TOKYO — Yahoo Japan is buying a 51% stake in Gyao, the video portal site run by media conglom Usen, for $5.3 million.

Under the pact, Yahoo will merge its Doga contents streaming portal with GyaO.

Launched in April 2005 and spun off as an independent subsidiary in October, Gyao offers everything from music clips to TV programs, toons, pics and other content.

The site has more than 20 million registered users, but has yet to successfully monetize its free content.

Since advertising revenues fail to cover content costs, Usen has been bleeding red ink, racking up $539 million in pretax losses for the first quarter of fiscal 2009, ending in August.