Video for lectures is most valuable for lectures that are passive where there is little participation from the student. In these types of lectures, students receive more value for their time in the classroom by watching a video and maximizing the time spent with a teacher's attention focused on activities.
The same principle applies to Video Books. The value of Video Books is not that they are a better experience than a teacher reading a book to the class, in fact in many cases they are not as good as the teacher reading the book. The value of a Video Book is in how it allows the teacher to spend more time with each student during activities.
