Method and device for embedding a binary sequence in a compressed video stream

A method for embedding a binary sequence in a video sequence or a compressed video stream, said stream being able to be decomposed into several types of objects, the method being applied to at least one image contained in said video sequence and the method comprising:

• a) analyzing the video sequence in the compressed domain so as to define for a given compressed image at least one first type of objects or group of objects to be processed defining a zone of interest,
• b) generating a watermarking map defining the set of the blocks of pixels of the binary sequence that are eligible for the embedding operation, as well as two coefficients C1 and C2 arising from a frequency transform for each of said blocks, said coefficients C1 and C2 being drawn randomly from among the set of coefficients obtained by applying a frequency transform to a given block of pixels,
• c) excluding from the watermarking map, for the current compressed image, the blocks associated with the zone of interest, as well as those whose coefficients C1 and C2 defined by the watermarking map do not satisfy the following criterion:
• abs(abs(C1)−abs(C2))<S where S is a predetermined threshold and abs( ) the function returning the absolute value of an integer, and
• d) applying a digital watermarking function to each available block obtained in step c) so as to obtain a watermarked compressed stream by way of a binary sequence in the following manner:
• to insert a “1” bit of said binary sequence,
• if abs(C1) > abs(C2), nothing is changed,
• if abs(C1) ≦ abs(C2), then ε = abs(C2) − abs(C1) is calculated and the
• value of C1 is modified, C1 = C1 + ε + 1 if C1>0, C1= C1 − ε − 1;
• to insert a “0” bit of said binary sequence,
• if abs(C1) < abs(C2), nothing is changed,
• if abs(C1) ≧ abs(C2), ε = abs(C1) − abs(C2) is calculated and the
• value of C2 is modified, C2 = C2 + ε + 1 if C2>0, C2= C2 − ε − 1.