@audio/decode-aac

Decode AAC/M4A and ALAC (Apple Lossless) audio to PCM float samples. AAC via FAAD2 (WASM); ALAC via a pure-JS port of Apple's reference decoder — auto-detected from the M4A sample entry. Works in Node.js and browsers, no native dependencies.

Install

npm i @audio/decode-aac

Usage

import decode from '@audio/decode-aac'

// M4A or raw ADTS — auto-detected
let { channelData, sampleRate } = await decode(uint8array)
// channelData: Float32Array[] (one per channel)
// sampleRate: number

Streaming

import { decoder } from '@audio/decode-aac'

let dec = await decoder()
let { channelData, sampleRate } = dec.decode(chunk)
dec.free()

API

decode(src: Uint8Array | ArrayBuffer): Promise<AudioData>

Whole-file decode. Auto-detects M4A (MP4 container) vs raw ADTS.

decoder(): Promise<AACDecoder>

Creates a decoder instance for manual control.

• dec.decode(data) — decode chunk, returns { channelData, sampleRate }
• dec.flush() — flush remaining (returns empty for AAC)
• dec.free() — release WASM memory

AudioData

{ channelData: Float32Array[], sampleRate: number }

Formats

• M4A / MP4 with AAC audio (LC, HE-AAC v1/v2 — SBR, PS)
• M4A / MP4 with ALAC (Apple Lossless), 16/20/24/32-bit — pure JS, bit-exact
• Raw ADTS streams (.aac)

Metadata

import { parseMeta } from '@audio/decode-aac/meta'

let { meta, sampleRate } = parseMeta(m4aBytes)
// meta: { title, artist, album, year, genre, track, ..., pictures }

License

AAC decoding: GPL-2.0 (FAAD2). ALAC decoding: Apache-2.0 (port of Apple's ALAC reference). — krishnized