WebAssembly and MP4 rendering run in the browser without a backend

Since May, Simon Willison has been developing a web tool called markdown-svg-renderer. It solves one specific problem: how to share Markdown with embedded animated SVG images so others can view them immediately. A user can paste the code or the address of a CORS-accessible document.

Older platforms receive a static fallback

Many platforms do not support SVG animations. The PNG and JPEG tabs can therefore render the Markdown content into common formats that can be downloaded or copied. The result link remains bookmarkable.

WebAssembly taxes the local processor

The most interesting trick happens in the new MP4 tab. The tool checks whether an SVG contains animation and estimates the loop length. It then downloads more than 30 MB of the ffmpeg.wasm library, which assembles the individual frames into a final video inside the browser.

The developer cuts rendering infrastructure costs

The entire process runs exclusively through WebAssembly on the user's device. The author does not need to pay for a video-processing backend. The computational power is provided by the modern browser on the visitor's side.

Links keep the application stateless

When loaded from a URL, the page saves the reference directly in the address bar. A user can return at any time and share the result. The tool thereby shifts all the workload to the client and remains entirely passive infrastructure itself.

Lilith's verdict

Why pay Amazon for generated video minutes when you can make the visitor download 30 MB of WebAssembly and stress their own processor.