FastRTC

FastRTC is a Python library from the Gradio team for realtime audio and video communication. You wrap a plain Python function (a generator yielding audio tuples or video frames) in a Stream, and it handles WebRTC signaling, voice activity detection, and turn taking for you. It ships a built-in Gradio UI for instant prototyping (stream.ui.launch()), can be mounted on any FastAPI app to get a WebRTC or WebSocket endpoint for your own frontend (stream.mount(app)), and offers a fastphone() helper to attach a temporary phone number to a stream. Note (verified 2026-10-13): the official site fastrtc.org was unreachable at check time; the GitHub repo remains the canonical home.

1. pip install fastrtc (add extras for pause detection and TTS: pip install "fastrtc[vad, tts]" — Python 3.10+).
2. Write a handler: a function/generator taking (sample_rate, numpy_audio) and yielding a response tuple; wrap it with ReplyOnPause for automatic voice detection and turn taking.
3. Create the stream: stream = Stream(ReplyOnPause(echo), modality="audio", mode="send-receive") (or "audio-video" for video).
4. Prototype: stream.ui.launch() gives a WebRTC-enabled Gradio UI. Ship: mount it on your FastAPI app with stream.mount(app) for a WebRTC + WebSocket endpoint.