In this paper, an approach for knowledge and context-assisted content analysis and reasoning based on a multimedia ontology infrastructure is presented. This is one of the major objectives of the aceMedia Integrated Project. In aceMedia, ontologies will be extended and enriched to include lowlevel audiovisual features, descriptors and behavioural models in order to support automatic content annotation. This approach is part of an integrated framework consisting of: user-oriented design, knowledge-driven content processing and distributed system architecture. The overall objective of aceMedia is the implementation of a novel concept for unified media representation: the Autonomous Content Entity (ACE), which has three layers: content, its associated metadata, and an intelligence layer. The ACE concept will be verified by two user focused application prototypes, enabled for both home network and mobile communication environments.