EMBEDDING AUXILIARY DATA IN AN INFORMATION SIGNAL

摘要

Disclosed is a method of embedding auxiliary data in an information signal, the signal samples of which are variable-length encoded, for example, an MPEG compressed video signal. Selected signal samples, e.g. given transform coefficients of the blocks constituting a video image, are retrieved by decoding the corresponding variable-length code words. The selected signal samples are modified so as to represent a data symbol, and re-encoded. The modification of a signal sample is omitted if this causes the length of a given sequence of code words (a slice, an MPEG transport packet) to exceed its original length, or if it affects the position of clock reference time stamps in the bit stream. Insertion of dummy bits compensates for a shortage of data in the sequence.