Here's a s short clip in which a science teacher explains how he flipped his classroom. He offers a good explanation of how it works. Most flipped classrooms are in science and math but one school has flipped all core courses. The principal says that the video lectures for each course averages about ten minutes. This site lists 15 schools that use flipped classes. Some teachers use screen casting for their lectures and others use vod-casting. If you are interested, you might check out the "Flipped Class Network " here.