MPlayer can't show USF Subtitles. Specification can be found here : http://usf.corecodec.org "The Universal Subtitle Format (USF) is an ambitious project created in order to provide a clean, documented, powerfull and easy to use subtitle format. The format is based on the XML format for many reasons: flexibility, human readability, portability, unicode (UTF-8), hierarchy system and easier management." "The Matroska team (http://www.matroska.org) choose the USF as the primary subtitle format for their ambitious multimedia container file format (AVI replacement)."