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Using WebRTC for Video Publication to Flussonic Media Server

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About the WebRTC protocol

WebRTC (Web Real-Time Communications) is a P2P (peer-to-peer) protocol for bidirectional secure real-time communication between the two clients.*

Lets's break it down into sections. P2P (peer-to-peer) tells us that two agents (clients) interact directly with each other without the third party interfering. Bidirectional refers to functioning in two (opposite) directions. Secure means that the connection is encrypted by one or more security protocols. Real-time communication stands for nearly instant information exchange without or negligibly low delays.

WebRTC protocol is used for data exchange between the two browsers (no plugins or any extensions needed) or applications that support that protocol via the "one-to-one" or "client-client" type of communication. For example, visiting the same website, two browsers can interact with each other with WebRTC. That is why it is great for voice and video calling (Zoom), content sharing and more.

WebRTC has its advantages:

  • ultra-low latency (less than a second),
  • obligatory encryption with DTLS and SRTP protocols,
  • open-source standard,
  • no need to install any additional plugins or applications, etc.

A so-called signaling server is used for this purpose. Signaling server is a media mediator that manages the connections between devices. Thus "client-client" type of connection becomes "client-server-client".

For the clients, or agents, to start communicating with each other using WebRTC, four sequential steps are taken:

1. Signalling

WebRTC uses SDP (Session Description Protocol) to negotiate media parameters. One WebRTC Agent makes an "offer" to start a call, and the other Agent replies with an "answer" if it agrees to accept the "offer". It is called an "SDP offer/answer" model. This is a moment when the responder declines the unsupported codecs.

The SDP "messages" contain the details like IPs an ports that the agent is reachable on (ICE Сandidates), a number of video and audio tracks it is willing to send, what audio and video codecs each of the agents support, etc. ICE

Now the agents are ready to attempt to connect.

2. Connecting

ICE (Interactive Connectivity Establishment) protocol is used to find the best way to pair the agents using candidates. ICE candidates are simply combinations of IPs, ports and transport protocols of the agents. They are used to get the perfect match for the two agents to allow to establish a connection, overcoming NAT (Network Address Translation) and firewalls. STUN (Session Traversal Utilities for NAT) and TURN (Traversal Using Relays around NAT) servers are used to establish a connection between the agents.

3. Securing

WebRTC uses DTLS and SRTP security protocols to encrypt the messages and secure the connection. Every connection is secured and authenticated.

Now that the coast is clear and we have two agents with secure bidirectional connection, we can start communicating.

4. Communicating

Here the data exchange begins. Both WebRTC Agents start the data and media interchage. WebRTC supports 2 audio (Opus, G.711) and 2 video (VP8, H.264) codecs.

But what if we want to configure a data exchange between 3 or more browsers or applications that support WebRTC? For example, start a video/audio conference?

A so-called signaling server is used for this purpose. Signaling server is a media mediator that manages the connections between devices. Thus "client-client" type of connection becomes "client-server-client". As a result, "one-to-one" becomes "one-to-many", offering more to functionality to the user.

About publication through WebRTC to Flussonic

Flussonic Media Server uses WebRTC for publishing a media stream from a client device or app (the source) to Flussonic (the recipient). Then Flussonic becomes the source in order to play the stream on another client (the recipient). In both cases, Flussonic also acts as the signaling server to exchange the data about the connection.

Why do we use WebRTC to send media data between clients? Because with the WebRTC mechanism we can provide ultra-low latency.

Therefore, the exchange of video via Flussonic cannot be called peer-to-peer, rather, we call it video publication to Flussonic Media Server through WebRTC and video playback through WebRTC.

The diagram shows the process of initiating the connection between Flussonic and a client device, for publication:


The connection to Flussonic Media Server for a media stream publishing through WebRTC is established in the similar way as for video playback.

The principle here stays the same – parties should exchange SDPs via the mediator (signaling server - Flussonic), and then start the direct data transfer. In the case of video publishing, it's the client that initiates the process and sends an SDP offer.

Connection is established via WebSocket, and then video is transferred via RTP.

How to organize publication using WebRTC


Some browsers allow video and audio publishing through WebRTC by using secure connection only. The browser migth deny access to the camera and microphone from a page located not by HTTPS but by HTTP address. But this is allowed on local addresses (localhost,

On the Flussonic server, add a published stream to the configuration, this is a stream with the source publish://.

stream published {
  input publish://;

You can also add a stream through the Flussonic UI:

  1. Head to Media tab and add a stream clicking on Add button next to the Streams section.
  2. Then in the stream settings go to the Input tab and specify `publish://`` in the URL field. Make sure that Published input is accept:

Flussonic stream mixing

Published input accept

Now the code must be run on the client side that publishes video to the created stream. To write the code use the Flussonic WebRTC player library.

To configure publishing through WebRTC:

  • Head to options on the same Input tab:


  • Set the necessary values:

WebRTC settings

Installing the library components via NPM and webpack

To import our library to your project with webpack, download the package:

npm install --save @flussonic/flussonic-webrtc-player

Then import components to your application:

import {
} from "@flussonic/flussonic-webrtc-player";

The description of the library classes can be found at npm.

See also the demo application, which code is also found further on this page.

Installing the library components without NPM and webpack

Add this line to the script section of your HTML page:

<script src=""></script>

The example of a webpage containing the player code is further on this page.

WebRTC publication options

Audio podcasts through WebRTC

To publish only the audio track without video, in the options of the publisher instance use the following configuration in constraints:

import Publisher from '../publisher';
publisher = new Publisher(

    constraints: {
      video: false,
      audio: true,

If you omit the option video altogether, the result will be the same — only the audio track will be published to Flussonic.

To play such a stream, no additional configuring is needed.

Muting a publication

To mute a publication, use the mute method:

import Publisher from '../publisher';
publisher = new Publisher(*your options*);

If you bind the mute method to a button in your client app, the user will be able to disable the sound in the output stream during its publishing. The demo application has an example of such a button.