Simon Willison adds MP4 export to markdown-svg-renderer

Developer Simon Willison has released a significant update to his open-source markdown-svg-renderer tool, introducing the ability to convert animated SVG files into MP4 videos directly within the web browser. Released on August 16, 2026, this new feature addresses the common challenge of sharing animated vector graphics on social media and other online platforms that do not natively support the SVG format.

The tool operates entirely client-side. When a user inputs Markdown containing an animated SVG, the application analyzes the graphic to estimate the appropriate duration for a looped video. It then renders the individual frames of the animation and loads 30+ megabytes of ffmpeg.wasm, a WebAssembly port of the popular multimedia framework. This allows the browser to compile the rendered frames into a standard MP4 video file without relying on external server-side processing.

In addition to the new MP4 export functionality, markdown-svg-renderer offers tabs that render SVGs into static PNG and JPEG formats, which users can easily copy or download. To use the tool, practitioners can paste raw Markdown directly into the browser interface or input a CORS-friendly URL. It also supports loading documents directly from a GitHub Gist, which generates a shareable, bookmarkable URL containing the path to the source file.

For developers and designers, this update simplifies the workflow of documenting and sharing visual assets. Instead of relying on heavy desktop video editing software or command-line tools to convert web animations for presentations or social media, practitioners can now perform the entire conversion pipeline in a single browser tab. This makes sharing interactive transcripts and animated diagrams significantly more accessible.