@audio/decode-webm

Decode WebM and Matroska (MKV) audio to PCM float samples — the audio track of video files included (Opus, Vorbis, AAC, ALAC, MP3, FLAC, AC-3, DTS, PCM).

Install

npm i @audio/decode-webm

Usage

import decode, { decoder } from '@audio/decode-webm'

let { channelData, sampleRate } = await decode(webmBytes)

let dec = await decoder() // initialize Opus and Vorbis WASM
let result = dec.decode(chunk)
let tail = dec.flush()
dec.free()

Video tracks are skipped; the first audio track is decoded. Laced blocks (Xiph, EBML, fixed) are split into frames.

API

decode(src): Promise<AudioData>

Decode a complete Uint8Array or ArrayBuffer.

decoder(): Promise<WebmDecoder>

Initialize the codec runtimes and return a streaming decoder. For the WebM codecs (Opus, Vorbis) decode() and flush() are synchronous. For Matroska-only codecs the call that completes the track header returns a Promise while the codec package loads; later calls are synchronous. flush() ends the stream.

The factory prepares the Opus and Vorbis runtimes, then releases what the track does not need once the header is read.

Codecs

| CodecID | Decoded by | |---|---| | A_OPUS | bundled libopus WASM core from @audio/decode-opus | | A_VORBIS | bundled @audio/decode-vorbis | | A_AAC (all profiles) | @audio/decode-aac, loaded on demand | | A_ALAC | @audio/decode-aac, loaded on demand | | A_MPEG/L3 | @audio/decode-mp3, loaded on demand | | A_FLAC | @audio/decode-flac, loaded on demand | | A_PCM/INT/LIT, A_PCM/INT/BIG, A_PCM/FLOAT/IEEE | built in | | A_AC3 | @audio/decode-ac3, loaded on demand | | A_DTS (core of DTS-HD too) | @audio/decode-dts, loaded on demand | | A_EAC3 | @audio/decode-eac3, loaded on demand |

TrueHD, MPEG Layer I/II, WavPack, TTA and A_MS/ACM tracks throw an error naming the codec. DiscardPadding on Opus blocks is honoured, so files from @audio/encode-webm decode sample-exact.

On-demand codec packages are imported dynamically, which is unavailable inside an AudioWorklet — Opus and Vorbis work there, the others need the main thread or a Worker.

License

ॐ · MIT. Bundled libopus is BSD 3-Clause.