# Streaming Input
Source: https://docs.mserve.ai/docs/voice/streaming
Summary: The ElevenLabs stream-input WebSocket. Send text chunks as they are produced, receive audio chunks as they are synthesized. The protocol voice-agent frameworks speak.
Availability: available
Last reviewed: 2026-08-25

## Connect

```text
wss://api.mserve.ai/elevenlabs/v1/text-to-speech/{voice_id}/stream-input?output_format=mp3_44100_128
```

Auth is the `xi-api-key` header, the `Authorization` header, or `xi_api_key` in the first frame. `output_format` accepts the ElevenLabs enum. An unknown format closes the socket with code `1008` and an `invalid_output_format` error frame.

## Frames

### Start

Send a first frame with a single space. It can carry `voice_settings`, `generation_config`, and `xi_api_key`.

```json
{ "text": " ", "voice_settings": { "stability": 0.5, "similarity_boost": 0.8 }, "xi_api_key": "ms_live_your_key" }
```

### Send text

Send text as it arrives from your model. Words are buffered until a sentence boundary or a flush.

```json
{ "text": "Every model. " }
```

### Flush and close

`flush` forces synthesis of the buffer. An empty string closes the stream.

```json
{ "text": " ", "flush": true }
```

```json
{ "text": "" }
```

Server frames carry base64 audio, optional alignment, and `isFinal` on the last one:

```json
{ "audio": "SUQzBAAAAAAA…", "isFinal": false, "alignment": { "chars": ["E", "v"], "charStartTimesMs": [0, 50], "charDurationsMs": [50, 60] } }
```

## Frameworks

Pipecat, LiveKit Agents, and Vapi speak this protocol through their ElevenLabs plugins. Set the plugin's base URL to `https://api.mserve.ai/elevenlabs` and its key to an `ms_live_` key.

```python title="Pipecat"
from pipecat.services.elevenlabs.tts import ElevenLabsTTSService

tts = ElevenLabsTTSService(api_key="ms_live_your_key", voice_id="21m00Tcm4TlvDq8ikWAM", base_url="https://api.mserve.ai/elevenlabs")
```

## Billing

The stream is billed once at close, on the characters sent. A dropped connection bills the characters that were synthesized.