The invention relates to a method for determining where a next data unit of a bit stream of an image starts. The method comprises analyzing a first part of a bit stream entry, the bit stream entry being included in a data unit, determining from said analysis of the first part of the bit stream entry the number of bits used by the bit stream entry, skipping the number of bits determined to be used by the bit stream entry, and determining if an end of block symbol has been reached, if an end of block symbol has not been reached then a new bit stream entry starting at the end of the previous is analyzed.