1. A method for encoding watermark information into media data containing a series of digital samples in a sample domain, the method comprising: dividing the series of digital samples into a plurality of sections in the sample domain, each section comprising a corresponding plurality of samples; processing the corresponding plurality of samples in each section to obtain a single energy value associated with each section; grouping the sections into groups, each group containing three or more sections; assigning a nominal bit value to each group according to a bit assignment rule, the bit assignment rule based on the energy values of the sections in the group; assigning a watermark bit value to each group; for each group, comparing the watermark bit value to the nominal bit value and, if the nominal bit value and the watermark bit value of the watermark information bit do not match, modifying one or more energy values of one or more corresponding sections in the group such that re-application of the bit assignment rule would assign the watermark bit value to the group; wherein assigning the nominal bit value to each group according to the bit assignment rule comprises: categorizing each group into one of a plurality of categories according to a categorization rule; and for each category, assigning a nominal zero bit value or a nominal one bit value to each group according to a unique category bit assignment rule associated with the category.