Reference picture management in video coding

A method of encoding a coded video bitstream implemented by a video encoder, the method comprising:

• constructing a reference picture list for a current slice, wherein first entries in the reference picture list are always a plurality of active entries followed by a plurality of inactive entries, wherein one or more of the entries in the reference picture list are equal to “no reference picture” because corresponding pictures are not present in a decoded picture buffer (DPB), wherein each inactive entry in the reference picture list equal to the “no reference picture” is ignored, and wherein an unintentional picture loss is inferred for each active entry in the reference picture list equal to the “no reference picture”;
• obtaining, based on at least one active entry from the plurality of active entries in the reference picture list, at least one reconstructed block of the current slice;
• encoding a reference picture list syntax structure for the current slice into the coded video bitstream, wherein the reference picture list syntax structure contains a number of entries used to derive the entries in the reference picture list, and wherein the number of entries in the reference picture list and an order of entries in the reference picture list are both the same as in the reference picture list syntax structure;
• and
• obtaining a reference picture list flag from an active sequence parameter set (SPS) of the coded video bitstream, wherein the reference picture list flag equal to 1 specifies that reference picture list i of a current picture is derived based on a reference picture list structure in the active SPS, and wherein the reference picture list flag equal to 0 specifies that reference picture list i of the current picture is derived based on a reference picture list structure directly included in a slice header of the current picture,
• wherein a num_ref_idx_active_override_flag equal to 1 specifies that syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that syntax element num_ref_idx_active_minus1[1] is present for B slices, and when the current slice is a B slice and the num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1.

An encoding device, comprising:

• a memory storing instructions;
• and
• one or more processors coupled to the memory, the one or more processors configured to execute the instructions stored in the memory to cause the encoding device to:
• construct a reference picture list for a current slice, wherein first entries in the reference picture list are always a plurality of active entries followed by a plurality of inactive entries, wherein one or more of the entries in the reference picture list are equal to “no reference picture” because corresponding pictures are not present in a decoded picture buffer (DPB), wherein each inactive entry in the reference picture list equal to the “no reference picture” is ignored, and wherein an unintentional picture loss is inferred for each active entry in the reference picture list equal to the “no reference picture”;
• obtain, based on at least one active entry from the plurality of active entries in the reference picture list, at least one reconstructed block of the current slice;
• encode a reference picture list syntax structure for the current slice into a coded video bitstream, wherein the reference picture list syntax structure contains a number of entries used to derive the entries in the reference picture list, and the number of entries in the reference picture list and an order of entries in the reference picture list are both the same as in the reference picture list syntax structure;
• and
• obtain a reference picture list flag from an active sequence parameter set (SPS) of the coded video bitstream, wherein the reference picture list flag equal to 1 specifies that reference picture list i of a current picture is derived based on a reference picture list structure in the active SPS, and wherein the reference picture list flag equal to 0 specifies that reference picture list i of the current picture is derived based on a reference picture list structure directly included in a slice header of the current picture,
• wherein a num_ref_idx_active_override_flag equal to 1 specifies that syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that syntax element num_ref_idx_active_minus1[1] is present for B slices, and when the current slice is a B slice and the num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1.

A decoding device, comprising:

• a receiver configured to receive a coded video bitstream;
• a memory coupled to the receiver, the memory storing instructions;
• and
• one or more processors coupled to the memory, the one or more processors configured to execute the instructions stored in the memory to cause the decoding device to:
• obtain a reference picture list syntax structure for a current slice represented in the coded video bitstream, wherein the reference picture list syntax structure contains a number of entries;
• construct a reference picture list for the current slice based on the reference picture list syntax structure such that the number of entries in the reference picture list and an order of entries in the reference picture list are both the same as in the reference picture list syntax structure, wherein first entries in the reference picture list are always a plurality of active entries followed by a number of inactive entries, wherein one or more of the entries in the reference picture list are equal to “no reference picture” because corresponding pictures are not present in a decoded picture buffer (DPB), wherein each inactive entry in the reference picture list equal to the “no reference picture” is ignored, and wherein an unintentional picture loss is inferred for each active entry in the reference picture list equal to the “no reference picture”;
• obtain, based on at least one active entry of the reference picture list, at least one reconstructed block of the current slice;
• and
• obtain a reference picture list flag from an active sequence parameter set (SPS) of the coded video bitstream, wherein the reference picture list flag equal to 1 specifies that reference picture list i of a current picture is derived based on a reference picture list structure in the active SPS, and wherein the reference picture list flag equal to 0 specifies that reference picture list i of the current picture is derived based on a reference picture list structure directly included in a slice header of the current picture,
• wherein a num_ref_idx_active_override_flag equal to 1 specifies that syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that syntax element num_ref_idx_active_minus1[1] is present for B slices, and when the current slice is a B slice and the num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1.

A non-transitory storage medium which includes an encoded bitstream, the encoded bitstream being generated by dividing a current picture of a video signal or an image signal into a plurality of slices, and comprising a plurality of syntax elements, wherein the plurality of syntax elements comprises a reference picture list syntax structure for a current slice, wherein the reference picture list syntax structure contains a number of entries, wherein first entries in a reference picture list constructed based on the reference picture list syntax structure are always a plurality of active entries followed by a plurality of inactive entries, wherein one or more of the entries in the reference picture list are equal to “no reference picture” because corresponding pictures are not present in a decoded picture buffer (DPB), wherein each inactive entry in the reference picture list equal to the “no reference picture” is ignored, and wherein an unintentional picture loss is inferred for each active entry in the reference picture list equal to the “no reference picture”,

• wherein a reference picture list flag is obtained from an active sequence parameter set (SPS) of a coded video bitstream, wherein the reference picture list flag equal to 1 specifies that reference picture list i of the current picture is derived based on a reference picture list structure in the active SPS, and wherein the reference picture list flag equal to 0 specifies that reference picture list i of the current picture is derived based on a reference picture list structure directly included in a slice header of the current picture,
• wherein a num_ref_idx_active_override_flag equal to 1 specifies that syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that syntax element num_ref_idx_active_minus1[1] is present for B slices, and when the current slice is a B slice and the num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1.