Send TTS Audio Back

When you own the audio bridge for a call, everything that your text-to-speech engine produces goes to the caller through one method: publishDownlink(frame). Each call pushes a single encoded audio frame, typically a 20 ms Opus packet, onto the voice/<sid>/downlink track. The engine paces the frame to the caller’s leg. On a PSTN call, the engine transcodes to G.711 for you. This is the send side of the bring-your-own ASR/TTS pattern. For the receive side, which feeds caller speech into your recognizer, see Stream Audio to ASR.

Push TTS chunks as they arrive

Open the bridge with attach(). Then forward each synthesized chunk straight to publishDownlink. attach() always subscribes uplink too. For this reason, pass an onUplink callback even if you only care about playback here. A no-op is fine, or wire it to your ASR.

TypeScript
Python

import { Voice } from "@clutchcall/sdk/voice";

const v = new Voice({
  baseUrl: "https://engine.clutchcall.dev",
  apiKey:  process.env.CLUTCHCALL_CREDENTIALS!,
  orgId:   "org_abc",
});

const call = await v.calls.originate({
  to: "+15551234567",
  from: "+15558675309",
  trunkId: "trunk_main",
});

const bridge = await v.audioBridge.attach(call.sid, {
  codec: "opus",
  onUplink: (frame, tsUs) => {}, // playback-only here
});

// stream synthesized Opus straight to the caller
myTts.onChunk((opus) => bridge.publishDownlink(opus));

import os
from clutchcall.voice import Voice

v = Voice(
    base_url="https://engine.clutchcall.dev",
    api_key=os.environ["CLUTCHCALL_CREDENTIALS"],
    org_id="org_abc",
)

call = v.calls.originate(
    to="+15551234567", from_="+15558675309", trunk_id="trunk_main",
)

bridge = v.audio_bridge.attach(
    call.sid,
    codec="opus",
    on_uplink=lambda frame, ts_us: None,  # playback-only here
)

# stream synthesized Opus straight to the caller
tts.on_chunk(lambda opus: bridge.publish_downlink(opus))

publishDownlink expects an encoded frame in the codec that you asked for in attach(). With codec: "opus", push Opus packets. With codec: "pcm16", push raw PCM16. Send one frame per call, one 20 ms tick at a time. Do not send a whole utterance in a single buffer. This keeps playback smooth and lets barge-in cut the audio off cleanly.

Feed a model that emits raw PCM

Many realtime and TTS models give you 16-bit PCM rather than Opus. Ask for pcm16. The bridge then transcodes both directions. You push exactly what the model gives you.

TypeScript
Python

const bridge = await v.audioBridge.attach(call.sid, {
  codec: "pcm16",
  sampleRate: 16000,
  onUplink: (pcm, tsUs) => model.appendAudio(pcm),
});

// model → caller: no re-encode in your process
model.onAudioOut((pcm) => bridge.publishDownlink(pcm));

bridge = v.audio_bridge.attach(
    call.sid,
    codec="pcm16",
    sample_rate=16000,
    on_uplink=lambda pcm, ts_us: model.append_audio(pcm),
)

# model → caller: no re-encode in your process
model.on_audio_out(lambda pcm: bridge.publish_downlink(pcm))

Time playback yourself

When you omit the timestamp, publishDownlink stamps each frame with a monotonic clock. This is fine for live streaming. If you replay buffered audio or splice clips, pass a microsecond timestamp so that frames land in order.

TypeScript
Python

let tsUs = 0n;
for (const frame of opusFrames) {
  bridge.publishDownlink(frame, tsUs);
  tsUs += 20_000n; // 20 ms per frame, in microseconds
}

ts_us = 0
for frame in opus_frames:
    bridge.publish_downlink(frame, timestamp_us=ts_us)
    ts_us += 20_000  # 20 ms per frame, in microseconds

Keep the bridge reference alive for the whole call. If the garbage collector removes it, both tracks drop. When the call ends, call close() on the bridge before you call hangup() so that the downlink track closes cleanly.

Stream Audio to ASR

The uplink companion: feed caller speech to your recognizer.

BYO ASR / LLM / TTS

Run the full custom-brain loop end to end.

Hand off to a human

Escalate the live call and keep the same sid.

Python SDK

Full AudioBridge signatures for Python.

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Push TTS chunks as they arrive

Feed a model that emits raw PCM

Time playback yourself

Stream Audio to ASR

BYO ASR / LLM / TTS

Hand off to a human

Python SDK

​Push TTS chunks as they arrive

​Feed a model that emits raw PCM

​Time playback yourself

​Related

Stream Audio to ASR

BYO ASR / LLM / TTS

Hand off to a human

Python SDK

Push TTS chunks as they arrive

Feed a model that emits raw PCM

Time playback yourself

Related