WWE has broadcast pay-per-views since the 1980s, when its classic "big four" events (Royal Rumble, WrestleMania, SummerSlam, and Survivor Series) were first established. The company's PPV lineup expanded to a monthly basis in the mid-1990s, and reached its peak of sixteen shows a year in 2006 before returning to twelve in 2012. Pay-per-view shows are typically three hours in length, though budget priced events (e.g., In Your House) were shorter, while premium events such as WrestleMania can approach five hours. Since 2008, all WWE pay-per-views have been broadcast in High-definition. Pay-per-view events are a significant part of the revenue stream for WWE.