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Overview

AssemblyAISTTService provides real-time speech-to-text capabilities using AssemblyAI’s WebSocket API. It supports streaming transcription with both interim and final results.

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Installation

To use AssemblyAISTTService, install the required dependencies:

pip install pipecat-ai[assemblyai]

You’ll also need to set up your AssemblyAI API key as an environment variable: ASSEMBLYAI_API_KEY.

You can obtain a AssemblyAI API key by signing up at AssemblyAI.

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Configuration

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Constructor Parameters

api_key
str
required

Your AssemblyAI API key

sample_rate
int
default: "16000"

Audio sample rate in Hz

encoding
AudioEncoding
default: "pcm_s16le"

Audio encoding format

language
Language
default: "Language.EN"

Transcription language (currently only English supported for real-time)

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Input

The service processes raw audio data with the following requirements:

  • PCM audio format
  • 16-bit depth
  • 16kHz sample rate (default)
  • Single channel (mono)

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Output Frames

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TranscriptionFrame

Generated for final transcriptions, containing:

text
string

Transcribed text

user_id
string

User identifier

timestamp
string

ISO 8601 formatted timestamp

language
Language

Transcription language

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InterimTranscriptionFrame

Generated during ongoing speech, containing the same fields as TranscriptionFrame but with preliminary results.

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ErrorFrame

Generated when transcription errors occur, containing error details.

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Methods

See the STT base class methods for additional functionality.

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Language Setting

await service.set_language(Language.FR)

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Language Support

Assembly STT supports the following languages and regional variants:

Language CodeDescriptionService Codes
Language.ENEnglishen

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Usage Example

from pipecat.services.assemblyai import AssemblyAISTTService
from pipecat.transcriptions.language import Language

# Configure service
stt_service = AssemblyAISTTService(
    api_key="your-api-key",
    sample_rate=16000,
    language=Language.EN
)

# Use in pipeline
pipeline = Pipeline([
    transport.input(),   # Produces audio frames
    stt_service,         # Processes audio → produces transcription frames
    text_handler         # Consumes transcription frames
])

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Frame Flow

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Metrics Support

The service collects processing metrics:

  • Time to First Byte (TTFB)
  • Processing duration
  • Connection status

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Notes

  • Currently supports English-only real-time transcription
  • Handles WebSocket connection management
  • Provides both interim and final transcriptions
  • Thread-safe processing with proper event loop handling
  • Automatic error handling and reporting
  • Manages connection lifecycle
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