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WebRTC ABR Player

The example shows how a stream published to WCS server may be played in a number of video qualities via WebRTC.

On the screenshot below:

  • Server url - WCS server websocket URL
  • Stream name - stream name to play
  • h, s, m send - quality switching buttons named by quality profiles from /usr/local/FlashphonerWebCallServer/conf/wcs_sfu_bridge_profiles.yml file


Audio track is playing separately in audio page element

Example source code

The source code consists of the following modules:

  • player.html - HTML page
  • player.css - HTML page styles
  • player.js - main application logic

Analyzing the code

To analyze the example source code, take the file player.js version available here

1. Local variables

Local variables declaration to work with constants, SFU SDK, to display video and to work with client configuration


const constants = SFU.constants;
const sfu = SFU;
const PRELOADER_URL="../commons/media/silence.mp3"

2. Object to store current publishing/playback state

The object should keep Websocket session data, WebRTC connection data, room data and object to display tracks data


const CurrentState = function() {
    let state = {
        pc: null,
        session: null,
        room: null,
        remoteDisplay: null,
        set: function(pc, session, room) {
            state.pc = pc;
            state.session = session;
   = room;
        clear: function() {
   = null;
            state.session = null;
            state.pc = null;
        setDisplay: function(display) {
            state.remoteDisplay = display;
        disposeDisplay: function() {
            if (state.remoteDisplay) {
                state.remoteDisplay = null;
    return state;

3. Initialization

init() code

The init() function is called on page load and:

  • initializes state objects
  • initializes input fields
const init = function() {
    $("#playBtn").prop('disabled', true);
    $("#url").prop('disabled', true);
    $("#streamName").prop('disabled', true);

4. Establishing server connection

connect(), SFU.createRoom() code

The connect() function is called by Play button click and does the following:

  • creates PeerConnection object
  • cleans the previous session state displayed
  • sets up room configuration and creates Websocket session
  • subscribes to Websocket session events
const connect = function(state) {
    // Create peer connection
    let pc = new RTCPeerConnection();
    // Create a config to connect to SFU room
    const roomConfig = {
        // Server websocket URL
        url: $("#url").val(),
        // Use stream name as room name to play ABR
        roomName: $("#streamName").val(),
        // Make a random participant name from stream name
        nickname: "Player-" + $("#streamName").val() + "-" + createUUID(4),
        // Set room pin
        pin: 123456
    // Clean state display items
    setStatus("playStatus", "");
    setStatus("playErrorInfo", "");
    // Connect to the server (room should already exist)
    const session = sfu.createRoom(roomConfig);
    session.on(constants.SFU_EVENT.CONNECTED, function() {
        state.set(pc, session,;
        setStatus("playStatus", "CONNECTING...", "black");
    }).on(constants.SFU_EVENT.DISCONNECTED, function() {
        setStatus("playStatus", "DISCONNECTED", "green");
    }).on(constants.SFU_EVENT.FAILED, function(e) {
        setStatus("playStatus", "FAILED", "red");
        setStatus("playErrorInfo", e.status + " " + e.statusText, "red");

5. Playback start after session establishing

onConnected() code

The onConnected() function:

  • sets up Stop button click actions
  • subscribes to SFU_ROOM_EVENT.PARTICIPANT_LIST event to check if the stream is published in the room
  • subscribes to room error events
  • calls playback function
const onConnected = function(state) {
    $("#playBtn").text("Stop").off('click').click(function () {
    }).prop('disabled', false);
    $('#url').prop('disabled', true);
    $("#streamName").prop('disabled', true);
    // Add room event handling, function(e) {
        // If the room is empty, the stream is not published yet
        if(!e.participants || e.participants.length === 0) {
            setStatus("playErrorInfo", "ABR stream is not published", "red");
        else {
            setStatus("playStatus", "ESTABLISHED", "green");
    }).on(constants.SFU_ROOM_EVENT.FAILED, function(e) {
        // Display error state
        setStatus("playErrorInfo", e, "red");
    }).on(constants.SFU_ROOM_EVENT.OPERATION_FAILED, function (e) {
        // Display the operation failed
        setStatus("playErrorInfo", e.operation + " failed: " + e.error, "red");
    }).on(constants.SFU_ROOM_EVENT.ENDED, function () {
        // Publishing is stopped, dispose playback and close connection
        setStatus("playErrorInfo", "ABR stream is stopped", "red");

6. Streams playback

playStreams(), Room.join() code

The playStreams() function:

  • initializes a base container tag to display incoming media streams
  • negotiates WebRTC connection
const playStreams = function(state) {
    // Create remote display item to show remote streams
        div: document.getElementById("remoteVideo"),
        peerConnection: state.pc,
        displayOptions: {
            publisher: false,
            quality: true

7. Playback stopping

stopStreams(), CurrentState.disposeDisplay() code

const stopStreams = function(state) {

8. Play click action

onStartClick(), playFirstSound(), connect() code

The onStartClick() function:

  • validates input fields
  • in Safari browser, calls playFirstSound() before playback to automatically play incoming audio
  • calls connect() function
const onStartClick = function(state) {
    if (validateForm("connectionForm")) {
        $("#playBtn").prop('disabled', true);
        if (Browser().isSafariWebRTC()) {
            playFirstSound(document.getElementById("main"), PRELOADER_URL).then(function () {
        } else {

9. Stop click actions

onStopClick(), Session.disconnect() code

The onStopClick() function:

  • stops playback
  • disconnects Websocket session
const onStopClick = function(state) {
    $("#playBtn").prop('disabled', true);

10. Websocket session disconnection actions

onDisconnected() code

The onDisconnected() function:

  • sets up Play click actions
  • enables Server url and Room name fields access
const onDisconnected = function(state) {
    $("#playBtn").text("Play").off('click').click(function () {
    }).prop('disabled', false);
    $('#url').prop('disabled', false);
    $("#streamName").prop('disabled', false);