That's what I always assumed you got back when you create a MediaRecorder like so:
new MediaRecorder(stream, { mimeType: 'video/webm;codecs=h264' })
Which is what this project does. Is it actually returning something else behind the scenes?
While WebM usually contains VP8 or VP9, it isn't impossible to throw an h264 stream in there
WebM is Matroška, and it can contain H.264 as far as I'm aware. Not sure precisely what browsers decide to do here, but apparently it's something.
WebM is a subset of Matroska, if something is returning h.264 inside a WebM container...that's not conforming to the WebM subset. But I guess nothing matters.