@matroska-js/remux

WebAssembly MKV / Matroska → fragmented-MP4 remuxer, compiled from Rust. It parses a .mkv / .webm container directly in the browser and rewrites its tracks into fMP4 segments you feed to a <video> element through Media Source Extensions — the video is remuxed, never transcoded, so nothing is uploaded and no server-side conversion is involved.

This is the low-level engine behind @matroska-js/player. If you want a ready-made player — controls, subtitles, audio transcoding — use that instead. Reach for @matroska-js/remux directly only when you're building your own MSE pipeline.

Install

npm i @matroska-js/remux

Usage

Built with wasm-pack --target web: import the default init function (which loads the .wasm), then drive MatroskaPlayer.

import init, { MatroskaPlayer } from '@matroska-js/remux';

await init();                                    // instantiate the wasm module
const player = await MatroskaPlayer.open(url);   // ranged HTTP reads — the server must support Range

// Per track: one fMP4 init segment, then media segments for a time window.
const initSeg = player.init_segment(trackNumber);                        // Uint8Array
const media   = await player.media_segment(trackNumber, startMs, endMs); // Uint8Array
// …append these to a MediaSource SourceBuffer.

The full API — track listing, cue-based seeking, chapters, font attachments, ASS/PGS subtitle extraction, and audio-chunk export for transcoding — is documented in the bundled TypeScript declarations (matroska_remux.d.ts).

Bundler note

The package resolves its .wasm via new URL('…', import.meta.url). With Vite, keep it out of dependency pre-bundling so that reference survives and the asset is emitted:

optimizeDeps: { exclude: ['@matroska-js/remux'] }

Codecs

Remuxes web-decodable tracks — H.264/AVC, HEVC/H.265, VP9, AV1 video; AAC, Opus, AC-3, E-AC-3, FLAC, MP3 audio — into fMP4. It never transcodes, so a track plays only if the browser can decode that codec in MP4 via MSE. (In-browser audio transcoding for non-decodable audio is provided by @matroska-js/player, not this package.)

License

AGPL-3.0-only. © David Schneider. A separate commercial license — without the AGPL's source-disclosure obligations — is available; contact [email protected].