Media Streaming over Websockets

Media Streaming provides instant access to your raw call media. With it, you can deliver exceptional customer experiences—from unlocking new insights through sentiment analysis to providing fast resolutions using AI solutions. You can also bring your own AI engine and use real-time media streaming to connect it directly to call control, enabling custom AI-powered voice applications. When your call is established, Telnyx takes the call media and forks it, so recipients receive the call simultaneously. The Telnyx network ensures that call media can be duplicated, delivered, analyzed, and returned in real-time. The secondary delivery recipient never occupies the call stream, so you never have to worry about degraded quality or dropped connections. This guide covers how to set up media streaming over Websockets.

Requesting streaming using Dial Command

The requesting dial command can be extended in the following way to request streaming using WebSockets:

curl -X POST \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --header "Authorization: Bearer YOUR_API_KEY" \
  --data '{
    "connection_id": "uuid", 
    "to": "+18005550199", 
    "from": "+18005550100", 
    "stream_url": "wss://yourdomain.com",
    “stream_track”:”inbound_track|outbound_track|both_tracks”}' \
  https://api.telnyx.com/v2/calls

The following additional attributes need to be added to the request:

stream_url - the destination address when the stream is going to be delivered.
stream_track - specifies which track should be streamed, with possible options:
- inbound_track (default)
- outbound_track
- both_tracks

As a response, a regular confirmation is sent:

{
  "data": {
    "call_control_id": "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ",
    "call_leg_id": "2dc6fc34-f9e0-11ea-b68e-02420a0f7768",
    "call_session_id": "2dc1b3c8-f9e0-11ea-bc5a-02420a0f7768",
    "is_alive": false,
    "record_type": "call"
  }
}

Requesting streaming using Answer Command

Using the same attributes as above, streaming can be requested while answering the call:

curl -X POST \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --header "Authorization: Bearer YOUR_API_KEY" \
  --data '{
    "client_state":"aGF2ZSBhIG5pY2UgZGF5ID1d",
    "command_id":"891510ac-f3e4-11e8-af5b-de00688a4901",
    "stream_url": "wss://yourdomain.com", 
    "stream_track":"inbound_track|outbound_track|both_tracks”}' \
  https://api.telnyx.com/v2/calls/{call_control_id}/actions/answer

In this case, confirmation that the call has been answered includes streaming details:

{
  "data": {
    "event_type": "call.answered",
    "id": "0ccc7b54-4df3-4bca-a65a-3da1ecc777f0",
    "occurred_at": "2018-02-02T22:25:27.521992Z",
    "payload": {
      "call_control_id":     "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ",
      "call_leg_id": "428c31b6-7af4-4bcb-b7f5-5013ef9657c1",
      "call_session_id": "428c31b6-abf3-3bc1-b7f4-5013ef9657c1",
      "client_state": "aGF2ZSBhIG5pY2UgZGF5ID1d",
      "connection_id": "7267xxxxxxxxxxxxxx",
      "from": "+35319605860",
      "state": "answered",
      "stream_url": "wss://yourdomain.com",
      "stream_track”:”inbound_track|outbound_track|both_tracks",
      "to": "+13129457420"
    },
    "record_type": "event"
  }
}

Streaming process flow

When the WebSocket connection is established, the following event is being sent:

{ 
  "event": "connected", 
  "version": "1.0.0"
}

Before the stream begins, the streaming.started webhook is sent:

{
  "data": {
   "event_type": "streaming.started",
   "id": "0ccc7b54-4df3-4bca-a65a-3da1ecc777f0",
   "occurred_at": "2018-02-02T22:25:27.521992Z",
   "payload": {
     "call_control_id": "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ",
     "stream_url": "wss://yourdomain.com"
    },
  "record_type": "event"
  }
}

An event over WebSockets which contains information in the mediaFormat section about the encoding and stream_id that identifies a particular stream:

{ 
 "event": "start",  
 "sequence_number": "1", 
 "start": {
   "user_id": "3E6F995F-85F7-4705-9741-53B116D28237", 
   "call_control_id": "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ", 
   "call_session_id": "ff55a038-6f5d-11ef-9692-02420aeffb1f",
   "from": "+13122010094",
   "to": "+13122123456",
   "tags": ["TAG1", "TAG2"], 
   "client_state": "aGF2ZSBhIG5pY2UgZGF5ID1d",
   "media_format": { 
     "encoding": "PCMU",
     "sample_rate": 8000, 
     "channels": 1 
   } 
 },
 "stream_id": "32DE0DEA-53CB-4B21-89A4-9E1819C043BC"
}

The following media events follow the start event:

{ 
 "event": "media",
 "sequence_number": "4",
 "media": { 
   "track": "inbound/outbound", 
   "chunk": "2",
   "timestamp": "5",
   "payload": "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"                        
 },
 "stream_id": "32DE0DEA-53CB-4B21-89A4-9E1819C043BC" 
}

The payload contains a base64-encoded RTP payload (no headers).

The order of events is not guaranteed and the chunk number can be used to reorder the events.

When the call ends, the streaming.stopped webhook is sent:

{
  "data": {
    "event_type": "streaming.stopped",
    "id": "0ccc7b54-4df3-4bca-a65a-3da1ecc777f0",
    "occurred_at": "2018-02-02T22:25:27.521992Z",
    "payload": {
      "call_control_id": "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ",
      "stream_url": "wss://yourdomain.com"
    },
    "record_type": "event"
  }
}

And the stop event over WebSockets connection is sent:

{ 
 "event": "stop",
 "sequence_number": "5",
 "stop": {
  "user_id": "3E6F995F-85F7-4705-9741-53B116D28237",
  "call_control_id": "v2:T02llQxIyaRkhfRKxgAP8nY511EhFLizdvdUKJiSw8d6A9BborherQ"
  },
  "stream_id": "32DE0DEA-53CB-4B21-89A4-9E1819C043BC" 
}

Currently only one streaming/fork operation is supported per call. In case of requesting media forking the WebSocket stream will be stopped and replaced by a RTP connection.

Bidirectional media streaming

Sending RTP stream

The RTP stream can be sent to the call using websocket. The functionality can be enabled by setting stream_bidirectional_mode to rtp. For dial command it should look as follows:

curl -X POST \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --header "Authorization: Bearer YOUR_API_KEY" \
  --data '{
    "connection_id": "uuid", 
    "to": "+18005550199", 
    "from": "+18005550100", 
    "stream_url": "wss://yourdomain.com",
    "stream_track":"inbound_track|outbound_track|both_tracks"}',
    "stream_bidirectional_mode":"rtp" \
  https://api.telnyx.com/v2/calls

It can be requested using answer and streaming_start commands in the same way. The RTP streaming can be sent using media events:

{
  "event": "media",
  "media": {
    "payload": "your base64 encoded RTP stream"
  }
}

Provided chunks of audio can be in a size of 20 milliseconds to 30 seconds.

The number of bidirectional RTP streams per call is limited to 1.

RTP stream codec

There are the following codecs supported by bidirectional streaming:

PCMU, 8 kHz (default)
PCMA, 8 kHz
G722, 8 kHz
OPUS, 8 kHz, 16 kHz
AMR-WB, 8 kHz, 16 kHz
L16, 16 kHz

When the audio is sent using a different encoding than on the call, it will be transcoded, which may cause a degradation in quality.

The L16 codec provides improved support for AI voice agent integrations by offering reduced latency and eliminating transcoding overhead when interfacing with many AI platforms that natively support linear PCM audio.

The codec can be set when the streaming start is requested. For dial command, it looks as follows:

curl -X POST \
  --header "Content-Type: application/json" \
  --header "Accept: application/json" \
  --header "Authorization: Bearer YOUR_API_KEY" \
  --data '{
    "connection_id": "uuid", 
    "to": "+18005550199", 
    "from": "+18005550100", 
    "stream_url": "wss://yourdomain.com",
    "stream_track":"inbound_track|outbound_track|both_tracks"}',
    "stream_bidirectional_mode": "rtp",
    "stream_bidirectional_codec": "PCMU|PCMA|G722|OPUS|AMR-WB|L16" \ 
  https://api.telnyx.com/v2/calls

Sending media files

Media files can also be sent back to the call through the websocket. This is done similarly to the playback_start command when using a base64-encoded mp3 file in the payload. Send a packet to the websocket connection as follows:

{
  "event": "media",
  "media": {
    "payload" : "your base64 encoded mp3 file"
  }
}

The payload, which is a base64-encoded mp3 file, will be played on the call. Multiple media messages will be queued and played in the order they were submitted. Some limitations to be aware of:

Media payloads can only be submitted once per second.
Media must be base64 encoded mp3.

Clear message

Sending a clear message will immediately stop the media playing on the stream and clear the media queue.

{
  "event": "clear"
}

Mark message

Mark messages can be used to keep track of media ending on the stream:

You can send a mark message to the stream after a media message.
When the media immediately preceding the mark finishes you will receive the same mark back.

Example mark message sent to the stream:

{
  "event": "mark",
  "mark": {
    "name": "some_mark_name"
  }
}

Example mark message received from the stream:

{
  "event": "mark",
  "stream_id": "32DE0DEA-53CB-4B21-89A4-9E1819C043BC",
  "sequence_number": "5",
  "mark": {
    "name": "some_mark_name"
  }
}

Submitting marks when no audio is played or queued will result in them being immediately sent back. Similarly, the clear message will also result in all queued marks being sent back.

DTMF message

In case of DTMF events on the call, the following message will be sent over websocket:

{
  "event": "dtmf",
  "stream_id": "32DE0DEA-53CB-4B21-89A4-9E1819C043BC",
  "occurred_at": "2025-06-05T08:54:19.698408Z",
  "sequence_number": "5",
  "dtmf": {
    "digit": "1"
  }
}

occurred_at field is a timestamp captured on the Telephony engine side. These are consumed as asynchronous events and in certain circumstances may arrive out of order. This field can be used to ensure proper order.

Error message

In case of any case of error during media streaming, an error frame in the following format is sent:

{
  "event": "error",
  "payload": {
    "code": integer,
    "title": string,
    "detail": string
  },
  "stream_id": uuid
}

The list of the potential errors:

Code	Title	Description
100002	unknown_error	An unknown error occurred on the stream
100003	malformed_frame	Received frame was not formed correctly
100004	invalid_media	Media provided was not base64 encoded
100005	rate_limit_reached	Too many requests

Example of integration

In the Telnyx GitHub repository there are several examples of integrations with external services using Media streaming:

Voice API Fundamentals

Voice Features

AI Capabilities

Tutorials

Regional & Restrictions

API Reference

For AI Agents

Media Streaming over Websockets

Requesting streaming using Dial Command

Requesting streaming using Answer Command

Streaming process flow

Bidirectional media streaming

Sending RTP stream

RTP stream codec

Sending media files

Clear message

Mark message

DTMF message

Error message

Example of integration

​Requesting streaming using Dial Command

​Requesting streaming using Answer Command

​Streaming process flow

​Bidirectional media streaming

​Sending RTP stream

​RTP stream codec

​Sending media files

​Clear message

​Mark message

​DTMF message

​Error message

​Example of integration

Requesting streaming using Dial Command

Requesting streaming using Answer Command

Streaming process flow

Bidirectional media streaming

Sending RTP stream

RTP stream codec

Sending media files

Clear message

Mark message

DTMF message

Error message

Example of integration