEVC) video with AAC or MP3 audio so the target platform should be able to play that.

If the ABR SLDP stream is produced, each single bitrate stream within ABR stream may use its own codec or different profile of the same codec. So your FullHD streams may use high profile and other lower resolution streams will use H.264 baseline.

You can play SLDP with Opus audio on iPhone in audio-only mode when taking WebRTC as a source without transcoding.

SLDP setup in Nimble Streamer

From scenarios setup perspective, SLDP is just one more protocol in our bundle.
Use this article as a setup reference and this FAQ for some specific details.

Amazon CloudFront has full support for WebSockets which means SLDP can be delivered via CloudFront network seamlessly.
Take a look at CloudFront setup for SLDP delivery to learn more about proper settings.

Also, learn more about ABR streams setup for Nimble Streamer output and real-time ABR setup for SLDP.

Browser support

SLDP can be played in HTML5 browsers with MSE on support using SLDP HTML5 player.
You can also add playback to your own players using JavaScript SDK.

Mobile support

Mobile Larix Player SDKs for Android and iOS are available for adding playback capabilities to your own apps. This includes SLDP and RTMP support.
Visit our players page to see what you can use on client side.

Synchronized playback

SLDP technology allows performing synchronized simultaneous playback in multiple player instances, browsers and devices. This is important for cases like these:

  • One big screen with audio on individual devices.
  • A second screen application.
  • Multiple screens with single source of sound.
  • Surveillance cameras shown on the same page.
This capability is supported in Nimble Streamer server, HTML5 SLDP player and Larix Player for Android/iOS.
Read this article which explains the setup and usage.

Server-Side Ads Insertion

Nimble Advertizer supports inserting of advertising into SLDP live streams on server side. This means you can have ads in your SLDP streams regardless of the viewer's platform and player.
Advertizer allows implementing your custom business logic for pre-roll and mid-roll with user-specific insertion.
Visit Advertizer page for technical specs and other details.


Usage snapshots show examples of combined usage of Softvelum products with SLDP technology.

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Easy installation and upgrade

Nimble Streamer can be installed in a couple of small steps and upgraded to the latest version by running two or three simple commands in console.

Let us know if you need any help and search through our documentation to find more information.

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