An apparatus includes means for indicating an extraction reference map entry used to assign a group identifier to at least one extraction reference, the extraction reference map entry indicating a subpicture layout; wherein the at least one extraction reference causes extraction of a network abstraction layer unit data by reference from another track; wherein the at least one extraction reference comprises an index of a track reference having a subpicture type within a subpicture order sample group description entry; and means for indicating, using the at least one extraction reference, subpictures or slices of a coded picture in decoding order.
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