Traditionally, web apps that needed media processing had to choose between server-side pipelines, massive FFmpeg WASM builds, or work with the limited set of HTML5 media APIs. These solutions were often slow, expensive, or too inflexible for more complex use cases. WebCodecs changed the game by exposing direct access to the browser’s media pipeline, making us dream about what the web could deliver: powerful, super-fast video editors, DAWs, recorders, converters, all running entirely on-device. But if you’ve used WebCodecs, you’ll know it’s low-level, somewhat advanced, and only one piece of the puzzle. To build serious media apps, you need much more. Enter Mediabunny, a new library purpose-built from scratch for the web to be a full toolkit for client-side media processing. It unifies muxing, demuxing, encoding, decoding, converting and streaming under a single API and embraces the web as a platform. I’ll share the origin story of how a 3D platformer game accidentally pulled me into media processing, and how lessons learned from my previous libraries mp4-muxer and webm-muxer shaped Mediabunny’s final design. We’ll briefly explore its architecture and show a demo, and discuss how it can power a new generation of highly performant web-based media tools. This talk was presented at Demuxed 2025 in London, a conference by and for engineers working in video. Every year we host a conference with lots of great new talks like this – learn more at https://demuxed.com