TIL canvas.captureStream() is video-only — here's how I mixed voiceover + music into a MediaRecorder export" published:

TL;DR — canvas.captureStream() only carries video tracks. To get audio into your MediaRecorder export you need to build an AudioContext graph that lets every and element play through speakers AND tap into a MediaStreamDestination simultaneously. There are at least five footguns along the way. Here's the singleton wrapper that finally got it right. I've been building a client-side video editor over the last few months ( AetherCut — 100% in-browser, nothing uploads, no SaaS backend for the editing