@silyze/async-audio-mixer NPM

Async Audio Mixer

@silyze/async-audio-mixer is a lightweight, battery‑included audio mixer built on top of \ @silyze/async-audio-stream.
It lets you combine any number of PCM/encoded streams, produce a single mixed \ output, and even bridge two full‑duplex AudioStreams with automatic \ transcoding when their formats differ.

Install

npm install @silyze/async-audio-mixer

Quick start

import AudioMixer from "@silyze/async-audio-mixer";
import { OpusFormat } from "@silyze/async-audio-format-webm";

// Imagine three incoming Opus/WebM streams (8 kHz mono):
const format = new OpusFormat(8000);
const speakers = [streamA, streamB, streamC].map((s) => format.decode(s));

// Mix to PCM and then re‑encode to Opus:
const mixedOpus = AudioMixer.mix(speakers, { format });

// Pipe to a WebSocket or file:
await mixedOpus.pipe(wsWritable);

API

`AudioMixer.mix(streams, config?) ⇒ AsyncReadStream<Buffer>`

Parameter	Type & Default	Description
`streams`	`Iterable<AudioOutputStream>`	Any audio output streams to be mixed. All must share the same PCM sample‑rate.
`config.signal`	`AbortSignal` (optional)	Cancel mixing early.
`config.buffer`	`number` (ms) default 100	Length of each mixing frame in milliseconds.
`config.live`	`boolean` default false	If `true`, the mixer starts emitting only new audio frames (live broadcast). If `false`, the full buffer history is replayed once a consumer attaches.
`config.format`	`AudioFormat` (optional)	If supplied, the PCM mix is encoded with `format.encode()` before being returned.

The returned stream is PCM‑16‑LE unless you supply config.format.

`AudioMixer.connect(a, b, pipeConfig?) ⇒ Promise<void>`

Bidirectionally connects two AudioStreams (a ⇆ b).
If the streams already share the same format & sample‑rate, raw data is piped.
Otherwise each direction is transcoded on‑the‑fly using the respective \ encode/decode methods.

pipeConfig is forwarded to AsyncTransform.pipe() for back‑pressure and error \ handling options.

Example – Simple Voice Chat Room

// listenerStreams: Set<AudioOutputStream> coming from WebRTC peers
const mix = AudioMixer.mix(listenerStreams, {
  buffer: 20, // 20 ms frames → low latency
  live: true,
});

// Broadcast the mixed PCM to a speech‑to‑text service …
await mix.pipe(sttInputWritable);

Internals

Frame‑based mixing – samples are summed per frame, with hard clipping at \ ±32768 to avoid overflow.
Mono‑only – each input is treated as mono; stereo mixing is out of scope \ (PRs welcome!).
Sample‑rate safety – a runtime assertion prevents accidental mixing of \ streams that use different PCM sample‑rates.

@mojsoski/assert @mojsoski/async-stream @silyze/async-audio-stream

1.0.0

1 month ago