Decode access control for encoded multimedia signals

Multimedia signals are encoded with certain values to control a user's access to the decoding of the multimedia signals. In a preferred embodiment in which the multimedia signals contain video signals, a lock word and a checksum value are encoded into each frame header of the video stream. The lock word is the result of applying a specified hash function to the checksum value for the current frame and a specified access word. A decoder will decode the encoded video signals for the current frame only if the result of applying the hash function to the access word (received from a decoding application) and the checksum value (retrieved from the frame header) is equal to the lock word (retrieved from the frame header). If the hash function result does not equal the lock word, then the decoder assumes that decode access is not permitted. In that case, the decoder will not decode the current frame and instead will send an error message to the decoding application (preferably after a specified delay).