There have been a number of proposals for multimedia ontologies and mappings of multimedia vocabularies (cf. the excellent report from the W3C MM Semantics XG), differing in complexity and expressivity. Thus the W3C has chartered a working group to develop an ontology and API for multimedia content on the Web. The group is developing a lightweight core set of metadata properties and an API specification for accessing these properties, which may come from metadata documents in different standards. Thus mappings to many relevant standards have also been specified. The set of metadata properties will be formalized for interoperability with the Semantic Web. A W3C recommendation is expected in 2010.