An encoder, a decoder, corresponding encoding and decoding methods, video signal structure, and storage media are provided for scalable video encoding and decoding. A scalable video encoder includes an encoder (100) for encoding a picture to form a base layer bitstream and an enhancement layer bitstream. The base layer bitstream and the enhancement layer bitstream are formed by partitioning the picture into a plurality of image blocks, grouping the plurality of image blocks into one or more slice groups in the base layer bitstream and into two or more slice groups in the enhancement layer bitstream, encoding all of the one or more slice groups in the base layer bitstream and less than all of the two or more slice groups in the enhancement layer such that at least one slice group from among the two or more slice groups is intentionally un-encoded in the enhancement layer bitstream, encoding a syntax element in a header to indicate the at least one intentionally un-encoded slice group in the enhancement layer.