Audio & DTMF

Call sessions emit received audio and can stream a Buffer to the remote peer. The raw buffer format depends on the codec selected when constructing the Softphone.

Choose a codec

Codec	Raw input and decoded output	Playback example
OPUS/16000 (default)	16-bit signed little-endian PCM, 16 kHz, mono	ffplay -autoexit -f s16le -ar 16000 -ac 1 audio.raw
OPUS/48000/2	16-bit signed little-endian PCM, 48 kHz, stereo	ffplay -autoexit -f s16le -ar 48000 -ac 2 audio.raw
PCMU/8000	8-bit mu-law, 8 kHz, mono	ffplay -autoexit -f mulaw -ar 8000 -ac 1 audio.raw

Set the codec during construction:

const softphone = new Softphone({
  // SIP credentials...
  codec: "PCMU/8000",
});

Receive audio

For Opus codecs, the audio event provides decoded PCM. For PCMU, it provides mu-law bytes. The event payload is a Buffer.

import fs from "node:fs";

const output = fs.createWriteStream(`${callSession.callId}.raw`);

callSession.on("audio", (audio) => {
  output.write(audio);
});

callSession.once("disposed", () => output.close());

Stream audio

Pass a complete raw audio buffer in the selected codec's input format. Streaming starts automatically on the next event-loop turn, so a finished listener attached immediately after streamAudio() also observes short input.

import fs from "node:fs";

const streamer = callSession.streamAudio(fs.readFileSync("audio.raw"));
streamer.once("finished", () => console.log("Audio sent"));

pause() keeps the current position, resume() continues a paused run, stop() ends it without emitting finished, and start() restarts the original buffer.

Call these synchronous controls later in response to application state; they are not a sequence:

streamer.pause();
streamer.resume();
streamer.stop();
streamer.start(); // restart from the beginning

Pause streaming while the call is on hold, then resume after unholding.

Send DTMF

DTMF characters are limited to 0-9, *, and #. Send one character immediately:

callSession.sendDTMF("1");

Send a sequence with a delay after each character. The default delay is 500 milliseconds:

await callSession.sendDTMFs("101#", 500);

Receive DTMF

callSession.on("dtmf", (digit) => {
  console.log("DTMF:", digit);
});

For complete call flows, see the Demos page, including the meeting example.