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Salvaged from PR #47588 and rebased onto the post-campaign streaming core: the StreamingTTSProvider ABC/registry and the ElevenLabs/OpenAI streamers already live on main (tools/tts_streaming.py), so this ports the pieces main lacked: - GeminiStreamer: streamGenerateContent?alt=sse -> base64 PCM chunks (24 kHz mono int16), reusing main's DEFAULT_GEMINI_TTS_* constants. - XAIStreamer: WebSocket wss://api.x.ai/v1/tts -> binary PCM frames, async->sync bridged via the _collect_async test seam. - tts.streaming.provider config knob: pin one streamer, or 'auto' to walk the priority list elevenlabs -> gemini -> openai -> xai. Unset keeps the never-swap-the-user's-voice default. - docs/streaming-tts.md: architecture, capability matrix, how to add a provider. - Unit tests for the knob, SSE parsing, and the WS bridge; key-gated E2E tests (skipped without credentials). Refs: #47588
93 lines
4.3 KiB
Markdown
93 lines
4.3 KiB
Markdown
# Streaming TTS
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Hermes can stream TTS audio as it arrives from the provider, instead of waiting
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for the full audio before playing. This is used by voice mode (CLI/TUI live
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conversation), the dashboard speak-stream WebSocket, and — via the gateway
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`StreamingTTSConsumer` — any platform adapter that opts into streaming audio.
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Voice replies start speaking after the first clause instead of after full
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generation + synthesis.
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## Architecture
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The streaming pipeline has four parts:
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1. **Producer** — the LLM emits text deltas as it generates a response
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2. **Sentence chunker** — `tools.tts_streaming.SentenceChunker` accumulates
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deltas, strips `<think>` blocks (even split across deltas), and flushes
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complete sentences
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3. **TTS provider** — a registered `StreamingTTSProvider` turns each sentence
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into raw PCM chunks (int16 mono at the provider's declared `sample_rate`)
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4. **Audio sink** — `sounddevice.OutputStream` for local playback
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(`tools.tts_tool.stream_tts_to_speaker`), or a gateway platform adapter's
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`write_streaming_tts` seam (`gateway/streaming_tts_consumer.py`)
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Providers with no chunked API still get per-*sentence* playback via the proven
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sync `text_to_speech_tool` path, so edge (the default) is conversational too.
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All spoken text is cleaned by `tools.tts_text_normalize.prepare_spoken_text`
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(one cleaner, all paths).
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## How to pick a provider
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By default the dispatcher streams with the provider you already configured
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(`tts.provider`) when that provider has a chunked API — it never silently
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swaps your voice for a different provider just to get streaming.
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To override, set `tts.streaming.provider` in your `config.yaml`:
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- a provider name (`elevenlabs`, `gemini`, `openai`, `xai`) pins that streamer
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- `auto` walks the priority list `elevenlabs → gemini → openai → xai` and uses
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the first one whose credentials resolve — an explicit opt-in to "best
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chunked voice available"
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```yaml
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tts:
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provider: gemini
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streaming:
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provider: gemini # or "auto"
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gemini:
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model: gemini-2.5-flash-preview-tts
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voice: Kore
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```
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## Capability matrix
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| Provider | Transport | Chunked PCM | Credentials |
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|-------------|---------------------------------------|-------------|-------------|
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| elevenlabs | chunked HTTP (`pcm_24000`) | yes | `ELEVENLABS_API_KEY` / `tts.elevenlabs` |
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| openai | chunked HTTP (`with_streaming_response`, `pcm`) | yes | `tts.openai.api_key` → env → managed gateway |
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| gemini | SSE (`streamGenerateContent?alt=sse`) | yes | `GEMINI_API_KEY` / `GOOGLE_API_KEY` |
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| xai | WebSocket (`wss://api.x.ai/v1/tts`) | yes | xAI OAuth or `XAI_API_KEY` |
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| edge, piper, kitten, neutts, mistral, minimax, deepinfra, … | — | no (per-sentence sync fallback) | as usual |
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All credential lookups go through `resolve_provider_secret()`
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(config > env/.env > credential pool) — never bare env reads. Streamed bodies
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are capped at 16 MiB per sentence, mirroring the sync providers' bounded
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upstream-body invariant.
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## Adding a new streaming provider
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1. Subclass `StreamingTTSProvider` in `tools/tts_streaming.py`
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2. Set `sample_rate` (and `channels` / `sample_width` if not int16 mono)
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3. Implement `available()` (a pure probe — never install anything) and
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`stream(self, text) -> Iterator[bytes]` yielding raw PCM chunks
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4. Decorate with `@register("yourname")`
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5. Add tests in `tests/tools/test_tts_streaming.py`
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The ABC enforces the contract; the registry makes the provider discoverable;
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the dispatcher (`stream_tts_to_speaker`) and the gateway consumer handle the
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sentence buffer, stop events, and audio sink for free.
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## Gateway streaming (platform adapters)
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`gateway/streaming_tts_consumer.py` bridges agent deltas to an adapter's
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streaming-audio seam. Adapters opt in by overriding, on
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`BasePlatformAdapter`:
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- `supports_streaming_tts(chat_id, audio_format) -> bool`
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- `begin_streaming_tts / write_streaming_tts / finish_streaming_tts /
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abort_streaming_tts`
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All default to unsupported/no-op, so existing adapters are untouched. When a
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turn's streaming audio completes, the whole-file auto-TTS reply for that turn
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is suppressed (no double playback); when streaming fails before any audio was
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audible, the gateway falls back to the legacy whole-file voice reply.
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