  The increase in use of online educational tools has led to a large amount of
educational video materials made available for students. Finding the right
video content is usually supported by the overarching learning management
system and its interface that organises video items by course, categories and
weeks, and makes them searchable. However, once a video is found, students are
left without further guidance as to what parts in that video they should focus
on. In this article, an additional timeline visualisation to augment the
conventional playback timeline is introduced which employs a novel playback
weighting strategy in which the history of different video interactions
generate scores based on the context of each playback. The resultant scores are
presented on the additional timeline, making it in effect a playback-centric
usage graph nuanced by how each playback was executed. Students can selectively
watch those portions which the contour of the usage visualisation suggests. The
visualisation was implemented and deployed in an undergraduate course at a
university for two full semesters. 270 students used the system throughout both
semesters watching 52 videos, guided by visualisations on what to watch.
Analysis of playback logs revealed students selectively watched corresponding
to the most important portions of the videos as assessed by the instructor who
created the videos. The characteristics of this as a way of guiding students as
to where to watch as well as a complementary tool for playback analysis, are
discussed. Further insights into the potential values of this visualisation and
its underlying playback weighting strategy are also discussed.
