An encoder allows generating, starting from a sequence of digital video pictures, a time-scalable encoded bitstream obtained by applying to the pictures, a hierarchical prediction wherein the pictures are organized in Groups Of Pictures (GOPs). The GOPs may include base time layer pictures or Key Pictures for encoding as Inter or Intra, with and without motion-compensated prediction respectively. The GOPs may also include higher time layer pictures adapted to be selectively eliminated to effect time scalability of the encoded scalable bitstream. The encoder may detect scene changes in the sequence of digital video pictures, and, in the presence of a scene change, a first Key Picture after the scene change may be encoded as Intra.