NEW YORK (AdAge.com) -- Online video is no longer just a sideshow for marketers. Brands such as T-Mobile, Samsung and Cadbury have recently scored viral-video hits racking up 10 million or more views. Meanwhile, the science of tracking online-video audiences has made great strides in the past 18 months. Companies such as Visible Measures have developed systems that can monitor and measure online-video audiences across the internet, much the same way Nielsen measures TV or Arbitron measures radio. In this 10-minute "About Digital" report, Ad Age Digital Editor Abbey Klaassen explores some of the latest viral-video trends and insights emerging from that data.