Oh, I see that there already was/is a discussion on querying media format support ( http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2008-August/015620.html ).
Anyway, the question when error flags are supposed to be set and if such flags could be used to "query" media format support with the help of the type-attribute of the source-element may still be of interest. Maik
