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Audio Connector lets you send raw audio (PCM 16 khz/16bit) streams from a live Vonage Video session to external services such as AWS, GCP, Azure, etc., through your own servers for further processing and analysis.

Using Audio Connector, you can send audio streams individually or mixed. You can identify the speaker by sending the audio streams individually by opening multiple WS connections.

The further processing of audio streams in real-time and offline enables building capabilities such as captions, transcriptions, translations, search and index, content moderation, media intelligence, Electronic Health Records, sentiment analysis, etc.

Audio Connector is enabled by default for all projects, and it is a usage-based product. Audio Connector usage is charged based on the number of audio streams of participants (or stream IDs) that are sent to the WebSocket server. The Audio Connector feature is only supported in routed sessions (sessions that use the OpenTok Media Router). You can send up to 50 audio streams from a single session at a time.

This page includes the following sections:

• Starting a WebSocket connection
• WebSocket messages
• Stopping a WebSocket connection
• Automatic reconnections
• Sample application

Starting a WebSocket connection

To start an Audio Connector WebSocket connection, use the OpenTok REST API.

You can also you can also start an Audio Connector WebSocket connection using the OpenTok server SDKs:

• Java — See the OpenTok.connectAudioStream() method.
• Node — See the opentok.websocketConnect() method.
• PHP — See the OpenTok->connectAudio()] method.
• Python — See the opentok.connect_audio_to_websocket() method.
• Ruby — See the opentok.websocket.connect() method
• .NET — See the OpenTok.StartBroadcast() method

Make an HTTPS POST request to the following URL:

https://api.opentok.com/v2/project/:apiKey/connect

Replace apiKey with your OpenTok API key.

Set the Content-Type header to application/json. Set a custom X-OPENTOK-AUTH header to a JSON Web token that is valid for use with the OpenTok REST API calls. See the section on OpenTok REST API call authentication.

Set the body of the request to JSON data of the following format:

{
  "sessionId": "OpenTok session ID",
  "token": "A valid OpenTok token",
  "websocket": {
    "uri": "wss://service.com/ws-endpoint",
    "streams": [
      "streamId-1",
      "streamId-2"
    ],
    "headers": {
      "headerKey": "headerValue"
    },
    "audioRate" : 8000
  }
}

The JSON object includes the following properties:

• sessionId​ (required) — The OpenTok session ID that includes the OpenTok streams you want to include in the WebSocket stream.

• token​ (required) — The OpenTok token to be used for the Audio Connector connection to the OpenTok session. You can add token data to identify that the connection is the Audio Connector endpoint or for other identifying data. (The OpenTok client libraries include properties for inspecting the connection data for a client connected to a session.) See the Token Creation developer guide.

• websocket ​(required): Included details for the WebSocket:

  • uri ​(required): A publicly reachable WebSocket URI to be used for the destination of the audio stream (such as "wss://service.com/ws-endpoint").

  • streams (optional) — An array of stream IDs for the OpenTok streams you want to include in the WebSocket stream. If you omit this property, all streams in the session will be included.

  • headers​ (optional) — An object of key-value pairs of headers to be sent to your WebSocket server with each message, with a maximum length of 512 bytes.

  • audioRate (optional) — A number representing the audio sampling rate in Hz. Accepted values are 8000 and 16000 (the default).

A successful call results in a HTTP 200 response, with details included in the JSON response data:

{
  "id": "b0a5a8c7-dc38-459f-a48d-a7f2008da853",
  "connectionId": "e9f8c166-6c67-440d-994a-04fb6dfed007"
}

The JSON response data includes the following properties:

• id — A unique ID identifying the Audio Connector WebSocket connection.

• connectionId — The OpenTok connection ID for the Audio Connector WebSocket connection in the OpenTok session.

For more details, see the Audio Connector REST API documentation.

WebSocket messages

First message

The initial message sent on the established WebSocket connection is text-based, containing a JSON payload. The JSON details the audio format in content-type, along with any other metadata that you put in the headers property of the body in the POST request to start the WebSocket connection:

{
    "content-type":"audio/l16;rate=16000",
    "CUSTOM-HEADER-1": "value-1",
    "CUSTOM-HEADER-2": "value-2"
}

Binary audio messages

Messages that are binary represent the audio of the call. The audio codec supported on the WebSocket interface is Linear PCM 16-bit, with a 16kHz sample rate, and a 20ms frame size. This rate results in each message being 640 bytes.

Audio active/inactive messages

When audio in the streams included in the WebSocket is muted, a text message is sent with the following JSON payload (with active set to false):

{
    "content-type":"audio/l16;rate=16000",
    "method": "update",
    "event": "websocket:media:update",
    "active": false,
    "CUSTOM-HEADER-1": "value-1",
    "CUSTOM-HEADER-2": "value-2"
}

(The CUSTOM-HEADER properties in this example represent metadata that you include in the headers property of the body in the POST request to start the WebSocket connection.)

Audio may be muted because all clients stop publishing audio or as a result of a force mute moderation event.

When audio of one of the streams resumes, a text message is sent with the following JSON payload (with active set to true):

{
    "content-type":"audio/l16;rate=16000",
    "method": "update",
    "event": "websocket:media:update",
    "active": true,
    "CUSTOM-HEADER-1": "value-1",
    "CUSTOM-HEADER-2": "value-2"
}

Disconnected message

When the Audio Connector WebSocket stops because of a call to the force disconnect REST method) or because the 6-hour time limit is reached (see Stopping a WebSocket connection), a text message is sent with the following JSON payload:

{
    "content-type":"audio/l16;rate=16000",
    "method": "delete",
    "event": "websocket:disconnected",
    "CUSTOM-HEADER-1": "value-1",
    "CUSTOM-HEADER-2": "value-2"
}

This message marks the termination of the WebSocket connection.

(The CUSTOM-HEADER properties in this example represent metadata that you include in the headers property of the body in the POST request to start the WebSocket connection.)

Stopping a WebSocket connection

When your WebSocket server closes the connection, the the OpenTok connection for the call also ends. In each client connected to the session, the OpenTok client-side SDK dispatches events indicating the connection ended (just as it would when other clients disconnect from the session).

You can disconnect the Audio Connector WebSocket connection using the force disconnect REST method). Use the connection ID of the Audio Connector WebSocket connection with this method.

As a security measure, the WebSocket will be closed automatically after 6 hours.

Automatic reconnections

Audio Connector will make a few attempts to re-establish a WebSocket connection that closes unexpectedly (for example, if the WebSocket closes without resulting from a call to the force disconnect REST method).

Sample application

See the demo-video-node-audio_connector project for a sample Node application that uses Audio Connector.

More information

See this blog post.