This paper addresses explicit correlation and implicit correlation between various media streams in a composite multimedia document, the so-called navigated hypermedia document in our language learning system, in order to facilitate document retrieval and synchronized presentation. For replaying a recorded lecture in a form as close as possible to the original classroom experience, we devised a capturing mechanism to explicitly record all the lecturing media streams and relations between them, including instructors voice, slide change of the HTML lectures, and various guiding actions (e.g., tele-pointers, pen strokes, document scrolling, keyword highlighting, and text annotations) on HTML-based slides. In addition, for more effective learning, we study three different aspects - temporal, spatial, and content relation - of the implicit correlations that are inherently hidden between the media involved. The implicit relations are discovered by three designed processes: the speech-text alignment process for temporally synchronized speech-text presentation, the automatic scrolling process for the viewing windows spatial synchronization, and the content dependency checking process to ensure consistency of the content processed and the relations involved. The experimental results show that exploring cross-media correlations is helpful for system development in document presentation and retrieving. Users are allowed to replay a vivid and learning-effective multimedia lecture and to access the desired part of the document very easily via cross-media indexing. Hence the results have been applied to the development of online multimedia language learning systems aimed at improving students English and Chinese language capabilities.