A method of providing a video manifest to a client. A router manages, for each of a plurality of ad placement units, a measure of advertisement avails provided by the router to the ad placement unit for filling with advertisements, receives a client request for a video content, and chooses an ad placement unit from the plurality of ad placement units, to select advertisements to be placed in avails of the requested video content, at least partially responsive to the managed measures of advertisement avails. The received client request is directed to the chosen ad placement unit.