Politecnico di Milano, Milan, Italy;Politecnico di Milano, Milan, Italy;Politecnico di Milano, Milan, Italy;Engineering - Ingegneria Informatica SpA R&D Lab, Rome, Italy;FAST, a Microsoft® Subsidiary, Oslo, Norway;FAST, a Microsoft® Subsidiary, Oslo, Norway;L3S Research Center, Hanover, Germany;France Télécom R&D, Lannion, France;Fraunhofer Institute for Digital Media Technology IDMT , Ilmenau, Germany;VTT Technical Research Centre of Finland, Espoo, Finland;Universitat Pompeu Fabra, Barcelona, Spain;Knowledge Media Institute, Milton Keynes, United Kingdom;SAIL LABS Technology, Vienna, Austria;Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland;Engineering - Ingegneria Informatica SpA R&D Lab, Rome, Italy