@audio/encode-aac

Encode PCM audio samples to AAC (ADTS) format. Browser-only — uses the native WebCodecs AudioEncoder API. Zero bundle cost, hardware-accelerated. Not available in Node.js.

Browser support: Chromium 94+ and Safari 16+. Firefox does not reliably support AAC encoding via WebCodecs and will throw at init.

import aac from '@audio/encode-aac';

const encoder = await aac({ sampleRate: 44100, channels: 1, bitrate: 128 });
const chunk = encoder.encode(channelData); // → Uint8Array (ADTS frames)
const tail  = await encoder.flush();       // → Uint8Array (remaining frames)
// concatenate chunk + tail for a complete .aac file

Options

| Option | Default | Description | |--------|---------|-------------| | sampleRate | — | Input sample rate in Hz (required) | | channels | 1 | 1 (mono) or 2 (stereo) | | bitrate | 128 | Target bitrate in kbps |

Streaming

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); // → Uint8Array (ADTS frames)
const c = await encoder.flush();        // → Uint8Array (remaining frames)
// complete ADTS AAC = concat(a, b, c)
encoder.free();

Output is raw ADTS-framed AAC — each chunk is a self-contained sequence of ADTS frames playable as .aac. The ADTS header is built from the AudioSpecificConfig (ASC) returned by the browser encoder on the first output chunk.

Why WebCodecs?

No clean-licensed pure-JS/WASM AAC encoder exists — FDK-AAC is patent/Fraunhofer-encumbered. The WebCodecs AudioEncoder API provides hardware-accelerated AAC encoding with zero bundle cost, directly in the browser.

License

MIT

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