The invention relates to a method of adapting a scalable data stream organized in blocks of data units, each comprising at least one basic data unit and at least one enhancement data unit, making it possible to define a plurality of quality and bit rate levels (N1 to N3) depending on the number and the type of data units used, each data unit being initially classified in an initial level selected from said plurality of levels. According to the invention, the method implements a regulation mechanism (8) such that, if a data unit is reclassified in a reclassification level of lower priority than the initial level of said data unit, all the data units that depend on the decoding of said reclassified data unit are also reclassified in reclassification levels where all the data units essential to their decoding are accessible.