I believe that this is outside the scope of the browser, and is more up to the OS. However, despite whatever the case is, I don't think that this is something that you should mess with anyway.

accept doesn't have the best support (although might not be an issue), but as you can see here: http://www.iana.org/assignments/media-types/media-types.xhtml#audio the sheer number of allowed types probably falls outside of the scope of your application anyway. The best thing you should do is perform server side validation, using accept purely as a client indicator.

Also, while it is an older answer, I think it is still relevant and valid: File input 'accept' attribute - is it useful?