What is the rationale behind canPlayType?

Question

So, I recently saw a reference to canPlayType on Twitter. Basically the summary is:

The canPlayType() method checks if the browser can play the specified audio/video type.

The canPlayType() method can return one of the following values:

"probably" - the browser most likely supports this audio/video type
"maybe" - the browser might support this audio/video type
"" - (empty string) the browser does not support this audio/video type

Why does it not behave like a typical API and just return true/false?... And why the very ambiguous terms "maybe" and "probably"?

Answer 1

Why? Because that is what the spec says to do http://dev.w3.org/html5/spec-preview/media-elements.html#dom-navigator-canplaytype

The canPlayType(type) method must return the empty string if type is a type that the user agent knows it cannot render or is the type "application/octet-stream"; it must return "probably" if the user agent is confident that the type represents a media resource that it can render if used in with this audio or video element; and it must return "maybe" otherwise. Implementors are encouraged to return "maybe" unless the type can be confidently established as being supported or not. Generally, a user agent should never return "probably" for a type that allows the codecs parameter if that parameter is not present.