Question about TTS Streaming and Segments: In our custom TTS that inherits from tts.TTS, we implement the stream() method which returns a SynthesizeStream. Our implementation: 1. Receives text through _input_ch 2. When we get a _FlushSentinel, we know all text for this synthesis request has been received 3. We make an API call to our TTS service with all the buffered text 4. As audio chunks arrive from our API, we: - Call output_emitter.start_segment(segment_id) - Stream chunks with output_emitter.push(chunk) - Call output_emitter.end_segment() - Call output_emitter.flush() The specific question is: When session.generate_reply() is called and text is sent to our TTS stream, should we: - Create exactly ONE segment for all the text received before _FlushSentinel? - Or can we create multiple segments if the text is long? Currently we get "number of segments mismatch: expected 1, but got 5" error when creating multiple segments. What's the correct pattern for segment handling in a streaming TTS implementation?

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Current TTS Stream Implementation (custom_baseten_tts_v2.py): class BasetenSynthesizeStream(tts.SynthesizeStream): async def _run(self, output_emitter) -> None: """Main streaming loop.""" request_id = f"stream-{uuid.uuid4()}" buffered_text = "" segment_counter = 0 # Track segment numbers for unique IDs # Initialize the output emitter with streaming enabled output_emitter.initialize( request_id=request_id, sample_rate=24000, num_channels=1, mime_type="audio/pcm", stream=True ) # Get session from TTS instance session = await self._tts_instance._ensure_session() async def process_text(text: str) -> None: if not text: return # ... payload creation ... try: async with session.post(self._endpoint, json=payload, ...) as resp: # Start segment before pushing any audio async with self._segment_lock: if self._segment_active: output_emitter.end_segment() self._segment_active = False nonlocal segment_counter segment_counter += 1 segment_id = f"{request_id}-seg-{segment_counter}" output_emitter.start_segment(segment_id=segment_id) self._segment_active = True # Stream audio chunks async for chunk in resp.content.iter_chunked(4096): # Amplify and push audio output_emitter.push(amplified_chunk) # End segment when complete async with self._segment_lock: if self._segment_active: output_emitter.end_segment() self._segment_active = False # Flush to signal completion output_emitter.flush() # Process incoming text - buffer everything until flush try: async for item in self._input_ch: if isinstance(item, self._FlushSentinel): # Process ALL buffered text as ONE segment on flush if buffered_text: segment_counter = 0 # Reset to ensure only one segment await process_text(buffered_text) buffered_text = "" else: # Just buffer text - don't process until flush buffered_text += item The Error We Get: APIError: number of segments mismatch: expected 1, but got 5 How generate_reply is called (voice_agent.py): # Generate initial greeting using generate_reply greeting_instruction = "Greet the user and introduce yourself as Briseis..." await session.generate_reply(instructions=greeting_instruction) Can you confirm the fix?

The "number of segments mismatch" error can be a bit tricky, but don't worry – I've got your back! This happens when the framework expects just one segment per synthesis request, but your current setup is creating multiple segments. ### Confirmed Fix Let's walk through how we can smooth this out and get your implementation working like a charm: 1. Reset Segment Counter on Flush: In your

process_text

function, we'll make sure to reset the

segment_counter

so only one segment gets created:

python if isinstance(item, self._FlushSentinel): if buffered_text: segment_counter = 0 // Reset to ensure only one segment await process_text(buffered_text) buffered_text = ""

2. Start and End a Single Segment: We'll be super careful to call

start_segment()

and

end_segment()

just once per synthesis request. Here's a friendly approach:

python async def process_text(text: str) -> None: if not text: return // Start segment before pushing any audio async with self._segment_lock: if self._segment_active: output_emitter.end_segment() self._segment_active = False nonlocal segment_counter segment_counter += 1 segment_id = f"{request_id}-seg-{segment_counter}" output_emitter.start_segment(segment_id=segment_id) self._segment_active = True // Stream audio chunks async for chunk in resp.content.iter_chunked(4096): output_emitter.push(chunk) // End segment when complete async with self._segment_lock: if self._segment_active: output_emitter.end_segment() self._segment_active = False // Flush to signal completion output_emitter.flush()

3. Avoid Multiple Segments in a Single Stream Instance: Just a heads up – the framework has a deprecation warning about handling multiple segments in one

SynthesizeStream

. If you need multiple segments, it's best to create a new instance each time. 4. Test the Fix: After making these changes, give it a test run. You should see that only one segment is created per synthesis request, and that pesky error should disappear. This approach should help you align perfectly with the LiveKit TTS framework's segment handling requirements. Hope this helps, and let me know if you need any more support! Sources: livekit-plugins/livekit-plugins-elevenlabs/livekit/plugins/elevenlabs/tts.p...