Ultravox

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Overview

UltravoxSTTService provides real-time speech-to-text capabilities using the Ultravox multimodal model running locally. Ultravox directly encodes audio into the LLM’s embedding space, eliminating the need for a separate ASR component and providing faster, more efficient transcription.

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Installation

To use UltravoxSTTService, install the required dependencies:

pip install "pipecat-ai[ultravox]"

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Configuration

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Constructor Parameters

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Input

The service processes AudioRawFrame instances containing:

• Raw PCM audio data
• 16-bit depth (int16)
• 16kHz sample rate (recommended)
• Single channel (mono)

The service intelligently buffers audio between UserStartedSpeakingFrame and UserStoppedSpeakingFrame events.

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Output Frames

The service produces the following frame during transcription:

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TranscriptionFrame

Generated when speech processing is complete, containing:

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Usage Example

from pipecat.services.ultravox.stt import UltravoxSTTService
import os

# Configure service
stt = UltravoxSTTService(
    model_size="fixie-ai/ultravox-v0_4_1-llama-3_1-8b",
    hf_token=os.environ.get("HF_TOKEN"),
    temperature=0.5,
    max_tokens=150,
)

# Use in pipeline
pipeline = Pipeline([
    transport.input(),
    stt,
    llm,
    ...
])

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Internal Architecture

UltravoxSTTService uses the following internal components:

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AudioBuffer

Collects audio frames during speech events for batch processing:

• Manages frames between UserStartedSpeakingFrame and UserStoppedSpeakingFrame
• Tracks speech start timestamp
• Prevents concurrent processing with status flag

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UltravoxModel

Handles loading and running the Ultravox model:

• Initializes vLLM engine for optimal GPU inference
• Manages model tokenization and prompt formatting
• Provides streaming text generation from audio input

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Frame Flow

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Metrics Support

The service supports metrics collection:

• Time to First Byte (TTFB)
• Total processing duration
• Buffer collection time

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Error Handling

The service produces ErrorFrames in the following scenarios:

• Empty audio buffer
• Invalid audio data
• Model inference errors
• Timeout during processing

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Available Models

See the Fixie.ai Hugging Face page for the latest model availability.

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Memory Considerations

The Ultravox model requires GPU resources:

• For the 8B parameter model (fixie-ai/ultravox-v0_4_1-llama-3_1-8b):
  • Benchmarked on A100-40GB GPUs
  • Can run on consumer GPUs with appropriate memory (at least 8GB VRAM, but performance may vary)
• For larger variants like the 70B parameter model:
  • Requires significantly more memory (40GB+ VRAM recommended)
• Audio buffer size grows with speech duration
• Processing occurs in batches, not streaming