feat: stream MLX TTS audio chunks

[nwalker85]

Status

Draft/WIP. This has passed focused unit and syntax checks, but has not yet been tested against a real loaded MLX TTS model for time-to-first-audio or playback behavior. It should not be treated as ready for review until that real-model streaming test is done.

Summary

• expose MLX model generation as an async chunk stream instead of collecting the full waveform first
• make /generate/stream emit a WAV header plus PCM16 chunks for live-compatible requests
• keep the existing buffered fallback when normalization, effects, trim, or crossfade require whole-file processing, and label responses with X-Voicebox-Stream-Mode
• document the live streaming contract and add focused unit tests for the streaming helpers

Validation

• uv run --with pytest --with pytest-asyncio --with soundfile --with librosa --with numpy python -m pytest tests/test_streaming_audio.py
• uvx ruff check --select F,I,RUF100 backends/mlx_backend.py utils/audio.py utils/chunked_tts.py routes/generations.py tests/test_streaming_audio.py
• python -m compileall backends/mlx_backend.py utils/audio.py utils/chunked_tts.py routes/generations.py

Still needed

• run against a real Voicebox profile/model locally
• measure time-to-first-audio on /generate/stream with normalize: false
• verify browser/client playback and lip-sync analyser behavior

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d15aef7a-298e-46eb-99c3-ba76c0341601

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}