mtx-decompressor

A zero-dependency TypeScript library that decompresses MicroType Express (MTX) compressed font data found inside EOT (Embedded OpenType) containers, producing standard TrueType (.ttf) font binaries.

MTX is a font compression format developed by Monotype, used inside EOT containers commonly found in older web pages and embedded in Microsoft Office documents. This library extracts the compressed data and reconstructs a standard .ttf file usable with standard font APIs (e.g. the FontFace API). It has no dependencies and works in both the browser and Node.js.

▶️ Live demo · 📦 npm

Demo

Try it right in your browser — drop in an .eot file, download the extracted .ttf, and preview text rendered in the decompressed font:

https://christophervr.github.io/mtx-decompressor/

Install

npm install mtx-decompressor

Quick start

import { decompressMtx, decompressEotFont } from 'mtx-decompressor';

// Decompress MTX-compressed font data
const fontData: Uint8Array = /* extracted from EOT container */;
const ttfBytes = decompressMtx(fontData, { encrypted: false, compressed: true });
// => Uint8Array containing a valid TrueType font

// Convenience wrapper with explicit boolean parameters
const ttf = decompressEotFont(fontData, /* compressed */ true, /* encrypted */ false);

// XOR-obfuscated data
const decrypted = decompressMtx(encryptedData, { encrypted: true, compressed: true });

API

decompressMtx(fontData, options?)

Decompress an MTX-compressed font into a TrueType binary.

| Parameter | Type | Description | | -------------------- | ---------------------------- | ----------------------------------------------------------------------------- | | fontData | Uint8Array | Raw font bytes (MTX-compressed, optionally encrypted) | | options.encrypted | boolean (default: false) | If true, XOR-decrypt with key 0x50 before decompression | | options.compressed | boolean (default: true) | If false, skip decompression and return the (possibly decrypted) data as-is | | Returns | Uint8Array | A valid TrueType (.ttf) font binary |

decompressEotFont(fontData, compressed, encrypted)

Convenience wrapper around decompressMtx taking explicit boolean parameters; returns a TrueType binary.

unpackMtx(data, size)

Low-level: unpack an MTX blob into three LZCOMP-decompressed streams. Returns { streams: Uint8Array[], sizes: number[] }.

The exported SFNTContainer and SFNTTable types describe the reconstructed font tables.

How it works

The pipeline: optional XOR decryption → MTX header parsing (splits into three LZCOMP blocks) → LZCOMP decompression (sliding-window LZ with adaptive Huffman coding) → CTF parsing (reconstructs TrueType tables from the three Compact TrueType Font streams) → SFNT assembly (table directory, alignment, checksums).

Provenance

A TypeScript port of the MTX decompression code from libeot by Brennan Vincent (MPL-2.0). The original C implementation is based on the MicroType Express specification submitted to the W3C by Monotype Imaging.

License

MPL-2.0. As a TypeScript port of the MPL-2.0-licensed libeot, this library inherits the Mozilla Public License 2.0 — modifications to the licensed files must remain open under the same terms.