Interest is key to learning. Video is a promising tool for interest development in education, but professionals in education are in need of more theory-grounded guidance for production, selection, and use of videos. In previous studies, we developed and validated a model on film's interest raising mechanisms in educational contexts, called the FIRM model. In the qualitative study reported here, we used the model to explain how pupils' appraisals of video characteristics relate to their interest in the video. We evaluated the use of five videos in seven 12th-grade science and mathematics classrooms (177 pupils). We measured interest at scene level and grouped pupils on general interest. We performed video analyses, case studies (N = 5), and a cross-case analysis. Our findings resulted in three relationships between appraisals and interest, regarding the video's complexity level and the pupils' knowledge level, pupils' recognition of video categories, and pupils' expectations of videos.