Streaming

Learn how to transcribe live audio streams

Streaming Speech-to-Text

AssemblyAI’s Streaming Speech-to-Text (STT) allows you to transcribe live audio streams with high accuracy and low latency. By streaming your audio data to our secure WebSocket API, you can receive transcripts back within a few hundred milliseconds.

Supported languages

Streaming Speech-to-Text is only available for English. See Supported languages.

Getting started

Get started with any of our official SDKs:

Getting Started Guides

• Python
• JavaScript / TypeScript
• Go
• Java
• C#

If your programming language isn’t supported yet, see the WebSocket API:

• Streaming API reference
• Python guide on using Streaming Speech-to-Text

Audio requirements

The audio format must conform to the following requirements:

• PCM16 or Mu-law encoding (See Specify the encoding)
• A sample rate that matches the value of the supplied sample_rate parameter
• Single-channel
• 100 to 2000 milliseconds of audio per message

Audio segments with a duration between 100 ms and 450 ms produce the best results in transcription accuracy.

Specify the encoding

By default, transcriptions expect PCM16 encoding. If you want to use Mu-law encoding, you must set the encoding parameter to aai.AudioEncoding.pcm_mulaw:

Python

transcriber = aai.RealtimeTranscriber(
...,
encoding=aai.AudioEncoding.pcm_mulaw
)

Encoding	SDK Parameter	Description
PCM16 (Default)	aai.AudioEncoding.pcm_s16le	PCM signed 16-bit little-endian.
Mu-law	aai.AudioEncoding.pcm_mulaw	PCM Mu-law.

Add custom vocabulary

You can add up to 2500 characters of custom vocabulary to boost their transcription probability.

For this, create a list of strings and set the word_boost parameter:

Python

transcriber = aai.RealtimeTranscriber(
    ...,
    word_boost=["aws", "azure", "google cloud"]
)

If you’re not using one of the SDKs, you must ensure that the word_boost parameter is a JSON array that is URL encoded. See this code example.

Authenticate with a temporary token

If you need to authenticate on the client, you can avoid exposing your API key by using temporary authentication tokens. You should generate this token on your server and pass it to the client.

1. To generate a temporary token, call aai.RealtimeTranscriber.create_temporary_token(). Use the expires_in parameter to specify how long the token should be valid for, in seconds.

   Python

   token = aai.RealtimeTranscriber.create_temporary_token(
       expires_in=60
   )
   

   Note

   The expiration time must be a value between 60 and 360000 seconds.

2. The client should retrieve the token from the server and use the token to authenticate the transcriber.

   Note

   Each token has a one-time use restriction and can only be used for a single session.

   To use it, specify the token parameter when initializing the streaming transcriber.

   Python

   transcriber = aai.RealtimeTranscriber(
       ...,
       token=token
   )
   

Manually end current utterance

To manually end an utterance, call force_end_utterance():

Python

transcriber.force_end_utterance()

Manually ending an utterance immediately produces a final transcript.

Configure the threshold for automatic utterance detection

You can configure the threshold for how long to wait before ending an utterance.

To change the threshold, you can specify the end_utterance_silence_threshold parameter when initializing the streaming transcriber.

After the session has started, you can change the threshold by calling configure_end_utterance_silence_threshold().

Python

transcriber = aai.RealtimeTranscriber(
    ...,
    end_utterance_silence_threshold=500
)

transcriber.configure_end_utterance_silence_threshold(300)

Note

By default, Streaming Speech-to-Text ends an utterance after 700 milliseconds of silence. You can configure the duration threshold any number of times during a session after the session has started. The valid range is between 0 and 20000.

Disable partial transcripts

If you’re only using the final transcript, you can disable partial transcripts to reduce network traffic.

To disable partial transcripts, set the disable_partial_transcripts parameter to True.

Python

transcriber = aai.RealtimeTranscriber(
    ...,
    disable_partial_transcripts=True
)

Enable extra session information

If you enable extra session information, the client receives a RealtimeSessionInformation message right before receiving the session termination message.

To enable it, define a callback function to handle the event and cofigure the on_extra_session_information parameter.

Python

# Define a callback to handle the session information message
def on_extra_session_information(data: aai.RealtimeSessionInformation):
    print(data.audio_duration_seconds)

# Configure the RealtimeTranscriber
transcriber = aai.RealtimeTranscriber(
    ...,
    on_extra_session_information=on_extra_session_information,
)

Learn more

To learn about using Streaming Speech-to-Text, see the following resources:

• Blog post: Automatically Transcribe Zoom Calls in Real Time
• Blog post: Transcribe Twilio Phone Calls
• Blog post: Real Time Speech Recognition with Python and PyAudio
• GitHub: End-to-end examples
• GitHub: Cookbook examples
• GitHub: Use Express.js for Streaming Speech-to-Text
• Streaming API reference