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Assist pipelines

The Assist pipeline integration runs the common steps of a voice assistant:

  1. Wake word detection
  2. Speech to text
  3. Intent recognition
  4. Text to speech

Pipelines are run via a WebSocket API:

"type": "assist_pipeline/run",
"start_stage": "stt",
"end_stage": "tts",
"input": {
"sample_rate": 16000,

The following input fields are available:

start_stageenumRequired. The first stage to run. One of wake_word, stt, intent, tts.
end_stageenumRequired. The last stage to run. One of stt, intent, tts.
inputdictDepends on start_stage:
  • wake_word only:
    • timeout - seconds before wake word detection times out (int, default: 3)
    • noise_suppression_level - amount of noise suppression (int, 0 = disabled, 4 = max)
    • auto_gain_dbfs - automatic gain (int, 0 = disabled, 31 = max)
    • volume_multiplier - fixed volume amplification (float, 1.0 = no change, 2.0 = twice as loud)
  • wake_word and stt:
    • sample_rate - sample rate of incoming audio (int, hertz)
  • intent and tts:
    • text - input text (string)
pipelinestringOptional. ID of the pipeline (use assist_pipeline/pipeline/list to get names).
conversation_idstringOptional. Unique id for conversation.
timeoutnumberOptional. Number of seconds before pipeline times out (default: 300).


As the pipeline runs, it emits events back over the WebSocket connection. The following events can be emitted:

run-startStart of pipeline runalwayspipeline - ID of the pipeline
language - Language used for pipeline
runner_data - Extra WebSocket data:
  • stt_binary_handler_id is the prefix to send speech data over.
  • timeout is the max run time for the whole pipeline.
run-endEnd of pipeline runalways
wake_word-startStart of wake word detectionaudio onlyengine: wake engine used
metadata: incoming audio
timeout: seconds before wake word timeout metadata
wake_word-endEnd of wake word detectionaudio onlywake_word_output - Detection result data:
  • wake_word_id is the id of detected wake word
  • timestamp is the detection time relative to start of audio stream (milliseconds, optional)
stt-startStart of speech to textaudio onlyengine: STT engine used
metadata: incoming audio metadata
stt-vad-startStart of voice commandaudio onlytimestamp: time relative to start of audio stream (milliseconds)
stt-vad-endEnd of voice commandaudio onlytimestamp: time relative to start of audio stream (milliseconds)
stt-endEnd of speech to textaudio onlystt_output - Object with text, the detected text.
intent-startStart of intent recognitionalwaysengine - Agent engine used
language: Processing language.
intent_input - Input text to agent
intent-endEnd of intent recognitionalwaysintent_output - conversation response
tts-startStart of text to speechaudio onlyengine - TTS engine used
language: Output language.
voice: Output voice.
tts_input: Text to speak.
tts-endEnd of text to speechaudio onlymedia_id - Media Source ID of the generated audio
url - URL to the generated audio
mime_type - MIME type of the generated audio
errorError in pipelineon errorcode - Error code (see below)
message - Error message

Error codes

The following codes are returned from the pipeline error event:

  • wake-engine-missing - No wake word engine is installed
  • wake-provider-missing - Configured wake word provider is not available
  • wake-stream-failed - Unexpected error during wake word detection
  • wake-word-timeout - Wake word was not detected within timeout
  • stt-provider-missing - Configured speech-to-text provider is not available
  • stt-provider-unsupported-metadata - Speech-to-text provider does not support audio format (sample rate, etc.)
  • stt-stream-failed - Unexpected error during speech-to-text
  • stt-no-text-recognized - Speech-to-text did not return a transcript
  • intent-not-supported - Configured conversation agent is not available
  • intent-failed - Unexpected error during intent recognition
  • tts-not-supported - Configured text-to-speech provider is not available or options are not supported
  • tts-failed - Unexpected error during text-to-speech

Sending speech data

After starting a pipeline with stt as the first stage of the run and receiving a stt-start event, speech data can be sent over the WebSocket connection as binary data. Audio should be sent as soon as it is available, with each chunk prefixed with a byte for the stt_binary_handler_id.

For example, if stt_binary_handler_id is 1 and the audio chunk is a1b2c3, the message would be (in hex):


To indicate the end of sending speech data, send a binary message containing a single byte with the stt_binary_handler_id.

Wake word detection

When start_stage is set to wake_word, the pipeline will not run until a wake word has been detected. Clients should avoid unnecessary audio streaming by using a local voice activity detector (VAD) to only start streaming when human speech is detected.

For wake_word, the input object should contain a timeout float value. This is the number of seconds of silence before the pipeline will time out during wake word detection (error code wake-word-timeout). If enough speech is detected by Home Assistant's internal VAD, the timeout will be continually reset.

Audio enhancements

The following settings are available as part of the input object when start_stage is set to wake_word:

  • noise_suppression_level - level of noise suppression (0 = disabled, 4 = max)
  • auto_gain_dbfs - automatic gain control (0 = disabled, 31 = max)
  • volume_multiplier - audio samples multiplied by constant (1.0 = no change, 2.0 = twice as loud)

If your device's microphone is fairly quiet, the recommended settings are:

  • noise_suppression_level - 2
  • auto_gain_dbfs - 31
  • volume_multiplier - 2.0

Increasing noise_suppression_level or volume_multiplier may cause audio distortion.