End-user generated content is responsible for the success of several collaborative applications, as it can be noted in the context of the web. The collaborative use of some of these applications is made possible, in many cases, by the availability of annotation features which allow users to include commentaries on each other's content. In this paper we first discuss the opportunity of defining vocabularies that allow third-party applications to integrate annotations to end-user generated documents, and present a proposal for such a vocabulary. We then illustrate the usefulness of our proposal by detailing a tool which allows users to add multimedia annotations to end-user generated video content.