According to The Diffusion Group, legacy TV is set to decline by more than 25% in the next six years, from 90% of all video viewed in 2013 to approximately two-thirds in 2020, with online video sources making up the difference.

TDG believes the decline is being driven by the evolution of Amazon (NASDAQ:AMZN), Apple (NASDAQ:AAPL), Google (NASDAQ:GOOG) and Microsoft (NASDAQ:MSFT). These "Big 4" are building global ecosystems to support multiscreen, multi-context, personalized video, and also run larger businesses that can subsidize their video platforms. In addition, they're increasingly producing their own original content.