Segment position signalling with subpicture slice position deriving

A method performed by an encoder, the method comprising:

• generating a coded video stream (CVS), wherein
• the CVS comprises a slice header comprising a first codeword that encodes a first value representing a first part of a slice address, wherein the first value is a subpicture ID which indicates the subpicture that the slice belongs to,
• the slice header comprises a second codeword that encodes a second value representing a second part of the slice address, wherein the second value is a local slice address which indicates the spatial positioning of the slice relative to the subpicture position that the slice belongs to,
• the slice address specifies the spatial location of a slice within a picture, and
• the CVS further comprises a third codeword that encodes a third value representing a third part of the address and the third part of the address represents an address in a second hierarchy level that is lower than a first hierarchy level.

A decoding apparatus, comprising:

• memory;
• and
• processing circuitry coupled to the memory, wherein the decoding apparatus is configured to:
• obtain a coded video stream (CVS);
• and
• process the obtained CVS, wherein:
• the CVS comprises a slice header comprising a first codeword that encodes a first value representing a first part of a slice address, wherein the first value is a subpicture ID which indicates the subpicture that the slice belongs to,
• the slice header comprises a second codeword that encodes a second value representing a second part of the slice address, wherein the second value is a local slice address which indicates the spatial positioning of the slice relative to the subpicture position that the slice belongs to, and
• the slice address specifies the spatial location of a slice within a picture, wherein
• processing the CVS comprises, prior to decoding the second value from the second codeword, deriving a length of the second codeword using a value N derived from a third codeword in the CVS.

An encoding apparatus, comprising:

• memory;
• and
• processing circuitry coupled to the memory, wherein the encoding apparatus is configured to generating a coded video stream (CVS), wherein
• the CVS comprises a slice header comprising a first codeword that encodes a first value representing a first part of a slice address, wherein the first value is a subpicture ID which indicates the subpicture that the slice belongs to,
• the slice header comprises a second codeword that encodes a second value representing a second part of the slice address, wherein the second value is a local slice address which indicates the spatial positioning of the slice relative to the subpicture position that the slice belongs to,
• the slice address specifies the spatial location of a slice within a picture, and
• the CVS further comprises a third codeword that encodes a third value representing a third part of the address and the third part of the address represents an address in a second hierarchy level that is lower than a first hierarchy level.