videoElement.canPlayType shows AV1 is supported, which is not

Hi,

videoElement.canPlayType('video/webm; codecs="av01.0.05M.08"') shows "probably", which indicates that video codec is safe to us:

https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/canPlayType

But AV1 video is not supported in Microsoft Edge, tested in Dev and Canary. Is this a Bug?

 

Thanks,

Elvis Xia