Video encoding and decoding

An apparatus comprising at least one processor and at least one memory, said at least one memory stored with code thereon, which when executed by said at least one processor, causes an apparatus to perform at least the following:

• encode pictures into a bitstream, the bitstream comprising at least two scalability layers, pictures being associated individually with one of the at least two scalability layers;
• indicate in the bitstream inter-layer prediction dependencies, indicative of direct reference layers, if any, of a first scalability layer and indirect reference layers, if any, of the first scalability layer, a direct reference layer being such that a picture associated with the direct reference layer is useable as or for derivation of a reference picture for prediction of a picture associated with the first scalability layer, and an indirect reference layer being such that a picture associated with an indirect reference layer is unusable as a reference picture for prediction of a picture associated with the first scalability layer but useable as or for derivation of a reference picture for prediction of a picture associated with a direct or indirect reference layer of the first scalability layer;
• select an earlier picture in decoding order as a basis for deriving picture order count (POC) related variables for a current picture based on a pre-defined algorithm, the current picture being associated with a current scalability layer,
• wherein the earlier picture is the closest preceding picture, in decoding order, to the current picture among a set of pictures that are associated with the current scalability layer or any direct or indirect reference layer of the current scalability layer, and
• wherein the apparatus is further caused, as a part of or in connection with encoding the current picture into the bitstream, to perform:
• determine that POC values are to be reset;
• encode into the bitstream an indication of resetting POC values;
• and
• use the earlier picture in deriving a value decremented from POC values of a plurality of pictures in a decoded picture buffer.

A method comprising:

• decoding pictures from a bitstream, the bitstream comprising at least two scalability layers, pictures being associated individually with one of the at least two scalability layers;
• obtaining an indication from the bitstream relating to inter-layer prediction dependencies, indicative of direct reference layers, if any, of a first scalability layer and indirect reference layers, if any, of the first scalability layer, a direct reference layer being such that a picture associated with the direct reference layer is useable as or for derivation of a reference picture for prediction of a picture associated with the first scalability layer, and an indirect reference layer being such that a picture associated with an indirect reference layer is unusable as a reference picture for prediction of a picture associated with the first scalability layer but useable as or for derivation of a reference picture for prediction of a picture associated with a direct or indirect reference layer of the first scalability layer;
• selecting an earlier picture in decoding order as a basis for deriving picture order count (POC) related variables for a current picture based on a pre-defined algorithm, the current picture being associated with a current scalability layer,
• wherein the earlier picture is the closest preceding picture, in decoding order, to the current picture among a set of pictures that are associated with the current scalability layer or any direct or indirect reference layer of the current scalability layer, and
• wherein the method further comprises as a part of or in connection with decoding the current picture from the bitstream:
• decoding from the bitstream an indication of resetting POC values;
• determining that POC values are to be reset;
• and
• using the earlier picture in deriving a value decremented from POC values of a plurality of pictures in a decoded picture buffer.