opus-media-recorder is a MediaRecorder API polyfill written in ES6 and WebAssembly. It aims for cross-browser Opus codec support with various audio formats such as Ogg and WebM. opus-media-recorder can be used as a polyfill, or it can replace the built-in MediaRecorder since opus-media-recorder supports more MIME types.

opus-media-recorder uses WebAssembly compiled from popular libraries (e.g libopus, libogg, libwebm, and speexdsp) to ensure performance and standards-compliance.

See https://github.com/kbumsik/opus-media-recorder