turns: add TranscriptionUserTurnStartStrategy

src/pipecat/turns/user/transcription_user_turn_start_strategy.py

@@ -0,0 +1,51 @@
+#
+# Copyright (c) 2024–2025, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+"""User turn start strategy based on transcriptions."""
+
+from pipecat.frames.frames import BotStartedSpeakingFrame, Frame, TranscriptionFrame
+from pipecat.turns.user.base_user_turn_start_strategy import BaseUserTurnStartStrategy
+
+
+class TranscriptionUserTurnStartStrategy(BaseUserTurnStartStrategy):
+    """User turn start strategy based on transcriptions.
+
+    This strategy signals the start of a user turn when a transcription is
+    received while the bot is speaking. It is useful as a fallback in scenarios
+    where VAD-based detection fails (for example, when the user speaks very
+    softly) but the STT service still produces transcriptions.
+
+    """
+
+    def __init__(self):
+        """Initialize the base interruption strategy."""
+        super().__init__()
+        self._bot_speaking = False
+
+    async def reset(self):
+        """Reset the interruption strategy."""
+        await super().reset()
+        self._bot_speaking = False
+
+    async def process_frame(self, frame: Frame):
+        """Process an incoming frame to detect the start of a user turn.
+
+        Args:
+            frame: The frame to be processed.
+        """
+        await super().process_frame(frame)
+
+        if isinstance(frame, BotStartedSpeakingFrame):
+            await self._handle_bot_started_speaking(frame)
+        elif isinstance(frame, TranscriptionFrame):
+            await self._handle_transcription(frame)
+
+    async def _handle_bot_started_speaking(self, _: BotStartedSpeakingFrame):
+        self._bot_speaking = True
+
+    async def _handle_transcription(self, _: TranscriptionFrame):
+        if self._bot_speaking:
+            await self.trigger_user_turn_started()

tests/test_user_turn_start_strategy.py

@@ -7,12 +7,16 @@
 import unittest
 
 from pipecat.frames.frames import (
+    BotStartedSpeakingFrame,
     InterimTranscriptionFrame,
     TranscriptionFrame,
     VADUserStartedSpeakingFrame,
     VADUserStoppedSpeakingFrame,
 )
 from pipecat.turns.user.min_words_user_turn_start_strategy import MinWordsUserTurnStartStrategy
+from pipecat.turns.user.transcription_user_turn_start_strategy import (
+    TranscriptionUserTurnStartStrategy,
+)
 from pipecat.turns.user.vad_user_turn_start_strategy import VADUserTurnStartStrategy
 
 
@@ -104,3 +108,24 @@ class TestVADUserTurnStartStrategy(unittest.IsolatedAsyncioTestCase):
 
         await strategy.process_frame(VADUserStartedSpeakingFrame())
         self.assertTrue(should_start)
+
+
+class TestTranscriptionUserTurnStartStrategy(unittest.IsolatedAsyncioTestCase):
+    async def test_transcription_strategy(self):
+        strategy = TranscriptionUserTurnStartStrategy()
+
+        should_start = None
+
+        @strategy.event_handler("on_user_turn_started")
+        async def on_user_turn_started(strategy):
+            nonlocal should_start
+            should_start = True
+
+        await strategy.process_frame(TranscriptionFrame(text="Hello!", user_id="", timestamp="now"))
+        self.assertFalse(should_start)
+
+        await strategy.process_frame(BotStartedSpeakingFrame())
+        self.assertFalse(should_start)
+
+        await strategy.process_frame(TranscriptionFrame(text="Hello!", user_id="", timestamp="now"))
+        self.assertTrue(should_start)