## 1 Introduction  
Within the context of education, and more specifically in higher education, the global pandemic situation over the past two years has led to a widespread use of remote teaching/learning and lecture recordings as part of the teaching material. This new online teaching-learning setting has largely impacted university classes. Regardless of the type of educational system prevailing in each country, university classes typically follow a lecture-based instructional approach where the lecture is verbally delivered by an instructor who supports their academic discourse by using a slide presentation and/or a writing surface. This has not changed much over the pandemic, with the most notable exception that lectures are now recorded and so students replace note-taking by video-watching when studying. While online teaching technology tools have highly improved over the past two years, the same has not occurred in supporting students during online learning. Lecture recordings have become a key learning means for millions of students regardless of the availability of in-person class attendance. Everyone wishes to have access to a backup material that one can resort to for post-lecture learning. The benefits of lesson recordings to support the learning experience of students are diverse such as providing content that can be reviewed multiple times, accessibility to material in case of an impossibility to attend in-person or focusing on listening to the lecturer rather than taking notes. Despite these clear benefits, several investigations have revealed that using learning technology is one of the most common challenges that students face during online learning [1; 2]. The impact of lecture videos on students' academic performance has been investigated from different perspectives such as analyzing the actual time spent on the usage of recorded lectures in relation to lecture attendance and the effect on exam performance, or studying the impact of combining lecture videos with written materials on students' outcomes [3; 4; 5]. There have also been works that explore if the usage of video recordings by the students varies for different subjects or if it is different for subgroups of students [6]. However, finding literature on how to support students to engage with the recordings is less frequent, mostly because students have different learning styles, different study strategies and skills. There is though one functionality that would be very helpful for post-lecture learning from class recordings (or any recording in general) and that is the ability to find and view the desired contents in the recorded lecture video. This becomes particularly relevant when the recording is used to strengthen the contents acquired during an in-person session. Moreover, providing class recordings for supplementary use has been lately advised in regular nonpandemic educational environments, since no negative effect of the use of recordings has generally been evidenced in university students [7]. The work presented in this paper intends to be a first step toward facilitating the view of particular contents in a class recording without the need to play the video back and forth until the desired segment is found. Imagine, for instance, a student who wants to find in a two-hour video recording the segment where the lecturer delivers a task assignment or a student who just wants to watch the part of the video in which the lecturer is solving an exercise. In general, replaying the audio-video recording repeatedly is not an effective studying method for university students, who need to adjust their study strategies to suit this mode. Our contribution puts the focus on a classification model that identifies the type of teaching activity (solving an exercise, explaining a theoretical concept, talking about a task assignment, interacting with students, etc.) that is being undertaken by the lecturer at each instant of the video recording.