Simon Willison exports animated SVG as MP4 in the browser

Willison shipped browser-side video export for animated SVG on August 16, per simonwillison.net. Plenty of platforms won't render an animated SVG in a feed or a chat window, but they'll play an MP4 without complaint. LLMs make animated SVGs easy to generate, which raises the odds someone wants to share one somewhere it won't render.

The tool detects whether an SVG has SMIL or CSS animation, then guesses the loop duration. It renders the frames and hands them to ffmpeg.wasm, which compiles an MP4 entirely in the browser. No server, no upload step. The commit is verifiable in simonw/tools as 73e0327, per simonwillison.net.

Why this workaround, not a format fix

This is a patch on a platform problem, not a fix to the format itself. The SVG format works fine. The tool exists because sharing surfaces refuse to render it. As more people generate throwaway animations with LLMs, expect more conversion shims like this one. A client-side export tool ships in a day. A platform format change does not.

The source doesn't say how long the ffmpeg.wasm compile takes for longer animations, or whether the loop-duration guess ever misfires on irregular timing.