# # Copyright (c) 2024-2026, Daily # # SPDX-License-Identifier: BSD 2-Clause License # """Base classes for Speech-to-Text services with continuous and segmented processing.""" import asyncio import io import time import warnings import wave from abc import abstractmethod from typing import Any, AsyncGenerator, Optional from loguru import logger from websockets.protocol import State from pipecat.frames.frames import ( AudioRawFrame, ErrorFrame, Frame, InterruptionFrame, ServiceSwitcherRequestMetadataFrame, StartFrame, STTMetadataFrame, STTMuteFrame, STTUpdateSettingsFrame, TranscriptionFrame, VADUserStartedSpeakingFrame, VADUserStoppedSpeakingFrame, ) from pipecat.processors.frame_processor import FrameDirection from pipecat.services.ai_service import AIService from pipecat.services.settings import STTSettings, is_given from pipecat.services.stt_latency import DEFAULT_TTFS_P99 from pipecat.services.websocket_service import WebsocketService from pipecat.transcriptions.language import Language # Duration in seconds of silent audio sent for WebSocket keepalive (100ms). _KEEPALIVE_SILENCE_DURATION = 0.1 class STTService(AIService): """Base class for speech-to-text services. Provides common functionality for STT services including audio passthrough, muting, settings management, and audio processing. Subclasses must implement the run_stt method to provide actual speech recognition. Includes an optional keepalive mechanism that sends silent audio when no real audio has been sent for a configurable timeout, preventing servers from closing idle connections (e.g. when behind a ServiceSwitcher). Subclasses that enable keepalive must override ``_send_keepalive()`` to deliver the silence in the appropriate service-specific protocol. Event handlers: on_connected: Called when connected to the STT service. on_disconnected: Called when disconnected from the STT service. on_connection_error: Called when a connection to the STT service error occurs. Example:: @stt.event_handler("on_connected") async def on_connected(stt: STTService): logger.debug(f"STT connected") @stt.event_handler("on_disconnected") async def on_disconnected(stt: STTService): logger.debug(f"STT disconnected") @stt.event_handler("on_connection_error") async def on_connection_error(stt: STTService, error: str): logger.error(f"STT connection error: {error}") """ _settings: STTSettings def __init__( self, *, audio_passthrough=True, sample_rate: Optional[int] = None, stt_ttfb_timeout: float = 2.0, ttfs_p99_latency: Optional[float] = None, keepalive_timeout: Optional[float] = None, keepalive_interval: float = 5.0, settings: Optional[STTSettings] = None, **kwargs, ): """Initialize the STT service. Args: audio_passthrough: Whether to pass audio frames downstream after processing. Defaults to True. sample_rate: The sample rate for audio input. If None, will be determined from the start frame. stt_ttfb_timeout: Time in seconds to wait after VAD stop before reporting TTFB. This delay allows the final transcription to arrive. Defaults to 2.0. Note: STT "TTFB" differs from traditional TTFB (which measures from a discrete request to first response byte). Since STT receives continuous audio, we measure from when the user stops speaking to when the final transcript arrives—capturing the latency that matters for voice AI applications. ttfs_p99_latency: P99 latency from speech end to final transcript in seconds. This is broadcast via STTMetadataFrame at pipeline start for downstream processors (e.g., turn strategies) to optimize timing. Subclasses provide measured defaults; pass a value here to override for your deployment. keepalive_timeout: Seconds of no audio before sending silence to keep the connection alive. None disables keepalive. Useful for services that close idle connections (e.g. behind a ServiceSwitcher). keepalive_interval: Seconds between idle checks when keepalive is enabled. settings: The runtime-updatable settings for the STT service. **kwargs: Additional arguments passed to the parent AIService. """ super().__init__( settings=settings # Here in case subclass doesn't implement more specific settings # (which hopefully should be rare) or STTSettings(), **kwargs, ) self._audio_passthrough = audio_passthrough self._init_sample_rate = sample_rate self._sample_rate = 0 self._muted: bool = False self._user_id: str = "" self._ttfs_p99_latency = ttfs_p99_latency # STT TTFB tracking state self._stt_ttfb_timeout = stt_ttfb_timeout self._ttfb_timeout_task: Optional[asyncio.Task] = None self._user_speaking: bool = False self._finalize_pending: bool = False self._finalize_requested: bool = False self._last_transcript_time: float = 0 # Keepalive state self._keepalive_timeout = keepalive_timeout self._keepalive_interval = keepalive_interval self._keepalive_task: Optional[asyncio.Task] = None self._last_audio_time: float = 0 self._register_event_handler("on_connected") self._register_event_handler("on_disconnected") self._register_event_handler("on_connection_error") @property def is_muted(self) -> bool: """Check if the STT service is currently muted. Returns: True if the service is muted and will not process audio. """ return self._muted def request_finalize(self): """Mark that a finalize request has been sent, awaiting server confirmation. For providers that have explicit server confirmation of finalization (e.g., Deepgram's from_finalize field), call this when sending the finalize request. Then call confirm_finalize() when the server confirms. For providers without server confirmation, don't call this method - just send the finalize/flush/commit command and rely on the TTFB timeout. """ self._finalize_requested = True def confirm_finalize(self): """Confirm that the server has acknowledged the finalize request. Call this when the server response confirms finalization (e.g., Deepgram's from_finalize=True). The next TranscriptionFrame pushed will be marked as finalized. Only has effect if request_finalize() was previously called. """ if self._finalize_requested: self._finalize_pending = True self._finalize_requested = False @property def sample_rate(self) -> int: """Get the current sample rate for audio processing. Returns: The sample rate in Hz. """ return self._sample_rate async def set_model(self, model: str): """Set the speech recognition model. .. deprecated:: 0.0.104 Use ``STTUpdateSettingsFrame(model=...)`` instead. Args: model: The name of the model to use for speech recognition. """ with warnings.catch_warnings(): warnings.simplefilter("always") warnings.warn( "'set_model' is deprecated, use 'STTUpdateSettingsFrame(model=...)' instead.", DeprecationWarning, stacklevel=2, ) logger.info(f"Switching STT model to: [{model}]") settings_cls = type(self._settings) await self._update_settings(settings_cls(model=model)) async def set_language(self, language: Language): """Set the language for speech recognition. .. deprecated:: 0.0.104 Use ``STTUpdateSettingsFrame(language=...)`` instead. Args: language: The language to use for speech recognition. """ with warnings.catch_warnings(): warnings.simplefilter("always") warnings.warn( "'set_language' is deprecated, use 'STTUpdateSettingsFrame(language=...)' instead.", DeprecationWarning, stacklevel=2, ) logger.info(f"Switching STT language to: [{language}]") settings_cls = type(self._settings) await self._update_settings(settings_cls(language=language)) def language_to_service_language(self, language: Language) -> Optional[str]: """Convert a language to the service-specific language format. Args: language: The language to convert. Returns: The service-specific language identifier, or None if not supported. """ return Language(language) @abstractmethod async def run_stt(self, audio: bytes) -> AsyncGenerator[Frame, None]: """Run speech-to-text on the provided audio data. This method must be implemented by subclasses to provide actual speech recognition functionality. Args: audio: Raw audio bytes to transcribe. Yields: Frame: Frames containing transcription results (typically TextFrame). """ pass async def start(self, frame: StartFrame): """Start the STT service. Args: frame: The start frame containing initialization parameters. """ await super().start(frame) self._sample_rate = self._init_sample_rate or frame.audio_in_sample_rate async def cleanup(self): """Clean up STT service resources.""" await super().cleanup() await self._cancel_ttfb_timeout() await self._cancel_keepalive_task() async def _update_settings(self, delta: STTSettings) -> dict[str, Any]: """Apply an STT settings delta. Handles ``model`` (via parent). Translates ``Language`` enum values before applying so the stored value is a service-specific string. Concrete services should override this method and handle language changes (including any reconnect logic) based on the returned changed-field dict. Args: delta: An STT settings delta. Returns: Dict mapping changed field names to their previous values. """ # Translate language *before* applying so the stored value is canonical if is_given(delta.language) and isinstance(delta.language, Language): converted = self.language_to_service_language(delta.language) if converted is not None: delta.language = converted changed = await super()._update_settings(delta) return changed async def process_audio_frame(self, frame: AudioRawFrame, direction: FrameDirection): """Process an audio frame for speech recognition. If the service is muted, this method does nothing. Otherwise, it processes the audio frame and runs speech-to-text on it, yielding transcription results. If the frame has a user_id, it is stored for later use in transcription. Args: frame: The audio frame to process. direction: The direction of frame processing. """ if self._muted: return self._last_audio_time = time.monotonic() # UserAudioRawFrame contains a user_id (e.g. Daily, Livekit) if hasattr(frame, "user_id"): self._user_id = frame.user_id # AudioRawFrame does not have a user_id (e.g. SmallWebRTCTransport, websockets) else: self._user_id = "" if not frame.audio: # Ignoring in case we don't have audio to transcribe. logger.warning( f"Empty audio frame received for STT service: {self.name} {frame.num_frames}" ) return await self.process_generator(self.run_stt(frame.audio)) async def process_frame(self, frame: Frame, direction: FrameDirection): """Process frames, handling VAD events and audio segmentation. Args: frame: The frame to process. direction: The direction of frame processing. """ await super().process_frame(frame, direction) if isinstance(frame, StartFrame): # Push StartFrame first, then metadata so downstream receives them in order await self.push_frame(frame, direction) await self._push_stt_metadata() elif isinstance(frame, ServiceSwitcherRequestMetadataFrame): await self._push_stt_metadata() await self.push_frame(frame, direction) elif isinstance(frame, AudioRawFrame): # In this service we accumulate audio internally and at the end we # push a TextFrame. We also push audio downstream in case someone # else needs it. await self.process_audio_frame(frame, direction) if self._audio_passthrough: await self.push_frame(frame, direction) elif isinstance(frame, VADUserStartedSpeakingFrame): await self._handle_vad_user_started_speaking(frame) await self.push_frame(frame, direction) elif isinstance(frame, VADUserStoppedSpeakingFrame): await self._handle_vad_user_stopped_speaking(frame) await self.push_frame(frame, direction) elif isinstance(frame, STTUpdateSettingsFrame): if frame.delta is not None: await self._update_settings(frame.delta) elif frame.settings: # Backward-compatible path: convert legacy dict to settings object. with warnings.catch_warnings(): warnings.simplefilter("always") warnings.warn( "Passing a dict via STTUpdateSettingsFrame(settings={...}) is deprecated " "since 0.0.104, use STTUpdateSettingsFrame(delta=STTSettings(...)) instead.", DeprecationWarning, stacklevel=2, ) delta = type(self._settings).from_mapping(frame.settings) await self._update_settings(delta) elif isinstance(frame, STTMuteFrame): self._muted = frame.mute logger.debug(f"STT service {'muted' if frame.mute else 'unmuted'}") elif isinstance(frame, InterruptionFrame): await self._reset_stt_ttfb_state() await self.push_frame(frame, direction) else: await self.push_frame(frame, direction) async def push_frame(self, frame: Frame, direction: FrameDirection = FrameDirection.DOWNSTREAM): """Push a frame downstream, tracking TranscriptionFrame timestamps for TTFB. Stores the timestamp of each TranscriptionFrame for TTFB calculation. If the frame is marked as finalized (via request_finalize/confirm_finalize), reports TTFB immediately and cancels any pending timeout. Otherwise, TTFB is reported after a timeout. Args: frame: The frame to push. direction: The direction to push the frame. """ if isinstance(frame, TranscriptionFrame): # Store the transcript time for TTFB calculation self._last_transcript_time = time.time() # Set finalized from pending state and auto-reset if self._finalize_pending: frame.finalized = True self._finalize_pending = False # If this is a finalized transcription, report TTFB immediately if frame.finalized: await self.stop_ttfb_metrics() # Cancel the timeout since we've already reported await self._cancel_ttfb_timeout() await super().push_frame(frame, direction) async def _push_stt_metadata(self): """Push STT metadata frame for downstream processors (e.g., turn strategies).""" ttfs = self._ttfs_p99_latency if ttfs is None: ttfs = DEFAULT_TTFS_P99 logger.warning(f"{self.name}: ttfs_p99_latency not set, using default {ttfs}s") await self.broadcast_frame(STTMetadataFrame, service_name=self.name, ttfs_p99_latency=ttfs) async def _cancel_ttfb_timeout(self): """Cancel any pending TTFB timeout task.""" if self._ttfb_timeout_task: await self.cancel_task(self._ttfb_timeout_task) self._ttfb_timeout_task = None async def _reset_stt_ttfb_state(self): """Reset STT TTFB measurement state. Called when starting a new utterance or on interruption to ensure we don't use stale state for TTFB calculations. This specifically guards against the case where a TranscriptionFrame is received without corresponding VADUserStartedSpeakingFrame and VADUserStoppedSpeakingFrame frames. Note: Does not reset _user_speaking since InterruptionFrame can arrive while user is still speaking. """ await self._cancel_ttfb_timeout() async def _handle_vad_user_started_speaking(self, frame: VADUserStartedSpeakingFrame): """Handle VAD user started speaking frame to start tracking transcriptions. Cancels any pending TTFB timeout, resets TTFB tracking state, and marks user as speaking. Also resets finalization state to prevent stale finalization from a previous utterance. Args: frame: The VAD user started speaking frame. """ await self._reset_stt_ttfb_state() self._user_speaking = True self._finalize_requested = False self._finalize_pending = False self._last_transcript_time = 0 async def _handle_vad_user_stopped_speaking(self, frame: VADUserStoppedSpeakingFrame): """Handle VAD user stopped speaking frame. Calculates the actual speech end time and starts a timeout task to wait for the final transcription before reporting TTFB. Args: frame: The VAD user stopped speaking frame. """ self._user_speaking = False # Skip TTFB measurement if stop_secs is not set if frame.stop_secs == 0.0: return # Calculate the actual speech end time (current time minus VAD stop delay). # This approximates when the last user audio was sent to the STT service, # which we use to measure against the eventual transcription response. speech_end_time = frame.timestamp - frame.stop_secs await self.start_ttfb_metrics(start_time=speech_end_time) # Start timeout task (any previous timeout was cancelled by VADUserStartedSpeakingFrame # or InterruptionFrame) self._ttfb_timeout_task = self.create_task( self._ttfb_timeout_handler(), name="stt_ttfb_timeout" ) async def _ttfb_timeout_handler(self): """Wait for timeout then report TTFB using the last transcript timestamp. This timeout allows the final transcription to arrive before we calculate and report TTFB. Uses _last_transcript_time as the end time so we measure to when the transcript actually arrived, not when the timeout fired. If no transcription arrived, no TTFB is reported. """ try: await asyncio.sleep(self._stt_ttfb_timeout) if self._last_transcript_time > 0: await self.stop_ttfb_metrics(end_time=self._last_transcript_time) except asyncio.CancelledError: # Task was cancelled (new utterance or interruption), which is expected behavior pass finally: self._ttfb_timeout_task = None def _create_keepalive_task(self): """Start the keepalive task if keepalive is enabled.""" if self._keepalive_timeout is not None: self._last_audio_time = time.monotonic() self._keepalive_task = self.create_task( self._keepalive_task_handler(), name="keepalive" ) async def _cancel_keepalive_task(self): """Stop the keepalive task if running.""" if self._keepalive_task: await self.cancel_task(self._keepalive_task) self._keepalive_task = None async def _keepalive_task_handler(self): """Send periodic silent audio to prevent the server from closing the connection. When keepalive is enabled, this task checks periodically if the connection has been idle (no audio sent) for longer than keepalive_timeout seconds. If so, it generates silent 16-bit mono PCM audio and passes it to _send_keepalive() for service-specific formatting and sending. """ while True: await asyncio.sleep(self._keepalive_interval) try: if not self._is_keepalive_ready(): continue elapsed = time.monotonic() - self._last_audio_time if elapsed < self._keepalive_timeout: continue num_samples = int(self.sample_rate * _KEEPALIVE_SILENCE_DURATION) silence = b"\x00" * (num_samples * 2) await self._send_keepalive(silence) self._last_audio_time = time.monotonic() logger.trace(f"{self} sent keepalive silence") except Exception as e: logger.warning(f"{self} keepalive error: {e}") break def _is_keepalive_ready(self) -> bool: """Check if the service is ready to send keepalive. Subclasses should override this to check their connection state. Returns: True if keepalive can be sent. """ return True async def _send_keepalive(self, silence: bytes): """Send silent audio to keep the connection alive. Subclasses that enable keepalive must override this to deliver silence in their service-specific protocol. Args: silence: Silent 16-bit mono PCM audio bytes. """ raise NotImplementedError("Subclasses must override _send_keepalive") class SegmentedSTTService(STTService): """STT service that processes speech in segments using VAD events. Uses Voice Activity Detection (VAD) events to detect speech segments and runs speech-to-text only on those segments, rather than continuously. Requires VAD to be enabled in the pipeline to function properly. Maintains a small audio buffer to account for the delay between actual speech start and VAD detection. """ def __init__(self, *, sample_rate: Optional[int] = None, **kwargs): """Initialize the segmented STT service. Args: sample_rate: The sample rate for audio input. If None, will be determined from the start frame. **kwargs: Additional arguments passed to the parent STTService. """ super().__init__(sample_rate=sample_rate, **kwargs) self._content = None self._wave = None self._audio_buffer = bytearray() self._audio_buffer_size_1s = 0 self._user_speaking = False async def start(self, frame: StartFrame): """Start the segmented STT service and initialize audio buffer. Args: frame: The start frame containing initialization parameters. """ await super().start(frame) self._audio_buffer_size_1s = self.sample_rate * 2 async def push_frame(self, frame: Frame, direction: FrameDirection = FrameDirection.DOWNSTREAM): """Push a frame, marking TranscriptionFrames as finalized. Segmented STT services process complete speech segments and return a single TranscriptionFrame per segment, so every transcription is inherently finalized. Args: frame: The frame to push. direction: The direction of frame flow in the pipeline. """ if isinstance(frame, TranscriptionFrame): frame.finalized = True await super().push_frame(frame, direction) async def process_frame(self, frame: Frame, direction: FrameDirection): """Process frames, handling VAD events and audio segmentation.""" await super().process_frame(frame, direction) if isinstance(frame, VADUserStartedSpeakingFrame): await self._handle_user_started_speaking(frame) elif isinstance(frame, VADUserStoppedSpeakingFrame): await self._handle_user_stopped_speaking(frame) async def _handle_user_started_speaking(self, frame: VADUserStartedSpeakingFrame): self._user_speaking = True async def _handle_user_stopped_speaking(self, frame: VADUserStoppedSpeakingFrame): self._user_speaking = False content = io.BytesIO() wav = wave.open(content, "wb") wav.setsampwidth(2) wav.setnchannels(1) wav.setframerate(self.sample_rate) wav.writeframes(self._audio_buffer) wav.close() content.seek(0) # Start clean. self._audio_buffer.clear() await self.process_generator(self.run_stt(content.read())) async def process_audio_frame(self, frame: AudioRawFrame, direction: FrameDirection): """Process audio frames by buffering them for segmented transcription. Continuously buffers audio, growing the buffer while user is speaking and maintaining a small buffer when not speaking to account for VAD delay. If the frame has a user_id, it is stored for later use in transcription. Args: frame: The audio frame to process. direction: The direction of frame processing. """ # UserAudioRawFrame contains a user_id (e.g. Daily, Livekit) if hasattr(frame, "user_id"): self._user_id = frame.user_id # AudioRawFrame does not have a user_id (e.g. SmallWebRTCTransport, websockets) else: self._user_id = "" # If the user is speaking the audio buffer will keep growing. self._audio_buffer += frame.audio # If the user is not speaking we keep just a little bit of audio. if not self._user_speaking and len(self._audio_buffer) > self._audio_buffer_size_1s: discarded = len(self._audio_buffer) - self._audio_buffer_size_1s self._audio_buffer = self._audio_buffer[discarded:] class WebsocketSTTService(STTService, WebsocketService): """Base class for websocket-based STT services. Combines STT functionality with websocket connectivity, providing automatic error handling, reconnection capabilities, and optional silence-based keepalive. The keepalive feature (inherited from STTService) sends silent audio when no real audio has been sent for a configurable timeout, preventing servers from closing idle connections (e.g. when behind a ServiceSwitcher). Subclasses can override ``_send_keepalive()`` to wrap the silence in a service-specific protocol. """ def __init__( self, *, reconnect_on_error: bool = True, **kwargs, ): """Initialize the Websocket STT service. Args: reconnect_on_error: Whether to automatically reconnect on websocket errors. **kwargs: Additional arguments passed to parent classes (including keepalive_timeout and keepalive_interval for STTService). """ STTService.__init__(self, **kwargs) WebsocketService.__init__(self, reconnect_on_error=reconnect_on_error, **kwargs) async def _connect(self): """Connect and start keepalive task if enabled.""" await super()._connect() self._create_keepalive_task() async def _disconnect(self): """Disconnect and cancel keepalive task.""" await super()._disconnect() await self._cancel_keepalive_task() async def _reconnect_websocket(self, attempt_number: int) -> bool: """Reconnect and restart keepalive task. The keepalive task breaks out of its loop on send errors, so it may be dead after the websocket failure that triggered this reconnect. """ result = await super()._reconnect_websocket(attempt_number) if result: await self._cancel_keepalive_task() self._create_keepalive_task() return result def _is_keepalive_ready(self) -> bool: """Check if the websocket is open and ready for keepalive.""" return self._websocket is not None and self._websocket.state is State.OPEN async def _send_keepalive(self, silence: bytes): """Send silent audio over the websocket to keep the connection alive. The default implementation sends raw PCM bytes directly. Subclasses can override this to wrap the silence in a service-specific protocol. Args: silence: Silent 16-bit mono PCM audio bytes. """ await self._websocket.send(silence) async def _report_error(self, error: ErrorFrame): await self._call_event_handler("on_connection_error", error.error) await self.push_error_frame(error)