The ACAV project aims to explore how the accessibility of web videos can be improved by providing rich descriptions of video content in order to personalize the rendering of the content according to user disabilities. We present a motivating scenario, the results of a preliminary study as well as the different technologies that will be developed. Categories and Subject Descriptors H.5.1 [Multimedia Information System]: Audio, Video and Hypertext Interactive Systems; K.4.2 [Social Issues]: Assistive technologies for people with disabilities General Terms Languages, Standardization Keywords Video Accessibility, Media Fragments, Media Annotations