Constraints on the entries in the reference image list

Abstract

Methods and apparatus for video processing, such as video encoding or decoding, are described. An example video processing method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies a condition that no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an active entry in a reference picture list of a current slice of a current picture.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on International Patent Application No. PCT / US2021 / 022576, filed on March 16, 2021, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 992,046, filed on March 19, 2020. All of the above patent applications are hereby incorporated by reference in their entirety. Technical Field

[0003] This patent document relates to image and video encoding and decoding. Background Art

[0004] Digital video accounts for the largest use of bandwidth on the Internet and other digital communications networks. As the number of connected user devices capable of receiving and displaying video increases, bandwidth demand for digital video usage is expected to continue to grow. Summary of the Invention

[0005] This document discloses techniques that can be used by video encoders and decoders to process codec representations of video using a bitstream syntax that provides improved performance. The disclosed methods can be used by devices that perform video processing such as video encoding or video decoding or video transcoding.

[0006] In one example aspect, a video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the codec representation is organized according to a rule that specifies that a first video picture that is an intra random access point picture of the second picture and a second picture are constrained to belong to the same video layer.

[0007] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule that specifies that subsequent pictures of a first type that are intra random access points in the codec representation are also permitted to be associated with a second type of picture including a gradual decoding refresh picture.

[0008] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule that specifies a constraint on an output order of pictures preceding an intra random access point in decoding order such that the output order applies only to pictures in the same video layer.

[0009] In another example aspect, another video processing method is disclosed. The method includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule that specifies the following constraints: (1) a post-picture must follow an associated intra random access point picture (IRAP) or gradual decoder refresh (GDR) picture in output order, or (2) a picture having the same layer id as a GDR picture must precede the GDR picture and all associated pictures of the GDR picture in output order.

[0010] In another example aspect, another video processing method is disclosed. The method includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule that an order constraint applies to pictures, intra random access point (IRAP) pictures, and non-pre-previous pictures if and only if the pictures, intra random access point (IRAP) pictures, and non-pre-previous pictures are in the same layer, wherein the rule is one of: (a) a first rule that specifies a value and decoding order of a sequence of fields, or (b) an order of pre-previous and / or non-pre-previous pictures of a layer.

[0011] In another example aspect, another video processing method is disclosed. The method includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule specifying an order of leading pictures, random access decodable leading (RADL) pictures, and random access skipped leading (RASL) pictures associated with a gradual decoding refresh (GDR) picture.

[0012] In another example aspect, another video processing method is disclosed that includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule specifying that a constraint on a reference picture list for fully random access pictures is limited to the layer.

[0013] In another example aspect, another video processing method is disclosed. The method includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule specifying conditions under which a current picture is allowed to reference an entry in a reference picture list generated by a decoding process for generating an unusable reference picture.

[0014] In another example aspect, another video processing method is disclosed that includes performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule regarding an order between a current picture and a reference picture list corresponding to the current picture.

[0015] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, wherein the format rule specifies that a first video picture that is an associated intra random access point picture of the second picture and a second picture are constrained to belong to the same video layer.

[0016] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, wherein the format rule specifies that a subsequent picture in the bitstream is permitted to be associated with a progressive decoding refresh picture.

[0017] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, wherein the format rule specifies that a constraint on an output order of pictures preceding an intra random access point in decoding order applies to pictures in the same video layer.

[0018] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, and wherein the format rule specifies the following constraints: (1) a post-picture follows an associated intra random access point picture or a gradual decoder refresh picture in output order, or (2) a picture having the same NAL (network abstraction layer) unit header layer identifier as a gradual decoder refresh picture precedes the gradual decoder refresh picture and all associated pictures of the gradual decoder refresh picture in output order.

[0019] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies that a constraint on decoding order of pictures and non-previous pictures applies if and only if a picture associated with an intra random access point picture, the intra random access point picture, and the non-previous picture are in the same layer.

[0020] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies an order of leading pictures associated with a progressive decoding refresh picture, a random access decodable leading picture, and a random access skipped leading picture.

[0021] In another example aspect, another video processing method is disclosed that includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies that a constraint on reference picture lists for slices of fully random access pictures is limited to the layer.

[0022] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies a condition that no picture generated by a decoding process for generating an unusable reference picture is referenced by an active entry in a reference picture list of a current slice of a current picture.

[0023] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies a condition that no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of a current picture.

[0024] In another example aspect, another video processing method is disclosed that includes performing conversion between a video having one or more video layers including a current picture including a current slice and a bitstream of video according to a rule, wherein the rule specifies a condition that a reference picture list of the current slice is not allowed to have an active entry referencing a picture that precedes an intra random access point picture associated with the current picture in decoding order or output order.

[0025] In another example aspect, another video processing method is disclosed. The method includes performing conversion between a video having one or more video layers including a current picture including a current slice and a bitstream of the video according to a rule, wherein the rule specifies a condition that a reference picture list of the current slice is not allowed to have an entry referencing a picture that precedes an intra random access point picture associated with the current picture in decoding order or output order.

[0026] In yet another exemplary aspect, a video encoder apparatus is disclosed. The video encoder includes a processor configured to implement the above method.

[0027] In yet another exemplary aspect, a video decoder apparatus is disclosed. The video decoder includes a processor configured to implement the above method.

[0028] In yet another exemplary aspect, a computer-readable medium storing code is disclosed. The code is in the form of processor-executable code embodying one of the methods described herein.

[0029] These and other features are described throughout this document. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a block diagram of an example video processing system.

[0031] Figure 2 It is a block diagram of a video processing device.

[0032] Figure 3 is a flow chart of an example method of video processing.

[0033] Figure 4 is a block diagram illustrating a video encoding and decoding system according to some embodiments of the present disclosure.

[0034] Figure 5 is a block diagram illustrating an encoder according to some embodiments of the present disclosure.

[0035] Figure 6 is a block diagram illustrating a decoder according to some embodiments of the present disclosure.

[0036] Figures 7A to 7G A flowchart illustrating an example method of video processing based on some implementations of the disclosed technology is shown.

[0037] Figure 8A and Figure 8B A flowchart illustrating an example method of video processing based on some implementations of the disclosed technology is shown.

[0038] Figure 9A and Figure 9B A flowchart illustrating an example method of video processing based on some implementations of the disclosed technology is shown. DETAILED DESCRIPTION

[0039] Section headings are used throughout this document for ease of understanding and do not limit the applicability of the techniques and embodiments disclosed in each section to that section. Furthermore, H.266 technical terminology is used in some descriptions solely for ease of understanding and is not intended to limit the scope of the disclosed techniques. Therefore, the techniques described herein are also applicable to other video codec protocols and designs.

[0040] 1. Brief Summary

[0041] This document relates to video codec technology. Specifically, it addresses various aspects of supporting random access, sub-layer switching, and scalability, including the definition of different types of pictures and their relationships in terms of decoding order, output order, and prediction relationships. The concepts can be applied, alone or in various combinations, to any video codec standard or non-standard video codec that supports multi-layer video coding, such as the Versatile Video Codec (VVC) under development.

[0042] 2. Abbreviation

[0043] APS Adaptive Parameter Set

[0044] AU Access Unit

[0045] AUD Access Unit Delimiter

[0046] AVC Advanced Video Codec

[0047] CLVS codec layer video sequence

[0048] CPB codec picture buffer

[0049] CRA Completely Random Access

[0050] CTU Codec Tree Unit

[0051] CVS codec video sequence

[0052] DCI decoding capability information

[0053] DPB decoded picture buffer

[0054] EOB End of bitstream

[0055] EOS sequence end

[0056] GDR Gradual Decode Refresh

[0057] HEVC High-Efficiency Video Codec

[0058] HRD Hypothesized Reference Decoder

[0059] IDR Instant Decode Refresh

[0060] JEM Joint Exploration Model

[0061] MCTS motion constraint set

[0062] NAL Network Abstraction Layer

[0063] OLS output layer set

[0064] PH Image Header

[0065] PPS Picture Parameter Set

[0066] PTL Profiles, Hierarchies, and Levels

[0067] PU picture unit

[0068] RADL Random Access Decodable Preamble (Image)

[0069] RAP Random Access Point

[0070] RASL Random Access Skip Preamble (image)

[0071] RBSP Raw Byte Sequence Payload

[0072] RPL Reference Image List

[0073] SEI auxiliary enhancement information

[0074] SPS sequence parameter set

[0075] STSA Stepwise Temporal Sublayer Access

[0076] SVC Scalable Video Codec

[0077] VCL video codec layer

[0078] VPS Video Parameter Set

[0079] VTM VVC test model

[0080] VUI Video Availability Information

[0081] VVC multifunctional video codec

[0082] 3. Preliminary Discussion

[0083] Video codec standards have evolved primarily through the development of the well-known ITU-T and ISO / IEC standards. ITU-T developed H.261 and H.263, ISO / IEC developed MPEG-1 and MPEG-4 Visual, and the two organizations jointly developed H.262 / MPEG-2 Video, H.264 / MPEG-4 Advanced Video Coding (AVC), and H.265 / HEVC. Since H.262, video codec standards have been based on a hybrid video codec architecture that employs temporal prediction plus transform coding. To explore future video codec technologies beyond HEVC, VCEG and MPEG jointly established the Joint Video Exploration Team (JVET) in 2015. Since then, JVET has adopted many new approaches and incorporated them into reference software called the Joint Exploration Model (JEM). JVET meetings are held concurrently every quarter, with the goal of achieving a 50% bitrate reduction compared to HEVC for the new codec standard. The new video codec standard was officially named the Versatile Video Codec (VVC) at the JVET meeting in April 2018, and the first version of the VVC Test Model (VTM) was also released at that time. Due to the ongoing efforts to standardize VVC, new codec technologies are adopted into the VVC standard at each JVET meeting. The VVC working draft and test model (VTM) are updated after each meeting. The VVC project is currently aiming for technical completion (FDIS) at the July 2020 meeting.

[0084] 3.1. Scalable Video Codec (SVC) in General and VVC

[0085] Scalable Video Codec (SVC, sometimes also referred to as scalability in video codecs) refers to video codecs that use a base layer (BL) (sometimes referred to as a reference layer (RL)) and one or more scalable enhancement layers (EL). In SVC, the base layer can carry video data with a basic quality level. One or more enhancement layers can carry additional video data to support, for example, higher spatial, temporal, and / or signal-to-noise ratio (SNR) levels. Enhancement layers can be defined relative to previously coded layers. For example, the bottom layer can serve as the BL, while the top layer can serve as the EL. Intermediate layers can serve as the EL, the RL, or both. For example, an intermediate layer (e.g., a layer that is neither the lowest nor the highest layer) can serve as the EL for a layer below the intermediate layer (such as the base layer or any intervening enhancement layer) and simultaneously serve as the RL for one or more enhancement layers above the intermediate layer. Similarly, in the multi-view or 3D extension of the HEVC standard, there can be multiple views, and information from one view can be used to encode (e.g., encode or decode) information from another view (e.g., motion estimation, motion vector prediction, and / or other redundancy).

[0086] In SVC, parameters used by an encoder or decoder are grouped into parameter sets based on the codec level at which they can be utilized (e.g., video level, sequence level, picture level, slice level, etc.). For example, parameters that can be utilized by one or more codec video sequences of different layers in a bitstream can be included in a video parameter set (VPS), and parameters that can be utilized by one or more pictures in a codec video sequence can be included in a sequence parameter set (SPS). Similarly, parameters utilized by one or more slices in a picture can be included in a picture parameter set (PPS), and other parameters specific to individual slices can be included in a slice header. Similarly, indications of which parameter set(s) a particular layer is using at a given time can be provided at various codec levels.

[0087] Due to the support for reference picture resampling (RPR) in VVC, support for bitstreams containing multiple layers (for example, two layers with SD and HD resolutions in VVC) can be designed without the need for any additional signal processing level codec tools, because the upsampling required for spatial scalability support can use only RPR upsampling filters. However, for scalability support, high-level syntax changes are required (compared to not supporting scalability). Scalability support is specified in VVC version 1. Unlike scalability support in any earlier video codec standards (including extensions of AVC and HEVC), the design of VVC scalability has been as friendly to single-layer decoder design as possible. The decoding capabilities of multi-layer bitstreams are specified as if there is only a single layer in the bitstream. For example, decoding capabilities such as DPB size are specified in a way that is independent of the number of layers in the bitstream to be decoded. Basically, a decoder designed for a single-layer bitstream does not need too many changes to be able to decode multi-layer bitstreams. Compared to the design of multi-layer extensions of AVC and HEVC, the HLS aspect is significantly simplified at the expense of some flexibility. For example, an IRAP AU is required to contain pictures of each layer present in the CVS.

[0088] 3.2. Random Access and Support in HEVC and VVC

[0089] Random access refers to accessing and decoding a bitstream starting from a picture that is not the first picture in the bitstream in decoding order. To support tuning and channel switching in broadcast / multicast and multi-party video conferencing, seeking in local playback and streaming, and stream adaptation in streaming, the bitstream needs to include closely spaced random access points, which are usually intra-frame codec pictures, but can also be inter-frame codec pictures (for example, in the case of gradual decoding refresh).

[0090] HEVC includes signaling of intra random access point (IRAP) pictures in the NAL unit header via the NAL unit type. Three types of IRAP pictures are supported, namely Instantaneous Decoder Refresh (IDR), Complete Random Access (CRA), and Broken Link Access (BLA) pictures. IDR pictures constrain the inter picture prediction structure to not reference any pictures before the current group of pictures (GOP), which is traditionally referred to as a closed GOP random access point. CRA pictures are less restrictive by allowing specific pictures to reference pictures before the current GOP, where all pictures are discarded in the case of random access. CRA pictures are traditionally referred to as open GOP random access points. BLA pictures typically originate from the concatenation of two bitstreams or parts thereof at a CRA picture, for example during stream switching. In order to better enable the system to use IRAP pictures, a total of six different NAL units are defined to signal the properties of IRAP pictures, which can be used to better match the stream access point types defined in the ISO Base Media File Format (ISOBMFF) for random access support in Dynamic Adaptive Streaming over HTTP (DASH).

[0091] VVC supports three types of IRAP pictures, two types of IDR pictures (one type with or without an associated RADL picture), and one type of CRA picture. These are essentially the same as in HEVC. The BLA picture type in HEVC is not included in VVC for two main reasons: i) The basic functionality of a BLA picture can be implemented by a CRA picture plus a sequence NAL unit end, the presence of which indicates that the subsequent picture starts a new CVS in a single-layer bitstream. ii) During the development of VVC, it was desired to specify fewer NAL unit types than in HEVC, as indicated by the use of 5 bits instead of 6 bits for the NAL unit type field in the NAL unit header.

[0092] Another key difference in random access support between VVC and HEVC is that GDR is supported in a more standardized way in VVC. In GDR, decoding of the bitstream can start from an inter-frame coded picture, and although not the entire picture region can be correctly decoded at the beginning, after several pictures, the entire picture region will be correct. GDR random access points and recovery points are signaled using the recovery point SEI message, and AVC and HEVC also support GDR. In VVC, a new NAL unit type is specified for the indication of GDR pictures, and the recovery point is signaled in the picture header syntax structure. CVS and bitstreams are allowed to start with GDR pictures. This means that the entire bitstream is allowed to contain only inter-frame coded pictures, without a single intra-frame coded picture. The main benefit of specifying GDR support in this way is to provide consistent behavior of GDR. GDR enables the encoder to smooth the bitrate of the bitstream by distributing intra-coded slices or blocks across multiple pictures, as opposed to intra-coding the entire picture, allowing for significant end-to-end latency reduction, which is considered more important today than ever before as ultra-low latency applications such as wireless displays, online gaming, and drone-based applications become more popular.

[0093] Another GDR-related feature in VVC is virtual boundary signaling. The boundary between the refresh area (i.e., correctly decoded area) and the unrefreshed area at the picture between the GDR picture and its recovery point can be signaled as a virtual boundary, and when signaled, loop filtering across the boundary will not be applied, so there will be no decoding mismatch of some samples at or near the boundary. This can be useful when the application determines to display the correctly decoded area during the GDR process.

[0094] IRAP pictures and GDR pictures may be collectively referred to as random access point (RAP) pictures.

[0095] 3.3. Reference Picture Management and Reference Picture List (RPL)

[0096] Reference picture management is a core function required for any video codec that uses inter-frame prediction. It manages the storage and removal of reference pictures in the decoded picture buffer (DPB) and places the reference pictures in their correct order in the RPL.

[0097] HEVC's reference picture management, including reference picture marking and removal from the decoded picture buffer (DPB), and reference picture list construction (RPLC), differs from AVC's. Instead of the sliding window-based reference picture marking mechanism with adaptive memory management control operations (MMCO) in AVC, HEVC specifies a reference picture management and marking mechanism based on so-called reference picture sets (RPSs), and RPLC is therefore based on the RPS mechanism. An RPS consists of a reference picture set associated with a picture, consisting of all reference pictures that precede the associated picture in decoding order and can be used for inter prediction of the associated picture or any picture that follows the associated picture in decoding order. A reference picture set consists of five reference picture lists. The first three lists contain all reference pictures that can be used for inter prediction of the current picture and for inter prediction of one or more pictures that follow the current picture in decoding order. The other two lists consist of all reference pictures that are not used for inter prediction of the current picture, but can be used for inter prediction of one or more pictures that follow the current picture in decoding order. RPS provides "intra-frame codec" signaling of the DPB state, rather than "inter-frame codec" signaling as in AVC, mainly to improve error tolerance. The RPLC process in HEVC is based on RPS and notifies the index of the RPS subset by signaling for each reference index; this process is simpler than the RPLC process in AVC.

[0098] Reference picture management in VVC is more similar to that of HEVC than AVC, but slightly simpler and more robust. As in those standards, two RPLs are derived, List 0 and List 1, but they are not based on the reference picture set concept used in HEVC or the automatic sliding window process used in AVC; instead, they are signaled more directly. Reference pictures are listed for the RPL as active and inactive entries, and only active entries can be used as reference indices in inter prediction of CTUs of the current picture. Inactive entries indicate other pictures to be kept in the DPB for reference by other pictures arriving later in the bitstream.

[0099] Parameter Set

[0100] AVC, HEVC, and VVC specify parameter sets. Parameter set types include SPS, PPS, APS, and VPS. SPS and PPS are supported in all of AVC, HEVC, and VVC. VPS was introduced starting with HEVC and is included in HEVC and VVC. APS is not included in AVC or HEVC, but is included in the latest VVC draft text.

[0101] The SPS is designed to carry sequence-level header information, and the PPS is designed to carry infrequently changing picture-level header information. With SPS and PPS, infrequently changing information does not need to be repeated for every sequence or picture, thus avoiding redundant signaling of this information. Furthermore, the use of SPS and PPS enables out-of-band transmission of important header information, thereby avoiding the need for redundant transmission and improving fault tolerance.

[0102] The VPS is introduced to carry sequence-level header information common to all layers in a multi-layer bitstream.

[0103] APS is introduced to carry such picture-level or slice-level information, which requires quite a lot of bits to encode and decode, can be shared by multiple pictures, and can have quite a lot of different variations in a sequence.

[0104] 3.5. Related definitions in VVC

[0105] The relevant definitions in the latest VVC text (JVET-Q2001-vE / v15) are as follows.

[0106] Associated IRAP picture (of a specific picture): The previous IRAP picture in decoding order (when present) has the same nuh_layer_id value as the specific picture.

[0107] Completely random access (CRA) PU: The coded picture is a PU of a CRA picture.

[0108] Completely random access (CRA) picture: An IRAP picture with each VCL NAL unit having nal_unit_type equal to CRA_NUT.

[0109] Coded Video Sequence (CVS): A sequence of AUs consisting of CVSS AUs, in decoding order, followed by zero or more AUs that are not CVSS AUs, including all subsequent AUs up to but not including any subsequent AU that is a CVSS AU.

[0110] Codec Video Sequence Start (CVSS) AU: An AU in which there is a PU for each layer in CVS and the coded picture in each PU is a CLVSS picture.

[0111] Gradual Decoding Refresh (GDR) AU: Each AU in which the codec picture in the current PU is a GDR picture.

[0112] Gradual Decoding Refresh (GDR) PU: The PU of the coded picture is a GDR picture.

[0113] Gradual Decoding Refresh (GDR) picture: A picture where every VCL NAL unit has nal_unit_type equal to GDR_NUT.

[0114] Instantaneous Decoding Refresh (IDR) PU: A PU whose coded picture is an IDR picture.

[0115] Instantaneous Decoding Refresh (IDR) picture: An IRAP picture with each VCL NAL unit having nal_unit_type equal to IDR_W_RADL or IDR_N_LP.

[0116] Intra Random Access Point (IRAP) AU: An AU in which there is a PU for each layer in the CVS and the codec picture in each PU is an IRAP picture.

[0117] Intra Random Access Point (IRAP) PU: A PU whose codec picture is an IRAP picture.

[0118] Intra Random Access Point (IRAP) picture: A codec picture whose all VCL NAL units have the same nal_unit_type value in the range of IDR_W_RADL to CRA_NUT, inclusive.

[0119] Preceding picture: A picture that is in the same layer as the associated IRAP picture and precedes the associated IRAP picture in output order.

[0120] Random Access Decodable Front (RADL) PU: A PU whose codec picture is a RADL picture.

[0121] Random Access Decodable Leading (RADL) picture: A picture with each VCL NAL unit having nal_unit_type equal to RADL_NUT.

[0122] Random Access Skip Leading (RASL) PU: The PU of the coded picture is a RASL picture.

[0123] Random Access Skip Leading (RASL) picture: A picture where each VCL NAL unit has nal_unit_type equal to RASL_NUT.

[0124] Step-by-step temporal sub-layer access (STSA) PU: The coded picture is a PU of a STSA picture.

[0125] Step-by-step temporal sub-layer access (STSA) picture: A picture with nal_unit_type equal to STSA_NUT per VCL NAL unit.

[0126] NOTE – An STSA picture does not use pictures with the same TemporalId as the STSA picture for inter prediction reference. Pictures that follow the STSA picture in decoding order and have the same TemporalId as the STSA picture do not use pictures that precede the STSA picture in decoding order and have the same TemporalId as the STSA picture for inter prediction reference. STSA pictures implement an upward switch from the immediately lower sublayer to the sublayer containing the STSA picture at the STSA picture. STSA pictures must have a TemporalId greater than 0.

[0127] Posting picture: A non-IRAP picture that follows the associated IRAP picture in output order and is not a STSA picture.

[0128] NOTE – Posting pictures associated with an IRAP picture also follow the IRAP picture in decoding order. Pictures that follow the associated IRAP picture in output order and precede the associated IRAP picture in decoding order are not allowed.

[0129] 3.6.NAL Unit Header Syntax and Semantics in VVC

[0130] In the latest VVC text (in JVET-Q2001-vE / v15), the NAL unit header syntax and semantics are as follows.

[0131] 7.3.1.2 NAL unit header syntax

[0132]

[0133] 7.4.2.2 NAL unit header semantics

[0134] forbidden_zero_bit should be equal to 0.

[0135] nuh_reserved_zero_bit shall be equal to 0. A value of 1 for nuh_reserved_zero_bit may be specified in the future by ITU-T | ISO / IEC. A decoder shall ignore (ie, remove from the bitstream and discard) NAL units with nuh_reserved_zero_bit equal to 1.

[0136] nuh_layer_id specifies the identifier of the layer to which the VCL NAL unit belongs or the identifier of the layer to which the non-VCL NAL unit applies. The value of nuh_layer_id shall be in the range of 0 to 55, inclusive. Other values of nuh_layer_id are reserved for future use by ITU-T | ISO / IEC.

[0137] The value of nuh_layer_id shall be the same for all VCL NAL units of a codec picture.The value of nuh_layer_id of a codec picture or PU is the value of nuh_layer_id of the VCL NAL unit of the codec picture or PU.

[0138] The value of nuh_layer_id for AUD, PH, EOS, and FD NAL units is constrained as follows:

[0139] - If nal_unit_type is equal to AUD_NUT, nuh_layer_id shall be equal to vps_layer_id[0].

[0140] - Otherwise, when nal_unit_type is equal to PH_NUT, EOS_NUT or FD_NUT, nuh_layer_id shall be equal to the nuh_layer_id of the associated VCL NAL unit.

[0141] NOTE 1 – The value of nuh_layer_id of DCI, VPS and EOB NAL units is not constrained.

[0142] The value of nal_unit_type should be the same for all pictures of a CVSS AU.

[0143] nal_unit_type specifies the NAL unit type, ie, the type of RBSP data structure contained in the NAL unit as specified in Table 5.

[0144] NAL units with a nal_unit_type in the range UNSPEC_28..UNSPEC_31 (unspecified semantics), inclusive, shall not affect the decoding process specified in this specification.

[0145] NOTE 2 – NAL unit types in the range of UNSPEC_28..UNSPEC_31 may be used as determined by the application. The decoding process for these values of nal_unit_type is not specified in this specification. Because different applications may use these NAL unit types for different purposes, special care must be taken in the design of encoders that generate NAL units with these nal_unit_type values, and in the design of decoders that interpret the content of NAL units with these nal_unit_type values. This specification does not define any management of these values. These nal_unit_type values may only be appropriate for use in contexts where "conflicts" of usage (i.e., different definitions of the meaning of the content of NAL units with the same nal_unit_type value) are not important, are not possible, or are managed (e.g., defined or managed in a controlling application or transport specification, or in an environment where the bitstream is distributed).

[0146] For purposes other than determining the amount of data in a DU of the bitstream (as specified in Annex C), a decoder should ignore (remove from the bitstream and discard) the contents of all NAL units that use reserved values of nal_unit_type.

[0147] NOTE 3 – This requirement allows for the future definition of compatible extensions to this specification.

[0148] Table 5 – NAL unit type codes and NAL unit type classifications

[0149]

[0150]

[0151] NOTE 4 - A completely random access (CRA) picture may have an associated RASL or RADL picture present in the bitstream.

[0152] NOTE 5 - An Instantaneous Decoding Refresh (IDR) picture with nal_unit_type equal to IDR_N_LP does not have an associated preceding picture present in the bitstream. An IDR picture with nal_unit_type equal to IDR_W_RADL does not have an associated RASL picture present in the bitstream, but may have an associated RADL picture in the bitstream.

[0153] The value of nal_unit_type shall be the same for all VCL NAL units of a sub-picture. A sub-picture is said to have the same NAL unit type as the VCL NAL units of the sub-picture.

[0154] For any particular picture's VCL NAL unit, the following applies:

[0155] If mixed_nalu_types_in_pic_flag is equal to 0, the value of nal_unit_type shall be the same for all VCL NAL units of a picture, and the picture or PU is said to have the same NAL unit type as the codec slice NAL units of the picture or PU.

[0156] Otherwise (mixed_nalu_types_in_pic_flag is equal to 1), the picture shall have at least two sub-pictures, and the VCL NAL units of the picture shall have exactly two different nal_unit_type values, as follows: the VCL NAL units of at least one sub-picture of the picture shall all have a specific value of nal_unit_type equal to STSA_NUT, RADL_NUT, RASL_NUT, IDR_W_RADL, IDR_N_LP, or CRA_NUT, while the VCL NAL units of the other sub-pictures in the picture shall all have different specific values of nal_unit_type equal to TRAIL_NUT, RADL_NUT, or RASL_NUT.

[0157] For single-layer bitstreams, the following constraints apply:

[0158] - Every picture except the first picture in the bitstream in decoding order is considered to be associated with the previous IRAP picture in decoding order.

[0159] - When a picture is the preceding picture of an IRAP picture, it shall be a RADL or RASL picture.

[0160] - When a picture is a subsequent picture of an IRAP picture, it shall not be a RADL or RASL picture.

[0161] - There shall be no RASL pictures associated with an IDR picture in the bitstream.

[0162] - There shall be no RADL pictures associated with an IDR picture with nal_unit_type equal to IDR_N_LP in the bitstream.

[0163] NOTE 6 – Random access can be performed at the location of an IRAP PU (and correctly decode the IRAP picture and all subsequent non-RASL pictures in decoding order) by discarding all PUs preceding the IRAP PU, provided that each parameter set is available (in the bitstream or by external means not specified in this specification) at the time it is referenced.

[0164] - Any picture that precedes an IRAP picture in decoding order shall precede the IRAP picture in output order, and shall precede any RADL pictures associated with the IRAP picture in output order.

[0165] - Any RASL pictures associated with a CRA picture shall precede any RADL pictures associated with the CRA picture in output order.

[0166] - Any RASL pictures associated with a CRA picture shall follow, in output order, any IRAP pictures that precede the CRA picture in decoding order.

[0167] - If field_seq_flag is equal to 0 and the current picture is a leading picture associated with an IRAP picture, then it shall precede all non-leading pictures associated with the same IRAP picture in decoding order. Otherwise, let picA and picB be the first and last leading pictures associated with the IRAP picture in decoding order, respectively, there shall be at most one non-leading picture before picA in decoding order, and there shall be no non-leading pictures between picA and picB in decoding order.

[0168] nuh_temporal_id_plus1 minus 1 specifies the temporal identifier of the NAL unit.

[0169] The value of nuh_temporal_id_plus1 shall not be equal to 0.

[0170] The variable TemporalId is derived as follows:

[0171] TemporalId=nuh_temporal_id_plus1-1 (36)

[0172] When nal_unit_type is in the range of IDR_W_RADL to RSV_IRAP_12 (inclusive), TemporalId shall be equal to 0.

[0173] When nal_unit_type is equal to STSA_NUT and vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1, TemporalId shall not be equal to 0.

[0174] The value of TemporalId shall be the same for all VCL NAL units of an AU. The value of TemporalId for a codec picture, PU, or AU shall be the value of TemporalId of the VCL NAL unit of the codec picture, PU, or AU. The value of TemporalId for a sublayer representation shall be the maximum value of the TemporalIds of all VCL NAL units in the sublayer representation.

[0175] The value of TemporalId for non-VCL NAL units is constrained as follows:

[0176] - If nal_unit_type is equal to DCI_NUT, VPS_NUT or SPS_NUT, TemporalId shall be equal to 0, and the TemporalId of the AU containing the NAL unit shall be equal to 0.

[0177] - Otherwise, if nal_unit_type is equal to PH_NUT, TemporalId shall be equal to the TemporalId of the PU containing the NAL unit.

[0178] - Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT, TemporalId shall be equal to 0.

[0179] - Otherwise, if nal_unit_type is equal to AUD_NUT, FD_NUT, PREFIX_SEI_NUT or SUFFIX_SEI_NUT, TemporalId shall be equal to the TemporalId of the AU containing the NAL unit.

[0180] - Otherwise, when nal_unit_type is equal to PPS_NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT, TemporalId shall be greater than or equal to the TemporalId of the PU containing the NAL unit.

[0181] NOTE 7 – When the NAL unit is a non-VCL NAL unit, the value of TemporalId is equal to the minimum of the TemporalId values of all AUs to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, PREFIX_APS_NUT, or SUFFIX_APS_NUT, TemporalId may be greater than or equal to the TemporalId of the containing AU, because all PPSs and APSs may be included at the beginning of the bitstream (e.g., when they are transmitted out-of-band and the receiver places them at the beginning of the bitstream), where the first codec picture has a TemporalId equal to 0.

[0182] 3.7. Picture Header Structure Syntax and Semantics in VVC

[0183] In the latest VVC text (in JVET-Q2001-vE / v15), the picture header structure syntax and semantics that are most relevant to the present invention are as follows.

[0184] 7.3.2.7 Picture header structure syntax

[0185]

[0186] 7.4.3.7 Image header structure semantics

[0187] The PH syntax structure contains information that is common to all slices of the codec picture associated with the PH syntax structure.

[0188] gdr_or_irap_pic_flag equal to 1 specifies that the current picture is a GDR or IRAP picture. gdr_or_irap_pic_flag equal to 0 specifies that the current picture may or may not be a GDR or IRAP picture.

[0189] gdr_pic_flag equal to 1 specifies that the picture associated with the PH is a GDR picture. gdr_pic_flag equal to 0 specifies that the picture associated with the PH is not a GDR picture. When not present, the value of gdr_pic_flag is inferred to be equal to 0. When gdr_enabled_flag is equal to 0, the value of gdr_pic_flag shall be equal to 0.

[0190] NOTE 1 – When gdr_or_irap_pic_flag is equal to 1 and gdr_pic_flag is equal to 0, the picture associated with the PH is an IRAP picture. ...

[0192] ph_pic_order_cnt_lsb specifies the picture order count of the current picture modulo MaxPicOrderCntLsb. The length of the ph_pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4 + 4 bits. The value of ph_pic_order_cnt_lsb shall be in the range of 0 to MaxPicOrderCntLsb-1, inclusive.

[0193] no_output_of_prior_pics_flag affects the output of previously decoded pictures in the DPB as specified in Annex C after decoding a CLVSS picture that is not the first picture in the bitstream.

[0194] recovery_poc_cnt specifies the recovery point of the decoded picture in output order. If the current picture is a GDR picture associated with PH, and there is a picture picA that follows the current GDR picture in decoding order in the CLVS with PicOrderCntVal equal to the value of the current GDR picture plus recovery_poc_cnt, then picture picA is called the recovery point picture. Otherwise, the first picture in output order with a PicOrderCntVal greater than the value of the current picture's PicOrderCntVal plus recovery_poc_cnt is called the recovery point picture. The recovery point picture should not precede the current GDR picture in decoding order. The value of recovery_poc_cnt should be in the range of 0 to MaxPicOrderCntLsb-1 (including 0 and MaxPicOrderCntLsb-1).

[0195] When the current picture is a GDR picture, the variable RpPicOrderCntVal is derived as follows:

[0196] RpPicOrderCntVal=PicOrderCntVal+recovery_poc_cnt (81)

[0197] NOTE 2 - When gdr_enabled_flag is equal to 1 and the PicOrderCntVal of the current picture is greater than or equal to the RpPicOrderCntVal of the associated GDR picture, the current decoded picture and subsequent decoded pictures in output order exactly match the corresponding pictures produced by starting the decoding process from the previous IRAP picture (if any) that precedes the associated GDR picture in decoding order. ...

[0199] 3.8. Constraints on RPL in VVC

[0200] In the latest VVC text (in JVET-Q2001-vE / v15), the constraints on RPL in VVC are as follows (as part of the decoding process of clause 8.3.2 Reference picture list construction of VVC).

[0201] 8.3.2 Decoding Process of Reference Picture List Construction ...

[0203] For each i equal to 0 or 1, the first NumRefIdxActive[i] entries in RefPicList[i] are referred to as active entries in RefPicList[i], and the other entries in RefPicList[i] are referred to as inactive entries in RefPicList[i].

[0204] NOTE 2 – A particular picture may be referenced by an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may also be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1].

[0205] NOTE 3 – The active entries in RefPicList[0] and the active entries in RefPicList[1] jointly reference all reference pictures that can be used for inter prediction of the current picture and one or more pictures following the current picture in decoding order. The inactive entries in RefPicList[0] and the inactive entries in RefPicList[1] jointly reference all reference pictures that are not used for inter prediction of the current picture but can be used for inter prediction of one or more pictures following the current picture in decoding order.

[0206] NOTE 4 – There may be one or more entries in RefPicList[0] or RefPicList[1] that are equal to "no reference picture" because the corresponding pictures are not present in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equal to "no reference picture" shall be ignored. An unintentional picture loss shall be inferred for each active entry in RefPicList[0] or RefPicList[1] that is equal to "no reference picture".

[0207] The requirements for bitstream conformance are that the following constraints apply:

[0208] - For each i equal to 0 or 1, num_ref_entries[i][RplsIdx[i]] shall not be less than NumRefIdxActive[i].

[0209] - The picture referenced by each active entry in RefPicList[0] or RefPicList[1] shall be present in the DPB and shall have a TemporalId less than or equal to the TemporalId of the current picture.

[0210] - Each entry in RefPicList[0] or RefPicList[1] shall refer to a picture that is not the current picture and shall have non_reference_picture_flag equal to 0.

[0211] - A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture shall not refer to the same picture.

[0212] - There shall be no PicOrderCntVal in RefPicList[0] or RefPicList[1] where the difference between the current picture's PicOrderCntVal and the picture referenced by the entry is greater than or equal to 2 24 LTRP entry.

[0213] - Let setOfRefPics be the set of unique pictures referenced by all entries in RefPicList[0] with the same nuh_layer_id as the current picture and all entries in RefPicList[1] with the same nuh_layer_id as the current picture. The number of pictures in setOfRefPics shall be less than or equal to MaxDpbSize-1 (inclusive), where MaxDpbSize is as specified in clause A.4.2, and setOfRefPics shall be the same for all slices of the picture.

[0214] - When the current slice has nal_unit_type equal to STSA_NUT, there shall be no active entry in RefPicList[0] or RefPicList[1] with TemporalId equal to the current picture's TemporalId and nuh_layer_id equal to the current picture's nuh_layer_id.

[0215] - When the current picture is a picture with a TemporalId equal to the current picture's TemporalId and a TemporalId equal to

[0216] When a picture with nuh_layer_id equal to the nuh_layer_id of the current picture follows the STSA picture in decoding order, pictures that precede the STSA picture in decoding order, have a TemporalId equal to the TemporalId of the current picture, and have a nuh_layer_id equal to the nuh_layer_id of the current picture should not be included as active entries in RefPicList[0] or RefPicList[1].

[0217] - When the current picture is a CRA picture, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede any preceding IRAP picture (when present) in decoding order, either in output order or decoding order.

[0218] - When the current picture is a post-picture, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that were generated by the decoding process of unavailable reference pictures used to generate the IRAP picture associated with the current picture.

[0219] - When the current picture is a subsequent picture that follows one or more preceding pictures (if any) associated with the same IRAP picture in both decoding order and output order, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that were generated by the decoding process for generating unavailable reference pictures for the IRAP picture associated with the current picture.

[0220] - When the current picture is a recovery point picture or a picture that follows the recovery point picture in output order, there should be no entries in RefPicList[0] or RefPicList[1] that contain pictures generated by the decoding process of unavailable reference pictures of the GDR picture used to generate the recovery point picture.

[0221] - When the current picture is a subsequent picture, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0222] - When the current picture is a subsequent picture that follows one or more preceding pictures (if any) associated with the same IRAP picture in both decoding order and output order, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0223] - When the current picture is a RADL picture, in RefPicList[0] or RefPicList[1]

[0224] There should not be any active entries that are any of the following:

[0225] οRASL pictures

[0226] o Pictures generated by a decoding process that generates unavailable reference pictures

[0227] o pictures that precede the associated IRAP picture in decoding order

[0228] - The pictures referenced by each ILRP entry in RefPicList[0] or RefPicList[1] of the slice of the current picture shall be in the same AU as the current picture.

[0229] - The picture referenced by each ILRP entry in RefPicList[0] or RefPicList[1] of the slice of the current picture shall be present in the DPB and shall have a nuh_layer_id that is less than the nuh_layer_id of the current picture.

[0230] - Each ILRP entry in the stripe's RefPicList[0] or RefPicList[1] shall be an active entry. ...

[0232] 4. Technical problems solved by the disclosed technical solutions

[0233] The existing design in the latest VVC text (JVET-Q2001-vE / v15) has the following problems:

[0234] 1) The definition of associated IRAP pictures should be updated so that the associated IRAP pictures of a specific picture belong to the same layer as the specific picture.

[0235] 2) The current definition of the post-image is as follows:

[0236] Posting picture: A non-IRAP picture that follows the associated IRAP picture in output order and is not a STSA picture.

[0237] Therefore, an IRAP picture needs to be present in the bitstream for the trailing picture to be present, and if the bitstream does not have an IRAP picture, the NAL unit type value TRAIL_NUT cannot be used. However, non-STSA pictures associated with GDR pictures need to use the NAL unit type value TRAIL_NUT.

[0238] 3) Existing constraints on the output order of pictures that precede the IRAP picture in decoding order need to be specified to apply only to pictures within a layer.

[0239] 4) There are no constraints on the relative decoding and output order between a GDR picture and the preceding and following pictures in decoding order.

[0240] 5) Existing constraints on the decoding order of pictures associated with IRAP pictures and some non-previous pictures need to be specified to apply only to pictures within a layer.

[0241] 6) Currently, pre-images, RADL images, and RASL images associated with GDR images are not supported.

[0242] 7) Existing constraints on the RPL of CRA pictures need to be specified to apply only to pictures within a layer.

[0243] 8) For STSA pictures, post-pictures associated with GDR pictures, and GDR pictures with NoOutputBeforeRecoveryFlag equal to 0, there is a lack of constraints on active entries in the RPL that are not generated by the decoding process for generating unusable reference pictures.

[0244] 9) For STSA pictures, IDR pictures, CRA pictures with NoOutputBeforeRecoveryFlag equal to 0, etc., there is a lack of constraints on entries in the RPL that are not generated by the decoding process for generating unusable reference pictures.

[0245] 10) For STSA pictures, there is a lack of constraints on active entries in the RPL that do not precede the associated IRAP picture in output order or decoding order.

[0246] 11) For STSA pictures, there is a lack of constraints on entries in the RPL that do not precede the associated IRAP picture in output order or decoding order.

[0247] 5. Examples of embodiments and technical solutions

[0248] In order to solve the above problems and other problems, the following methods are disclosed. The present invention should be considered as an example to explain the general concept and should not be interpreted in a narrow way. In addition, these inventions can be applied alone or combined in any way.

[0249] 1) To solve problem 1, the definition of associated IRAP pictures is updated so that the associated IRAP pictures of a specific picture belong to the same layer as the specific picture.

[0250] 2) To solve problem 2, the definition of the post-image is updated so that the post-image can also be associated with the GDR image.

[0251] a. In addition, the definition of associated GDR pictures is added, and the definition of associated IRAP pictures is updated so that, except for the first picture of a layer in the bitstream, each picture of the layer is designated as being associated with the previous IRAP or GDR picture of the same layer in decoding order, whichever is closer.

[0252] b. In addition, a constraint is added to require that the post-picture should follow the associated IRAP or GDR picture in output order.

[0253] 3) To address issue 3, the existing constraint on the output order of pictures preceding the IRAP picture in decoding order is updated so that it only imposes restrictions on pictures within a layer.

[0254] a. In one example, the constraint is specified as follows: any picture with nuh_layer_id equal to a specific value layerId that precedes the IRAP picture with nuh_layer_id equal to layerId in decoding order shall precede the IRAP picture and all its associated RADL pictures in output order.

[0255] 4) To solve problem 4, add one or more of the following constraints:

[0256] a. A post-image should follow the associated IRAP or GDR image in output order.

[0257] b. Any picture with nuh_layer_id equal to a specific value layerId that precedes the GDR picture with nuh_layer_id equal to layerId in decoding order shall precede the GDR picture and all its associated pictures in output order.

[0258] 5) To address issue 5, the existing constraint on the decoding order of pictures associated with IRAP pictures and some non-previous pictures is updated so that it only imposes restrictions on pictures within a layer.

[0259] a. In one example, the constraint is specified as follows: If field_seq_flag is equal to 0 and the current picture with nuh_layer_id equal to a specific value layerId is a leading picture associated with an IRAP picture, then it should precede all non-leading pictures associated with the same IRAP picture in decoding order. Otherwise, let picA and picB be the first and last leading pictures associated with the IRAP picture in decoding order, respectively, then there should be at most one non-leading picture with nuh_layer_id equal to layerId before picA in decoding order, and there should be no non-leading pictures with nuh_layer_id equal to layerId between picA and picB in decoding order.

[0260] b. In another example, the constraint is specified as follows: If field_seq_flag is equal to 0 and the current picture is a leading picture associated with an IRAP picture, then it shall precede all non-leading pictures associated with the same IRAP picture in decoding order. Otherwise, let picA and picB be the first and last leading pictures associated with the IRAP picture in decoding order, respectively, then there shall be at most one non-leading picture associated with the IRAP picture that precedes picA in decoding order, and there shall be no non-leading pictures associated with the IRAP picture between picA and picB in decoding order.

[0261] 6) To solve problem 6, define and specify the preceding pictures, RADL pictures, and RASL pictures associated with the GDR pictures.

[0262] a. Preceding pictures associated with a GDR picture are those pictures that follow the GDR picture in decoding order and precede the GDR picture in output order.

[0263] b. A RADL picture associated with a GDR picture is a preceding picture associated with the GDR picture and having nal_unit_type equal to RADL_NUT.

[0264] c. A RASL picture associated with a GDR picture is a preceding picture associated with the GDR picture and having nal_unit_type equal to RASL_NUT.

[0265] 7) To address issue 7, the existing constraints on the RPL of CRA pictures are updated so that it only imposes restrictions on pictures within a layer.

[0266] a. In one example, the constraint is specified as follows: When the current picture with nuh_layer_id equal to a particular value layerId is a CRA picture, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede, in output order or decoding order, any previous IRAP picture (when present) with nuh_layer_id equal to layerId in decoding order.

[0267] 8) To solve Problem 8, the following constraints are specified:

[0268] When the current picture with nuh_layer_id equal to a specific value layerId is not a RASL picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a GDR picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId, there should be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] generated by the decoding process for generating unavailable reference pictures.

[0269] 9) To solve Problem 9, the following constraints are specified:

[0270] When the current picture with nuh_layer_id equal to a particular value layerId is not a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a picture preceding in decoding order the preceding picture associated with the same CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a preceding picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a GDR picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] generated by the decoding process used to generate unusable reference pictures.

[0271] 10) To solve Problem 10, the following constraints are specified:

[0272] When the current picture is associated with an IRAP picture and follows the IRAP picture in output order, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0273] 11) To solve Problem 11, the following constraints are specified:

[0274] When the current picture is associated with an IRAP picture, follows the IRAP picture in output order, and follows the preceding picture (if any) associated with the same IRAP picture in both decoding order and output order, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0275] 6. Examples

[0276] The following are some example embodiments of some aspects of the invention summarized in Section 5 above, which can be applied to the VVC specification. The changed text is based on the latest VVC text in JVET-Q2001-vE / v15. The most relevant parts that have been added or modified are highlighted in bold italics, and some deleted parts are marked with double brackets (e.g., [[a]] indicates the deletion of the character "a"). Some other changes are editorial in nature and are therefore not highlighted.

[0277] 6.1. First embodiment

[0278] This embodiment addresses items 1, 2, 3, 4, 5, and 5a.

[0279] 3 Definition ...

[0281] Associated GDR pictures (of a specific picture with a specific value of nuh_layer_id layerId): the previous GDR picture in decoding order (when present) with nuh_layer_id equal to layerId, where there is no IRAP picture with nuh_layer_id equal to layerId between this picture and the specific picture in decoding order.

[0282] Associated IRAP pictures (of a specific picture with a specific value of nuh_layer_id layerId): the previous IRAP picture in decoding order (when present) with nuh_layer_id equal to layerId, where there is no GDR picture with nuh_layer_id equal to layerId between this picture and the specific picture in decoding order.

[0283] Output order: The order of pictures or sub-pictures within the CLVS indicated by increasing POC values, and for decoded pictures output from the DPB, this is the order in which the decoded pictures are output from the DPB.

[0284] Trailing picture: A picture with each VCL·NAL unit having nal_unit_type equal to TRAIL_NUT.

[0285] NOTE – A subsequent picture associated with an IRAP or GDR picture also follows the IRAP or GDR picture in decoding order. Pictures that follow the associated IRAP or GDR picture in output order and precede the associated IRAP or GDR picture in decoding order are not allowed. ...

[0287] 7.4.2.2 NAL unit header semantics ...

[0289] [[For a single-layer bitstream, the bitstream conformance requirement is that the following constraints apply:

[0290] - Every picture except the first picture in the bitstream in decoding order is considered to be associated with the previous IRAP picture in decoding order. ]]

[0291] - A post-image shall follow the associated IRAP or GDR image in output order.

[0292] - When a picture is the preceding picture of an IRAP picture, it shall be a RADL or RASL picture.

[0293] - There shall be no RASL pictures associated with an IDR picture in the bitstream.

[0294] - There shall be no RADL pictures associated with an IDR picture with nal_unit_type equal to IDR_N_LP in the bitstream.

[0295] NOTE 6 – Random access can be performed at the location of an IRAP PU (and correctly decode the IRAP picture and all subsequent non-RASL pictures in decoding order) by discarding all PUs preceding the IRAP PU, provided that each parameter set is available (in the bitstream or by external means not specified in this specification) at the time it is referenced.

[0296] - Any picture with nuh_layer_id equal to a particular value layerId that precedes the IRAP picture with nuh_layer_id equal to layerId in decoding order shall precede the IRAP picture and all its associated RADL pictures in output order.

[0297] - Any picture with nuh_layer_id equal to the specific value layerId that precedes the GDR picture with nuh_layer_id equal to layerId in decoding order shall precede the GDR picture and all its associated pictures in output order.

[0298] - Any RASL pictures associated with a CRA picture shall precede any RADL pictures associated with the CRA picture in output order.

[0299] - Any RASL pictures associated with a CRA picture shall follow, in output order, any IRAP pictures that precede the CRA picture in decoding order.

[0300] - If field_seq_flag is equal to 0 and the current picture with nuh_layer_id equal to the specified value layerId is a leading picture associated with an IRAP picture, then it shall precede all non-leading pictures associated with the same IRAP picture in decoding order. Otherwise, let picA and picB be the first and last leading pictures associated with the IRAP picture in decoding order, respectively, then there shall be at most one non-leading picture with nuh_layer_id equal to layerId that precedes picA in decoding order, and there shall be no non-leading pictures with nuh_layer_id equal to layerId between picA and picB in decoding order. ...

[0302] 7.4.3.7 Image header structure semantics ...

[0304] recovery_poc_cnt specifies the recovery point of the decoded picture in output order.

[0305] When the current picture is a GDR picture, the variable recoveryPointPocVal is derived as follows:

[0306] recoveryPointPocVal=PicOrderCntVal+recovery_poc_cnt (81)

[0307] If the current picture is a GDR picture [[associated with PH]] and there is a picture picA that follows the current GDR picture in decoding order in the CLVS with PicOrderCntVal equal to recoveryPointPocVal[[the PicOrderCntVal of the current GDR picture plus the value of recovery_poc_cnt]], then picture picA is called the recovery point picture. Otherwise, the first picture in the CLVS in output order with a PicOrderCntVal greater than recoveryPointPocVal[[the PicOrderCntVal of the current picture plus the value of recovery_poc_cnt]] is called the recovery point picture. The recovery point picture should not precede the current GDR picture in decoding order. The picture associated with the current GDR picture and with a PicOrderCntVal less than recoveryPointPocVal is called the recovery picture of the GDR picture. The value of recovery_poc_cnt shall be in the range of 0 to MaxPicOrderCntLsb-1, inclusive.

[0308] [[When the current picture is a GDR picture, the variable RpPicOrderCntVal is derived as follows:

[0309] RpPicOrderCntVal=PicOrderCntVal+recovery_poc_cnt (81)]]

[0310] NOTE 2 - When gdr_enabled_flag is equal to 1 and PicOrderCntVal of the current picture is greater than or equal to recoveryPointPocVal[[RpPicOrderCntVal]] of the associated GDR picture, the current decoded picture and subsequent decoded pictures in output order exactly match the corresponding pictures produced by starting the decoding process from the previous IRAP picture (if any) that precedes the associated GDR picture in decoding order. ...

[0312] 8.3.2 Decoding Process of Reference Picture List Construction ...

[0314] The requirements for bitstream conformance are that the following constraints apply:

[0315] -...

[0316] - When the current picture with nuh_layer_id equal to the particular value layerId is a CRA picture, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede, in output order or decoding order, any preceding IRAP picture (when present) with nuh_layer_id equal to layerId in decoding order.

[0317] - When the current picture with nuh_layer_id equal to a specific value layerId [[is a subsequent picture]] is not a RASL picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a GDR picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] generated by the decoding process used to generate unavailable reference pictures [[of the IRAP picture associated with the current picture]].

[0318] - When the current picture with nuh_layer_id equal to the specific value layerId [[is a subsequent picture that follows one or more preceding pictures (if any) associated with the same IRAP picture in both decoding order and output order]] is not a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a picture that precedes in decoding order the preceding picture associated with the same CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a preceding picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a GDR picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] generated by the decoding process used to generate unusable reference pictures [[of the IRAP picture associated with the current picture]].

[0319] -[[When the current picture is a recovery point picture or a picture that follows the recovery point picture in output order, there shall be no entries in RefPicList[0] or RefPicList[1] that contain pictures generated by the decoding process of unusable reference pictures of the GDR picture used to generate the recovery point picture. ]]

[0320] - When the current picture [[is a subsequent picture]] is associated with an IRAP picture and follows the IRAP picture in output order, there shall be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0321] - When the current picture is associated with an IRAP picture, follows the IRAP picture in output order, and follows the preceding picture (if any) associated with the same IRAP picture in both decoding order and output order, there shall be no RefPicList[0] that precedes the associated IRAP picture in output order or decoding order.

[0322] Or the picture referenced by an entry in RefPicList[1].

[0323] - When the current picture is a RADL picture, there shall be no active entry in RefPicList[0] or RefPicList[1] that is any of the following:

[0324] οRASL pictures

[0325] [[Picture generated by a decoding process that generates an unavailable reference picture]]

[0326] o pictures that precede the associated IRAP picture in decoding order

[0327] -...

[0328] Figure 1 1 is a block diagram illustrating an example video processing system 1900 in which the various techniques disclosed herein may be implemented. Various implementations may include some or all of the components of system 1900. System 1900 may include an input 1902 for receiving video content. The video content may be received in a raw or uncompressed format, such as 8 or 10-bit multi-component pixel values, or in a compressed or encoded format. Input 1902 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interfaces include wired interfaces such as Ethernet, a passive optical network (PON), and wireless interfaces such as Wi-Fi or a cellular interface.

[0329] System 1900 may include a codec component 1904 that can implement the various codecs or encoding methods described in this document. Codec component 1904 can reduce the average bit rate of the video from input 1902 to the output of codec component 1904 to produce a coded representation of the video. Codec technology is therefore sometimes referred to as video compression or video transcoding technology. The output of codec component 1904 can be stored or transmitted via a communication connection such as represented by component 1906. The stored or communicated bitstream (or codec) representation of the video received at input 1902 can be used by component 1908 to generate pixel values or transmit to a displayable video of display interface 1910. The process of generating user-viewable video from the bitstream representation is sometimes referred to as video decompression. In addition, although some video processing operations are referred to as "codec" operations or tools, it will be understood that the codec tools or operations are used at the encoder, and the corresponding decoding tools or operations that reverse the codec results will be performed by the decoder.

[0330] Examples of peripheral bus interfaces or display interfaces may include Universal Serial Bus (USB), High-Definition Multimedia Interface (HDMI), or DisplayPort, etc. Examples of storage interfaces include SATA (Serial Advanced Technology Attachment), PCI, IDE interfaces, etc. The technology described in this document may be embodied in various electronic devices, such as mobile phones, laptops, smart phones, or other devices capable of performing digital data processing and / or video display.

[0331] Figure 2 36 is a block diagram of a video processing device 3600. Device 3600 can be used to implement one or more methods described herein. Device 3600 can be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, etc. Device 3600 may include one or more processors 3602, one or more memories 3604, and video processing hardware 3606. Processor(s) 3602 can be configured to implement one or more methods described herein. Memory(s) 3604 can be used to store data and code used to implement the methods and techniques described herein. Video processing hardware 3606 can be used to implement some of the techniques described in this document in hardware circuitry.

[0332] Figure 4 is a block diagram illustrating an example video coding system 100 that may utilize the techniques of this disclosure.

[0333] like Figure 4As shown, the video encoding and decoding system 100 may include a source device 110 and a target device 120. The source device 110 generates encoded video data, wherein the source device 110 may be referred to as a video encoding device. The target device 120 may decode the encoded video data generated by the source device 110, wherein the target device 120 may be referred to as a video decoding device.

[0334] Source device 110 may include a video source 112 , a video encoder 114 , and an input / output (I / O) interface 116 .

[0335] The video source 112 may include a source such as a video capture device, an interface for receiving video data from a video content provider, and / or a computer graphics system for generating video data, or a combination of these sources. The video data may include one or more pictures. The video encoder 114 encodes the video data from the video source 112 to generate a bitstream. The bitstream may include a sequence of bits that form a codec representation of the video data. The bitstream may include a codec picture and associated data. The codec picture is a codec representation of the picture. Associated data may include a sequence parameter set, a picture parameter set, and other syntax structures. The I / O interface 116 may include a modulator / demodulator (modem) and / or a transmitter. The encoded video data may be directly sent to the target device 120 via the network 130a via the I / O interface 116. The encoded video data may also be stored on a storage medium / server 130b for access by the target device 120.

[0336] Target device 120 may include an I / O interface 126 , a video decoder 124 , and a display device 122 .

[0337] I / O interface 126 may include a receiver and / or a modem. I / O interface 126 may obtain coded video data from source device 110 or storage medium / server 130b. Video decoder 124 may decode the coded video data. Display device 122 may display the decoded video data to a user. Display device 122 may be integrated with target device 120, or may be external to target device 120 configured to interface with an external display device.

[0338] The video encoder 114 and the video decoder 124 may operate according to a video compression standard, such as the High Efficiency Video Codec (HEVC) standard, the Versatile Video Codec (VVC) standard, and other current and / or additional standards.

[0339] Figure 5 is a block diagram illustrating an example of a video encoder 200, which may be Figure 4 The video encoder 114 in the system 100 is shown.

[0340] Video encoder 200 may be configured to perform any or all of the techniques of this disclosure. Figure 5 In the example of , video encoder 200 includes multiple functional components. The techniques described in this disclosure can be shared among the various components of video encoder 200. In some examples, a processor can be configured to perform any or all of the techniques described in this disclosure.

[0341] The functional components of the video encoder 200 may include a segmentation unit 201, a prediction unit 202 (which may include a mode selection unit 203, a motion estimation unit 204, a motion compensation unit 205 and an intra-frame prediction unit 206), a residual generation unit 207, a transform unit 208, a quantization unit 209, an inverse quantization unit 210, an inverse transform unit 211, a reconstruction unit 212, a buffer 213 and an entropy coding unit 214.

[0342] In other examples, the video encoder 200 may include more, fewer, or different functional components. In an example, the prediction unit 202 may include an intra block copy (IBC) unit. The IBC unit may perform prediction in IBC mode, where at least one reference picture is a picture in which the current video block is located.

[0343] Furthermore, some components such as the motion estimation unit 204 and the motion compensation unit 205 may be highly integrated, but for the purpose of explanation, they are not shown in FIG. Figure 5 are represented separately in the examples.

[0344] The segmentation unit 201 may segment a picture into one or more video blocks. The video encoder 200 and the video decoder 300 may support various video block sizes.

[0345] The mode selection unit 203 can select one of the coding modes (e.g., intra or inter) based on the error result, and provide the resulting intra-coded block or inter-coded block to the residual generation unit 207 to generate residual block data, and to the reconstruction unit 212 to reconstruct the coded block for use as a reference picture. In some examples, the mode selection unit 203 can select a combination of intra and inter prediction mode (CIIP), where prediction is based on an inter prediction signal and an intra prediction signal. In the case of inter prediction, the mode selection unit 203 can also select the resolution of the motion vector of the block (e.g., sub-pixel or integer pixel precision).

[0346] To perform inter-frame prediction on the current video block, the motion estimation unit 204 may generate motion information for the current video block by comparing the current video block with one or more reference frames from the buffer 213. The motion compensation unit 205 may determine a predicted video block for the current video block based on the motion information and decoded samples of pictures from the buffer 213 other than the picture associated with the current video block.

[0347] Motion estimation unit 204 and motion compensation unit 205 may perform different operations on the current video block, eg, depending on whether the current video block is in an I slice, a P slice, or a B slice.

[0348] In some examples, motion estimation unit 204 may perform unidirectional prediction on the current video block, and motion estimation unit 204 may search for a reference picture in list 0 or list 1 for a reference video block of the current video block. Motion estimation unit 204 may then generate a reference index indicating a reference picture in list 0 or list 1, the reference index including the reference video block and a motion vector indicating a spatial displacement between the current video block and the reference video block. Motion estimation unit 204 may output the reference index, the prediction direction indicator, and the motion vector as motion information for the current video block. Motion compensation unit 205 may generate a predicted video block for the current block based on the reference video block indicated by the motion information for the current video block.

[0349] In other examples, the motion estimation unit 204 may perform bidirectional prediction on the current video block. The motion estimation unit 204 may search for a reference video block for the current video block in the reference pictures in list 0 and may also search for another reference video block for the current video block in list 1. The motion estimation unit 204 may then generate a reference index indicating the reference pictures in list 0 and list 1 containing the reference video block and a motion vector indicating the spatial displacement between the reference video block and the current video block. The motion estimation unit 204 may output the reference index and motion vector for the current video block as motion information for the current video block. The motion compensation unit 205 may generate a predicted video block for the current video block based on the reference video block indicated by the motion information of the current video block.

[0350] In some examples, motion estimation unit 204 may output a complete motion information set for use in a decoding process by a decoder.

[0351] In some examples, motion estimation unit 204 may not output a complete set of motion information for the current video. Instead, motion estimation unit 204 may reference motion information of another video block to signal the motion information of the current video block. For example, motion estimation unit 204 may determine that the motion information of the current video block is sufficiently similar to the motion information of a neighboring video block.

[0352] In one example, motion estimation unit 204 may indicate a value in a syntax structure associated with the current video block that indicates to video decoder 300 that the current video block has the same motion information as another video block.

[0353] In another example, the motion estimation unit 204 may identify another video block and a motion vector difference (MVD) in a syntax structure associated with the current video block. The motion vector difference indicates the difference between the motion vector of the current video block and the motion vector of the indicated video block. The video decoder 300 may use the motion vector of the indicated video block and the motion vector difference to determine the motion vector of the current video block.

[0354] As discussed above, the video encoder 200 may predictively signal motion vectors.Two examples of predictive signaling techniques that may be implemented by the video encoder 200 include Advanced Motion Vector Prediction (AMVP) and Merge mode signaling.

[0355] The intra-frame prediction unit 206 can perform intra-frame prediction on the current video block. When the intra-frame prediction unit 206 performs intra-frame prediction on the current video block, the intra-frame prediction unit 206 can generate prediction data for the current video block based on decoded samples of other video blocks in the same picture. The prediction data for the current video block can include the predicted video block and various syntax elements.

[0356] The residual generation unit 207 can generate residual data for the current video block by subtracting (e.g., indicated by a minus sign) the predicted video block(s) of the current video block from the current video block. The residual data for the current video block may include residual video blocks corresponding to different sample components of the samples in the current video block.

[0357] In other examples, such as in skip mode, there may be no residual data for the current video block, and the residual generation unit 207 may not perform a subtraction operation.

[0358] Transform processing unit 208 may generate one or more transform coefficient video blocks for a current video block by applying one or more transforms to a residual video block associated with the current video block.

[0359] After transform processing unit 208 generates a transform coefficient video block associated with the current video block, quantization unit 209 may quantize the transform coefficient video block associated with the current video block based on one or more quantization parameter (QP) values associated with the current video block.

[0360] The inverse quantization unit 210 and the inverse transform unit 211 may apply inverse quantization and inverse transform, respectively, to the transform coefficient video block to reconstruct a residual video block from the transform coefficient video block. The reconstruction unit 212 may add the reconstructed residual video block to corresponding samples of one or more predicted video blocks generated by the prediction unit 202 to generate a reconstructed video block associated with the current block for storage in the buffer 213.

[0361] After the reconstruction unit 212 reconstructs the video block, a loop filtering operation may be performed to reduce video blocking artifacts in the video block.

[0362] The entropy coding unit 214 may receive data from other functional components of the video encoder 200. When the entropy coding unit 214 receives the data, the entropy coding unit 214 may perform one or more entropy coding operations to generate entropy-coded data and output a bitstream including the entropy-coded data.

[0363] Figure 6 is a block diagram illustrating an example of a video decoder 300, which may be Figure 4 The video decoder 114 in the system 100 is shown.

[0364] Video decoder 300 may be configured to perform any or all of the techniques of this disclosure. Figure 6 In the example of FIG, video decoder 300 includes multiple functional components. The techniques described in this disclosure can be shared among the various components of video decoder 300. In some examples, a processor can be configured to perform any or all of the techniques described in this disclosure.

[0365] exist Figure 6 In the example of FIG. 3 , the video decoder 300 includes an entropy decoding unit 301, a motion compensation unit 302, an intra-frame prediction unit 303, an inverse quantization unit 304, an inverse transform unit 305, a reconstruction unit 306, and a buffer 307. In some examples, the video decoder 300 can perform the same operations as those generally performed for the video encoder 200 ( Figure 5 ) is the reverse of the encoding process described in .

[0366] The entropy decoding unit 301 can retrieve a coded bitstream. The coded bitstream can include entropy-encoded video data (e.g., coded blocks of video data). The entropy decoding unit 301 can decode the entropy-encoded video data, and from the entropy-decoded video data, the motion compensation unit 302 can determine motion information including motion vectors, motion vector precision, reference picture list index, and other motion information. The motion compensation unit 302 can determine such information, for example, by implementing AMVP and Merge modes.

[0367] The motion compensation unit 302 may generate a motion compensated block and may perform interpolation based on an interpolation filter. An identifier of the interpolation filter to be used with sub-pixel precision may be included in a syntax element.

[0368] Motion compensation unit 302 may calculate interpolated values for sub-integer pixels of a reference block using interpolation filters such as those used by video encoder 200 during encoding of the video block. Motion compensation unit 302 may determine the interpolation filters used by video encoder 200 based on received syntax information and use the interpolation filters to generate a prediction block.

[0369] The motion compensation unit 302 may use some syntax information to determine the size of blocks used to encode frame(s) and / or slice(s) of the coded video sequence, partitioning information describing how each macroblock of a picture of the coded video sequence is partitioned, a mode indicating how each partition is encoded, one or more reference frames (and reference frame lists) for each inter-coded block, and other information used to decode the coded video sequence.

[0370] The intra prediction unit 303 can form a prediction block from spatially adjacent blocks using, for example, an intra prediction mode received in the bitstream. The inverse quantization unit 303 inversely quantizes, i.e., dequantizes, the quantized video block coefficients provided in the bitstream and decoded by the entropy decoding unit 301. The inverse transform unit 303 applies an inverse transform.

[0371] The reconstruction unit 306 can add the residual block to the corresponding prediction block generated by the motion compensation unit 202 or the intra prediction unit 303 to form a decoded block. If necessary, a deblocking filter can also be applied to filter the decoded block to remove blocking artifacts. The decoded video block is then stored in the buffer 307 to provide reference blocks for subsequent motion compensation / intra prediction and also to generate decoded video for presentation on a display device.

[0372] A list of some preferred examples of embodiments is provided below.

[0373] The first set of items illustrates example embodiments of the techniques discussed in the previous section.The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 1).

[0374] 1. A video processing method (e.g., Figure 3 ), comprising: performing a conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video (3002); wherein the codec representation is organized according to a rule that specifies that a first video picture that is an intra random access point picture of the second picture and the second picture are constrained to belong to the same video layer.

[0375] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 2).

[0376] 2. A video processing method, comprising: performing conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule that specifies that subsequent pictures of a first type that are intra random access points in the codec representation are also permitted to be associated with a second type of picture comprising a gradual decoding refresh picture.

[0377] 3. A method according to clause 2, wherein the format rule further specifies that, for each layer, except for the first picture of the layer in the bitstream, each picture of the layer is specified to be associated with the previous intra random access point or gradual decoder refresh picture of the same layer that is closer in decoding order.

[0378] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 3).

[0379] 4. A video processing method, comprising: performing conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule, the format rule specifying constraints on an output order of pictures preceding an intra-frame random access point in decoding order such that the output order applies only to pictures in the same video layer.

[0380] 5. A method as described in clause 1, wherein the constraint specifies that any picture with nuh_layer_id equal to a particular value layerId that precedes the intra random access point picture with nuh_layer_id equal to layerId in decoding order is required to precede the intra random access point picture and all associated random access decodable preceding pictures in output order.

[0381] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 4).

[0382] 6. A video processing method comprising: performing conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the codec representation conforms to a format rule that specifies the following constraints: (1) a post-picture must follow an associated intra random access point picture (IRAP) or gradual decoder refresh (GDR) picture in output order, or (2) a picture having the same layer id as a GDR picture must precede the GDR picture and all associated pictures of the GDR picture in output order.

[0383] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 5).

[0384] 7. A video processing method, comprising: performing conversion between a video having one or more video layers including one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule that an order constraint applies to pictures, intra random access point (IRAP) pictures, and non-previous pictures if and only if the pictures, IRAP pictures, and non-previous pictures are in the same layer, wherein the rule is one of the following:

[0385] (a) a first rule that specifies the value and decoding order of a sequence of fields, or

[0386] (b) The order of leading and / or non-leading pictures of a layer.

[0387] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 6).

[0388] 8. A video processing method comprising: performing a conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule specifying an order of leading pictures, random access decodable leading (RADL) pictures, and random access skipped leading (RASL) pictures associated with gradual decoding refresh (GDR) pictures.

[0389] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 7).

[0390] 9. A video processing method comprising: performing a conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule specifying that constraints on reference picture lists for fully random access pictures are limited to layers.

[0391] 10. A method according to clause 9, wherein the constraint specifies that, for layers with fully random access pictures, the preceding intra random access point picture in decoding or output order is not referenced by an entry in the reference picture list.

[0392] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, item 8).

[0393] 11. A video processing method comprising: performing a conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the conversion complies with rules specifying conditions under which a current picture is allowed to reference an entry in a reference picture list generated by a decoding process for generating an unavailable reference picture.

[0394] 12. A method according to clause 11, wherein the condition is that the current picture is a random access skipped preceding RASL picture associated with a fully random access CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a gradual decoder refresh GDR picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1.

[0395] The following items illustrate example embodiments of the techniques discussed in the previous section (eg, items 9, 10, 11).

[0396] 13. A video processing method comprising: performing a conversion between a video having one or more video layers comprising one or more video pictures and a codec representation of the video, wherein the conversion complies with a rule regarding an order between a current picture and a reference picture list corresponding to the current picture.

[0397] 14. A method according to clause 13, wherein the rule specifies that when the current picture with nuh_layer_id equal to a particular value layerId is not a completely random access (CRA) picture with NoOutputBeforeRecoveryFlag equal to 1, a picture that precedes in decoding order the previous picture associated with the same CRA picture with NoOutputBeforeRecoveryFlag equal to 1, the previous picture associated with a CRA picture with NoOutputBeforeRecoveryFlag equal to 1, a gradual decoder refresh (GDR) picture with NoOutputBeforeRecoveryFlag equal to 1, or a recovery picture of a GDR picture with NoOutputBeforeRecoveryFlag equal to 1 and nuh_layer_id equal to layerId, there shall be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that were generated by a decoding process used to generate unusable reference pictures.

[0398] 15. A method according to clause 13, wherein the rule specifies that when the current picture is associated with an intra random access point (IRAP) picture and follows the IRAP picture in output order, there should be no pictures referenced by active entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0399] 16. A method according to clause 13, wherein the rule specifies that when the current picture is associated with an intra random access point (IRAP) picture, follows the IRAP picture in output order, and follows the preceding picture (if any) associated with the same IRAP picture in both decoding order and output order, there should be no pictures referenced by entries in RefPicList[0] or RefPicList[1] that precede the associated IRAP picture in output order or decoding order.

[0400] 17. A method according to any of clauses 1 to 16, wherein the converting comprises encoding the video into a codec representation.

[0401] 18. A method according to any of clauses 1 to 16, wherein the converting comprises decoding the codec representation to generate pixel values of the video.

[0402] 19. A video decoding apparatus comprising a processor configured to implement the method according to one or more of clauses 1 to 18.

[0403] 20. A video encoding apparatus comprising a processor configured to implement the method according to one or more of clauses 1 to 18.

[0404] 21. A computer program product having stored thereon computer code which, when executed by a processor, causes the processor to carry out the method according to any one of clauses 1 to 18.

[0405] 22. A method, apparatus or system as described in this document.

[0406] The second set of items illustrates example embodiments of the techniques discussed in the previous section (eg, items 1-7).

[0407] 1. A method for video processing (e.g., Figure 7A The method 710 shown includes performing conversion 712 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, and wherein the format rule specifies that a first video picture that is an associated intra random access point picture of the second picture and the second picture are constrained to belong to the same video layer.

[0408] 2. The method of clause 1 , wherein there are no progressive decoding refresh pictures in the same video layer between the first video picture and the second picture in decoding order.

[0409] 3. The method of clause 1, wherein the first video picture and the second video picture have the same identifier of a layer to which a video codec layer network abstraction layer unit belongs or the same identifier of a layer to which a non-video codec layer network abstraction layer unit is applicable.

[0410] 4. A method according to any of clauses 1-3, wherein there is no progressive decoding refresh picture with the same identifier between the first video picture and the second picture in decoding order.

[0411] 5. The method of clause 1, wherein the format rule further specifies that the subsequent picture follows the associated intra random access point picture or progressive decoding refresh picture in output order.

[0412] 6. A method of video processing (e.g., Figure 7B The method 720 shown includes performing conversion 722 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, and wherein the format rule specifies that a subsequent picture in the bitstream is permitted to be associated with a progressive decoding refresh picture.

[0413] 7. The method of clause 6, wherein the post-picture is a picture where each video codec layer network abstraction layer unit has a post-network abstraction layer unit type.

[0414] 8. A method according to clause 6 or 7, wherein a post-picture is permitted to be associated with an intra random access point picture.

[0415] 9. A method according to any of clauses 6-8, wherein a subsequent picture associated with an intra random access point picture or a gradual decoding refresh picture follows the intra random access point picture or the gradual decoding refresh picture in decoding order.

[0416] 10. A method according to any of clauses 6-8, wherein pictures that follow the associated intra random access point picture in output order and precede the associated intra random access point picture in decoding order are not allowed.

[0417] 11. A method according to clause 6, wherein the format rule further specifies that, for each layer, except for the first picture of the layer in the bitstream, each picture of the layer is specified to be associated with the previous intra random access point or gradual decoder refresh picture of the same layer that is closer in decoding order.

[0418] 12. A method according to clause 6 or 11, wherein the subsequent picture is required to follow the associated intra random access point or gradual decoder refresh picture in output order.

[0419] 13. A method of video processing (e.g., Figure 7C The method 730 shown includes performing conversion 732 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, and wherein the format rule specifies that a constraint on the output order of pictures preceding an intra random access point in decoding order applies to pictures in the same video layer.

[0420] 14. A method according to clause 13, wherein the constraint specifies that any picture having a NAL (Network Abstraction Layer) unit header layer identifier equal to a particular value and preceding an intra random access point picture having the NAL unit header layer identifier equal to the particular value in decoding order is required to precede the intra random access point picture and all associated random access decodable preceding pictures in output order.

[0421] 15. The method of clause 14, wherein the NAL (Network Abstraction Layer) unit header layer identifier is nuh_layer_id.

[0422] 16. The method of clause 14, wherein the NAL (Network Abstraction Layer) unit header layer identifier specifies an identifier of a layer to which the video codec layer Network Abstraction Layer unit belongs or an identifier of a layer to which the non-video codec layer Network Abstraction Layer unit applies.

[0423] 17. A method of video processing (e.g., Figure 7D The method 740 shown includes performing conversion 742 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a format rule, and wherein the format rule specifies the following constraints: (1) a post-picture follows an associated intra random access point picture or a gradual decoder refresh picture in output order, or (2) a picture having the same NAL (Network Abstraction Layer) unit header layer identifier as a gradual decoder refresh picture precedes the gradual decoder refresh picture and all associated pictures of the gradual decoder refresh picture in output order.

[0424] 18. A method of video processing (e.g., Figure 7E 750), comprising performing conversion 752 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, and wherein the rule specifies that a constraint on the decoding order of pictures and non-previous pictures applies if and only if a picture associated with an intra random access point picture, the intra random access point picture, and the non-previous picture are in the same layer.

[0425] 19. A method according to clause 18, wherein the constraint specifies that if a picture with a field sequence flag value equal to 0 and a NAL (Network Abstraction Layer) unit header layer identifier equal to a specific value is a preceding picture associated with an intra random access point picture, the picture precedes all non-preceding pictures associated with the intra random access point picture in decoding order.

[0426] 20. The method of clause 19, wherein a value of the field sequence flag equal to 0 indicates that the codec layer video sequence conveys pictures representing frames.

[0427] 21. A method according to clause 18, wherein the constraint specifies that if the value of the field sequence flag is equal to 0 and the picture is a preceding picture associated with an intra random access point picture, the picture precedes all non-preceding pictures associated with the intra random access point picture in decoding order.

[0428] 22. A method of video processing (e.g., Figure 7F The method 760 shown includes performing conversion 762 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, and wherein the rule specifies an order of leading pictures associated with a progressive decoding refresh picture, a random access decodable leading picture, and a random access skipped leading picture.

[0429] 23. A method according to clause 22, wherein a preceding picture associated with the gradually decoding refresh picture follows the gradually decoding refresh picture in decoding order and precedes the gradually decoding refresh picture in output order.

[0430] 24. A method according to clause 22, wherein the random access decodable previous picture associated with the gradually decoded refresh picture is a previous picture associated with the gradually decoded refresh picture and has a NAL (Network Abstraction Layer) unit type corresponding to a codec slice of the random access decodable previous picture.

[0431] 25. A method according to clause 22, wherein the random access decodable previous picture associated with the gradually decoded refresh picture is a previous picture associated with the gradually decoded refresh picture and has a NAL (Network Abstraction Layer) unit type corresponding to a codec slice of the random access decodable previous picture.

[0432] 26. A method of video processing (e.g., Figure 7G The method 770 shown includes performing conversion 772 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, wherein the rule specifies that a constraint on a reference picture list for a slice of a fully random access picture is limited to the layer.

[0433] 27. A method according to clause 26, wherein the constraint specifies that, for layers with fully random access pictures, the preceding intra random access point picture in decoding or output order is not referenced by an entry in the reference picture list.

[0434] 28. A method according to any of clauses 1 to 27, wherein the converting comprises encoding the video into a bitstream.

[0435] 29. A method according to any of clauses 1 to 27, wherein the converting comprises decoding the video from a bitstream.

[0436] 30. The method of clauses 1 to 27, wherein the converting comprises generating a bitstream from the video, and the method further comprises storing the bitstream in a non-transitory computer-readable recording medium.

[0437] 31. A video processing apparatus comprising a processor configured to implement the method according to any one or more of clauses 1 to 30.

[0438] 32. A method of storing a bitstream of video, comprising the method of any one of clauses 1 to 30, and further comprising storing the bitstream to a non-transitory computer-readable recording medium.

[0439] 33. A computer readable medium storing program code which, when executed, causes a processor to carry out the method according to any one or more of clauses 1 to 30.

[0440] 34. A computer-readable medium storing a bitstream generated according to any one of the above methods.

[0441] 35. A video processing apparatus for storing a bitstream representation, wherein the video processing apparatus is configured to implement the method according to any one or more of clauses 1 to 30.

[0442] The third set of items illustrates example embodiments of the techniques discussed in the previous section (eg, items 8 and 9).

[0443] 1. A video processing method (e.g., Figure 8A 810 ), comprising: performing conversion between a video having one or more video layers including one or more video pictures and a bitstream of a video according to a rule, and wherein the rule specifies a condition that no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an active entry in a reference picture list of a current slice of a current picture.

[0444] 2. A method according to clause 1, wherein the active entry corresponds to an entry that can be used as a reference index in inter-frame prediction of the current picture.

[0445] 3. A method according to clause 1, wherein the condition is that the current picture whose NAL (Network Abstraction Layer) unit header layer identifier is equal to a specific value is not a random access skipped pre-picture associated with a fully random access picture whose variable indicating no output before recovery is equal to 1, a gradual decoder refresh picture whose variable is equal to 1, or a recovery picture of a gradual decoder refresh picture whose variable is equal to 1 and the NAL unit header layer identifier is equal to a specific value.

[0446] 4. A video processing method (e.g., Figure 8B The method 820 shown includes performing conversion 822 between a video having one or more video layers including one or more video pictures and a bitstream of the video according to a rule, and wherein the rule specifies a condition that no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

[0447] 5. A method according to clause 4, wherein the condition is that the current picture whose NAL (Network Abstraction Layer) unit header layer identifier is equal to a specific value is not a fully random access picture whose variable indicating no output before recovery is equal to 1, a picture preceding the preceding picture associated with the fully random access picture whose variable is equal to 1 in decoding order, a gradual decoder refresh picture whose variable is equal to 1, or a recovery picture of a gradual decoder refresh picture whose variable is equal to 1 and the NAL unit header layer identifier is equal to a specific value.

[0448] 6. A method according to any of clauses 1 to 5, wherein the converting comprises encoding the video into a bitstream.

[0449] 7. A method according to any of clauses 1 to 5, wherein the converting comprises decoding the video from a bitstream.

[0450] 8. The method of any one of clauses 1 to 5, wherein the converting comprises generating a bitstream from the video, and the method further comprises storing the bitstream in a non-transitory computer-readable recording medium.

[0451] 9. A video processing apparatus comprising a processor configured to implement the method according to any one or more of clauses 1 to 8.

[0452] 10. A method of storing a bitstream of video, comprising the method according to any one of clauses 1 to 8, and further comprising storing the bitstream to a non-transitory computer-readable recording medium.

[0453] 11. A computer-readable medium storing program code which, when executed, causes a processor to carry out the method according to any one or more of clauses 1 to 8.

[0454] 12. A computer-readable medium storing a bitstream generated according to any one of the above methods.

[0455] 13. A video processing device for storing a bitstream representation, wherein the video processing device is configured to implement the method according to any one or more of clauses 1 to 12.

[0456] The fourth set of items illustrates example embodiments of the techniques discussed in the previous section (eg, items 10 and 11).

[0457] 1. A method for video processing (e.g., Figure 9A 9. The method 910 of claim 1 , comprising performing conversion 912 between a video having one or more video layers including a current picture comprising a current slice and a bitstream of video according to a rule, and wherein the rule specifies a condition that a reference picture list of the current slice is not allowed to have an active entry referencing a picture that precedes an intra random access point picture associated with the current picture in decoding order or output order.

[0458] 2. A method according to clause 1, wherein the active entry corresponds to an entry that can be used as a reference index in inter-frame prediction of the current picture.

[0459] 3. A method according to clause 1 or 2, wherein the rule specifies a condition that the reference picture list of the current picture is not allowed to have an active entry that refers to a picture that precedes the intra random access point picture associated with the current picture in decoding order.

[0460] 4. A method according to any of clauses 1 to 3, wherein the rule specifies a condition that the reference picture list of the current picture is not allowed to have an active entry that refers to a picture that precedes the intra random access point picture associated with the current picture in output order.

[0461] 5. A method according to any of clauses 1 to 4, wherein the condition is that the current picture is associated with an intra random access point picture and follows the intra random access point picture in decoding order and / or output order.

[0462] 6. A method according to any one of clauses 1 to 4, wherein the condition is that the current picture follows, in decoding order and / or output order, an intra random access point picture having the same value of an identifier of a layer to which a video codec layer network abstraction layer unit belongs or an identifier of a layer to which a non-video codec layer network abstraction layer unit is applicable.

[0463] 7. A method of video processing (e.g., Figure 9B The method 920 shown includes performing conversion 922 between a video having one or more video layers including a current picture including a current slice and a bitstream of video according to a rule, and wherein the rule specifies a condition that a reference picture list of the current slice is not allowed to have an entry that references a picture that precedes an intra random access point picture associated with the current picture in decoding order or output order.

[0464] 8. A method according to clause 7, wherein the rule specifies a condition that the reference picture list of the current picture is not allowed to have an entry that refers to a picture that precedes the intra random access point picture associated with the current picture in decoding order.

[0465] 9. A method according to clause 7 or 8, wherein the rule specifies a condition that the reference picture list of the current picture is not allowed to have an entry that refers to a picture that precedes the intra random access point picture associated with the current picture in output order.

[0466] 10. A method according to any of clauses 7 to 9, wherein an intra random access point picture is associated with zero or more preceding pictures, and wherein the condition is that the current picture is associated with the intra random access point picture, follows the intra random access point picture in decoding order and / or output order, and follows the zero or more preceding pictures associated with the intra random access point picture in both decoding order and output order.

[0467] 11. A method according to any of clauses 7 to 9, wherein an intra random access point picture is associated with zero or more preceding pictures, and wherein the condition is that the current picture follows the intra random access point picture having the same value of the identifier of the layer to which the video codec layer network abstraction layer unit belongs or the identifier of the layer to which the non-video codec layer network abstraction layer unit is applicable and the zero or more preceding pictures in decoding order and / or output order.

[0468] 12. A method according to any of clauses 1 to 11, wherein the converting comprises encoding the video into a bitstream.

[0469] 13. A method according to any of clauses 1 to 11, wherein the converting comprises decoding the video from a bitstream.

[0470] 14. The method of any one of clauses 1 to 11, wherein the converting comprises generating a bitstream from the video, and the method further comprises storing the bitstream in a non-transitory computer-readable recording medium.

[0471] 15. A video processing apparatus comprising a processor configured to implement the method according to any one or more of clauses 1 to 14.

[0472] 16. A method of storing a bitstream of video, comprising the method according to any one of clauses 1 to 14, and further comprising storing the bitstream to a non-transitory computer-readable recording medium.

[0473] 17. A computer-readable medium storing program code which, when executed, causes a processor to carry out the method according to any one or more of clauses 1 to 14.

[0474] 18. A computer-readable medium storing a bitstream generated according to any one of the above methods.

[0475] 19. A video processing device for storing a bitstream representation, wherein the video processing device is configured to implement the method according to any one or more of clauses 1 to 14.

[0476] In this document, the term "video processing" may refer to video encoding, video decoding, video compression, or video decompression. For example, during conversion from a pixel representation of a video to a corresponding bitstream representation, or vice versa, a video compression algorithm may be applied. The bitstream representation of the current video block may, for example, correspond to bits that are co-located or scattered in different places within the bitstream, as defined by the syntax. For example, a macroblock may be encoded according to error residual values from a transform and a codec and also using bits from a header and other fields in the bitstream. Furthermore, during conversion, a decoder may, based on this determination, parse the bitstream knowing that some fields may or may not be present, as described in the above solution. Similarly, an encoder may determine whether to include or not include particular syntax fields and generate the codec representation accordingly by including the syntax fields or excluding the syntax fields from the codec representation.

[0477] The disclosed and other solutions, examples, embodiments, modules, and functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware (including the structures disclosed in this document and their structural equivalents), or in a combination of one or more thereof. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer-readable medium for execution by a data processing apparatus or for controlling the operation of the data processing apparatus. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a combination of substances that affect a machine-readable propagated signal, or a combination of one or more thereof. The term "data processing apparatus" encompasses all apparatuses, devices, and machines for processing data, including, for example, a programmable processor, a computer, or multiple processors or computers. In addition to hardware, an apparatus may also include code that creates an execution environment for the computer program in question, for example, code constituting processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more thereof. A propagated signal is an artificially generated signal, such as a machine-generated electrical signal, an optical signal, or an electromagnetic signal, that is generated to encode information for transmission to a suitable receiver device.

[0478] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language (including compiled or interpreted languages), and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, subroutines, or code portions). A computer program can be deployed to execute on one computer or on multiple computers located at one site or distributed across multiple sites and interconnected by a communication network.

[0479] The processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0480] Processors suitable for executing computer programs include, for example, general-purpose and special-purpose microprocessors, and any one or more processors of any type of digital computer. Typically, a processor will receive instructions and data from read-only memory or random access memory, or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Typically, a computer will also include one or more mass storage devices (e.g., magnetic, magneto-optical, or optical disks) for storing data, or be operatively coupled to receive data from or transfer data to or from such one or more mass storage devices. However, a computer does not require such devices. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and storage devices, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and memory may be supplemented by or incorporated into dedicated logic circuitry.

[0481] Although this patent document contains many details, these details should not be interpreted as limitations on any subject matter or the scope of what may be claimed, but rather as descriptions of features specified for particular embodiments of particular technologies. Certain features described in this patent document in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately in multiple embodiments or in any suitable subcombination. Furthermore, although features may be described above as working in certain combinations and even initially claimed as such, one or more features from the claimed combination may be excluded from the combination in some cases, and the claimed combination may be directed to subcombinations or variations of subcombinations.

[0482] Similarly, while operations are depicted in a particular order in the drawings, this should not be understood as requiring that such operations be performed in the particular order shown, or in sequential order, or that all illustrated operations be performed, in order to achieve desired results. Furthermore, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[0483] Only a few implementations and examples are described, and other implementations, enhancements, and variations can be made based on what is described and illustrated in this patent document.

Claims

1. A video processing method, comprising: performing conversion between a video having one or more video layers comprising one or more video pictures and a bitstream of said video according to rules, The rule specifies a condition, the condition comprising: when a current picture having a network abstraction layer (NAL) unit header layer identifier equal to a specific value is not a random access skipped pre-picture associated with a pure random access picture having a variable indicating no output before recovery equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

2. The method according to claim 1, wherein The entry is the active entry in the reference picture list.

3. The method according to claim 2, wherein: The active entry refers to a reference picture that can be used for inter-frame prediction of the current picture.

4. The method according to claim 2, wherein: The condition also includes: when the current picture having the NAL unit header layer identifier equal to a specific value is not a progressive decoding refresh picture having a variable indicating no output before recovery equal to 1, or a recovery picture of the progressive decoding refresh picture having the variable equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

5. The method according to claim 1, wherein The condition also includes: when the current picture with the NAL unit header layer identifier equal to a specific value is not a pure random access picture with a first variable indicating no output before recovery equal to 1, a picture preceding the preceding picture associated with the pure random access picture with the first variable equal to 1 in decoding order, a first progressive decoding refresh picture with a second variable indicating no output before recovery equal to 1, or a recovery picture of a second progressive decoding refresh picture with a third variable indicating no output before recovery equal to 1 and the NAL unit header layer identifier equal to the specific value, no picture that has been generated by the decoding process for generating an unusable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

6. The method according to claim 1, wherein The converting includes encoding the video into the bitstream.

7. The method according to claim 1, wherein The converting includes decoding the video from the bitstream.

8. An apparatus for processing video data, comprising a processor and non-transitory memory having instructions thereon, wherein the instructions, when executed by the processor, cause the processor to: performing conversion between a video having one or more video layers comprising one or more video pictures and a bitstream of said video according to rules, in, The rule specifies a condition, the condition including: when a current picture having a network abstraction layer (NAL) unit header layer identifier equal to a specific value is not a random access skipped pre-picture associated with a pure random access picture having a variable indicating no output before recovery equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

9. The device according to claim 8, wherein The entry is the active entry in the reference picture list.

10. The device according to claim 9, wherein The active entry refers to a reference picture that can be used for inter-frame prediction of the current picture.

11. The device according to claim 9, wherein The condition also includes: when the current picture having the NAL unit header layer identifier equal to a specific value is not a progressive decoding refresh picture having the variable equal to 1, or a recovery picture of the progressive decoding refresh picture having the variable equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

12. The device according to claim 8, wherein The condition also includes: when the current picture with the NAL unit header layer identifier equal to a specific value is not a pure random access picture with a first variable indicating no output before recovery equal to 1, a picture preceding the preceding picture associated with the pure random access picture with the first variable equal to 1 in decoding order, a first progressive decoding refresh picture with a second variable indicating no output before recovery equal to 1, or a recovery picture of a second progressive decoding refresh picture with a third variable indicating no output before recovery equal to 1 and the NAL unit header layer identifier equal to the specific value, no picture that has been generated by the decoding process for generating an unusable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

13. A non-transitory computer-readable storage medium storing instructions that cause a processor to: performing conversion between a video having one or more video layers comprising one or more video pictures and a bitstream of said video according to rules, in, The rule specifies a condition, the condition including: when a current picture having a network abstraction layer (NAL) unit header layer identifier equal to a specific value is not a random access skipped pre-picture associated with a pure random access picture having a variable indicating no output before recovery equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

14. The non-transitory computer-readable storage medium of claim 13, wherein: The entry is the active entry in the reference picture list.

15. The non-transitory computer-readable storage medium of claim 14, wherein: The active entry refers to a reference picture that can be used for inter-frame prediction of the current picture.

16. The non-transitory computer-readable storage medium of claim 14, wherein: The condition also includes: when the current picture having the NAL unit header layer identifier equal to a specific value is not a progressive decoding refresh picture having the variable equal to 1, or a recovery picture of the progressive decoding refresh picture having the variable equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

17. The non-transitory computer-readable storage medium of claim 13, wherein: The condition also includes: when the current picture with the NAL unit header layer identifier equal to a specific value is not a pure random access picture with a first variable indicating no output before recovery equal to 1, a picture preceding the preceding picture associated with the pure random access picture with the first variable equal to 1 in decoding order, a progressive decoding refresh picture with a second variable indicating no output before recovery equal to 1, or a recovery picture of a second progressive decoding refresh picture with a third variable indicating no output before recovery equal to 1 and the NAL unit header layer identifier equal to the specific value, no picture that has been generated by the decoding process for generating an unusable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

18. A non-transitory computer-readable recording medium storing a bit stream of a video generated by a method performed by a video processing apparatus, wherein the method comprises: generating the bitstream of the video having one or more video layers including one or more video pictures according to a rule, The rule specifies a condition, the condition comprising: when a current picture having a network abstraction layer (NAL) unit header layer identifier equal to a specific value is not a random access skipped pre-picture associated with a pure random access picture having a variable indicating no output before recovery equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

19. The non-transitory computer-readable recording medium according to claim 18, wherein The entry is the active entry in the reference picture list; And wherein the condition further includes: when the current picture whose NAL unit header layer identifier is equal to a specific value is not a progressive decoding refresh picture with the variable equal to 1, or a recovery picture of the progressive decoding refresh picture with the variable equal to 1, no picture that has been generated by the decoding process for generating an unavailable reference picture is referenced by an entry in the reference picture list of the current slice of the current picture.

20. A method for storing a bitstream of a video, comprising: generating, according to a rule, the bitstream of the video having one or more video layers comprising one or more video pictures; as well as storing the bitstream in a non-transitory computer-readable recording medium, The rule specifies a condition, the condition comprising: when a current picture having a network abstraction layer (NAL) unit header layer identifier equal to a specific value is not a random access skipped pre-picture associated with a pure random access picture having a variable indicating no output before recovery equal to 1, no picture that has been generated by a decoding process for generating an unusable reference picture is referenced by an entry in a reference picture list of a current slice of the current picture.

Images