Enable Real Time Text (RTT)

Note

RTT is an accessibility compliance requirement for voice and video platforms in the EU starting June 30, 2025. For more information, see Directive 2019/882.

Integrate Real Time Text (RTT) into your calling applications to enhance accessibility and ensure that all participants can communicate effectively during meetings.

RTT allows users who have difficulty speaking to participate actively by typing their messages, which are then broadcast in near real-time to other meeting participants. This feature operates seamlessly alongside existing captions and ensures that typed messages are promptly delivered without disrupting the flow of conversation.

Real Time Text Feature Overview

Real Time Text (RTT) facilitates communication for users who might have difficulty speaking during calls. By enabling users to type their messages, RTT ensures that everyone in the meeting can stay engaged and informed. Messages are transmitted over Data Channels (ID 24) and are always active, appearing automatically when the first message is sent.

On supported platforms, RTT data can display alongside captions derived from Speech to Text, providing a comprehensive view of all communications during a call.

Note

RTT for PSTN or Teams Interop isn't available at this time

Naming Conventions

Different platforms might use varying terminology for RTT-related properties. The following table summarizes the differences:

Mobile (Android/iOS)	Windows (C#)
Type	Kind
Info	Details

These aliases are functionally equivalent and are used to maintain consistency across different platforms.

RealTimeTextInfo/Details Class

The RealTimeTextInfo (or RealTimeTextDetails on Windows) class encapsulates information about each RTT message. The following table shows key properties:

Property	Description
SequenceId	Unique identifier for the message sequence.
Text	The content of the RTT message.
Sender	Information about the sender of the message.
ResultType/ Kind	Indicates whether the message is partial or final.
IsLocal	Determines if a local user sent the message.
ReceivedTime	Timestamp when the message was received.
UpdatedTime	Timestamp when the message was last updated.

Models

Name	Description
RealTimeTextFeature	API for RealTimeText
RealTimeTextInfo	Data structure received for each RealTimeText event
RealTimeTextReceivedEventHandler	Callback definition for handling RealTimeTextReceivedEventType event

Get RealTimeText feature

let realTimeTextFeature: SDK.RealTimeTextFeature = call.feature(SDK.Features.RealTimeText);

Subscribe to listeners

Add a listener for RealTimeText data received

Handle the returned RealTimeTextInfo data object. Ideally, you would have this on handler set once call is connected.

Note: The object contains a resultType prop that indicates whether the data is a partial text or a finalized version of the text. ResultType Partial indicates live messages that are subject to change, while Final indicates completed messages with no further changes pending.

const realTimeTextReceivedHandler: SDK.RealTimeTextReceivedEventHandler = (data: SDK.RealTimeTextInfo) => { 
    /** USER CODE HERE - E.G. RENDER TO DOM 
     *  data.sequenceId
     *  data.sender
     *  data.text
     *  data.resultType
     *  data.receivedTimestamp
     *  data.updatedTimestamp
     *  data.isLocal
    */
    // Example code:
    // Create a dom element, i.e. div, with id "rttArea" before proceeding with the sample code
    let mri: string = '';
    let displayName: string = '';
    switch (data.sender.identifier.kind) {
        case 'communicationUser': { mri = data.sender.identifier.communicationUserId; displayName = data.sender.displayName; break; }
        case 'microsoftTeamsUser': { mri = data.sender.identifier.microsoftTeamsUserId; displayName = data.sender.displayName; break; }
        case 'phoneNumber': { mri = data.sender.identifier.phoneNumber;  displayName = data.sender.displayName; break; }
    }

    const newClassName = `prefix${mri.replace(/:/g, '').replace(/-/g, '').replace(/\+/g, '')}`;
    const rttText = `${(data.receivedTimestamp).toUTCString()} ${displayName ?? mri}: `;

    let foundRTTContainer = this.elements.rttArea.querySelector(`.${newClassName}[isNotFinal='true']`);
    if (!foundRTTContainer) {
        let rttContainer = document.createElement('div');
        rttContainer.setAttribute('isNotFinal', 'true');
        rttContainer.style['borderBottom'] = '1px solid';
        rttContainer.style['whiteSpace'] = 'pre-line';
        rttContainer.textContent = rttText + data.text;
        rttContainer.classList.add(newClassName);

        this.elements.rttArea.appendChild(rttContainer);

        setTimeout(() => {
            this.elements.rttArea.removeChild(rttContainer);
        }, 40000);
    } else {
        if (data.text === '') {
            this.elements.rttArea.removeChild(foundRTTContainer);
        }
        if (data.resultType === 'Final') {
            foundRTTContainer.setAttribute('isNotFinal', 'false');
            if (data.isLocal) {
                let rttTextField = this.elements.rttMessage;
                rttTextField.value = '';
            }
        } else {
            foundRTTContainer.textContent = rttText + data.text;
        }
    }
}; 
realTimeTextFeature.on('realTimeTextReceived', realTimeTextReceivedHandler); 

Send RealTimeText live handler

In order to simulate live messaging, you will need to set up a live handler to send RealTimeText as the user types.

let rttTextField = document.getElementById("rttMessage") as HTMLInputElement;
rttTextField.addEventListener('keyup', (event) => {
    await realTimeTextFeature.sendRealTimeText(rttTextField.value);
});

Send Finalized RealTimeText

Once you are certain that the message has been finalized, for example, the user clicks on send message or presses enter, pass true to the sendRealTimeText function.

try {
    let rttTextField = document.getElementById("rttMessage") as HTMLInputElement;
    await realTimeTextFeature.sendRealTimeText(rttTextField.value, true);
    rttTextField.value = '';
} catch (e) {
    console.log('ERROR Send RTT failed', e);
}

Unsubscribe to listeners

realTimeTextFeature.off('realTimeTextReceived', realTimeTextReceivedHandler); 

RealTimeTextInfo Class

The RealTimeTextInfo class provides detailed information about each real-time text message:

• sender: Information about who sent the message.
• sequenceId: Unique identifier for the message.
• text: The content of the message.
• resultType: Indicates if the message is partial or finalized.
• receivedTimestamp: Timestamp when the message was received.
• updatedTimestamp: Timestamp when the message was last updated.
• isLocal: Indicates if the message was sent by the local user.

Other Links

• Get started with RTT in the UI Library

Models

Name	Description
RealTimeTextInfo	Represents a real-time text message entry, including sender information, message content, sequence ID, and status.

Get Real Time Text Feature

To access the Real Time Text feature, retrieve it from the Call object:

RealTimeTextCallFeature rttFeature = call.feature(Features.REAL_TIME_TEXT);

Feature Usage

Sending Real Time Text Messages

Bind a text input field to the send() method to transmit messages as the user types:

EditText messageEditText = findViewById(R.id.messageEditText);
messageEditText.addTextChangedListener(new TextWatcher() {
    @Override
    public void afterTextChanged(Editable s) {
        String text = s.toString();
        rttFeature.send(text);
    }
    // Other overridden methods...
});

Receiving Real Time Text Messages

Subscribe to the OnInfoReceived event to handle incoming messages:

rttFeature.addOnInfoReceivedListener((eventArgs) -> {
    RealTimeTextInfo info = eventArgs.getInfo();
    
    // Update your message list with the new info
    updateMessageList(info);
    
    // Clear the text input if the message is local and finalized
    if (info.isLocal() && info.getResultType() == RealTimeTextResultType.FINAL) {
        messageEditText.getText().clear();
    }
});

RealTimeTextInfo Class

The RealTimeTextInfo class provides detailed information about each real-time text message:

• Sender: Information about who sent the message.
• SequenceId: Unique identifier for the message.
• Text: The content of the message.
• ResultType: Indicates if the message is partial or finalized.
• ReceivedTime: Timestamp when the message was received.
• UpdatedTime: Timestamp when the message was last updated.
• IsLocal: Indicates if the message was sent by the local user.

Models

Name	Description
RealTimeTextInfo	Represents a real-time text message entry, including sender information, message content, sequence ID, and status.

Get Real Time Text Feature

Access the Real Time Text feature from your Call object:

let rttFeature = call.feature(Features.realTimeText)

Feature Usage

Sending Real Time Text Messages

Bind a text input field to the send method to transmit messages as the user types:

@State var messageText: String = ""

TextField("Type your message", text: $messageText)
    .onChange(of: messageText) { newText in
        rttFeature?.send(newText)
    }

Receiving Real Time Text Messages

Subscribe to the OnInfoReceived event to handle incoming messages:

rttFeature?.addOnInfoReceivedListener { eventArgs in
    if let info = eventArgs.info {
        // Update your message list with the new info
        updateMessageList(info)
        
        // Clear the text input if the message is local and finalized
        if info.isLocal && info.resultType == .final {
            self.messageText = ""
        }
    }
}

RealTimeTextInfo Class

The RealTimeTextInfo class provides detailed information about each real-time text message:

• Sender: Information about who sent the message.
• SequenceId: Unique identifier for the message.
• Text: The content of the message.
• ResultType: Indicates if the message is partial or finalized.
• ReceivedTime: Timestamp when the message was received.
• UpdatedTime: Timestamp when the message was last updated.
• IsLocal: Indicates if the message was sent by the local user.

Models

Name	Description
RealTimeTextDetails	Represents a real-time text message entry, including sender information, message content, sequence ID, and status.

Get Real Time Text Feature

Retrieve the Real Time Text feature from the Call object:

RealTimeTextCallFeature rttFeature = call.GetRealTimeTextCallFeature();

Feature Usage

Sending Real Time Text Messages

Connect a text input field to the Send method to transmit messages as the user types:

TextBox messageTextBox = new TextBox();
messageTextBox.TextChanged += (sender, args) => {
    string text = messageTextBox.Text;
    rttFeature.Send(text);
};

Receiving Real Time Text Messages

Subscribe to the DetailsReceived event to handle incoming messages:

rttFeature.DetailsReceived += (sender, e) => {
    RealTimeTextDetails details = e.Details;
    
    // Update your message list with the new details
    UpdateMessageList(details);
    
    // Clear the text input if the message is local and finalized
    if (details.IsLocal && details.Kind == RealTimeTextResultKind.Final) {
        messageTextBox.Text = string.Empty;
    }
};

RealTimeTextDetails Class

The RealTimeTextDetails class provides comprehensive information about each real-time text message:

• Sender: Information about who sent the message.
• SequenceId: Unique identifier for the message.
• Text: The content of the message.
• Kind: Indicates if the message is partial or finalized.
• ReceivedTime: Timestamp when the message was received.
• UpdatedTime: Timestamp when the message was last updated.
• IsLocal: Indicates if the message was sent by the local user.

Next steps

• Learn more about RTT in our Real Time Text Conceptual Doc.
• Learn more with our Azure Communication Services Calling Documentation.
• Learn more about Closed captions.