In this paper we present a domain-independent multimedia retrieval (MMR) platform. Currently, the use of MMR systems for different domains poses several limitations, mainly related to the poor flexibility and adaptability to different domains and user requirements. A semantic-based platform that uses ontologies for describing not only the application domain but also the processing workflow to be followed for the retrieval, according to user's requirements and domain characteristics is here proposed. In detail, an ontological model (domain-processing ontology) that integrates domain peculiarities and processing algorithms allows self-adaptation of the retrieval mechanism to the specified application domain. According to the instances generated for each user request, our platform generates the appropriate interface (GUI) for the specified application domain (e.g. music, sport video, medical images, etc...) by a procedure guided by the defined domain-processing ontology. A use case on content based music retrieval is here presented in order to show how the proposed platform also facilitates the process of multimedia retrieval system implementation.