webrtc.signaling.answer

WebRTC answer signaling event

Triggered when a WebRTC answer is received through the unified WebSocket connection. This is the response to a WebRTC offer.

Event Properties

type · string

Event type. Always "webrtc.signaling.answer" for this event.

data · object

Event data object containing WebRTC answer information.

data.sdp · object

The SDP (Session Description Protocol) answer object. This is an RTCSessionDescription object that needs to be set as the remote description.

Example:

{
  "type": "answer",
  "sdp": "v=0\r\no=- 123456789 123456789 IN IP4 0.0.0.0\r\n..."
}

Example

{
  "type": "webrtc.signaling.answer",
  "data": {
    "sdp": {
      "type": "answer",
      "sdp": "v=0\r\no=- 123456789 123456789 IN IP4 0.0.0.0\r\n..."
    }
  }
}

Sending Answer

After receiving a WebRTC offer, you need to create an answer and send it back. Here’s how to send the answer:

const NavTalkMessageType = Object.freeze({
    WEB_RTC_OFFER: "webrtc.signaling.offer",
    WEB_RTC_ANSWER: "webrtc.signaling.answer",
    // ... other event types
});

// Function to send answer
function sendAnswerMessage(sdp) {
    const message = {
        type: NavTalkMessageType.WEB_RTC_ANSWER,
        data: { sdp: sdp }
    };
    socket.send(JSON.stringify(message));
    console.log('Sent answer:', message);
}

// Handle received offer and send answer
async function handleOffer(offerData) {
    const offer = new RTCSessionDescription(offerData.sdp);
    peerConnection = new RTCPeerConnection(configuration);
    
    await peerConnection.setRemoteDescription(offer);
    const answer = await peerConnection.createAnswer();
    await peerConnection.setLocalDescription(answer);
    
    // Send the answer (peerConnection.localDescription is an RTCSessionDescription object)
    sendAnswerMessage(peerConnection.localDescription);
}

Message Structure:

When sending an answer, the message structure should be:

{
  "type": "webrtc.signaling.answer",
  "data": {
    "sdp": {
      "type": "answer",
      "sdp": "v=0\r\no=- 8643312983218886913 2 IN IP4 127.0.0.1\r\ns=-\r\nt=0 0\r\na=group:BUNDLE 0 1\r\na=msid-semantic: WMS\r\nm=video 9 UDP/TLS/RTP/SAVPF 97 98 99 100 101 102\r\nc=IN IP4 0.0.0.0\r\na=rtcp:9 IN IP4 0.0.0.0\r\na=ice-ufrag:lwyK\r\na=ice-pwd:DL6EkCNVmdcrlsmJsjry5CiG\r\na=ice-options:trickle\r\na=fingerprint:sha-256 FE:A4:ED:91:41:78:BB:35:7D:CC:77:36:84:05:60:5D:6F:12:0A:B0:0E:A1:94:DA:90:3B:EF:6F:39:56:7F:E0\r\na=setup:active\r\na=mid:0\r\na=extmap:3 http://www.webrtc.org/experiments/rtp-hdrext/abs-send-time\r\na=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=recvonly\r\na=rtcp-mux\r\na=rtpmap:97 VP8/90000\r\na=rtcp-fb:97 goog-remb\r\na=rtcp-fb:97 nack\r\na=rtcp-fb:97 nack pli\r\na=rtpmap:98 rtx/90000\r\na=fmtp:98 apt=97\r\na=rtpmap:99 H264/90000\r\na=rtcp-fb:99 goog-remb\r\na=rtcp-fb:99 nack\r\na=rtcp-fb:99 nack pli\r\na=fmtp:99 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42001f\r\na=rtpmap:100 rtx/90000\r\na=fmtp:100 apt=99\r\na=rtpmap:101 H264/90000\r\na=rtcp-fb:101 goog-remb\r\na=rtcp-fb:101 nack\r\na=rtcp-fb:101 nack pli\r\na=fmtp:101 level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42e01f\r\na=rtpmap:102 rtx/90000\r\na=fmtp:102 apt=101\r\nm=audio 9 UDP/TLS/RTP/SAVPF 96 9 0 8\r\nc=IN IP4 0.0.0.0\r\na=rtcp:9 IN IP4 0.0.0.0\r\na=ice-ufrag:lwyK\r\na=ice-pwd:DL6EkCNVmdcrlsmJsjry5CiG\r\na=ice-options:trickle\r\na=fingerprint:sha-256 FE:A4:ED:91:41:78:BB:35:7D:CC:77:36:84:05:60:5D:6F:12:0A:B0:0E:A1:94:DA:90:3B:EF:6F:39:56:7F:E0\r\na=setup:active\r\na=mid:1\r\na=extmap:2 urn:ietf:params:rtp-hdrext:ssrc-audio-level\r\na=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid\r\na=recvonly\r\na=rtcp-mux\r\na=rtpmap:96 opus/48000/2\r\na=fmtp:96 minptime=10;useinbandfec=1\r\na=rtpmap:9 G722/8000\r\na=rtpmap:0 PCMU/8000\r\na=rtpmap:8 PCMA/8000\r\n"
    }
  }
}

Key Points:

• The sdp parameter in data.sdp should be an RTCSessionDescription object (or equivalent plain object) with:
  • type: "answer"
  • sdp: The SDP string containing the answer description
• Send the answer immediately after you receive an offer and create an answer using peerConnection.createAnswer()
• Use peerConnection.localDescription as the sdp value when sending

Receiving Answer

When you receive an answer (if you sent an offer), handle it like this:

async function handleReceivedMessage(data) {
    const nav_data = data.data;
    
    switch (data.type) {
        case NavTalkMessageType.WEB_RTC_ANSWER:
            const answer = new RTCSessionDescription(nav_data.sdp);
            await peerConnection.setRemoteDescription(answer);
            break;
    }
}

• When to send: Send an answer immediately after receiving an offer and creating an answer with peerConnection.createAnswer()
• What to send: Send peerConnection.localDescription (which is an RTCSessionDescription object) as the sdp value
• WebRTC signaling is sent through the unified WebSocket connection