A key server for controlling access of a client device to a subset of different quality copies of media content to be delivered over a network to the client device. In one embodiment, a key server receives a request for playback permission of media content by a client device, and applies a set of one or more business rules to determine which copies of the media content, if any, can be played by the client device, and allows access to a subset of the copies that can be played back by the client device and restricts access to the copies that are not part of the subset.