Mobile phones now transmit video signals to each other. Such video signals are transmitted at a relatively slow bit rates. The signals transmitted are compressed using inter-frame prediction where sufficient similarity exists between successive picture frames. The receiver includes a decoder (18) which acts to reconstitute the compressed signals received using signals stored on a buffer (22) representing a previous picture frame. A mode decision circuit (24) compares the signal at the output of the decoder (18) with the previous signal stored in the buffer (22) and using the same decision criterion as used for the original compression generates a signal which indicates that either the signal is suitable for inter-frame prediction or not. This signal is then compared in a comparator (26) with the signal in the decoder (18) indicating whether or not the current signal was inter-frame predicted or not. If equality is not detected, then an error may have taken place. Then, error concealment techniques can be used to reduce the effects of the errors.
