Video decoding apparatus, video coding apparatus, video decoding method, and video coding method

A video decoding apparatus for deriving a prediction image by using a reference picture in a reference picture list, the video decoding apparatus comprising:

• parameter decoding circuitry that decodes:
• (i) a reference picture list structure in a sequence parameter set,
• (ii) a first flag indicating whether first reference picture list information is present in a slice header whose nal_unit_type indicates an Instantaneous Decoding Refresh picture, wherein the first flag is included in the sequence parameter set,
• (iii) a first syntax element indicating a number of the reference picture list structure, wherein the first syntax element is included in the sequence parameter set,
• (iv) a second syntax element indicating a number of entries in the reference picture list structure, wherein the second syntax element is included in the reference picture list structure, and
• (v) a second flag indicating whether second reference picture list information is present in a picture header, wherein the second flag is included in a picture parameter set;
• and
• prediction parameter derivation circuitry that derives:
• (i) one of the first reference picture list information in the slice header by using (a) the nal_unit_type or the first flag and (b) the second flag, and the second reference picture list information in a picture header by using the second flag, and
• (ii) a reference picture list based on the reference picture list structure, wherein
• in a case that the nal_unit_type indicates the Instantaneous Decoding Refresh picture, a value of the second syntax element indicated by the first syntax element is set equal to 0.

A video encoding apparatus for deriving a prediction image by using a reference picture in a reference picture list, the video encoding apparatus comprising:

• parameter encoding circuitry that encodes:
• (i) a reference picture list structure in a sequence parameter set,
• (ii) a first flag indicating whether first reference picture list information is present in a slice header whose nal_unit_type indicates an Instantaneous Decoding Refresh picture, wherein the first flag is included in the sequence parameter set,
• (iii) a first syntax element indicating a number of the reference picture list structure, wherein the first syntax element is included in the sequence parameter set,
• (iv) a second syntax element indicating a number of entries in the reference picture list structure, wherein the second syntax element is included in the reference picture list structure, and
• (v) a second flag indicating whether second reference picture list information is present in a picture header, wherein the second flag is included in a picture parameter set;
• and
• prediction parameter derivation circuitry that derives:
• (i) one of the first reference picture list information in the slice header by using (a) the nal_unit_type or the first flag and (b) the second flag, and the second reference picture list information in a picture header by using the second flag, and
• (ii) a reference picture list based on the reference picture list structure, wherein
• in a case that the nal_unit_type indicates the Instantaneous Decoding Refresh picture, a value of the second syntax element indicated by the first syntax element is set equal to 0.

A video decoding method for deriving a prediction image by using a reference picture in a reference picture list, the video decoding method including:

• decoding a reference picture list structure in a sequence parameter set;
• decoding a first flag indicating whether first reference picture list information is present in a slice header whose nal_unit_type indicates an Instantaneous Decoding Refresh picture, wherein the first flag is included in the sequence parameter set;
• decoding a first syntax element indicating a number of the reference picture list structure, wherein the first syntax element is included in the sequence parameter set;
• decoding a second syntax element indicating a number of entries in the reference picture list structure, wherein the second syntax element is included in the reference picture list structure;
• decoding a second flag indicating whether second reference picture list information is present in a picture header, wherein the second flag is included in a picture parameter set;
• deriving one of the first reference picture list information in the slice header by using (a) the nal_unit_type or the first flag and (b) the second flag, and the second reference picture list information in a picture header by using the second flag;
• and
• deriving a reference picture list based on the reference picture list structure, wherein
• in a case that the nal_unit_type indicates the Instantaneous Decoding Refresh picture, a value of the second syntax element indicated by the first syntax element is set equal to 0.