Just like search engine market share, or perhaps even more so, online video market share is relatively static. YouTube completely dominates the market, in the US at least, and everyone else battles it out among themselves, sometimes trading places.
YouTube dominated in every metric in December, unique viewers, video views, and time spent on the site. Three times as many people visit it than Vevo, which also serves YouTube videos.
The only site to come close to YouTube in time spent is Hulu, but only because it specializes in long form videos, TV shows and such. Facebook, the largest website in the world, is only fifth when it comes to video.
"More than 43 billion videos views occurred during the month, with Google Sites generating the highest number at 21.9 billion. The average viewer watched 23.2 hours of online video content, with Google Sites (7.9 hours) and Hulu (3 hours) demonstrating the highest average engagement among the top ten properties," comScore reported