Universal Compress

Drop any file, make it smaller. PDFs, video, images and audio — compressed entirely in your browser. Nothing is uploaded.

Live at opensource.unisim.co.uk/compress.

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The idea

Every "compress your PDF online" result is the same site with a different logo: you upload your file to somebody's server, they squeeze it, and you download it back. That works, and it means your tax return, your NDA and your kid's birthday video all sat on a stranger's disk for a while.

This one doesn't upload anything. The four engines it uses are all already in the browser you are reading this in.

There is one drop target — a circle — and it takes anything. What you dropped decides what the options column shows: drop a PDF and you get PDF settings, drop a PDF and four photos and you get one panel for each. There is no format to pick first and no tab to find.

And there is one control that matters — Light / Balanced / Maximum — asked once, in the same words, for every kind of file. Each engine translates that into whatever its own knobs happen to be. Everything under Advanced is for people who already know which knob they want; nobody has to open it.

What it compresses

Kind	In	Out	Engine
PDF	.pdf	.pdf	pdf-lib (lossless repack) or pdf.js + JPEG (rasterise)
Video	.mp4 .m4v .mov	.mp4 (H.264 + AAC)	WebCodecs, via @unisim/media
Images	.jpg .png .webp .avif .heic .gif .bmp	JPEG / WebP / AVIF	the browser's canvas encoder
Animated GIF	.gif	.gif, still animated	ours — src/lib/gif/, no dependency
Audio	.mp3 .wav .m4a .flac .ogg .opus .aiff	.mp3 / .m4a	WebAudio + LAME (JS) or WebCodecs AAC

Anything else stays in the list with a sentence explaining why it can't be opened — a .mkv is told to remux, a .zip is told it is already compressed. Files are never silently dropped.

Animated GIFs

An animated GIF gets its own codec rather than the canvas path, because the canvas path destroyed it: createImageBitmap() returns frame one of an animation and gives no indication it dropped the rest, so a 4.2 MB animation came out as a 2 KB still and the app reported "−100%" — its biggest saving — for having thrown the file away.

No browser will read past frame one or write a GIF at all, so both halves are here and neither has a dependency: src/lib/gif/decode.ts (block chain, LZW, compositing, disposal methods, interlacing) and src/lib/gif/encode.ts (median- cut palette, quantiser, LZW, frame differencing — forked from Universal Converter's, which had no reader). The saving comes from a single global palette narrowed by the quality slider, from sending only the rectangle that changes between frames, from the longest-edge cap, and at Maximum from dropping every second frame while keeping the animation's length.

Measured on two real screen recordings: 13% and 34% at Balanced, 15% and 44% at Maximum. Both were already optimised; a GIF exported as whole frames does far better.

npm run test:gif is the check that matters — it decodes real GIFs written by other tools and compares every pixel against ffmpeg, then has ffmpeg read back what we write. npm test covers the same code without needing ffmpeg installed, but a reader and a writer that share a misunderstanding round-trip perfectly and produce files nothing else can open, so an outside reader is the only honest test.

Two things it deliberately will not do

• It won't trim your video. Cutting a clip down is Universal Video's job, and it does it properly, with a preview and a timeline. A pair of naked start/end boxes here would be the worse half of that feature.
• It won't hand you back something bigger. Re-encoding an already-optimised JPEG or a tightly-packed PDF routinely produces a larger file. When that happens the original is returned instead and the row says so.

Running it locally

cd D:/Github/UNISIM/Universal_Apps/Universal_Compress   # or the Mac equivalent
npm install
npm run dev -- --port 5200 --strictPort

Or ./scripts/preview.sh / .\scripts\preview.ps1, which do the same and install on first run. Port 5200 is this app's slot in the suite's port registry.

Video compression needs a browser with a WebCodecs H.264 encoder — Chrome, Edge, or Safari 16.4+. Firefox loads the page and says so in the video panel; PDFs, images and audio work everywhere.

Nothing here needs the internet. There is no engine to download and no file is ever sent.

npm run typecheck   # tsc -b --noEmit
npm run build       # tsc -b && vite build

Licence

AGPL-3.0-or-later, with an added permission for app-store distribution.

Part of the Universal Simulation suite — the Universal Apps are free forever and open source.