Consider a "native-" or "host-" role prefix for elements like audio/video that would require complex API support out of scope for ARIA. Authors SHOULD NOT use these in content, but test tools like the WebKit inspector, could return these values where no specific ARIA role matched.

<button> -> button (concrete)
<input type="range"> -> slider (concrete)
<video> -> native-video, host-video,

[Update: Another option from comment below.]

videoElement.computedRole; // "html:video"
mfracElement.computedRole; // "math:mfrac"

[Update March 2023: or html-video] (like abstract roles, authors should not use in role attr)