Layer ID signaling using extension mechanism

A signaling of the layer ID is described which each of the packets of a multi-layered video signal is associated with. In particular, an efficient way of signaling this layer association is achieved, with nevertheless maintaining the backward compatibility with codecs according to which a certain value of the base layer-ID field is restricted to be non-extendable such as base layer-ID value 0 in the base layer-ID field. Instead of circumventing this restriction specifically with respect to this non-extendable base layer-ID value, the layer-ID of portions of the multi-layer data stream is signaled in an extendable manner by sub-dividing the base layer-ID field into a first sub-field and a second sub-field: whenever the first sub-field of the base layer-ID field fulfills a predetermined criterion, an extension layer-ID field is provided, and if the first sub-field of the base layer-ID field does not fulfill the predetermined criterion, the extension layer-ID field is omitted.