The granularity of forum posts is at the course-level, which makes it hard for instructors to figure out which specific parts of the lecture need to be improved. Singh et al. [19] and Lee et al. [14] facilitate discussion among learners within a lecture video. Although instructors can get more specific learner comments, it has limitation as feedback in that instructors cannot control the types of learner comments. In this paper, we explore in-video prompting, which yields specific and controlled learner comments, as a channel for collecting more useful feedback.