Typical web lectures consist of two different kinds of media linked together: an audio- or video-recording and the corresponding slides or desktop recording. Both media are synchronized so that the slide or image shown corresponds to the position currently played in the time-based media stream. Web lectures are thus composite media consisting of a structured presentation and a continuous media stream. Current navigation paradigms focus on either one of these components. Time-based overviews do, however, provide different contextual information than structural overviews and vice versa. Instead of enhancing either time- or structure-based navigation by establishing unidirectional connections to structure and time respectively, the approach presented in this article connects time- and structure-based navigation in a bidirectional fashion to combine the advantages of both navigation paradigms. (Contains 8 figures and 2 tables.)