Async Audio Format A‑law (G.711)

@silyze/async-audio-format-alaw adds A‑law (G.711) support to the
@silyze/async-audio-stream
ecosystem.
It performs in‑memory conversion between 8‑bit A‑law and 16‑bit little‑endian PCM,
streaming‑friendly and fully async.

Install

npm install @silyze/async-audio-format-alaw

Depends on alawmulaw for the actual codec maths (bundled as a normal dependency).

Usage

import ALawFormat from "@silyze/async-audio-format-alaw";

// Typically, G.711 A‑law telephony audio is 8 kHz mono:
const format = new ALawFormat(8000);

// Encode raw PCM → A‑law:
const alawStream = format.encode(pcmStream);

// Decode A‑law → raw PCM:
const pcmStream = format.decode(alawStream);

Available Format

| Class | Container | Codec | Channels | Notes | | ------------- | --------- | --------- | -------- | ------------------------------------- | | ALawFormat | Raw bytes | A‑law | Mono | Bidirectional encode / decode streams |

API

class ALawFormat extends AudioFormat {
  constructor(sampleRate: number); // e.g. 8000

  readonly name: string; // "alaw"
  readonly pcmSampleRate: number; // constructor value

  /** PCM‑16‑LE → A‑law (8‑bit) */
  encode(input: AsyncReadStream<Buffer>): AsyncReadStream<Buffer>;

  /** A‑law (8‑bit) → PCM‑16‑LE */
  decode(input: AsyncReadStream<Buffer>): AsyncReadStream<Buffer>;
}

Both encode() and decode() are implemented with the
alawmulaw library (using its alaw codec)
and run inside stream map() transforms, so they start processing as soon as data arrives.

Implementation Notes

• Sample‑rate‑agnostic – although typical G.711 A‑law telephony audio is 8 kHz, you
  may instantiate ALawFormat with any sample rate if your pipeline uses
  different values.
• Lossy – A‑law is a companded 8‑bit representation; converting back to PCM
  cannot fully restore the original 16‑bit dynamic range.