Online educational videos are often difficult to navigate. Furthermore, most video interfaces do not lend themselves to note-taking. Described system detects and reuses boundaries that tend to occur in these types of videos. In particular, many educational videos are organized around distinct breaks that correspond to slide changes, scroll events, or a combination of both. Described algorithms can detect these structural changes in the video content. From these events the system can generate navigable overviews to help users searching for specific content. Furthermore, these boundary events can help the system automatically associate rich media annotations to manually-defined bookmarks. Finally, when manual or automatically recovered spoken transcripts are available, the spoken text can be combined with the temporal segmentation implied by detected events for video indexing and retrieval. This text can also be used to seed a set of text annotations for user selection or be combined with user text input.