Abstract: A system for encryption, and subsequent decryption, of encoded data allows for transcoding of the encrypted data. The data is encoded in such a way that different packets have different importance levels, so that some or all of the packets at the lower importance levels can be discarded or truncated in order to reduce the data rate. This is achieved by introducing dependencies into the encoding process. The packets at the highest importance level are encoded with reference only to other packets at the highest importance level, while the encoding of packets at lower importance levels also depend on the encoding of the packets at the highest importance level. The encoded data is then encrypted in such a way that the encryption process has dependencies that correspond to the dependencies in the encoding process.

Abstract: A temporal error concealment is described. A video stream comprises a current frame comprising a lost image region, and a reference frame. The method comprises forming a list of motion vector candidates, the list of motion vector candidates including a set of one or more motion vectors from the current frame and a set of one or more motion vectors from the reference frame; testing each of the motion vector candidates using a matching error measure; selecting a replacement motion vector from the list based on the matching error measures; and using the selected replacement motion vector to conceal the lost image region. A mode selection method is also described. A motion vector is used to identify a motion compensated reference image region in the reference frame. A motion compensated temporal activity of an image region in the current frame is calculated based on a comparison between the image region in the current frame and the motion compensated reference image region in the reference frame.

Abstract: A system for encryption, and subsequent decryption, of encoded data allows for transcoding of the encrypted data. The data is encoded in such a way that different packets have different importance levels, so that some or all of the packets at the lower importance levels can be discarded or truncated in order to reduce the data rate. This is achieved by introducing dependencies into the encoding process. The packets at the highest importance level are encoded with reference only to other packets at the highest importance level, while the encoding of packets at lower importance levels also depend on the encoding of the packets at the highest importance level. The encoded data is then encrypted in such a way that the encryption process has dependencies that correspond to the dependencies in the encoding process.

Abstract: A temporal error concealment is described. A video stream comprises a current frame comprising a lost image region, and a reference frame. The method comprises forming a list of motion vector candidates, the list of motion vector candidates including a set of one or more motion vectors from the current frame and a set of one or more motion vectors from the reference frame; testing each of the motion vector candidates using a matching error measure; selecting a replacement motion vector from the list based on the matching error measures; and using the selected replacement motion vector to conceal the lost image region. A mode selection method is also described. A motion vector is used to identify a motion compensated reference image region in the reference frame. A motion compensated temporal activity of an image region in the current frame is calculated based on a comparison between the image region in the current frame and the motion compensated reference image region in the reference frame.

Abstract: An OFDM receiver includes an adaptive equalizer, which acts on a received signal, after conversion to digital samples. After filtering by the equalizer, any guard interval is removed, and a Fast Fourier Transform is applied to the signal. The data signal is then estimated and the estimated data is supplied as an output. The estimated data also has any guard interval reinserted, and is applied to an Inverse Fast Fourier Transform, and is fed back to the equalizer to allow adaptation of the tap coefficients thereof.