@audio/encode-aac
Encode PCM audio samples to AAC (ADTS) format, in browsers and Node.
Where the browser's WebCodecs AudioEncoder supports the configuration (Chromium 94+, Safari 16+) it encodes there: zero bundle cost, hardware-accelerated. Everywhere else (Node, Firefox) it runs the Fraunhofer FDK AAC encoder (v2.0.3) compiled to WebAssembly, loaded on first use.
import aac from '@audio/encode-aac';
const encoder = await aac({ sampleRate: 44100, channels: 2, bitrate: 128 });
const a = await encoder.encode(chunk1); // → Uint8Array (ADTS frames)
const b = await encoder.encode(chunk2);
const c = await encoder.flush(); // → Uint8Array (remaining frames); frees the encoder
// complete ADTS AAC = concat(a, b, c)
Options
| Option | Default | Description |
|---|---|---|
sampleRate | — | Input sample rate in Hz (required) |
channels | 1 | 1 or 2; FDK also 3–6 and 8 (WAV channel order) |
bitrate | 128 | Target bitrate in kbps |
profile | 'lc' | 'lc' AAC-LC, 'he' HE-AAC (SBR), 'hev2' HE-AACv2 (SBR + PS, stereo only) |
The encoder reports priming (its delay in samples: FDK 2048 for AAC-LC) and frameLength (1024; 2048 for HE-AAC), which a container needs for gapless playback. @audio/encode-mp4 uses them.
Output is raw ADTS-framed AAC: each chunk is a sequence of whole ADTS frames, playable as .aac. HE-AAC signals SBR implicitly (an LC header at the core rate), as ADTS must.
License
MIT. The FDK encoder inside (src/fdk.wasm.js) is the Fraunhofer FDK AAC Codec Library, distributed under its own license (LICENSE.fdk-aac): free to redistribute with that notice, and granting no patent license. AAC is covered by patents; commercial distributors may need a license from the patent pool (Via LA).