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The example shows how to publish and play a number of streams in one WebRTC connection with simulcast. A room is considered to be a publishing unit, that is, viewers who connect to this room receive all the streams published in it.

On the screenshots below:

  • Server url - Websocket URL of WCS server
  • Room name - room name
  • Publisher - publisher user name

  • Player - viewer user name
  • 360p, 720p, 180p send - quality switch buttons

Note that audio tracks are playing in a separate audio tags.

Example source code

To analyze the example source code, take the version available here, which can be downloaded with build 1.0.1.36

The source code consists of the following modules:

  • two-way-streaming.html - HTML page
  • two-way-streaming.css - HTML page styles
  • two-way-streaming.js - main application logic
  • config.json - client configuration file, contains streams publishing description

Analyzing the code

To analyze the example source code, take the file two-way-streaming.js version available here, which can be downloaded with build 1.0.41

1. Local variables

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

code

const constants = SFU.constants;
const sfu = SFU;
let mainConfig;
let localDisplay;
let remoteDisplay;
let publishState;
let playState;
const PUBLISH = "publish";
const PLAY = "play";
const STOP = "stop";
const PRELOADER_URL="../commons/media/silence.mp3"

2. Default configuration

Default room configuration and stream publishing configuration to use if there is no config.json file found

code

const defaultConfig = {
    room: {
        url: "wss://127.0.0.1:8888",
        name: "ROOM1",
        pin: "1234",
        nickName: "User1"
    },
    media: {
        audio: {
            tracks: [
                {
                    source: "mic",
                    channels: 1
                }
            ]
        },
        video: {
            tracks: [
                {
                    source: "camera",
                    width: 640,
                    height: 360,
                    codec: "H264",
                    encodings: [
                        { rid: "360p", active: true, maxBitrate: 500000 },
                        { rid: "180p", active: true, maxBitrate: 200000, scaleResolutionDownBy: 2 }
                    ]
                }
            ]
        }
    }
};

3. Object to store current publishing/playback state

The object should keep Websocket session data, WebRTC connection data and room data, and shoukd form HTML tags ids to access them from code.

code

const CurrentState = function(prefix) {
    let state = {
        prefix: prefix,
        pc: null,
        session: null,
        room: null,
        timer: null,
        set: function(pc, session, room) {
            state.pc = pc;
            state.session = session;
            state.room = room;
        },
        clear: function() {
            state.stopWaiting();
            state.room = null;
            state.session = null;
            state.pc = null;
        },
        waitFor: function(div, timeout) {
            state.stopWaiting();
            state.timer = setTimeout(function () {
                if (div.innerHTML !== "") {
                    // Enable stop button
                    $("#" + state.buttonId()).prop('disabled', false);
                }
                else if (state.isConnected()) {
                    setStatus(state.errInfoId(), "No media capturing started in " + timeout + " ms, stopping", "red");
                    onStopClick(state);
                }
            }, timeout);        
        },
        stopWaiting: function() {
            if (state.timer) {
                clearTimeout(state.timer);
                state.timer = null;                
            }
        },
        buttonId: function() {
            return state.prefix + "Btn";
        },
        buttonText: function() {
            return (state.prefix.charAt(0).toUpperCase() + state.prefix.slice(1));
        },
        inputId: function() {
            return state.prefix + "Name";
        },
        statusId: function() {
            return state.prefix + "Status";
        },
        formId: function() {
            return state.prefix + "Form";
        },
        errInfoId: function() {
            return state.prefix + "ErrorInfo";
        },
        is: function(value) {
            return (prefix === value);
        },
        isActive: function() {
            return (state.room && state.pc);
        },
        isConnected: function() {
            return (state.session && state.session.state() == constants.SFU_STATE.CONNECTED);
        }
    };
    return state;
}

4. Initialization

init() code

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

  • initializes state objects
  • reads config.json file or default configuration
  • initializes input fields
const init = function() {
    let configName = getUrlParam("config") || "./config.json";
    ...
    publishState = CurrentState(PUBLISH);
    playState = CurrentState(PLAY);
    $.getJSON(configName, function(cfg){
        mainConfig = cfg;
        onDisconnected(publishState);
        onDisconnected(playState);
    }).fail(function(e){
        //use default config
        console.error("Error reading configuration file " + configName + ": " + e.status + " " + e.statusText)
        console.log("Default config will be used");
        mainConfig = defaultConfig;
        onDisconnected(publishState);
        onDisconnected(playState);
    });
    $("#url").val(setURL());
    $("#roomName").val("ROOM1-"+createUUID(4));
    $("#publishName").val("Publisher1-"+createUUID(4));
    $("#playName").val("Player1-"+createUUID(4));
}

5. Establishing server connection

connect(), SFU.createRoom() code

The connect() function is called by Publish or Play click:

  • creates PeerConnection object
  • cleans previous session state displayed
  • sets up room configuration and creates Websocket session
  • subscribes to Websocket session events
const connect = function(state) {
    //create peer connection
    pc = new RTCPeerConnection();
    //get config object for room creation
    const roomConfig = getRoomConfig(mainConfig);
    roomConfig.pc = pc;
    roomConfig.url = $("#url").val();
    roomConfig.roomName = $("#roomName").val();
    roomConfig.nickname = $("#" + state.inputId()).val();
    // clean state display items
    setStatus(state.statusId(), "");
    setStatus(state.errInfoId(), "");
    // connect to server and create a room if not
    const session = sfu.createRoom(roomConfig);
    session.on(constants.SFU_EVENT.CONNECTED, function(room) {
        state.set(pc, session, room);
        onConnected(state);
        setStatus(state.statusId(), "ESTABLISHED", "green");
    }).on(constants.SFU_EVENT.DISCONNECTED, function() {
        state.clear();
        onDisconnected(state);
        setStatus(state.statusId(), "DISCONNECTED", "green");
    }).on(constants.SFU_EVENT.FAILED, function(e) {
        state.clear();
        onDisconnected(state);
        setStatus(state.statusId(), "FAILED", "red");
        setStatus(state.errInfoId(), e.status + " " + e.statusText, "red");
    });
}

6. Publishing or playback start after session establishing

onConnected() code

The onConnected() function:

  • sets up Stop button click actions
  • subscribes to room error events
  • calls publishing or playback function
const onConnected = function(state) {
    $("#" + state.buttonId()).text("Stop").off('click').click(function () {
        onStopClick(state);
    });
    ...
    // Add errors displaying
    state.room.on(constants.SFU_ROOM_EVENT.FAILED, function(e) {
        setStatus(state.errInfoId(), e, "red");
        stopStreaming(state);
    }).on(constants.SFU_ROOM_EVENT.OPERATION_FAILED, function (e) {
        setStatus(state.errInfoId(), e.operation + " failed: " + e.error, "red");
        stopStreaming(state);
    });
    startStreaming(state);
}

7. Streams publishing

publishStreams(), SFURoom.join() code

The publishStreams() function:

  • initializes a basic HTML container tag to display local video
  • gets local media access accorging to configuration file
  • adds media tracks to WEbRTC connection
  • joins the room on server
  • starts a timer to wait for successful local video tags initializaton
const publishStreams = async function(state) {
    if (state.isConnected()) {
        //create local display item to show local streams
        localDisplay = initLocalDisplay(document.getElementById("localVideo"));
        try {
            //get configured local video streams
            let streams = await getVideoStreams(mainConfig);
            let audioStreams = await getAudioStreams(mainConfig);
            if (state.isConnected() && state.isActive()) {
                //combine local video streams with audio streams
                streams.push.apply(streams, audioStreams);
                let config = {};
                //add our local streams to the room (to PeerConnection)
                streams.forEach(function (s) {
                    //add local stream to local display
                    localDisplay.add(s.stream.id, $("#" + state.inputId()).val(), s.stream);
                    //add each track to PeerConnection
                    s.stream.getTracks().forEach((track) => {
                        if (s.source === "screen") {
                            config[track.id] = s.source;
                        }
                        addTrackToPeerConnection(state.pc, s.stream, track, s.encodings);
                        subscribeTrackToEndedEvent(state.room, track, state.pc);
                    });
                });
                state.room.join(config);
                // TODO: Use room state or promises to detect if publishing started to enable stop button
                state.waitFor(document.getElementById("localVideo"), 3000);
            }
        } catch(e) {
            console.error("Failed to capture streams: " + e);
            setStatus(state.errInfoId(), e.name, "red");
            state.stopWaiting();
            if (state.isConnected()) { 
                onStopClick(state);
            }
        }
    }
}

7.1. Media tracks addition to WebRTC connection

addTrackToPeerConnection(), PeerConnection.addTransceiver() code

const addTrackToPeerConnection = function(pc, stream, track, encodings) {
    pc.addTransceiver(track, {
        direction: "sendonly",
        streams: [stream],
        sendEncodings: encodings ? encodings : [] //passing encoding types for video simulcast tracks
    });
}

7.2. Tracks onended event subscription

subscribeTrackToEndedEvent(), MediaTrack.addEventListener(), SFURoom.updateState() code

const subscribeTrackToEndedEvent = function(room, track, pc) {
    track.addEventListener("ended", function() {
        //track ended, see if we need to cleanup
        let negotiate = false;
        for (const sender of pc.getSenders()) {
            if (sender.track === track) {
                pc.removeTrack(sender);
                //track found, set renegotiation flag
                negotiate = true;
                break;
            }
        }
        if (negotiate) {
            //kickoff renegotiation
            room.updateState();
        }
    });
};

8. Streams playback

playStreams(), SFURoom.join() code

The playStreams() function:

  • initializes a base container tag to display incoming media streams
  • joins to the room on server
const playStreams = function(state) {
    if (state.isConnected() && state.isActive()) {
        //create remote display item to show remote streams
        remoteDisplay = initRemoteDisplay(document.getElementById("remoteVideo"), state.room, state.pc);
        state.room.join();
    }
    $("#" + state.buttonId()).prop('disabled', false);
}

9. Publishing stopping

unPublishStreams(), localDisplay.stop() code

const unPublishStreams = function(state) {
    if (localDisplay) {
        localDisplay.stop();
    }
}

10. Playback stopping

stopStreams(), remoteDisplay.stop() code

const stopStreams = function(state) {
    if (remoteDisplay) {
        remoteDisplay.stop();
    }
}

11. Publish/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") && validateForm(state.formId())) {
        $("#" + state.buttonId()).prop('disabled', true);
        if (state.is(PLAY) && Browser().isSafariWebRTC()) {
            playFirstSound(document.getElementById("main"), PRELOADER_URL).then(function () {
                connect(state);
            });
        } else {
            connect(state);
        }
    }
}

12. Stop click actions

onStopClick(), Session.disconnect() code

The onStopClick() function:

  • stops playback or publishing
  • disconects Websocket session
const onStopClick = function(state) {
    $("#" + state.buttonId()).prop('disabled', true);
    stopStreaming(state);
    if (state.isConnected()) {
        state.session.disconnect();
    }
}

13. Websocket session disconnection actions

onDisconnected() code

The onDisconnected() functions:

  • sets up Publish/Play click actions
  • enables Server url and Room name fields access, if there's no parallel session
const onDisconnected = function(state) {
    $("#" + state.buttonId()).text(state.buttonText()).off('click').click(function () {
        onStartClick(state);
    }).prop('disabled', false);
    $("#" + state.inputId()).prop('disabled', false);
    // Check if other session is active
    if ((state.is(PUBLISH) && playState.session)
       || (state.is(PLAY) && publishState.session)) {
        return;
    }
    $('#url').prop('disabled', false);
    $("#roomName").prop('disabled', false);
}

14. Helper functions

14.1. Start publishing or playback

startStreaming() code

const startStreaming = function(state) {
    if (state.is(PUBLISH)) {
        publishStreams(state);
    } else if (state.is(PLAY)) {
        playStreams(state);
    }
}

14.2. Stop publishing or playback

stopStreaming() code

const stopStreaming = function(state) {
    state.stopWaiting();
    if (state.is(PUBLISH)) {
        unPublishStreams(state);
    } else if (state.is(PLAY)) {
        stopStreams(state);
    }
}
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