How much more could you get done if your students watched at least some lectures at home? Or you could lecture even when you're not at school. I've started doing this a number of years ago. Some would watch on their iPods and a couple, who don't have reliable internet watched them on DVD. The first year was the hardest, but most of my lectures were re-usable. This idea is not that original. These guys in Colorado beat me to it and so did Dale Eizenga.
This is often paired with the flipped classroom. In this sort of setting students work independently or in small groups and work through material at their own rate. Videos are huge in this setting as it allows the teacher to be delivering any number of lectures simultaneously. It also makes it easy for students to go back and review earlier lessons. In the strictest sense students in a Mastery classroom would not advance until obtaining mastery in earlier lessons. In my Electronics class students are allowed to progress through material at whatever pace they deem appropriate. Some will race through the early lessons only to realize they "don't really get it" and then go back. In some sense these students often gain a higher level of mastery than those who take their time the first time through.
Record Lecture as They Happen
Even if you don't want to replace in class lecture time with videos students watch at home you still might want to capture your lectures as you deliver them so that your students can go back over them at a later date. This will also help students who were absent. Even just recording the audio will help. An absent student (or one who was there) can listing to the lecture while going over class notes. EduCause also did a "7 things you should know" on lecture capture. It's worth a look.
You may want to read this article on vodcasting lectures in college. These were not replacements of lecture as in a reverse lecture model. They were recordings of lectures. This paper is a research study looking at attendance of students and when they actually watch the videos produced.
As a science teacher, I do lots of important demonstrations to teach concepts. Unfortunately there are always some students who are absent. Now, most teachers tell absent students to get notes from a friend. But usually someone else's notes aren't enough for demos. If they were you wouldn't really need to do a live demo, would you?
What do you do for those students who "don't get it" the first time? Videos offer a great chance for re-teaching. You can be in many places at the same time delivering the content the individual student needs. Now, I'm not advocating against one on one tutoring. In fact I think this is the best way to work with students. Unfortunately, quite often when a student has time to learn you don't have time to meet. Or, the student never comes in for help. It is also possible that your LMS can log when a student has watched a video or not. This can be some great data to have in your hands when talking with parents about how they can help.