@audio/encode-webm

Encode PCM audio samples to WebM (Opus) format. WASM (libopus via opusscript) with built-in EBML/Matroska muxer — works in both node and browser.

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

const encoder = await webm({ sampleRate: 48000, channels: 1, bitrate: 96 });
const chunk = encoder.encode(channelData); // → Uint8Array (WebM header + cluster)
const tail = encoder.flush();              // → Uint8Array (final cluster)
// concatenate chunk + tail for complete WebM file

Options

| Option | Default | Description | |--------|---------|-------------| | sampleRate | — | Input sample rate (required). Resampled to 48kHz internally. | | channels | 1 | 1 (mono) or 2 (stereo) | | bitrate | 64 | Target bitrate in kbps | | application | 'audio' | 'audio', 'voip', or 'lowdelay' |

Opus always encodes at 48kHz. If the input sample rate differs, Lanczos-3 resampling is applied automatically.

Output uses unknown-size Segment and Clusters (streaming/live WebM), matching MediaRecorder output.

Streaming

const encoder = await webm({ sampleRate: 44100, channels: 1, bitrate: 128 });
const a = encoder.encode(chunk1); // → Uint8Array (EBML header + Segment + Tracks + first Cluster)
const b = encoder.encode(chunk2); // → Uint8Array (additional Cluster)
const c = encoder.flush();        // → Uint8Array (final Cluster with remaining samples)
// complete WebM = concat(a, b, c)
encoder.free();

License

MIT

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