Exotel

OverviewCopy Anchor Link

ExotelFrameSerializer speaks the WebSocket protocol of Exotel's Stream and Voicebot applets. Paired with FastAPIWebsocketTransport, it lets a bot answer phone calls:

• Caller audio (16-bit PCM at 8 kHz, base64 in media events) becomes InputAudioRawFrames at the pipeline's input rate.
• Bot audio is resampled to 8 kHz and sent as media events.
• Touch-tone digits become InputDTMFFrames.
• An InterruptionFrame sends clear.

There is no hang-up REST call: the call ends when the stream closes. See How phone calls connect for the overall flow.

InstallationCopy Anchor Link

bun add @pipedog/serializer-exotel @pipedog/transport-websocket @pipedog/runner

import { ExotelFrameSerializer } from "@pipedog/serializer-exotel/exotel";

PrerequisitesCopy Anchor Link

• An Exotel account with a call flow whose Voicebot applet points at your WebSocket URL.
• The stream SID (and call SID), which Exotel sends in its start message.

ExotelFrameSerializerCopy Anchor Link

ConfigurationCopy Anchor Link

InputParamsCopy Anchor Link

params is an ExotelFrameSerializer.InputParams (ExotelFrameSerializerInputParams):

UsageCopy Anchor Link

import { parseTelephonyWebsocket } from "@pipedog/runner/utils";
import { ExotelFrameSerializer } from "@pipedog/serializer-exotel/exotel";
import {
  FastAPIWebsocketParams,
  FastAPIWebsocketTransport,
} from "@pipedog/transport-websocket/fastapi";
import { websocketFetchHandler } from "@pipedog/transport-websocket/fetch";
import type { WebsocketConnection } from "@pipedog/transport-websocket/socket";

async function runCall(connection: WebsocketConnection): Promise<void> {
  // Exotel sends "connected", then "start" with the stream and call SIDs.
  const [, callData] = await parseTelephonyWebsocket(connection);

  const serializer = new ExotelFrameSerializer({
    streamSid: callData.streamId ?? "",
    callSid: callData.callId,
  });

  const transport = new FastAPIWebsocketTransport(
    connection,
    new FastAPIWebsocketParams({
      audioInEnabled: true,
      audioOutEnabled: true,
      addWavHeader: false,
      serializer,
    }),
  );
  // ... build and run the pipeline with transport.input() and transport.output()
}

// The Voicebot applet's WebSocket URL points here.
const handler = websocketFetchHandler(runCall);

NotesCopy Anchor Link

• callSid is stored but not used: Exotel has no hang-up call here.
• The audio is linear PCM, not μ-law: only resampled, never companded.
• An invalid DTMF digit is logged at info level and ignored.

Runtime notesCopy Anchor Link

Generated from pipecat.runtimes and pipecat.compat in packages/serializer-exotel/package.json: ✅ means the compat smoke test passes on that runtime.

Runs on Bun, Node, Deno and Cloudflare Workers. The package's golden tests replay vectors recorded from upstream: at 8 kHz the wire output is byte-identical.