1. A television set-top box, comprising: a receiver receiving a digital television signal comprising: a plurality of unencrypted packets; and a plurality of encrypted packets, where the encrypted packets consist of packets that carry data describing an active region of a video frame, where the active region comprises between approximately ⅓ to ¾ of the overall area of the frame; a decrypter that decrypts the encrypted packets; and a decoder that decodes the unencrypted packets and the decrypted packets to produce a signal suitable for play on a television set.