The present invention concerns a method for building a watermarked content for sending to at least one user unit having a user unit identifier, the watermarked content comprising a first series of packets, at least some from the first series of packets being available in at least two different qualities, wherein said method comprises the steps of: generating a watermark based on at least the user unit identifier, the watermark being formed by a first series of values from a predetermined set of values; mapping each of the at least two different qualities to one from the predetermined set of values; building the watermarked content by sequentially selecting from the first series of packets, a packet having a quality corresponding to each value from the first series of values forming the watermark. It further concerns a method for transmitting such a watermarked content.