Willison Adds Browser-Side Animated-SVG-to-MP4 Export to His Markdown Renderer, Using FFmpeg Compiled to WebAssembly
simonwillison.net·medium signal
Shipped August 16, the upgrade detects whether an SVG contains SMIL or CSS animation, guesses the loop duration, renders the frames, then loads ffmpeg.wasm to compile them into a downloadable MP4 entirely client-side — no server, no upload. The motivation is mundane and useful: platforms that won't render animated SVG will happily take a video, so this makes LLM-generated animations shareable. The change is verifiable in the simonw/tools repo as commit 73e0327 ('Add MP4 export for animated SVGs using ffmpeg.wasm', #314).