Telnyx WebRTC - Flutter SDK

Build real-time voice communication into Flutter applications (Android, iOS, Web).

Prerequisites: Create WebRTC credentials and generate a login token using the Telnyx server-side SDK. See the telnyx-webrtc-* skill in your server language plugin (e.g., telnyx-python, telnyx-javascript).

Quick Start Option

For faster implementation, consider Telnyx Common - a higher-level abstraction that simplifies WebRTC integration with minimal setup.

Installation

Add to pubspec.yaml:

dependencies:
  telnyx_webrtc: ^latest_version

Then run:

flutter pub get

Platform Configuration

Android

Add to AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />

iOS

Add to Info.plist:

<key>NSMicrophoneUsageDescription</key>
<string>$(PRODUCT_NAME) needs microphone access for calls</string>

---

Authentication

Option 1: Credential-Based Login

final telnyxClient = TelnyxClient();

final credentialConfig = CredentialConfig(
  sipUser: 'your_sip_username',
  sipPassword: 'your_sip_password',
  sipCallerIDName: 'Display Name',
  sipCallerIDNumber: '+15551234567',
  notificationToken: fcmOrApnsToken,  // Optional: for push
  autoReconnect: true,
  debug: true,
  logLevel: LogLevel.debug,
);

telnyxClient.connectWithCredential(credentialConfig);

Option 2: Token-Based Login (JWT)

final tokenConfig = TokenConfig(
  sipToken: 'your_jwt_token',
  sipCallerIDName: 'Display Name',
  sipCallerIDNumber: '+15551234567',
  notificationToken: fcmOrApnsToken,
  autoReconnect: true,
  debug: true,
);

telnyxClient.connectWithToken(tokenConfig);

Configuration Options

Parameter	Type	Description
sipUser / sipToken	String	Credentials from Telnyx Portal
sipCallerIDName	String	Caller ID name displayed to recipients
sipCallerIDNumber	String	Caller ID number
notificationToken	String?	FCM (Android) or APNS (iOS) token
autoReconnect	bool	Auto-retry login on failure
debug	bool	Enable call quality metrics
logLevel	LogLevel	none, error, warning, debug, info, all
ringTonePath	String?	Custom ringtone asset path
ringbackPath	String?	Custom ringback tone asset path

---

Making Outbound Calls

telnyxClient.call.newInvite(
  'John Doe',           // callerName
  '+15551234567',       // callerNumber
  '+15559876543',       // destinationNumber
  'my-custom-state',    // clientState
);

---

Receiving Inbound Calls

Listen for socket events:

InviteParams? _incomingInvite;
Call? _currentCall;

telnyxClient.onSocketMessageReceived = (TelnyxMessage message) {
  switch (message.socketMethod) {
    case SocketMethod.CLIENT_READY:
      // Ready to make/receive calls
      break;
      
    case SocketMethod.LOGIN:
      // Successfully logged in
      break;
      
    case SocketMethod.INVITE:
      // Incoming call!
      _incomingInvite = message.message.inviteParams;
      // Show incoming call UI...
      break;
      
    case SocketMethod.ANSWER:
      // Call was answered
      break;
      
    case SocketMethod.BYE:
      // Call ended
      break;
  }
};

// Accept the incoming call
void acceptCall() {
  if (_incomingInvite != null) {
    _currentCall = telnyxClient.acceptCall(
      _incomingInvite!,
      'My Name',
      '+15551234567',
      'state',
    );
  }
}

---

Call Controls

// End call
telnyxClient.call.endCall(telnyxClient.call.callId);

// Decline incoming call
telnyxClient.createCall().endCall(_incomingInvite?.callID);

// Mute/Unmute
telnyxClient.call.onMuteUnmutePressed();

// Hold/Unhold
telnyxClient.call.onHoldUnholdPressed();

// Toggle speaker
telnyxClient.call.enableSpeakerPhone(true);

// Send DTMF tone
telnyxClient.call.dtmf(telnyxClient.call.callId, '1');

---

Push Notifications - Android (FCM)

1. Setup Firebase

// main.dart
@pragma('vm:entry-point')
Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  
  if (defaultTargetPlatform == TargetPlatform.android) {
    await Firebase.initializeApp();
    FirebaseMessaging.onBackgroundMessage(_firebaseBackgroundHandler);
  }
  
  runApp(const MyApp());
}

2. Background Handler

Future<void> _firebaseBackgroundHandler(RemoteMessage message) async {
  // Show notification (e.g., using flutter_callkit_incoming)
  showIncomingCallNotification(message);
  
  // Listen for user action
  FlutterCallkitIncoming.onEvent.listen((CallEvent? event) {
    switch (event!.event) {
      case Event.actionCallAccept:
        TelnyxClient.setPushMetaData(
          message.data,
          isAnswer: true,
          isDecline: false,
        );
        break;
      case Event.actionCallDecline:
        TelnyxClient.setPushMetaData(
          message.data,
          isAnswer: false,
          isDecline: true,  // SDK handles decline automatically
        );
        break;
    }
  });
}

3. Handle Push When App Opens

Future<void> _handlePushNotification() async {
  final data = await TelnyxClient.getPushMetaData();
  if (data != null) {
    PushMetaData pushMetaData = PushMetaData.fromJson(data);
    telnyxClient.handlePushNotification(
      pushMetaData,
      credentialConfig,
      tokenConfig,
    );
  }
}

Early Accept/Decline Handling

bool _waitingForInvite = false;

void acceptCall() {
  if (_incomingInvite != null) {
    _currentCall = telnyxClient.acceptCall(...);
  } else {
    // Set flag if invite hasn't arrived yet
    _waitingForInvite = true;
  }
}

// In socket message handler:
case SocketMethod.INVITE:
  _incomingInvite = message.message.inviteParams;
  if (_waitingForInvite) {
    acceptCall();  // Accept now that invite arrived
    _waitingForInvite = false;
  }
  break;

---

Push Notifications - iOS (APNS + PushKit)

1. AppDelegate Setup

// AppDelegate.swift
func pushRegistry(_ registry: PKPushRegistry, 
                  didUpdate credentials: PKPushCredentials, 
                  for type: PKPushType) {
    let deviceToken = credentials.token.map { 
        String(format: "%02x", $0) 
    }.joined()
    SwiftFlutterCallkitIncomingPlugin.sharedInstance?
        .setDevicePushTokenVoIP(deviceToken)
}

func pushRegistry(_ registry: PKPushRegistry,
                  didReceiveIncomingPushWith payload: PKPushPayload,
                  for type: PKPushType,
                  completion: @escaping () -> Void) {
    guard type == .voIP else { return }
    
    if let metadata = payload.dictionaryPayload["metadata"] as? [String: Any] {
        let callerName = (metadata["caller_name"] as? String) ?? ""
        let callerNumber = (metadata["caller_number"] as? String) ?? ""
        let callId = (metadata["call_id"] as? String) ?? UUID().uuidString
        
        let data = flutter_callkit_incoming.Data(
            id: callId,
            nameCaller: callerName,
            handle: callerNumber,
            type: 0
        )
        data.extra = payload.dictionaryPayload as NSDictionary
        
        SwiftFlutterCallkitIncomingPlugin.sharedInstance?
            .showCallkitIncoming(data, fromPushKit: true)
    }
}

2. Handle in Flutter

FlutterCallkitIncoming.onEvent.listen((CallEvent? event) {
  switch (event!.event) {
    case Event.actionCallIncoming:
      PushMetaData? pushMetaData = PushMetaData.fromJson(
        event.body['extra']['metadata']
      );
      telnyxClient.handlePushNotification(
        pushMetaData,
        credentialConfig,
        tokenConfig,
      );
      break;
    case Event.actionCallAccept:
      // Handle accept
      break;
  }
});

---

Handling Late Notifications

const CALL_MISSED_TIMEOUT = 60;  // seconds

void handlePushMessage(RemoteMessage message) {
  DateTime now = DateTime.now();
  Duration? diff = now.difference(message.sentTime!);
  
  if (diff.inSeconds > CALL_MISSED_TIMEOUT) {
    showMissedCallNotification(message);
    return;
  }
  
  // Handle normal incoming call...
}

---

Call Quality Metrics

Enable with debug: true in config:

// When making a call
call.newInvite(
  callerName: 'John',
  callerNumber: '+15551234567',
  destinationNumber: '+15559876543',
  clientState: 'state',
  debug: true,
);

// Listen for quality updates
call.onCallQualityChange = (CallQualityMetrics metrics) {
  print('MOS: ${metrics.mos}');
  print('Jitter: ${metrics.jitter * 1000} ms');
  print('RTT: ${metrics.rtt * 1000} ms');
  print('Quality: ${metrics.quality}');  // excellent, good, fair, poor, bad
};

Quality Level	MOS Range
excellent	> 4.2
good	4.1 - 4.2
fair	3.7 - 4.0
poor	3.1 - 3.6
bad	≤ 3.0

---

AI Agent Integration

Connect to a Telnyx Voice AI Agent:

1. Anonymous Login

try {
  await telnyxClient.anonymousLogin(
    targetId: 'your_ai_assistant_id',
    targetType: 'ai_assistant',  // Default
    targetVersionId: 'optional_version_id',  // Optional
  );
} catch (e) {
  print('Login failed: $e');
}

2. Start Conversation

telnyxClient.newInvite(
  'User Name',
  '+15551234567',
  '',  // Destination ignored for AI Agent
  'state',
  customHeaders: {
    'X-Account-Number': '123',  // Maps to {{account_number}}
    'X-User-Tier': 'premium',   // Maps to {{user_tier}}
  },
);

3. Receive Transcripts

telnyxClient.onTranscriptUpdate = (List<TranscriptItem> transcript) {
  for (var item in transcript) {
    print('${item.role}: ${item.content}');
    // role: 'user' or 'assistant'
    // content: transcribed text
    // timestamp: when received
  }
};

// Get current transcript anytime
List<TranscriptItem> current = telnyxClient.transcript;

// Clear transcript
telnyxClient.clearTranscript();

4. Send Text to AI Agent

Call? activeCall = telnyxClient.calls.values.firstOrNull;

if (activeCall != null) {
  activeCall.sendConversationMessage(
    'Hello, I need help with my account'
  );
}

---

Custom Logging

class MyCustomLogger extends CustomLogger {
  @override
  log(LogLevel level, String message) {
    print('[$level] $message');
    // Send to analytics, file, server, etc.
  }
}

final config = CredentialConfig(
  // ... other config
  logLevel: LogLevel.debug,
  customLogger: MyCustomLogger(),
);

---

Troubleshooting

Issue	Solution
No audio on Android	Check RECORD_AUDIO permission
No audio on iOS	Check NSMicrophoneUsageDescription in Info.plist
Push not working (debug)	Push only works in release mode
Login fails	Verify SIP credentials in Telnyx Portal
10-second timeout	INVITE didn't arrive - check network/push setup
sender_id_mismatch	FCM project mismatch between app and server

API Reference

TxClient

Telnyx Client

TelnyxClient() is the core class of the SDK, and can be used to connect to our backend socket connection, create calls, check state and disconnect, etc.

    TelnyxClient _telnyxClient = TelnyxClient();

Logging into Telnyx Client

To log into the Telnyx WebRTC client, you'll need to authenticate using a Telnyx SIP Connection. Follow our quickstart guide to create JWTs (JSON Web Tokens) to authenticate. To log in with a token we use the connectWithToken() method. You can also authenticate directly with the SIP Connection username and password with the connectWithCredential() method:

    _telnyxClient.connectWithToken(tokenConfig)
                     //OR
    _telnyxClient.connectWithCredential(credentialConfig)             

Listening for events and reacting - Accepting a Call

In order to be able to accept a call, we first need to listen for invitations. We do this by getting the Telnyx Socket Response callbacks from our TelnyxClient:

Call

Call

The Call class is used to manage the call state and call actions. It is used to accept, decline, end, mute, hold, and send DTMF tones during a call.

Accept Call

In order to accept a call, we simply retrieve the instance of the call and use the .acceptCall(callID) method:

    _telnyxClient.call.acceptCall(_incomingInvite?.callID);

Decline / End Call

In order to end a call, we can get a stored instance of Call and call the .endCall(callID) method. To decline an incoming call we first create the call with the .createCall() method and then call the .endCall(callID) method:

    if (_ongoingCall) {
      _telnyxClient.call.endCall(_telnyxClient.call.callId);
    } else {
      _telnyxClient.createCall().endCall(_incomingInvite?.callID);
    }

DTMF (Dual Tone Multi Frequency)

In order to send a DTMF message while on a call you can call the .dtmf(callID, tone), method where tone is a String value of the character you would like pressed:

    _telnyxClient.call.dtmf(_telnyxClient.call.callId, tone);

Mute a call

To mute a call, you can simply call the .onMuteUnmutePressed() method:

    _telnyxClient.call.onMuteUnmutePressed();

Toggle loud speaker

To toggle loud speaker, you can simply call .enableSpeakerPhone(bool):

    _telnyxClient.call.enableSpeakerPhone(true);

Put a call on hold

To put a call on hold, you can simply call the .onHoldUnholdPressed() method:

    _telnyxClient.call.onHoldUnholdPressed();