1. A method performed by a data processing apparatus, the method comprising: determining video resources hosted on devices assigned to a domain; for each video resource determined to be hosted on the domain, determining a quality metric for the video resource; generating a quality score from the quality metrics for video resources hosted on the domain; generating a quantity score based a first percentile ranking of the domain, the first percentile ranking being based on a number of video resources that are hosted on the domain relative to respective numbers of video resources hosted on other domains; determining a domain video score from the quality score and the quantity score; and adjusting, based on the domain video score, one or more video search operations on the video resources hosted on the domain.