Avoiding errors in sub-bitstream extraction

Abstract

To provide a video coding mechanism for avoiding errors in sub-bitstream extraction.SOLUTION: A decryption method includes receiving a bitstream including a sequence parameter set (SPS) including an SPS video parameter set identifier, in which the bitstream also includes coded pictures in a set of video coding layer (VCL) network abstraction layer (NAL) units associated with the layer having the NAL unit header layer identifier (nuh_layer_id), the general layer index corresponding to nuh_layer_id is set equal to 0 when the SPS video parameter set identifier is equal to 0, and the coded picture is decoded from the VCL NAL unit on the basis of the common layer index to generate a decoded picture.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 911,808, entitled "Scalability in Video Coding," filed on October 7, 2019 by Ye-Kui Wang, which is incorporated herein by reference.

[0002] FIELD This disclosure relates generally to video coding, and more particularly to mechanisms for preventing errors when sub-bitstream extraction is performed on a multi-layer bitstream. [Background technology]

[0003] The amount of video data required to render even a relatively short video can be substantially large, resulting in complications when the data is streamed or otherwise transmitted over a communication network that has limited bandwidth capacity. Thus, in today's telecommunications networks, video data is typically compressed before being transmitted. The size of the video can also be an issue when the video is stored on a storage device, which may also have limited memory resources. Video compression devices often use software and / or hardware at the source to code the video data before transmission or storage, thereby reducing the amount of data required to represent a digital video image. The compressed data is then received at the destination by a video decompression device, which decodes the video data. Due to limited network resources and ever-increasing demands for video quality, improvements in compression and decompression techniques that improve compression ratios with little or no sacrifice in image quality are desirable. Summary of the Invention [Means for solving the problem]

[0004] In one embodiment, the disclosure includes a method implemented by a decoder, the method including receiving, by the decoder, a bitstream including a sequence parameter set (SPS) and a coded picture, where the SPS includes an SPS video parameter set identifier (sps_video_parameter_set_id) and the coded picture is in a set of video coding layer (VCL) network abstraction layer (NAL) units associated with a layer having a NAL unit header layer identifier (nuh_layer_id); setting, by the decoder, a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to the nuh_layer_id to be equal to 0 when sps_video_parameter_set_id is equal to 0; and decoding, by the decoder, the coded picture from the VCL NAL unit based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture.

[0005] Some video coding systems code a video sequence into layers of pictures. Pictures in different layers have different characteristics. Therefore, the encoder can transmit different layers to the decoder depending on the constraints on the decoder side. To perform this function, the encoder can encode all layers into a single bitstream. When requested, the encoder can perform a sub-bitstream extraction process to remove irrelevant information from the bitstream. The result is an extracted bitstream that contains only the data in the layers required by the decoder. The description of how the layers are related can be included in a video parameter set (VPS). A simulcast layer is a layer that is configured to be displayed without reference to other layers. When the simulcast layer is transmitted to the decoder, the sub-bitstream extraction process may remove the VPS because the layer relationships are not necessary to decode the simulcast layer. Unfortunately, some variables in other parameter sets may reference the VPS. Therefore, removing the VPS when the simulcast layer is transmitted may increase coding efficiency, but may also result in errors. This example includes a mechanism for encoding the SPS in a manner that avoids errors when the VPS is removed from the encoded bitstream as part of the sub-bitstream extraction process. The SPS includes sps_video_parameter_set_id, which indicates an identifier for the VPS that includes the layer relationship to the video sequence. In one example, sps_video_parameter_set_id is set to 0 when the VPS is removed prior to transmission of a bitstream that includes only the simulcast layer. In another example, the SPS used by the simulcast layer may include sps_video_parameter_set_id, which is set to 0 when encoded.In either case, when sps_video_parameter_set_id is set to 0, SPS-related variables that reference the VPS are set to default values ​​to avoid errors. For example, GeneralLayerIdx[nuh_layer_id] indicates the current layer index for the corresponding layer (e.g., simulcast layer). GeneralLayerIdx[nuh_layer_id] is set to / inferred to be 0 when sps_video_parameter_set_id is 0. As another example, the VPS independent layer flag (vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) for GeneralLayerIdx[nuh_layer_id] is stored in the VPS and specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. Inter-layer prediction is not used for simulcast layers. Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate no inter-layer prediction when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS is removed from the bitstream prior to transmission of the simulcast layer. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only the simulcast layer, thereby reducing the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0006] Optionally, in any of the aforementioned aspects, another implementation of the aspect provides that GeneralLayerIdx[nuh_layer_id] is equal to the current layer index.

[0007] Optionally, in any of the aforementioned aspects, another implementation form of the aspect provides that when sps_video_parameter_set_id is equal to 0, the decoder infers that the value of the VPS independent layer flag (vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) for GeneralLayerIdx[nuh_layer_id] is equal to 1.

[0008] Optionally, in any of the aforementioned aspects, another implementation form of the aspect provides that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the layer having index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction.

[0009] Optionally, in any of the aforementioned aspects, another implementation form of the aspect provides that sps_video_parameter_set_id specifies a value of a VPS parameter set identifier (vps_video_parameter_set_id) when greater than 0.

[0010] Optionally, in any of the above-mentioned aspects, another implementation form of the aspect specifies that when sps_video_parameter_set_id is equal to 0, the SPS does not reference the VPS, and the VPS is not referenced when decoding each coded layer video sequence that references the SPS.

[0011] Optionally, in any of the aforementioned aspects, another implementation of the aspect specifies that a set of VCL NAL units is part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id.

[0012] In one embodiment, this disclosure includes a method implemented by an encoder, the method including: encoding, by the encoder, a coded picture and an SPS into a bitstream, where the coded picture is encoded into a set of VCL NAL units, where the VCL NAL units are associated with a layer having nuh_layer_id, and the SPS includes sps_video_parameter_set_id; performing, by a hypothetical reference decoder operating at the encoder, a set of bitstream conformance tests on the bitstream by setting, by the HRD operating on the encoder, GeneralLayerIdx[nuh_layer_id] equal to 0 when sps_video_parameter_set_id is equal to 0, and decoding, by the HRD operating on the encoder, the coded picture from the VCL NAL units based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture; and storing, at the encoder, the bitstream for communication to a decoder.

[0013] Some video coding systems code a video sequence into layers of pictures. Pictures in different layers have different characteristics. Therefore, the encoder can transmit different layers to the decoder depending on the constraints on the decoder side. To perform this function, the encoder can encode all layers into a single bitstream. When requested, the encoder can perform a sub-bitstream extraction process to remove irrelevant information from the bitstream. The result is an extracted bitstream that contains only the data in the layers required by the decoder. The description of how the layers are related can be included in a video parameter set (VPS). A simulcast layer is a layer that is configured to be displayed without reference to other layers. When the simulcast layer is transmitted to the decoder, the sub-bitstream extraction process may remove the VPS because the layer relationships are not necessary to decode the simulcast layer. Unfortunately, some variables in other parameter sets may reference the VPS. Therefore, removing the VPS when the simulcast layer is transmitted may increase coding efficiency, but may also result in errors. This example includes a mechanism for encoding the SPS in a manner that avoids errors when the VPS is removed from the encoded bitstream as part of the sub-bitstream extraction process. The SPS includes sps_video_parameter_set_id, which indicates an identifier for the VPS that includes the layer relationship to the video sequence. In one example, sps_video_parameter_set_id is set to 0 when the VPS is removed prior to transmission of a bitstream that includes only the simulcast layer. In another example, the SPS used by the simulcast layer may include sps_video_parameter_set_id, which is set to 0 when encoded.In either case, when sps_video_parameter_set_id is set to 0, SPS-related variables that reference the VPS are set to default values ​​to avoid errors. For example, GeneralLayerIdx[nuh_layer_id] indicates the current layer index for the corresponding layer (e.g., simulcast layer). GeneralLayerIdx[nuh_layer_id] is set to / inferred to be 0 when sps_video_parameter_set_id is 0. As another example, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is stored in the VPS and specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. Inter-layer prediction is not used for simulcast layers. Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate no inter-layer prediction when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS is removed from the bitstream prior to transmission of the simulcast layer. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only the simulcast layer, thereby reducing the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0014] Optionally, in any of the aforementioned aspects, another implementation of the aspect provides that GeneralLayerIdx[nuh_layer_id] is equal to the current layer index.

[0015] Optionally, in any of the aforementioned aspects, another implementation form of the aspect provides that the HRD operating on the encoder further includes inferring that the value of vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1 when sps_video_parameter_set_id is equal to 0.

[0016] Optionally, in any of the aforementioned aspects, another implementation form of the aspect provides that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the layer having index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction.

[0017] Optionally, in any of the aforementioned aspects, another implementation of the aspect provides that sps_video_parameter_set_id specifies a value of vps_video_parameter_set_id when greater than 0.

[0018] Optionally, in any of the above-mentioned aspects, another implementation form of the aspect specifies that when sps_video_parameter_set_id is equal to 0, the SPS does not reference the VPS, and the VPS is not referenced when decoding each coded layer video sequence that references the SPS.

[0019] Optionally, in any of the aforementioned aspects, another implementation of the aspect specifies that a set of VCL NAL units is part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id.

[0020] In one embodiment, the present disclosure includes a video coding device comprising a processor, a receiver coupled to the processor, a memory coupled to the processor, and a transmitter coupled to the processor, wherein the processor, receiver, memory, and transmitter are configured to perform the method of any of the aforementioned aspects.

[0021] In one embodiment, the present disclosure includes a non-transitory computer-readable medium including a computer program product for use by a video coding device, the computer program product including computer-executable instructions stored on the non-transitory computer-readable medium that, when executed by a processor, cause the video coding device to perform the method of any of the aforementioned aspects.

[0022] In one embodiment, the disclosure includes a decoder comprising receiving means for receiving a bitstream including an SPS and a coded picture, where the SPS includes sps_video_parameter_set_id and the coded picture is in a set of VCL NAL units associated with a layer having nuh_layer_id; setting means for setting GeneralLayerIdx[nuh_layer_id] equal to 0 when sps_video_parameter_set_id is equal to 0; decoding means for decoding the coded picture from the VCL NAL unit based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture; and forwarding means for forwarding the decoded picture for display as part of a decoded video sequence.

[0023] Some video coding systems code a video sequence into layers of pictures. Pictures in different layers have different characteristics. Therefore, the encoder can transmit different layers to the decoder depending on the constraints on the decoder side. To perform this function, the encoder can encode all layers into a single bitstream. When requested, the encoder can perform a sub-bitstream extraction process to remove irrelevant information from the bitstream. The result is an extracted bitstream that contains only the data in the layers required by the decoder. The description of how the layers are related can be included in a video parameter set (VPS). A simulcast layer is a layer that is configured to be displayed without reference to other layers. When the simulcast layer is transmitted to the decoder, the sub-bitstream extraction process may remove the VPS because the layer relationships are not necessary to decode the simulcast layer. Unfortunately, some variables in other parameter sets may reference the VPS. Therefore, removing the VPS when the simulcast layer is transmitted may increase coding efficiency, but may also result in errors. This example includes a mechanism for encoding the SPS in a manner that avoids errors when the VPS is removed from the encoded bitstream as part of the sub-bitstream extraction process. The SPS includes sps_video_parameter_set_id, which indicates an identifier for the VPS that includes the layer relationship to the video sequence. In one example, sps_video_parameter_set_id is set to 0 when the VPS is removed prior to transmission of a bitstream that includes only the simulcast layer. In another example, the SPS used by the simulcast layer may include sps_video_parameter_set_id, which is set to 0 when encoded.In either case, when sps_video_parameter_set_id is set to 0, SPS-related variables that reference the VPS are set to default values ​​to avoid errors. For example, GeneralLayerIdx[nuh_layer_id] indicates the current layer index for the corresponding layer (e.g., simulcast layer). GeneralLayerIdx[nuh_layer_id] is set to / inferred to be 0 when sps_video_parameter_set_id is 0. As another example, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is stored in the VPS and specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. Inter-layer prediction is not used for simulcast layers. Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate no inter-layer prediction when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS is removed from the bitstream prior to transmission of the simulcast layer. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only the simulcast layer, thereby reducing the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0024] Optionally, in any of the aforementioned aspects, another implementation of the aspect provides that the decoder is further configured to perform the method of any of the aforementioned aspects.

[0025] In one embodiment, the disclosure includes an encoder comprising encoding means for encoding a coded picture and an SPS into a bitstream, where the coded picture is encoded into a set of VCL NAL units, where the VCL NAL units are associated with a layer having nuh_layer_id, and the SPS includes sps_video_parameter_set_id; HRD means for performing a set of bitstream conformance tests on the bitstream by setting GeneralLayerIdx[nuh_layer_id] equal to 0 when sps_video_parameter_set_id is equal to 0 and decoding the coded picture from the VCL NAL units based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture; and storage means for storing the bitstream for communication to a decoder.

[0026] Some video coding systems code a video sequence into layers of pictures. Pictures in different layers have different characteristics. Therefore, the encoder can transmit different layers to the decoder depending on the constraints on the decoder side. To perform this function, the encoder can encode all layers into a single bitstream. When requested, the encoder can perform a sub-bitstream extraction process to remove irrelevant information from the bitstream. The result is an extracted bitstream that contains only the data in the layers required by the decoder. The description of how the layers are related can be included in a video parameter set (VPS). A simulcast layer is a layer that is configured to be displayed without reference to other layers. When the simulcast layer is transmitted to the decoder, the sub-bitstream extraction process may remove the VPS because the layer relationships are not necessary to decode the simulcast layer. Unfortunately, some variables in other parameter sets may reference the VPS. Therefore, removing the VPS when the simulcast layer is transmitted may increase coding efficiency, but may also result in errors. This example includes a mechanism for encoding the SPS in a manner that avoids errors when the VPS is removed from the encoded bitstream as part of the sub-bitstream extraction process. The SPS includes sps_video_parameter_set_id, which indicates an identifier for the VPS that includes the layer relationship to the video sequence. In one example, sps_video_parameter_set_id is set to 0 when the VPS is removed prior to transmission of a bitstream that includes only the simulcast layer. In another example, the SPS used by the simulcast layer may include sps_video_parameter_set_id, which is set to 0 when encoded.In either case, when sps_video_parameter_set_id is set to 0, SPS-related variables that reference the VPS are set to default values ​​to avoid errors. For example, GeneralLayerIdx[nuh_layer_id] indicates the current layer index for the corresponding layer (e.g., simulcast layer). GeneralLayerIdx[nuh_layer_id] is set to / inferred to be 0 when sps_video_parameter_set_id is 0. As another example, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is stored in the VPS and specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. Inter-layer prediction is not used for simulcast layers. Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate no inter-layer prediction when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS is removed from the bitstream prior to transmission of the simulcast layer. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only the simulcast layer, thereby reducing the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0027] Optionally, in any of the aforementioned aspects, another implementation of the aspect provides that the encoder is further configured to perform the method of any of the aforementioned aspects.

[0028] For the sake of clarity, any one of the above-described embodiments may be combined with any one or more of the other above-described embodiments to form new embodiments within the scope of the present disclosure.

[0029] These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

[0030] For a more complete understanding of the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, in which like numerals represent like parts, and in which: [Brief description of the drawings]

[0031] [Figure 1] 1 is a flowchart of an exemplary method for coding a video signal. [Diagram 2] 1 is a schematic diagram of an example coding and decoding (codec) system for video coding. [Diagram 3] 1 is a schematic diagram illustrating an example video encoder. [Figure 4] 1 is a schematic diagram illustrating an exemplary video decoder. [Diagram 5] 1 is a schematic diagram illustrating an exemplary hypothetical reference decoder (HRD). [Figure 6] 1 is a schematic diagram illustrating an example multi-layer video sequence configured for inter-layer prediction. [Figure 7] FIG. 2 is a schematic diagram illustrating an exemplary bitstream. [Figure 8] 1 is a schematic diagram of an example video coding device. [Figure 9] 1 is a flowchart of an example method for encoding a multi-layer video sequence into a bitstream to support video parameter set (VPS) removal during sub-bitstream extraction for a simulcast layer. [Figure 10]1 is a flowchart of an example method for decoding a video sequence from a bitstream that includes a simulcast layer extracted from a multi-layer bitstream where the VPS has been removed during sub-bitstream extraction. [Figure 11] 1 is a schematic diagram of an example system for coding a multi-layer video sequence into a bitstream to support VPS removal during sub-bitstream extraction for a simulcast layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] First, while an exemplary implementation of one or more embodiments is presented below, it should be understood that the disclosed system and / or method may be implemented using any number of currently known or existing technologies. The present disclosure should in no way be limited to the exemplary implementations, drawings, and technologies illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with the full scope of equivalents.

[0033] The following terms are defined as follows unless used in the present specification in a contrary context. Specifically, the following definitions are intended to further clarify the present disclosure. However, terms may be explained differently in different contexts. Therefore, the following definitions should be considered as supplementary and not as limiting any other definitions of the explanations provided for such terms in the present specification.

[0034] A bitstream is a sequence of bits that includes video data that is compressed for transmission between an encoder and a decoder. An encoder is a device configured to compress video data into a bitstream using an encoding process. A decoder is a device configured to reconstruct video data into a bitstream for display using a decoding process. A picture is an array of luma samples and / or an array of chroma samples that make up a frame or a field thereof. A picture being encoded or decoded may be referred to as a current picture for clarity of description. A coded picture is a coded representation of a picture that includes a video coding layer (VCL) network abstraction layer (NAL) unit with a particular value of a NAL unit header layer identifier (nuh_layer_id) in an access unit (AU) and includes all coding tree units (CTUs) of the picture. A decoded picture is a picture that is generated by applying a decoding process to a coded picture. A NAL unit is a syntax structure that includes data in the form of a raw byte sequence payload (RBSP), an indication of the type of data, interspersed with emulation prevention bytes if desired. A VCL NAL unit is a NAL unit that is coded to contain video data, such as a coded slice of a picture. A non-VCL NAL unit is a NAL unit that contains non-video data, such as syntax and / or parameters that support decoding the video data, performing conformance checks, or other operations. A layer is a set of VCL NAL units and associated non-VCL NAL units that share specified characteristics (e.g., a common resolution, frame rate, picture size, etc.) as indicated by a layer Id (identifier). The NAL unit header layer identifier (nuh_layer_id) is a syntax element that specifies the identifier of the layer that contains the NAL unit.

[0035] A hypothetical reference decoder (HRD) is a decoder model that runs on an encoder that checks the variability of the bitstream generated by the encoding process to verify conformance to specified constraints. Bitstream conformance testing is a test to determine whether the encoded bitstream conforms to a standard such as Versatile Video Coding (VVC). A video parameter set (VPS) is a syntax structure that contains parameters related to an entire video. A sequence parameter set (SPS) is a syntax structure that contains syntax elements that apply to zero or more entire coded layer video sequences (CLVS). The SPS video parameter set identifier (sps_video_parameter_set_id) is a syntax element that specifies the identifier (ID) of the VPS reference by the SPS. The general layer index (GeneralLayerIdx[i]) is a derived variable that specifies the index of the corresponding layer i. Hence, the current layer with a layer ID of nuh_layer_id has an index specified by GeneralLayerIdx[nuh_layer_id]. The current layer index is the layer index that corresponds to the layer being encoded or decoded. The VPS independent layer flag (vps_independent_layer_flag[i]) is a syntax element that specifies whether the corresponding layer i uses inter-layer prediction. Hence, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the current layer uses inter-layer prediction. Inter-layer prediction is a mechanism for coding blocks of sample values ​​of the current picture of the current layer based on reference pictures from different layers (e.g., the same access unit). An access unit (AU) is a set of coded pictures in different layers that are all associated with the same output time.The VPS Parameter Set Identifier (vps_video_parameter_set_id) is a syntax element that provides an ID for the VPS for reference by other syntax elements / structures. A coded video sequence is a set of one or more coded pictures. A decoded video sequence is a set of one or more decoded pictures.

[0036] The following acronyms are used in this specification: Access Unit (AU), Coding Tree Block (CTB), Coding Tree Unit (CTU), Coding Unit (CU), Coded Layer Video Sequence (CLVS), Coded Layer Video Sequence Start (CLVSS), Coded Video Sequence (CVS), Coded Video Sequence Start (CVSS), Joint Video Experts Team (JVET), Hypothetical Reference Decoder (HRD), Motion Constrained Tile Set (MCTS), Maximum Transmission Unit (MTU), Network Abstraction Layer (NAL), Output Layer Set (OLS), Operation Point (OP), Picture Order Count (POC), Random Access Point (RAP), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set (SPS), Video Parameter Set (VPS), and Versatile Video Coding (VVC).

[0037] Many video compression techniques may be employed to reduce the size of a video file with minimal loss of data. For example, video compression techniques may include performing spatial (e.g., intra-picture) prediction and / or temporal (e.g., inter-picture) prediction to reduce or remove data redundancy in a video sequence. For block-based video coding, a video slice (e.g., a video picture, or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as tree blocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are coded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded unidirectionally predicted (P) or bidirectionally predicted (B) slice of a picture may be coded by employing spatial prediction with respect to reference samples in neighboring blocks in the same picture, or temporal prediction with respect to reference samples in other reference pictures. A picture may be referred to as a frame and / or an image, and a reference picture may be referred to as a reference frame and / or a reference image. Spatial or temporal prediction results in a predictive block representing an image block. The residual data represents pixel differences between the original image block and the predictive block. Thus, an inter-coded block is encoded according to a motion vector pointing to a block of reference samples forming the predictive block, and the residual data indicating the difference between the coded block and the predictive block. An intra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain. These result in residual transform coefficients, which may be quantized. The quantized transform coefficients may initially be arranged in a two-dimensional array. The quantized transform coefficients may be scanned to generate a one-dimensional vector of transform coefficients.Entropy coding may be applied to achieve even further compression. Such video compression techniques are described in more detail below.

[0038] To ensure that the encoded video can be accurately decoded, the video is encoded and decoded according to a corresponding video coding standard. Video coding standards include International Telecommunication Union (ITU) Standardization Sector (ITU-T) H.261, International Organization for Standardization / International Electrotechnical Commission (ISO / IEC) Motion Picture Experts Group (MPEG)-1 Part 2, Advanced Video Coding (AVC), also known as ITU-T H.262 or ISO / IEC MPEG-2 Part 2, ITU-T H.263, ISO / IEC MPEG-4 Part 2, ITU-T H.264 or ISO / IEC MPEG-4 Part 10, and High Efficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part 2. AVC includes extensions such as Scalable Video Coding (SVC), Multiview Video Coding (MVC), Multiview Video Coding plus Depth (MVC+D), and Three-Dimensional (3D) AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC). The ITU-T and ISO / IEC Joint Video Experts Team (JVET) has begun development of a video coding standard called Versatile Video Coding (VVC). VVC is contained in working drafts (WDs), including JVET-O2001-v14.

[0039] Some video coding systems code a video sequence into layers of pictures. Pictures in different layers have different characteristics. Therefore, the encoder can transmit different layers to the decoder depending on the constraints on the decoder side. To perform this function, the encoder can encode all layers into a single bitstream. When requested, the encoder can perform a sub-bitstream extraction process to remove irrelevant information from the bitstream. The result is an extracted bitstream that contains only the data in the layers required by the decoder. The description of how the layers are related can be included in a video parameter set (VPS). A simulcast layer is a layer that is configured to be displayed without reference to other layers. When the simulcast layer is transmitted to the decoder, the sub-bitstream extraction process may remove the VPS because the layer relationships are not necessary to decode the simulcast layer. Unfortunately, some variables in other parameter sets may reference the VPS. Therefore, removing the VPS when the simulcast layer is transmitted may increase coding efficiency, but may also result in errors.

[0040] Disclosed herein is a mechanism for encoding a sequence parameter set (SPS) in a manner that avoids errors when the VPS is removed from the encoded bitstream as part of the sub-bitstream extraction process. The SPS includes an SPS VPS identifier (sps_video_parameter_set_id). The sps_video_parameter_set_id indicates an identifier of the VPS, including its layer relationship to the video sequence. In one example, the sps_video_parameter_set_id is set to 0 when the VPS is removed prior to transmission of a bitstream including only simulcast layers. In another example, the SPS used by the simulcast layer may include a sps_video_parameter_set_id that is set to 0 at the time of encoding. In either case, when the sps_video_parameter_set_id is set to 0, the SPS-related variables that reference the VPS are set to default values ​​to avoid errors. For example, a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to a network abstraction layer (NAL) unit header layer identifier (nuh_layer_id) indicates the current layer index for the corresponding layer (e.g., simulcast layer). GeneralLayerIdx[nuh_layer_id] is set to / inferred to be 0 when sps_video_parameter_set_id is 0. As another example, a VPS independent layer flag (vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) for GeneralLayerIdx[nuh_layer_id] is stored in the VPS and specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. Inter-layer prediction is not used for simulcast layers.Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate no inter-layer prediction when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS is removed from the bitstream prior to transmission of the simulcast layer. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only the simulcast layer, thereby reducing the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0041] 1 is a flow chart of an exemplary operational method 100 of coding a video signal. Specifically, the video signal is encoded at an encoder. The encoding process compresses the video signal by using various mechanisms to reduce the video file size. The smaller file size allows the compressed video file to be transmitted to a user while reducing the associated bandwidth overhead. A decoder then decodes the compressed video file and reconstructs the original video signal for display to an end user. The decoding process generally mirrors the encoding process to allow the decoder to consistently reconstruct the video signal.

[0042] At step 101, a video signal is input to an encoder. For example, the video signal may be an uncompressed video file stored in memory. As another example, the video file may be captured by a video capture device, such as a video camera, and encoded to support live streaming of the video. The video file may include both audio and video components. The video component includes a series of image frames that, when viewed in sequence, give the visual impression of motion. The frames include pixels that are represented in terms of light, referred to herein as luma components (or luma samples), and color, referred to herein as chroma components (or color samples). In some examples, the frames may also include depth values ​​to support three-dimensional displays.

[0043] At step 103, the video is partitioned into several blocks. Partitioning involves subdividing pixels in each frame into square and / or rectangular blocks for compression. For example, in High Efficiency Video Coding (HEVC) (also known as H.265 and MPEG-H Part 2), a frame may first be partitioned into coding tree units (CTUs), which are blocks of a predefined size (e.g., 64 pixels by 64 pixels). A CTU contains both luma and chroma samples. A coding tree may be employed to partition a CTU into several blocks and then recursively subdivide the blocks until a configuration that supports further encoding is achieved. For example, the luma component of a frame may be subdivided until each block contains relatively homogenous illumination values. Furthermore, the chroma component of a frame may be subdivided until each block contains relatively homogenous color values. Thus, the partitioning mechanism differs depending on the content of the video frame.

[0044] At step 105, various compression mechanisms are employed to compress the image blocks partitioned at step 103. For example, inter prediction and / or intra prediction may be employed. Inter prediction is designed to take advantage of the fact that objects in a common scene tend to appear in consecutive frames. Thus, a block depicting an object in a reference frame does not need to be repeatedly described in adjacent frames. Specifically, an object such as a table may remain in a constant position across multiple frames. Thus, once a table is described, adjacent frames may refer back to the reference frame. A pattern matching mechanism may be employed to match objects across multiple frames. Furthermore, objects that move across multiple frames may be represented, such as due to object movement or camera movement. As a specific example, a video may show a car moving across the screen across multiple frames. A motion vector may be used to describe such movement. A motion vector is a two-dimensional vector that provides an offset from the coordinates of the object in the frame to the coordinates of the object in the reference frame. Hence, inter prediction may encode an image block in a current frame as a set of motion vectors that indicate an offset from a corresponding block in the reference frame.

[0045] Intra prediction encodes blocks within a common frame. Intra prediction exploits the fact that luma and chroma components tend to cluster within a frame. For example, a green patch in a part of a tree tends to be positioned adjacent to a similar patch of green. Intra prediction uses multiple directional prediction modes (e.g., 33 types in HEVC), planar mode, and direct current (DC) mode. These directional modes indicate that the current block is similar / same as the samples of neighboring blocks in the corresponding direction. Planar mode indicates that a series of blocks along a row / column (e.g., a plane) may be interpolated based on the neighboring blocks at the end of the row. Planar mode actually indicates a smooth transition of light / color across the row / column by using a relatively constant gradient in the changing values. DC mode is used for boundary smoothing and indicates that the block is similar / same as the average value associated with the samples of all neighboring blocks related to the angular direction of the directional prediction mode. Thus, intra prediction blocks can represent image blocks as various related prediction mode values ​​rather than actual values. Furthermore, inter prediction blocks can represent image blocks as motion vector values ​​rather than actual values. In either case, the prediction block may not exactly represent the image block in some cases. Any differences are contained within a residual block. To further compress the file, a transform may be applied to the residual block.

[0046] In step 107, various filtering techniques may be applied. In HEVC, filters are applied according to an in-loop filtering scheme. Block-based prediction, as described above, may result in blocky images at the decoder. Furthermore, the block-based prediction scheme may encode a block and then reconstruct the encoded block for later use as a reference block. The in-loop filtering scheme iteratively applies a noise suppression filter, a deblocking filter, an adaptive loop filter, and a sample adaptive offset (SAO) filter to the block / frame. These filters reduce such blocking artifacts, so that the encoded file can be accurately reconstructed. Furthermore, these filters reduce artifacts in the reconstructed reference block, so that the artifacts are less likely to cause further artifacts in subsequent blocks that are encoded based on the reconstructed reference block.

[0047] After the video signal has been partitioned, compressed, and filtered, the resulting data is encoded into a bitstream at step 109. The bitstream includes the data described above, as well as any signaling data desired to support proper video signal reconstruction at the decoder. For example, such data may include partition data, prediction data, residual blocks, and various flags that send coding instructions to the decoder. The bitstream may be stored in memory for transmission to the decoder upon request. The bitstream may also be broadcast and / or multicast to multiple decoders. Creation of the bitstream is an iterative process. Thus, steps 101, 103, 105, 107, and 109 may be performed sequentially and / or simultaneously across multiple frames and blocks. The order depicted in FIG. 1 is presented for clarity and ease of explanation and is not intended to limit the video coding process to a particular order.

[0048] The decoder receives the bitstream and begins the decoding process at step 111. Specifically, the decoder uses an entropy decoding scheme to convert the bitstream into corresponding syntax and video data. The decoder uses syntax data from the bitstream to determine a partition for the frame at step 111. The partition should match the result of the block partitioning at step 103. We now describe entropy encoding / decoding as employed at step 111. The encoder makes many choices during the compression process, such as selecting a block partitioning scheme from several possible choices based on the spatial positioning of values ​​in the input image. In signaling the exact choice, multiple bins may be used. As used herein, a bin is a binary value (e.g., a bit value that can change depending on the context) that is treated as a variable. Entropy coding allows the encoder to discard any options that are clearly infeasible for a particular case, leaving a set of acceptable options. Each acceptable option is then assigned a codeword. The length of the codeword is based on the number of allowable options (e.g., one bin for two options, two bins for three to four options, etc.). The encoder then encodes a codeword for the selected option. This scheme reduces the size of the codeword since it is desirable to uniquely indicate a selection from a small subset of allowable options, as opposed to uniquely indicating a selection from a potentially large set of all possible options. The decoder then decodes the selection by determining the set of allowable options in a manner similar to the encoder. By determining the set of allowable options, the decoder can read the codeword and determine the selection made by the encoder.

[0049] In step 113, the decoder performs block decoding. Specifically, the decoder employs an inverse transform to generate a residual block. The decoder then uses the residual block and a corresponding prediction block to reconstruct an image block according to the partitioning. The prediction block may include both intra-prediction blocks and inter-prediction blocks as generated in the encoder in step 105. The reconstructed image block is then positioned within a frame of the reconstructed video signal according to the partitioning data determined in step 111. The syntax for step 113 may also be signaled in the bitstream via entropy coding as described above.

[0050] At step 115, filtering is performed on the frames of the reconstructed video signal in a manner similar to step 107 at the encoder. For example, a noise suppression filter, a deblocking filter, an adaptive loop filter, and an SAO filter may be applied to the frames to remove blocking artifacts. After the frames are filtered, the video signal may be output to a display at step 117 for viewing by an end user.

[0051] FIG. 2 is a schematic diagram of an exemplary coding and decoding (codec) system 200 for video coding. Specifically, the codec system 200 provides functionality to support implementation of the operational method 100. The codec system 200 is generalized to depict components employed in both an encoder and a decoder. The codec system 200 receives and segments a video signal as described with respect to steps 101 and 103 of the operational method 100, resulting in a segmented video signal 201. The codec system 200 then compresses the segmented video signal 201 into a coded bitstream when operating as an encoder as described with respect to steps 105, 107, and 109 in the method 100. The codec system 200 generates an output video signal from the bitstream when operating as a decoder as described with respect to steps 111, 113, 115, and 117 of the operational method 100. Codec system 200 includes a general coder control component 211, a transform scaling and quantization component 213, an intra picture estimation component 215, an intra picture prediction component 217, a motion compensation component 219, a motion estimation component 221, a scaling and inverse transform component 229, a filter control analysis component 227, an in-loop filter component 225, a decoded picture buffer component 223, and a header formatting and context adaptive binary arithmetic coding (CABAC) component 231. Such components are coupled as shown. In FIG. 2, the black lines indicate the movement of data to be encoded / decoded, and the dashed lines indicate the movement of control data that controls the operation of the other components. The components of codec system 200 may all be present in an encoder. A decoder may include a subset of the components of codec system 200.For example, the decoder may include an intra-picture prediction component 217, a motion compensation component 219, a scaling and inverse transform component 229, an in-loop filter component 225, and a decoded picture buffer component 223. These components are now described.

[0052] The partitioned video signal 201 is a captured video sequence partitioned into several blocks of pixels by a coding tree. The coding tree employs various partitioning modes to subdivide the blocks of pixels into smaller blocks of pixels. These blocks may then be further subdivided into smaller blocks. The blocks may be referred to as nodes of the coding tree. Larger parent nodes are partitioned into smaller child nodes. The number of times a node is subdivided is referred to as the depth of the node / coding tree. The partitioned blocks may be included in a coding unit (CU) in some cases. For example, a CU may be a sub-part of a CTU that includes a luma block, a red-difference chroma (Cr) block, and a blue-difference chroma (Cb) block, along with corresponding syntax instructions for the CU. The partitioning modes may include a binary tree (BT), a ternary tree (TT), and a quad tree (QT), which are employed to partition a node into two, three, or four child nodes of various shapes, respectively, depending on the partitioning mode employed. The segmented video signal 201 is forwarded to a general coder control component 211, a transform scaling and quantization component 213, an intra-picture estimation component 215, a filter control analysis component 227, and a motion estimation component 221 for compression.

[0053] The general coder control component 211 is configured to make decisions related to the coding of images of a video sequence into a bitstream according to application constraints. For example, the general coder control component 211 manages the optimization of bitrate / bitstream size versus reconstruction quality. Such decisions may be based on storage space / bandwidth availability and image resolution requirements. The general coder control component 211 also manages buffer utilization in light of transmission rate to mitigate buffer under-run and over-run issues. To manage these issues, the general coder control component 211 manages segmentation, prediction, and filtering by other components. For example, the general coder control component 211 may dynamically increase compression complexity to increase resolution and bandwidth usage, or decrease compression complexity to decrease resolution and bandwidth usage. Thus, the general coder control component 211 controls other components of the codec system 200 to balance video signal reconstruction quality and bitrate considerations. The general coder control component 211 creates control data that controls the operation of other components. The control data is also forwarded to the header formatting and CABAC component 231 and encoded into the bitstream to signal parameters for decoding at the decoder.

[0054] The partitioned video signal 201 is also sent to a motion estimation component 221 and a motion compensation component 219 for inter prediction. A frame or slice of the partitioned video signal 201 may be divided into multiple video blocks. The motion estimation component 221 and the motion compensation component 219 perform inter predictive coding of the received video blocks with respect to one or more blocks in one or more reference frames to perform temporal prediction. The codec system 200 may perform multiple coding passes to, for example, select an appropriate coding mode for each block of video data.

[0055] The motion estimation component 221 and the motion compensation component 219 may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation performed by the motion estimation component 221 is a process of generating motion vectors, which estimate motion with respect to a video block. A motion vector may indicate, for example, the displacement of a coded object with respect to a predictive block. A predictive block is a block that is found to match well with a block to be coded with respect to pixel differences. A predictive block may also be referred to as a reference block. Such pixel differences may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics. HEVC employs several coded objects, including CTUs, coding tree blocks (CTBs), and CUs. For example, a CTU may be divided into CTBs, which may then be divided into CBs to be included in a CU. A CU may be encoded as a prediction unit (PU) that includes prediction data and / or a transform unit (TU) that includes transformed residual data for the CU. The motion estimation component 221 generates the motion vectors, PUs, and TUs by using a rate-distortion analysis as part of a rate-distortion optimization process. For example, the motion estimation component 221 may determine multiple reference blocks, multiple motion vectors, etc. for a current block / frame and select the reference block, motion vector, etc. with the best rate-distortion characteristics. The best rate-distortion characteristics balance both the quality of the video reconstruction (e.g., the amount of data lost due to compression) and the coding efficiency (e.g., the size of the final encoding).

[0056] In some examples, the codec system 200 may calculate values ​​for sub-integer pixel positions of reference pictures stored in the decoded picture buffer component 223. For example, the video codec system 200 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference pictures. Thus, the motion estimation component 221 may perform motion searches for full-pixel positions and fractional pixel positions and output motion vectors with fractional pixel accuracy. The motion estimation component 221 calculates motion vectors for PUs of video blocks in inter-coded slices by comparing the positions of the PUs with the positions of predictive blocks of the reference pictures. The motion estimation component 221 outputs the calculated motion vectors as header formatting for encoding and motion to the motion compensation component 219 and motion data to the CABAC component 231.

[0057] The motion compensation performed by the motion compensation component 219 may involve fetching or generating a predictive block based on a motion vector determined by the motion estimation component 221. Again, the motion estimation component 221 and the motion compensation component 219 may be functionally integrated in some examples. Upon receiving a motion vector for the PU of the current video block, the motion compensation component 219 may locate the predictive block to which the motion vector points. A residual video block is then formed by subtracting pixel values ​​of the predictive block from pixel values ​​of the current video block being coded to form pixel difference values. In general, the motion estimation component 221 performs motion estimation with respect to the luma component, and the motion compensation component 219 uses the motion vector calculated based on the luma component for both the chroma and luma components. The predictive block and the residual block are forwarded to the transform scaling and quantization component 213.

[0058] The partitioned video signal 201 is also sent to an intra-picture estimation component 215 and an intra-picture prediction component 217. As with the motion estimation component 221 and the motion compensation component 219, the intra-picture estimation component 215 and the intra-picture prediction component 217 may be highly integrated, but are illustrated separately for conceptual purposes. The intra-picture estimation component 215 and the intra-picture prediction component 217 intra-predict a current block with respect to blocks in a current frame, as an alternative to the inter-prediction performed by the motion estimation component 221 and the motion compensation component 219 between frames, as described above. In particular, the intra-picture estimation component 215 determines an intra-prediction mode to use to encode the current block. In some examples, the intra-picture estimation component 215 selects an appropriate intra-prediction mode to encode the current block from a plurality of tested intra-prediction modes. The selected intra-prediction mode is then forwarded to the header formatting and CABAC component 231 for encoding.

[0059] For example, the intra picture estimation component 215 calculates rate-distortion values ​​using a rate-distortion analysis for various tested intra prediction modes and selects an intra prediction mode with the best rate-distortion characteristics from among the tested modes. The rate-distortion analysis generally determines the amount of distortion (or error) between an encoded block and an original unencoded block that was encoded to generate the encoded block, as well as the bit rate (e.g., number of bits) used to generate the encoded block. The intra picture estimation component 215 calculates ratios from the distortion and rate for various encoded blocks to determine which intra prediction mode exhibits the best rate-distortion value for the block. In addition, the intra picture estimation component 215 may be configured to code a depth block of a depth map using a depth modeling mode (DMM) based on a rate-distortion optimization (RDO).

[0060] The intra picture prediction component 217 may generate a residual block from the prediction block based on a selected intra prediction mode determined by the intra picture estimation component 215 when implemented in an encoder, or may read the residual block from a bitstream when implemented in a decoder. The residual block includes value differences between the prediction block and the original block, represented as a matrix. The residual block is then forwarded to the transform scaling and quantization component 213. The intra picture estimation component 215 and the intra picture prediction component 217 may operate on both the luma and chroma components.

[0061] The transform scaling and quantization component 213 is configured to further compress the residual block. The transform scaling and quantization component 213 applies a transform to the residual block, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to generate a video block including residual transform coefficient values. A wavelet transform, an integer transform, a subband transform, or other types of transforms could also be used. The transform may convert the residual information from the pixel value domain to a transform domain, such as the frequency domain. The transform scaling and quantization component 213 is also configured to scale the transformed residual information, for example based on frequency. Such scaling involves applying a scale factor to the residual information such that different frequency information is quantized with different granularity, which may affect the final visual quality of the reconstructed video. The transform scaling and quantization component 213 is also configured to quantize the transform coefficients to further reduce the bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be changed by adjusting a quantization parameter. In some examples, the transform scaling and quantization component 213 may then perform a scan of a matrix containing the quantized transform coefficients, which are forwarded to the header formatting and CABAC component 231 and encoded into the bitstream.

[0062] The scaling and inverse transform component 229 applies the inverse operations of the transform scaling and quantization component 213 to support motion estimation. The scaling and inverse transform component 229 applies inverse scaling, transformation, and / or quantization to reconstruct a residual block in the pixel domain, for example, for later use as a reference block that may become a predictive block for another current block. The motion estimation component 221 and / or the motion compensation component 219 may calculate a reference block by adding the residual block back to the corresponding predictive block for use in motion estimation of a later block / frame. A filter is applied to the reconstructed reference block, thereby mitigating artifacts created during the scaling, quantization, and transformation. Such artifacts may otherwise cause inaccurate predictions (and create additional artifacts) when subsequent blocks are predicted.

[0063] The filter control analysis component 227 and the in-loop filter component 225 apply filters to the residual block and / or the reconstructed image block. For example, the transformed residual block from the scaling and inverse transform component 229 may be combined with a corresponding prediction block from the intra-picture prediction component 217 and / or the motion compensation component 219 to reconstruct the original image block. A filter may then be applied to the reconstructed image block. In some examples, the filter may be applied to the residual block instead. As with the other components of FIG. 2, the filter control analysis component 227 and the in-loop filter component 225 are highly integrated and may be implemented together, but are depicted separately for conceptual purposes. The filters applied to the reconstructed reference block are applied to a particular spatial region and include multiple parameters to adjust how such filters are applied. The filter control analysis component 227 analyzes the reconstructed reference block to determine where such filters should be applied and sets the corresponding parameters. Such data is forwarded to the header formatting and CABAC component 231 as filter control data for encoding. The in-loop filter component 225 applies such filters based on the filter control data. The filters may include deblocking filters, noise suppression filters, SAO filters, and adaptive loop filters. Such filters may be applied in the spatial / pixel domain (e.g., on reconstructed pixel blocks) or in the frequency domain, depending on the example.

[0064] When operating as an encoder, the filtered reconstructed image blocks, residual blocks, and / or predictive blocks are stored in the decoded picture buffer component 223 for later use in motion estimation as described above. When operating as a decoder, the decoded picture buffer component 223 stores the reconstructed and filtered blocks and forwards them to a display as part of the output video signal. The decoded picture buffer component 223 may be any memory device capable of storing predictive blocks, residual blocks, and / or reconstructed image blocks.

[0065] The header formatting and CABAC component 231 receives data from various components of the codec system 200 and encodes such data into a coded bitstream for transmission towards a decoder. In particular, the header formatting and CABAC component 231 generates various headers to encode control data, such as general control data and filter control data. In addition, prediction data, including intra prediction data and motion data, as well as residual data in the form of quantized transform coefficient data, are all encoded into the bitstream. The final bitstream contains all the information desired for a decoder to reconstruct the original partitioned video signal 201. Such information may also include an intra prediction mode index table (also referred to as a codeword mapping table), definitions of encoding contexts for various blocks, indications of the most likely intra prediction modes, indications of partition information, etc. Such data may be encoded by employing entropy coding. For example, the information may be encoded by employing Context-Adaptive Variable Length Coding (CAVLC), CABAC, Syntax-Based Context-Adaptive Binary Arithmetic Coding (SBAC), Probability Interval Partitioning Entropy (PIPE) coding, or another entropy coding technique. Following entropy coding, the coded bitstream may be transmitted to another device (e.g., a video decoder) or archived for later transmission or removal.

[0066] 3 is a block diagram illustrating an example video encoder 300. The video encoder 300 may be employed to implement the encoding functionality of the codec system 200 and / or to implement steps 101, 103, 105, 107, and / or 109 of the method of operation 100. The encoder 300 segments an input video signal, resulting in a segmented video signal 301, which is substantially similar to the segmented video signal 201. The segmented video signal 301 is then compressed and encoded into a bitstream by components of the encoder 300.

[0067] Specifically, the partitioned video signal 301 is forwarded to an intra-picture prediction component 317 for intra prediction. The intra-picture prediction component 317 may be substantially similar to the intra-picture estimation component 215 and the intra-picture prediction component 217. The partitioned video signal 301 is also forwarded to a motion compensation component 321 for inter prediction based on a reference block in a decoded picture buffer component 323. The motion compensation component 321 may be substantially similar to the motion estimation component 221 and the motion compensation component 219. The prediction block and the residual block from the intra-picture prediction component 317 and the motion compensation component 321 are forwarded to a transform and quantization component 313 for transforming and quantizing the residual block. The transform and quantization component 313 may be substantially similar to the transform scaling and quantization component 213. The transformed and quantized residual blocks and the corresponding prediction blocks (along with associated control data) are forwarded to an entropy coding component 331 for coding into the bitstream. The entropy coding component 331 may be substantially similar to the header formatting and CABAC component 231.

[0068] The transformed and quantized residual block and / or the corresponding prediction block are transferred from the transform and quantization component 313 to the inverse transform and quantization component 329 for reconstructing into a reference block and for use by the motion compensation component 321. The inverse transform and quantization component 329 may be substantially similar to the scaling and inverse transform component 229. An in-loop filter in the in-loop filter component 325 is also applied to the residual block and / or the reconstructed reference block, depending on the example. The in-loop filter component 325 may be substantially similar to the filter control analysis component 227 and the in-loop filter component 225. The in-loop filter component 325 may comprise multiple filters as described with respect to the in-loop filter component 225. The filtered block is then stored in the decoded picture buffer component 323 for use as a reference block by the motion compensation component 321. The decoded picture buffer component 323 may be substantially similar to the decoded picture buffer component 223.

[0069] 4 is a block diagram illustrating an example video decoder 400. The video decoder 400 may be employed to implement the decoding functionality of the codec system 200 and / or to implement steps 111, 113, 115, and / or 117 of the method of operation 100. The decoder 400 receives a bitstream, for example, from the encoder 300, and generates a reconstructed output video signal based on the bitstream for display to an end user.

[0070] The bitstream is received by the entropy decoding component 433. The entropy decoding component 433 is configured to implement an entropy decoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or other entropy coding techniques. For example, the entropy decoding component 433 may employ header information to provide a context for interpreting additional data encoded as codewords in the bitstream. The decoded information includes any desired information for decoding a video signal, such as general control data, filter control data, partition information, motion data, prediction data, and quantized transform coefficients from the residual block. The quantized transform coefficients are forwarded to the inverse transform and quantization component 429 for reconstruction into the residual block. The inverse transform and quantization component 429 may be similar to the inverse transform and quantization component 329.

[0071] The reconstructed residual block and / or predictive block are forwarded to the intra-picture prediction component 417 for reconstructing into an image block based on an intra-prediction operation. The intra-picture prediction component 417 may be similar to the intra-picture estimation component 215 and the intra-picture prediction component 217. Specifically, the intra-picture prediction component 417 employs a prediction mode to identify the location of a reference block in a frame and applies the residual block to the result to reconstruct an intra-predictive image block. The reconstructed intra-predictive image block and / or residual block and the corresponding inter-predictive data are forwarded to the decoded picture buffer component 423 via the in-loop filter component 425, which may be substantially similar to the decoded picture buffer component 223 and the in-loop filter component 225, respectively. The in-loop filter component 425 filters the reconstructed image block, the residual block and / or the predictive block, and such information is stored in the decoded picture buffer component 423. The reconstructed image block from the decoded picture buffer component 423 is forwarded to the motion compensation component 421 for inter prediction. The motion compensation component 421 may be substantially similar to the motion estimation component 221 and / or the motion compensation component 219. Specifically, the motion compensation component 421 employs a motion vector from a reference block to generate a prediction block and applies a residual block to the result to reconstruct an image block. The resulting reconstructed block may also be forwarded to the decoded picture buffer component 423 via the in-loop filter component 425. The decoded picture buffer component 423 continues to store additional reconstructed image blocks, which may be reconstructed into a frame via the partition information. Such frames may be placed into a sequence. The sequence is output to a display as a reconstructed output video signal.

[0072] 5 is a schematic diagram illustrating an exemplary HRD 500. The HRD 500 may be employed in the codec system 200 and / or an encoder, such as the encoder 300. The HRD 500 may check the bitstream created in step 109 of the method 100 before the bitstream is forwarded to a decoder, such as the decoder 400. In some examples, the bitstream may be continuously forwarded through the HRD 500 as the bitstream is encoded. If a portion of the bitstream fails to conform to an associated constraint, the HRD 500 may indicate such failure to the encoder, causing the encoder to re-encode the corresponding section of the bitstream using a different mechanism.

[0073] The HRD 500 includes a virtual stream scheduler (HSS) 541. The HSS 541 is a component configured to execute a virtual distribution mechanism. The virtual distribution mechanism is used to check the conformance of a bitstream or a decoder with respect to the timing and data flow of the bitstream 551 input to the HRD 500. For example, the HSS 541 may receive the bitstream 551 output from an encoder and manage a conformance test process for the bitstream 551. In a particular example, the HSS 541 may control the rate at which coded pictures move through the HRD 500 and verify that the bitstream 551 does not contain non-conforming data.

[0074] The HSS 541 may forward the bitstream 551 to the CPB 543 at a predefined rate. The HRD 500 may manage data in a decoding unit (DU) 553. A DU 553 is an access unit (AU) or a subset of an AU and associated non-video coding layer (VCL) network abstraction layer (NAL) unit. Specifically, an AU includes one or more pictures associated with an output time. For example, an AU may include a single picture in a single-layer bitstream and may include pictures for each layer in a multi-layer bitstream. Each picture of an AU may be divided into slices, each of which is included in a corresponding VCL NAL unit. Thus, a DU 553 may include one or more pictures, one or more slices of a picture, or a combination thereof. Also, parameters used to decode an AU / DU, a picture, and / or a slice may be included in a non-VCL NAL unit. Therefore, DU 553 includes non-VCL NAL units that contain data necessary to support decoding VCL NAL units within DU 553. CPB 543 is a first-in, first-out buffer within HRD 500. CPB 543 contains DU 553 that contains video data in decoding order. CPB 543 stores video data for use during bitstream conformance verification.

[0075] The CPB 543 forwards the DU 553 to the decoding process component 545. The decoding process component 545 is a component that conforms to the VVC standard. For example, the decoding process component 545 may emulate the decoder 400 employed by an end user. The decoding process component 545 decodes the DU 553 at a rate that can be achieved by an exemplary end user's decoder. If the decoding process component 545 cannot decode the DU 553 fast enough to prevent the CPB 543 from overflowing (or preventing a buffer underrun), the bitstream 551 does not conform to the standard and should be re-encoded.

[0076] The decoding process component 545 decodes the DU 553, which creates a decoded DU 555. The decoded DU 555 contains the decoded picture. The decoded DU 555 is forwarded to the DPB 547. The DPB 547 may be substantially similar to the decoded picture buffer components 223, 323, and / or 423. To support inter-prediction, pictures marked for use as reference pictures 556 obtained from the decoded DU 555 are returned to the decoding process component 545 to support further decoding. The DPB 547 outputs the decoded video sequence as a series of pictures 557. The pictures 557 are reconstructed pictures that generally mirror the pictures encoded by the encoder into the bitstream 551.

[0077] Picture 557 is forwarded to the output cropping component 549, which is configured to apply an adaptive cropping window to picture 557. This results in output cropped picture 559. Output cropped picture 559 is a perfectly reconstructed picture. Thus, output cropped picture 559 mimics what an end user would see when decoding bitstream 551. Hence, the encoder can review output cropped picture 559 to ensure that the encoding is satisfactory.

[0078] The HRD 500 is initialized based on HRD parameters in the bitstream 551. For example, the HRD 500 may read HRD parameters from a VPS, SPS, and / or SEI message. The HRD 500 may then perform a conformance test operation on the bitstream 551 based on information in such HRD parameters. As a specific example, the HRD 500 may determine one or more CPB delivery schedules from the HRD parameters. The delivery schedules specify the timing for delivery of video data to and / or from memory locations such as the CPB and / or DPB. Thus, the CPB delivery schedules specify the timing for delivery of AUs, DUs 553, and / or pictures to / from the CPB 543. It should be noted that the HRD 500 may adopt a DPB delivery schedule for the DPB 547, which is similar to the CPB delivery schedule.

[0079] Video may be coded into different layers and / or OLSs for use by decoders with various levels of hardware capabilities, and also for various network conditions. The CPB delivery schedule is selected to reflect these issues. Thus, the upper layer sub-bitstream is specified for optimal hardware and network conditions, and thus the upper layer may receive one or more CPB delivery schedules that employ large amounts of memory in the CPB 543 and short delays for the transfer of the DU 553 towards the DPB 547. Similarly, the lower layer sub-bitstream is specified for limited decoder hardware capabilities and / or poor network conditions. Thus, the lower layer may receive one or more CPB delivery schedules that employ small amounts of memory in the CPB 543 and longer delays for the transfer of the DU 553 towards the DPB 547. The OLSs, layers, sub-layers, or combinations thereof may then be tested according to the corresponding delivery schedules to ensure that the resulting sub-bitstreams can be correctly decoded under the conditions expected for the sub-bitstreams. Thus, the HRD parameters in the bitstream 551 may indicate the CPB delivery schedule and may further include sufficient data to enable the HRD 500 to determine the CPB delivery schedule and correlate the CPB delivery schedule to a corresponding OLS, layer, and / or sublayer.

[0080] 6 is a schematic diagram illustrating an example multi-layer video sequence 600 configured for inter-layer prediction 621. The multi-layer video sequence 600 may be encoded by an encoder, such as codec system 200 and / or encoder 300, and decoded by a decoder, such as codec system 200 and / or decoder 400, for example, according to method 100. Additionally, the multi-layer video sequence 600 may be checked for conformance by an HRD, such as HRD 500. The multi-layer video sequence 600 is included to illustrate an example application for layers in a coded video sequence. The multi-layer video sequence 600 is any video sequence employing multiple layers, such as layer N 631 and layer N+1 632.

[0081] In one example, the multi-layer video sequence 600 may employ inter-layer prediction 621. Inter-layer prediction 621 is applied between pictures 611, 612, 613, and 614 and pictures 615, 616, 617, and 618 in different layers. In the illustrated example, pictures 611, 612, 613, and 614 are part of layer N+1 632, and pictures 615, 616, 617, and 618 are part of layer N 631. A layer, such as layer N 631 and / or layer N+1 632, is a group of pictures that are all associated with similar values ​​of characteristics such as similar size, quality, resolution, signal-to-noise ratio, capacity, etc. A layer may be formally defined as a set of VCL NAL units and associated non-VCL NAL units. A VCL NAL unit is a NAL unit that is coded to contain video data, such as a coded slice of a picture. A non-VCL NAL unit is a NAL unit that contains non-video data, such as syntax and / or parameters that support decoding video data, performing conformance checks, or other operations.

[0082] In the illustrated example, layer N+1 632 is associated with a larger image size than layer N 631. Thus, pictures 611, 612, 613, and 614 in layer N+1 632 have a larger picture size (e.g., larger height and width, and therefore more samples) than pictures 615, 616, 617, and 618 in layer N 631 in this example. However, such pictures may be separated between layer N+1 632 and layer N 631 by other characteristics. Although only two layers, layer N+1 632 and layer N 631, are illustrated, a set of pictures may be separated into any number of layers based on associated characteristics. Layer N+1 632 and layer N 631 may also be represented by a layer Id. A layer Id is an item of data associated with a picture and indicates that the picture is part of the layer being shown. Thus, each picture 611-618 may be associated with a corresponding layer Id to indicate which layer N+1 632 or layer N 631 contains the corresponding picture. For example, the layer Id may include a NAL unit header layer identifier (nuh_layer_id), which is a syntax element that specifies an identifier of a layer that contains a NAL unit (e.g., containing slices and / or parameters of a picture within a layer). A layer associated with a lower quality / bitstream size, such as layer N 631, is generally assigned a lower layer Id and is referred to as a lower layer. Furthermore, a layer associated with a higher quality / bitstream size, such as layer N+1 632, is generally assigned a higher layer Id and is referred to as an upper layer.

[0083] Pictures 611-618 of different layers 631-632 are configured to be displayed in an alternative manner. As a specific example, a decoder may decode and display picture 615 at the current display time if a smaller picture is desired, or the decoder may decode and display picture 611 at the current display time if a larger picture is desired. Thus, pictures 611-614 in higher layer N+1 632 contain substantially the same image data as corresponding pictures 615-618 in lower layer N 631 (regardless of differences in picture size). Specifically, picture 611 contains substantially the same image data as picture 615, picture 612 contains substantially the same image data as picture 616, and so on.

[0084] Pictures 611-618 may be coded with reference to other pictures 611-618 in the same layer N 631 or N+1 632. Coding a picture with reference to another picture in the same layer results in inter prediction 623. Inter prediction 623 is indicated by a solid arrow. For example, picture 613 may be coded by employing inter prediction 623 using one or two of pictures 611, 612, and / or 614 in layer N+1 632 as references, one picture being referenced for unidirectional inter prediction and / or two pictures being referenced for bidirectional inter prediction. Furthermore, picture 617 may be coded by employing inter prediction 623 using one or two of pictures 615, 616, and / or 618 in layer N 631 as references, one picture being referenced for unidirectional inter prediction and / or two pictures being referenced for bidirectional inter prediction. When a picture is used as a reference for another picture in the same layer when performing inter prediction 623, the picture may be referred to as a reference picture. For example, picture 612 may be a reference picture used to code picture 613 according to inter prediction 623. Inter prediction 623 may also be referred to as intra-layer prediction in a multi-layer context. Hence, inter prediction 623 is a mechanism for coding samples of a current picture with reference to indicated samples in a reference picture different from the current picture when the reference picture and the current picture are in the same layer.

[0085] Pictures 611-618 may also be coded with reference to other pictures 611-618 in different layers. This process is known as inter-layer prediction 621 and is indicated by dashed arrows. Inter-layer prediction 621 is a mechanism for coding samples of a current picture with reference to indicated samples in reference pictures where the current picture and the reference picture are in different layers and therefore have different layer IDs. For example, a picture in a lower layer N 631 may be used as a reference picture for coding a corresponding picture in an upper layer N+1 632. As a specific example, picture 611 may be coded with reference to picture 615 according to inter-layer prediction 621. In such a case, picture 615 is used as an inter-layer reference picture. An inter-layer reference picture is a reference picture used for inter-layer prediction 621. In most cases, inter-layer prediction 621 is constrained such that a current picture, such as picture 611, can only use inter-layer reference pictures that are included in the same AU and are in a lower layer, such as picture 615. When multiple layers (eg, more than two) are available, inter-layer prediction 621 can encode / decode the current picture based on multiple inter-layer reference pictures at a lower level than the current picture.

[0086] A video encoder may employ the multi-layer video sequence 600 to encode pictures 611-618 via many different combinations and / or permutations of inter-prediction 623 and inter-layer prediction 621. For example, picture 615 may be coded according to intra-prediction. Pictures 616-618 may then be coded according to inter-prediction 623 by using picture 615 as a reference picture. Furthermore, picture 611 may be coded according to inter-layer prediction 621 by using picture 615 as an inter-layer reference picture. Pictures 612-614 may then be coded according to inter-prediction 623 by using picture 611 as a reference picture. Hence, a reference picture may serve as both a single layer reference picture and an inter-layer reference picture for different coding mechanisms. By coding the upper layer N+1 632 picture based on the lower layer N 631 picture, the upper layer N+1 632 can avoid employing intra prediction, which has much lower coding efficiency than inter prediction 623 and inter-layer prediction 621. Hence, the poor coding efficiency of intra prediction can be limited to the smallest / lowest quality pictures and thus limited to coding a minimum amount of video data. Pictures used as reference pictures and / or inter-layer reference pictures may be indicated in entries of a reference picture list included in a reference picture list structure.

[0087] It should be noted that layers, such as layer N+1 632 and layer N 631, may be included in an output layer set (OLS). An OLS is a set of one or more layers, with at least one layer being an output layer. For example, layer N 631 may be included in a first OLS, and layer N 631 and layer N-1 632 may both be included in a second OLS. This allows different OLSs to be sent to different decoders depending on the decoder-side conditions. For example, a sub-bitstream extraction process may remove data unrelated to the target OLS from the multi-layer video sequence 600 before the target OLS is sent to the decoder. Hence, an encoded copy of the multi-layer video sequence 600 may be stored in the encoder (or corresponding content server), and various OLSs may be extracted and sent to different decoders upon request.

[0088] A simulcast layer is a layer that does not employ inter-layer prediction 621. For example, layer N+1 632 is coded by referencing layer N 631 based on inter-layer prediction 621. However, layer 631 is not coded by referencing another layer. Hence, layer 631 is a simulcast layer. A scalable video sequence, such as multi-layer video sequence 600, typically employs a base layer and one or more enhancement layers that enhance some properties of the base layer. In FIG. 6, layer N 631 is a base layer. The base layer is typically coded as a simulcast layer. It should also be noted that FIG. 6 is exemplary and non-limiting because a video sequence with multiple layers may use many different combinations / permutations of dependencies. A bitstream may include any number of layers, and any number of such layers may be simulcast layers. For example, inter-layer prediction 621 may be omitted entirely, in which case all layers are simulcast layers. As another example, a multi-view application displays two or more output layers, and therefore may include two or more base layers, typically simulcast layers, and may include enhancement layers corresponding to each base layer.

[0089] Simulcast layers may be processed differently than layers that use inter-layer prediction 621. For example, when coding layers that use inter-layer prediction 621, the encoder should indicate the number of layers and even the dependencies between layers to support decoding. However, for simulcast layers, such information may be omitted. For example, the configuration of layer N+1 632 and layer N 631 may be indicated in the VPS as described in more detail below. However, layer N 631 may be decoded without such information. Hence, the VPS may be removed from the corresponding bitstream when only layer N 631 is transmitted to the decoder. However, this may cause errors if parameters remaining in the bitstream refer to the VPS. These and other issues are described in more detail below.

[0090] 7 is a schematic diagram illustrating an exemplary bitstream 700. For example, the bitstream 700 may be generated by the codec system 200 and / or the encoder 300 for decoding by the codec system 200 and / or the decoder 400 according to the method 100. Furthermore, the bitstream 700 may include the multi-layer video sequence 600. In addition, the bitstream 700 may include various parameters for controlling the operation of an HRD, such as the HRD 500. Based on such parameters, the HRD 500 may check the bitstream 700 for compliance with the standard before transmitting it to the decoder for decoding.

[0091] Bitstream 700 includes a VPS 711, one or more SPSs 713, multiple picture parameter sets (PPSs) 715, multiple slice headers 717, and image data 720. VPS 711 includes data related to the entire bitstream 700. For example, VPS 711 may include data related to the OLS, layers, and / or sublayers used in bitstream 700. SPS 713 includes sequence data that is common to all pictures in a coded video sequence included in bitstream 700. For example, each layer may include one or more coded video sequences, and each coded video sequence may reference SPS 713 for corresponding parameters. Parameters in SPS 713 may include picture sizing, bit depth, coding tool parameters, bit rate limits, etc. It should be noted that while each sequence references SPS 713, in some examples a single SPS 713 may include data for multiple sequences. PPS 715 includes parameters that apply to the entire picture. Thus, each picture in a video sequence may reference PPS 715. It should be noted that while each picture references a PPS 715, in some examples a single PPS 715 may contain data for multiple sequences. For example, multiple similar pictures may be coded according to similar parameters. In such a case, a single PPS 715 may contain data for such similar pictures. The PPS 715 may indicate available coding tools for slices, quantization parameters, offsets, etc. in the corresponding picture.

[0092] The slice header 717 includes parameters specific to each slice in a picture. Thus, there may be one slice header 717 for each slice in a video sequence. The slice header 717 may include slice type information, a picture order count (POC), a reference picture list, prediction weights, tile entry points, deblocking parameters, etc. Note that in some examples, the bitstream 700 may also include a picture header, which is a syntax structure that includes parameters that apply to all slices in a single picture. For this reason, picture header and slice header 717 may be used interchangeably in some contexts. For example, some parameters may be moved between slice header 717 and picture header depending on whether such parameters are common to all slices in a picture.

[0093] Image data 720 includes video data encoded according to inter-, inter-layer, and / or intra-prediction, as well as corresponding transformed and quantized residual data. For example, image data 720 may include layers 723 and 724, pictures 725 and 726, and / or slices 727 and 728. Layers 723 and 724 are sets of VCL NAL units 741 and associated non-VCL NAL units 742 that share specified characteristics (e.g., a common resolution, frame rate, image size, etc.) as indicated by a layer ID such as nuh_layer_id 732. For example, layer 723 may include a set of pictures 725 that share the same nuh_layer_id 732. Similarly, layer 724 may include a set of pictures 726 that share the same nuh_layer_id 732. Layers 723 and 724 may be substantially similar but include different content. For example, layers 723 and 724 may include layer N 631 and layer N+1 632, respectively, from Figure 6. Thus, coded bitstream 700 may include multiple layers 723 and 724. Although only two layers 723 and 724 are shown for clarity of explanation, any number of layers 723 and 724 may be included in bitstream 700.

[0094] nuh_layer_id 732 is a syntax element that specifies an identifier of layer 723 and / or 724 that contains at least one NAL unit. For example, the lowest quality layer, known as a base layer, may contain the lowest value of nuh_layer_id 732 with higher values ​​of nuh_layer_id 732 for higher quality layers. Thus, a lower layer is the layer 723 or 724 with a smaller value of nuh_layer_id 732, and a higher layer is the layer 723 or 724 with a larger value of nuh_layer_id 732. Data for layers 723 and 724 are correlated based on nuh_layer_id 732. For example, parameter sets and video data may be associated with the value of nuh_layer_id 732 that corresponds to the lowest layer 723 or 724 that contains such parameter sets / video data. Therefore, a set of VCL NAL units 741 is part of layer 723 and / or 724 when the set of VCL NAL units 741 all have a particular value of nuh_layer_id 732.

[0095] Pictures 725 and 726 are arrays of luma samples and / or arrays of chroma samples that make up a frame or a field thereof. For example, pictures 725 / 726 are coded images that may be output for display or used to support coding of other pictures for output. Pictures 725 and 726 are substantially similar, but picture 725 is included in layer 723 while picture 726 is included in layer 724. Pictures 725 and 726 include one or more slices 727 and 728, respectively. Slices 727 / 728 may be defined as an integer number of complete tiles or an integer number of consecutive complete coding tree unit (CTU) rows (e.g., within a tile) of picture 725 / 726 that are exclusively included in a single NAL unit, such as VCL NAL unit 741. Slice 727 and slice 728 are substantially similar, except that slice 727 is included in picture 725 and layer 723, while slice 728 is included in picture 726 and layer 724. Slice 727 / 728 are further divided into CTUs and / or coding tree blocks (CTBs). A CTU is a group of samples of a predefined size that may be partitioned by a coding tree. A CTB is a subset of a CTU and includes the luma or chroma components of the CTU. The CTUs / CTBs are further divided into coding blocks based on the coding tree. The coding blocks may then be encoded / decoded according to a prediction mechanism.

[0096] The bitstream 700 may be coded as a sequence of NAL units. A NAL unit is a container for video data and / or supporting syntax. A NAL unit may be a VCL NAL unit 741 or a non-VCL NAL unit 742. A VCL NAL unit 741 is a NAL unit coded to include video data, such as image data 720 and associated slice headers 717. As a specific example, each slice 727 and 728 and associated slice headers 717 may be encoded in a single VCL NAL unit 741. A non-VCL NAL unit 742 is a NAL unit that includes non-video data, such as syntax and / or parameters that support decoding video data, performing conformance checks, or other operations. For example, a non-VCL NAL unit 742 may include a VPS 711, an SPS 713, a PPS 715, a picture header, or other supporting syntax. Therefore, the bitstream 700 is a series of VCL NAL units 741 and non-VCL NAL units 742. Each NAL unit contains a nuh_layer_id 732, which allows an encoder or decoder to determine which layer 723 or 724 contains the corresponding NAL unit.

[0097] A bitstream 700 including multiple layers 723 and 724 may be encoded and stored until requested by a decoder. For example, a decoder may request an OLS including layer 723, layer 724, and / or multiple layers 723 and 724. In a particular example, layer 723 is a base layer and layer 724 is an enhancement layer. Additional layers may also be employed in the bitstream 700. The encoder and / or content server should send to the decoder only those layers 723 and / or 724 necessary to decode the requested output layers. For example, when layers are used for different picture sizes, a decoder requesting the largest picture size may receive the entire bitstream 700 having both layers 723 and 724. A decoder requesting the smallest picture size may receive only layer 723. A decoder requesting an intermediate picture size may receive layer 723 and other intermediate layers, but not the top layer 724, and therefore may not receive the entire bitstream. The same approach can be used for other layer characteristics such as frame rate, picture resolution, etc.

[0098] A sub-bitstream extraction process 729 is employed to extract a sub-bitstream 701 from the bitstream 700 to support the functionality described above. The sub-bitstream 701 is a subset of NAL units (e.g., non-VCL NAL units 742 and VCL NAL units 741) from the bitstream 700. Specifically, the sub-bitstream 701 may include data related to one or more layers, but may not include data related to other layers. In the illustrated example, the sub-bitstream 701 includes data related to layer 723, but not data related to layer 724. Thus, the sub-bitstream 701 includes the SPS 713, the PPS 715, the slice header 717, and the image data 720, including the layer 723, the picture 725, and the slice 727. The sub-bitstream extraction process 729 removes the NAL units based on the nuh_layer_id 732. For example, VCL NAL units 741 and non-VCL NAL units 742 associated only with upper layers 724 contain higher nuh_layer_id 732 values, and therefore removing all NAL units with higher nuh_layer_id 732 values ​​extracts lower layers 723 and associated parameters. Each NAL unit contains a nuh_layer_id 732 value that is less than or equal to the nuh_layer_id 732 of the lowest layer that contains the NAL unit to support the sub-bitstream extraction process 729. It should be noted that bitstream 700 and sub-bitstream 701 may each be referred to generally as a bitstream.

[0099] In the illustrated example, sub-bitstream 701 includes a simulcast layer (e.g., a base layer). As noted above, a simulcast layer is any layer that does not use inter-layer prediction. VPS 711 includes data that describes the configuration of layers 723 and 724. However, this data is not necessary to decode a simulcast layer, such as layer 723. Therefore, sub-bitstream extraction process 729 removes VPS 711 to support increased coding efficiency when extracting simulcast layers. This may cause problems for some video coding systems. Specifically, some parameters of SPS 713 may reference VPS 711. When VPS 711 is removed, the decoder and / or HRD may not be able to resolve such parameters because the data referenced by such parameters no longer exists. This may result in errors when performing conformance tests on the simulcast layer in the HRD. Alternatively, this may result in unpredictable errors in the decoder when the simulcast layer is transmitted for display at the decoder.

[0100] This disclosure addresses these errors. Specifically, SPS 713 includes sps_video_parameter_set_id 731, which is a syntax element that specifies the ID of the VPS 711 referenced by SPS 713. Specifically, VPS 711 includes vps_video_parameter_set_id 735, which is a syntax element that provides an ID for the VPS 711 for reference by other syntax elements / structures. When VPS 711 is present, sps_video_parameter_set_id 731 is set to the value of vps_video_parameter_set_id 735. However, when SPS 713 is used for a simulcast layer, sps_video_parameter_set_id 731 is set to 0. Stated another way, sps_video_parameter_set_id 731, when greater than 0, specifies the value of vps_video_parameter_set_id 735 for the VPS 711 referenced by the SPS 713. When sps_video_parameter_set_id 731 is equal to 0, the SPS 713 does not reference the VPS 711, and the VPS 711 is not referenced when decoding any precoded layer video sequence that references the SPS 713. This may be accomplished by using different SPSs 713 for different layers (e.g., one SPS for simulcast layers and another SPS for non-simulcast layers) or by changing the value of sps_video_parameter_set_id 731 during the sub-bitstream extraction process 729. In this way, sps_video_parameter_set_id 731 does not erroneously reference an ID that is unavailable when the VPS 711 is removed during the sub-bitstream extraction process 729.

[0101] Additionally, various variables derived by the HRD and / or decoder also reference parameters in the VPS 711. Thus, such variables are set to default values ​​when sps_video_parameter_set_id 731 is set to 0. This ensures that such variables can be properly resolved to operational values ​​when the VPS 711 is extracted for a simulcast layer, while still working correctly for a multi-layer bitstream. For example, the decoder and / or HRD can derive GeneralLayerIdx[i] based on the bitstream 700 and / or sub-bitstream 701. GeneralLayerIdx[i] is a derived variable that specifies the index of the corresponding layer i. Hence, GeneralLayerIdx[i] can be employed to determine the layer index of the current layer by including the nuh_layer_id 732 of the current layer as layer i in GeneralLayerIdx[i]. This can be represented as the general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to nuh_layer_id. Thus, GeneralLayerIdx[nuh_layer_id] indicates the current layer index for the corresponding layer. This process works correctly for non-simulcast layers, such as layer 724, but may cause errors for simulcast layer 723. Thus, GeneralLayerIdx[nuh_layer_id] is set to and / or inferred to be 0 when sps_video_parameter_set_id 731 is 0 (indicating a simulcast layer).

[0102] As another example, the VPS 711 may include a VPS independent layer flag (vps_independent_layer_flag) 733. The vps_independent_layer_flag 733 specifies whether the corresponding layer, such as layers 723 and / or 724, uses inter-layer prediction. Thus, the vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the current layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. However, the VPS 711 including the vps_independent_layer_flag 733 is not transmitted to the decoder when the layer 723 transmitted to the decoder is a simulcast layer. Hence, the reference may cause an error. However, the simulcast layer does not use inter-layer prediction. Hence, it can be inferred that the vps_independent_layer_flag 733 for the simulcast layer is equal to 1, which indicates that inter-layer prediction is not used for the corresponding layer 723. Therefore, it is inferred that vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is set to 1 to indicate that inter-layer prediction is not used for the current layer when sps_video_parameter_set_id is set to 0. In this manner, errors are avoided when VPS are removed from the bitstream prior to transmission of simulcast layers, such as layer 723. As a result, the functionality of the encoder and decoder is improved. Furthermore, coding efficiency is increased by successfully removing unnecessary VPS from a bitstream containing only simulcast layers, which reduces the use of processor, memory, and / or network signaling resources in both the encoder and the decoder.

[0103] Here, the aforementioned information will be described in more detail below in this specification. Layered video coding is also referred to as scalable video coding or video coding with scalability. Scalability in video coding may be supported by using multi-layer coding techniques. A multi-layer bitstream includes a base layer (BL) and one or more enhancement layers (EL). Examples of scalability include spatial scalability, quality / signal-to-noise ratio (SNR) scalability, multi-view scalability, frame rate scalability, etc. When a multi-layer coding technique is used, a picture or a part thereof may be coded without using a reference picture (intra prediction), may be coded by referencing a reference picture in the same layer (inter-layer prediction), and / or may be coded by referencing a reference picture in another layer (inter-layer prediction). A reference picture used for inter-layer prediction of a current picture is referred to as an inter-layer reference picture (ILRP). Figure 6 illustrates an example of multi-layer coding for spatial scalability where pictures in different layers have different resolutions.

[0104] Some video coding families provide support for scalability in separate profiles from profiles for single-layer coding. Scalable Video Coding (SVC) is a scalable extension of Advanced Video Coding (AVC) that provides support for spatial, temporal, and quality scalability. For SVC, a flag is signaled in each macroblock (MB) in an EL picture to indicate whether the EL MB is predicted using co-located blocks from lower layers. Prediction from co-located blocks may include texture, motion vectors, and / or coding modes. SVC implementations may not directly reuse unmodified AVC implementations in their design. The SVC EL macroblock syntax and decoding process are different from the AVC syntax and decoding process.

[0105] Scalable HEVC (SHVC) is an extension of HEVC that provides support for spatial and quality scalability. Multiview HEVC (MV-HEVC) is an extension of HEVC that provides support for multiview scalability. 3D HEVC (3D-HEVC) is an extension of HEVC that provides support for 3D video coding that is more advanced and more efficient than MV-HEVC. Temporal scalability can be included as an integral part of a single-layer HEVC codec. In multi-layer extensions of HEVC, decoded pictures used for inter-layer prediction come only from the same AU and are treated as long-term reference pictures (LTRPs). Such pictures are assigned a reference index in a reference picture list along with other temporal reference pictures in the current layer. Inter-layer prediction (ILP) is achieved at the prediction unit (PU) level by setting the value of the reference index to refer to an inter-layer reference picture in the reference picture list. Spatial scalability resamples a reference picture or a portion thereof when the ILRP has a different spatial resolution than the current picture being encoded or decoded. Reference picture resampling can be realized either at the picture level or at the coding block level.

[0106] VVC may also support layered video coding. A VVC bitstream may include multiple layers. The layers may all be independent of each other. For example, each layer may be coded without using inter-layer prediction. In this case, the layers are also referred to as simulcast layers. In some cases, some of the layers are coded using ILP. A flag in the VPS may indicate whether the layers are simulcast layers or whether some layers are using ILP. When some layers use ILP, layer dependencies between layers are also signaled in the VPS. Unlike SHVC and MV-HEVC, VVC may not specify an OLS. An OLS includes a specified set of layers, and one or more layers in the set of layers are specified to be output layers. An output layer is a layer of the OLS that is output. In some implementations of VVC, only one layer may be selected for decoding and output when a layer is a simulcast layer. In some implementations of VVC, the entire bitstream including all layers is specified to be decoded when any layer uses ILP. Additionally, certain of the layers are designated to be output layers, which may be indicated to be only the top layer, all layers, or a set of lower layers designated along with the top layer.

[0107] The aforementioned aspects include some scalability-related issues. Scalability designs in such systems include layer-specific profile, tier, and level (PTL) and even layer-specific Coded Picture Buffer (CPB) operations. PTL signaling efficiency should be improved. Signaling efficiency of sequence-level HRD parameters for sub-layers should be improved. DPB parameter signaling should be improved. Some designs cause single-layer bitstreams to reference VPS. The value range of num_ref_entries[ ][ ] in such designs is incorrect, causing unexpected errors for decoders. The decoding process in such designs involves sub-bitstream extraction, which increases the burden on decoder implementations. The general decoding process for such designs may not work for scalable bitstreams that include multiple layers with inter-layer prediction. The derivation of the value of the variable NoOutputOfPriorPicsFlag in such designs may be picture-based and not AU-based in such designs. The scalable nesting SEI message in such a design should be simplified to apply directly to the OLS, rather than to a layer of the OLS, when nesting_ols_flag is equal to 1. The non-scalable nesting SEI message may be specified to apply only to the 0th OLS when payloadType is equal to 0 (buffering period), 1 (picture timing), or 130 (decoding unit information).

[0108] In general, this disclosure describes various approaches for scalability in video coding. The description of the techniques is based on VVC. However, these techniques also apply to layered video coding based on other video codec specifications. One or more of the above-mentioned problems may be solved as follows. Specifically, this disclosure includes a method for improved scalability support in video coding.

[0109] The following are various exemplary definitions: OP may be a temporal subset of the OLS, identified by the OLS index and the highest value of TemporalId. Output layer may be a layer of the OLS that is output. The OLS may be a set of layers, and one or more layers in the set of layers are designated to be output layers. The OLS layer index may be an index of a layer in the OLS into a list of layers in the OLS. The sub-bitstream extraction process may be a designated process in which NAL units in the bitstream that do not belong to a target set, as determined by a target OLS index and a target highest TemporalId, are removed from the bitstream, and the output sub-bitstream includes NAL units in the bitstream that belong to the target set.

[0110] An example video parameter set RBSP syntax is as follows:

[0111] [Table 1A] [Table 1B] [Table 1C]

[0112] An exemplary sequence parameter set RBSP syntax is as follows:

[0113] [Table 2A] [Table 2B]

[0114] An exemplary DPB parameter syntax is as follows:

[0115] [Table 3]

[0116] An exemplary general HRD parameter syntax is as follows:

[0117] [Table 4A] [Table 4B]

[0118] An exemplary OLD HRD parameter syntax is as follows:

[0119] [Table 5]

[0120] An example sub-layer HRD parameter syntax is as follows:

[0121] [Table 6]

[0122] Exemplary video parameter set RBSP semantics are as follows: vps_max_layers_minus1+1 specifies the maximum allowed number of layers in each CVS that references the VPS. vps_max_sub_layers_minus1+1 specifies the maximum number of temporal sublayers that may exist in each CVS that references the VPS. The value of vps_max_sub_layers_minus1 may be in the range of 0 to 6, inclusive. vps_all_layers_same_num_sub_layers_flag equal to 1 specifies that the number of temporal sublayers is the same for all layers in each CVS that references the VPS. vps_all_layers_same_num_sub_layers_flag equal to 0 specifies that layers in each CVS that references the VPS may or may not have the same number of temporal sublayers. When not present, the value of vps_all_layers_same_num_sub_layers_flag may be inferred to be equal to 1. vps_all_independent_layers_flag equal to 1 specifies that all layers in the CVS are coded independently without using inter-layer prediction. vps_all_independent_layers_flag equal to 0 specifies that one or more of the layers in the CVS may use inter-layer prediction. When not present, the value of vps_all_independent_layers_flag may be inferred to be equal to 1. When vps_all_independent_layers_flag is equal to 1, the value of vps_independent_layer_flag[i] is inferred to be equal to 1. When vps_all_independent_layers_flag is equal to 0, the value of vps_independent_layer_flag[0] is inferred to be equal to 1.

[0123] vps_direct_dependency_flag[i][j] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag[i][j] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. The flag is inferred to be equal to 0 when vps_direct_dependency_flag[i][j] is not present for i and j in the range from 0 to vps_max_layers_minus1, inclusive. The variables DirectDependentLayerIdx[i][j], which specifies the jth directly dependent layer of the ith layer, and LayerUsedAsRefLayerFlag[j], which specifies whether the layer with layer index j is used as a reference layer by any other layer, may be derived as follows: for(i=0; i<=vps_max_layers_minus1; i++) LayerUsedAsRefLayerFlag[j]=0 for(i=1; i <vps_max_layers_minus1; i++) if(!vps_independent_layer_flag[i]) for(j=i-1, k=0; j>=0; j--) if(vps_direct_dependency_flag[i][j]) { DirectDependentLayerIdx[i][k++]=j LayerUsedAsRefLayerFlag[j]=1 }

[0124] The variable GeneralLayerIdx[i], which specifies the layer index of the layer whose nuh_layer_id is equal to vps_layer_id[i], may be derived as follows: for(i=0; i<=vps_max_layers_minus1; i++) GeneralLayerIdx[vps_layer_id[i]]=i

[0125] each_layer_is_an_ols_flag equal to 1 specifies that each output layer set contains only one layer, and each layer in the bitstream is itself an output layer set where the single contained layer is the only output layer. each_layer_is_an_ols_flag equal to 0 specifies that the output layer set may contain more than one layer. If vps_max_layers_minus1 is equal to 0, the value of each_layer_is_an_ols_flag is inferred to be equal to 1. Otherwise, when vps_all_independent_layers_flag is equal to 0, the value of each_layer_is_an_ols_flag is inferred to be equal to 0.

[0126] ols_mode_idc equal to 0 specifies that the total number of OLSs specified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLS contains layers with layer indices from 0 to i inclusive, and for each OLS, only the top layer in the OLS is output. ols_mode_idc equal to 1 specifies that the total number of OLSs specified by the VPS is equal to vps_max_layers_minus1+1, the i-th OLS contains layers with layer indices from 0 to i inclusive, and for each OLS, all layers within the OLS are output. ols_mode_idc equal to 2 specifies that the total number of OLSs specified by the VPS is explicitly signaled, and for each OLS, an explicitly signaled set of top and bottom layers in the OLS are output. The value of ols_mode_idc can be in the range from 0 to 2 inclusive. When vps_all_independent_layers_flag is equal to 1 and each_layer_is_an_ols_flag is equal to 0, the value of ols_mode_idc is inferred to be equal to 2. num_output_layer_sets_minus1+1 specifies the total number of OLS specified by the VPS when ols_mode_idc is equal to 2.

[0127] The variable TotalNumOlss, which specifies the total number of OLSs specified by the VPS, may be derived as follows: if(vps_max_layers_minus1==0) TotalNumOlss=1 else if(each_layer_is_an_ols_flag || ols_mode_idc==0 || ols_mode_idc==1) TotalNumOlss=vps_max_layers_minus1+1 else if(ols_mode_idc==2) TotalNumOlss=num_output_layer_sets_minus1+1

[0128] layer_included_flag[i][j] specifies whether the jth layer (e.g., the layer with nuh_layer_id equal to vps_layer_id[j]) is included in the ith OLS when ols_mode_idc is equal to 2. layer_included_flag[i][j] equal to 1 specifies that the jth layer is included in the ith OLS. layer_included_flag[i][j] equal to 0 specifies that the jth layer is not included in the ith OLS. The variables NumLayersInOls[i], which specifies the number of layers in the ith OLS, and LayerIdInOls[i][j], which specifies the value of nuh_layer_id of the jth layer in the ith OLS, may be derived as follows: NumLayersInOls[0] = 1 LayerIdInOls[0][0]=vps_layer_id[0] for(i=1, i <TotalNumOlss; i++) { if(each_layer_is_an_ols_flag) { NumLayersInOls[i] = 1 LayerIdInOls[i][0]=vps_layer_id[i] } else if(ols_mode_idc==0 | | ols_mode_idc==1) { NumLayersInOls[i]=i+1 for(j=0; j <NumLayersInOls[i]; j++) LayerIdInOls[i][j]=vps_layer_id[j] } else if(ols_mode_idc==2) { for(k=0, j=0; k<=vps_max_layers_minus1; k++) if(layer_included_flag[i][k]) LayerIdInOls[i][j++]=vps_layer_id[k] NumLayersInOls[i] = j } }

[0129] The variable OlsLayeIdx[i][j], which specifies the OLS layer index of the layer whose nuh_layer_id is equal to LayerIdInOls[i][j], may be derived as follows: for(i=0, i <TotalNumOlss; i++) for j=0; j <NumLayersInOls[i]; j++) OlsLayeIdx[i][LayerIdInOls[i][j]]=j

[0130] The lowest layer in each OLS shall be an independent layer. In other words, for each i in the range 0 to TotalNumOlss-1, inclusive, the value of vps_independent_layer_flag[GeneralLayerIdx[LayerIdInOls[i][0]]] shall be equal to 1. Each layer shall be contained within at least one OLS specified by the VPS. In other words, for each layer with a particular value of nuh_layer_id nuhLayerId equal to one of vps_layer_id[k] for k in the range 0 to vps_max_layers_minus1, inclusive, there shall be at least one pair of values ​​of i and j, where i is in the range 0 to TotalNumOlss-1, inclusive, and j is in the range NumLayersInOls[i]-1, inclusive, such that the value of LayerIdInOls[i][j] equals nuhLayerId. Any layer in the OLS may be either an output layer of the OLS or a reference layer (direct or indirect) of an output layer of the OLS.

[0131] vps_output_layer_flag[i][j] specifies whether the jth layer in the ith OLS is output when ols_mode_idc is equal to 2. vps_output_layer_flag[i] equal to 1 specifies that the jth layer in the ith OLS is output. vps_output_layer_flag[i] equal to 0 specifies that the jth layer in the ith OLS is not output. The value of vps_output_layer_flag[i] is inferred to be equal to 1 when vps_all_independent_layers_flag is equal to 1 and each_layer_is_an_ols_flag is equal to 0. The variable OutputLayerFlag[i][j], where a value of 1 specifies that the jth layer in the ith OLS is output and a value of 0 specifies that the jth layer in the ith OLS is not output, may be derived as follows: for(i=0, i <TotalNumOlss; i++) { OutputLayerFlag[i][NumLayersInOls[i]-1]=1 for(j=0; j <NumLayersInOls[i]-1; j++) if(ols_mode_idc[i]==0) OutputLayerFlag[i][j]=0 else if(ols_mode_idc[i]==1) OutputLayerFlag[i][j]=1 else if(ols_mode_idc[i]==2) OutputLayerFlag[i][j]=vps_output_layer_flag[i][j] }

[0132] Note that the 0th OLS only includes the lowest layers (e.g., layers with nuh_layer_id equal to vps_layer_id[0]) and for the 0th OLS, only included layers are output. vps_num_ptls specifies the number of profile_tier_level( ) syntax structures in the VPS. pt_present_flag[i] equal to 1 specifies that profile, tier, and general constraint information is present in the i-th profile_tier_level( ) syntax structure in the VPS. pt_present_flag[i] equal to 0 specifies that profile, tier, and general constraint information is not present in the i-th profile_tier_level( ) syntax structure in the VPS. The value of pt_present_flag[0] is inferred to be equal to 0. When pt_present_flag[i] is equal to 0, the profile, tier, and general constraint information for the i-th profile_tier_level( ) syntax structure in the VPS is inferred to be identical to that of the (i-1)-th profile_tier_level( ) syntax structure in the VPS.

[0133] ptl_max_temporal_id[i] specifies the TemporalId of the highest sublayer representation whose level information is present in the i-th profile_tier_level() syntax structure in the VPS. The value of ptl_max_temporal_id[i] shall be in the range from 0 to vps_max_sub_layers_minus1, inclusive. The value of ptl_max_temporal_id[i] is inferred to be equal to 0 when vps_max_sub_layers_minus1 is equal to 0. The value of ptl_max_temporal_id[i] is inferred to be equal to vps_max_sub_layers_minus1 when vps_max_sub_layers_minus1 is greater than 0 and vps_all_layers_same_num_sub_layers_flag is equal to 1. vps_ptl_byte_alignment_zero_bit shall be equal to 0.

[0134] ols_ptl_idx[i] specifies an index into the list of profile_tier_level() syntax structures in the VPS for the profile_tier_level() syntax structures that apply to the i-th OLS. When present, the value of ols_ptl_idx[i] should be in the range from 0 to vps_num_ptls-1, inclusive. When NumLayersInOls[i] is equal to 1, the profile_tier_level() syntax structures that apply to the i-th OLS are present in the SPS referenced by the layers in the i-th OLS. vps_num_dpb_params specifies the number of dpb_parameters() syntax structures in the VPS. The value of vps_num_dpb_params shall be in the range from 0 to 16, inclusive. When not present, the value of vps_num_dpb_params may be inferred to be equal to 0. same_dpb_size_output_or_nonoutput_flag equal to 1 specifies that the layer_nonoutput_dpb_params_idx[i] syntax element is not present in the VPS. same_dpb_size_output_or_nonoutput_flag equal to 0 specifies that the layer_nonoutput_dpb_params_idx[i] syntax element may or may not be present in the VPS. vps_sub_layer_dpb_params_present_flag is used to control the presence of the max_dec_pic_buffering_minus1[ ], max_num_reorder_pics[ ], and max_latency_increase_plus1[ ] syntax elements in the dpb_parameters() syntax structure in the VPS. When not present, vps_sub_dpb_params_info_present_flag is inferred to be equal to 0.

[0135] dpb_size_only_flag[i] equal to 1 specifies that the max_num_reorder_pics[ ] and max_latency_increase_plus1[ ] syntax elements are not present in the i-th dpb_parameters() syntax structure of the VPS. dpb_size_only_flag[i] equal to 1 specifies that the max_num_reorder_pics[ ] and max_latency_increase_plus1[ ] syntax elements may be present in the i-th dpb_parameters() syntax structure of the VPS. dpb_max_temporal_id[i] specifies the TemporalId of the highest sublayer representation for which a DPB parameter may be present in the i-th dpb_parameters() syntax structure in the VPS. The value of dpb_max_temporal_id[i] shall be in the range from 0 to vps_max_sub_layers_minus1, inclusive. The value of dpb_max_temporal_id[i] may be inferred to be equal to 0 when vps_max_sub_layers_minus1 is equal to 0. When vps_max_sub_layers_minus1 is greater than 0 and vps_all_layers_same_num_sub_layers_flag is equal to 1, the value of dpb_max_temporal_id[i] is inferred to be equal to vps_max_sub_layers_minus1. layer_output_dpb_params_idx[i] specifies an index into the list of dpb_parameters() syntax structures in the VPS for the dpb_parameters() syntax structure that applies to the i-th layer when it is an output layer in OLS. When present, the value of layer_output_dpb_params_idx[i] shall be in the range from 0 to vps_num_dpb_params-1, inclusive.

[0136] If vps_independent_layer_flag[i] is equal to 1, the dpb_parameters() syntax structure that applies to the i-th layer when it is an output layer is the dpb_parameters() syntax structure that exists in the SPS referenced by the layer. Otherwise (vps_independent_layer_flag[i] is equal to 0), the following applies: When vps_num_dpb_params is equal to 1, the value of layer_output_dpb_params_idx[i] is inferred to be equal to 0. Bitstream conformance may require that the value of layer_output_dpb_params_idx[i] be such that dpb_size_only_flag[layer_output_dpb_params_idx[i]] is equal to 0.

[0137] layer_nonoutput_dpb_params_idx[i] specifies an index into the list of dpb_parameters() syntax structures in the VPS for the dpb_parameters() syntax structures that apply to the ith layer when the ith layer is a non-output layer in OLS. When present, the value of layer_nonoutput_dpb_params_idx[i] should be in the range from 0 to vps_num_dpb_params-1, inclusive. If same_dpb_size_output_or_nonoutput_flag is equal to 1, the following applies: If vps_independent_layer_flag[i] is equal to 1, the dpb_parameters() syntax structures that apply to the ith layer when the ith layer is a non-output layer are the dpb_parameters() syntax structures that exist in the SPS referenced by the layer. Otherwise (vps_independent_layer_flag[i] is equal to 0), the value of layer_nonoutput_dpb_params_idx[i] is inferred to be equal to layer_output_dpb_params_idx[i]. Otherwise (same_dpb_size_output_or_nonoutput_flag is equal to 0), when vps_num_dpb_params is equal to 1, the value of layer_output_dpb_params_idx[i] is inferred to be equal to 0.

[0138] general_hrd_params_present_flag equal to 1 specifies that the syntax elements num_units_in_tick and time_scale and the syntax structure general_hrd_parameters( ) are present in the SPS RBSP syntax structure. general_hrd_params_present_flag equal to 0 specifies that the syntax elements num_units_in_tick and time_scale and the syntax structure general_hrd_parameters( ) are not present in the SPS RBSP syntax structure. num_units_in_tick is the number of time units of a clock running at a frequency time_scale Hertz (Hz) that corresponds to one increment (called a clock tick) of the clock tick counter. num_units_in_tick shall be greater than 0. Clock ticks in seconds are equal to the quotient of num_units_in_tick divided by time_scale. For example, when the picture rate of a video signal is 25 Hz, time_scale may be equal to 27,000,000 and num_units_in_tick may be equal to 1,080,000, so that a clock tick is equal to 0.04 seconds. time_scale is the number of time units that pass in one second. For example, a time coordinate system that measures time using a 27 MHz clock has a time_scale of 27,000,000. The value of time_scale shall be greater than 0.

[0139] vps_extension_flag equal to 0 specifies that the vps_extension_data_flag syntax element is not present in the VPS RBSP syntax structure. vps_extension_flag equal to 1 specifies that the vps_extension_data_flag syntax element is present in the VPS RBSP syntax structure. vps_extension_data_flag may have any value. The presence and value of vps_extension_data_flag may not affect a decoder's conformance to the profile. Conforming decoders may ignore all vps_extension_data_flag syntax elements.

[0140] Exemplary sequence parameter set RBSP semantics are as follows: An SPS RBSP should be available to the decoding process before being referenced, either included in at least one access unit with TemporalId equal to 0 or provided through external means, and an SPS NAL unit containing an SPS RBSP shall have nuh_layer_id equal to the value of the lowest nuh_layer_id of the PPS NAL units that reference the SPS NAL unit. All SPS NAL units with a particular value of sps_seq_parameter_set_id in a CVS should have the same content. sps_decoding_parameter_set_id, when greater than 0, specifies the value of dps_decoding_parameter_set_id for the DPS referenced by the SPS. When sps_decoding_parameter_set_id is equal to 0, the SPS does not reference a DPS, and the DPS is not referenced when decoding each CLVS that references the SPS. The value of sps_decoding_parameter_set_id should be the same in all SPSs referenced by coded pictures in the bitstream.

[0141] sps_video_parameter_set_id, when greater than 0, specifies the value of vps_video_parameter_set_id for the VPS referenced by the SPS. When sps_video_parameter_set_id is equal to 0, the SPS may not reference a VPS, the VPS is not referenced when decoding each CLVS that references the SPS, the value of GeneralLayerIdx[nuh_layer_id] should be inferred to be equal to 0, and the value of vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] may be inferred to be equal to 1. When vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1, an SPS referenced by a CLVS with a particular nuh_layer_id value nuhLayerId shall have nuh_layer_id equal to nuhLayerId.

[0142] sps_max_sub_layers_minus1+1 specifies the maximum number of temporal sub-layers that may be present in each CLVS that references an SPS. The value of sps_max_sub_layers_minus1 should be in the range from 0 to vps_max_sub_layers_minus1, inclusive. sps_reserved_zero_4bits should be equal to 0 in conforming bitstreams. Other values ​​for sps_reserved_zero_4bits may be reserved.

[0143] sps_ptl_dpb_present_flag equal to 1 specifies that the profile_tier_level() and dpb_parameters() syntax structures are present in the SPS. sps_ptl_dpb_present_flag equal to 0 specifies that neither the profile_tier_level() nor the dpb_parameters() syntax structures are present in the SPS. The value of sps_ptl_dpb_present_flag should be equal to vps_independent_layer_flag[nuh_layer_id]. If vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1, then the variable MaxDecPicBuffMinus1 is set equal to max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1] in the dpb_parameters() syntax structure in the SPS. Otherwise, MaxDecPicBuffMinus1 is set equal to max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1] in the layer_nonoutput_dpb_params_idx[GeneralLayerIdx[nuh_layer_id]]th dpb_parameters() syntax structure in the VPS. gdr_enabled_flag equal to 1 specifies that GDR pictures may be present in the CLVS that references the SPS. A gdr_enabled_flag equal to 0 specifies that there are no GDR pictures in the CLVS that references the SPS.

[0144] sps_sub_layer_dpb_params_flag is used to control the presence of max_dec_pic_buffering_minus1[i], max_num_reorder_pics[i], and max_latency_increase_plus1[i] syntax elements in the dpb_parameters() syntax in the SPS. When not present, sps_sub_dpb_params_info_present_flag is inferred to be equal to 0. long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for inter prediction of any coded pictures in the CLVS. long_term_ref_pics_flag equal to 1 specifies that LTRP may be used for inter prediction of one or more coded pictures in the CLVS.

[0145] Exemplary general profile, tier, and level semantics are as follows: The profile_tier_level( ) syntax structure provides level information and, optionally, profile, tier, subprofile, and general constraint information (expressed as PT information). When the profile_tier_level( ) syntax structure is included in a DPS, OlsInScope is an OLS that includes all layers in the entire bitstream that references the DPS. When the profile_tier_level( ) syntax structure is included in a VPS, OlsInScope is one or more OLSs specified by the VPS. When the profile_tier_level( ) syntax structure is included in an SPS, OlsInScope is an OLS that includes only layers that are the lowest layer among the layers that reference the SPS, which should be independent layers.

[0146] general_profile_idc indicates the profile to which OlsInScope conforms. general_tier_flag specifies the tier context for the interpretation of general_level_idc. num_sub_profiles specifies the number of general_sub_profile_idc[i] syntax elements. general_sub_profile_idc[i] indicates the ith interoperability metadata being registered. general_level_idc indicates the level to which OlsInScope conforms. Note that a higher value of general_level_idc indicates a higher level. The maximum level signaled in the DPS for OlsInScope may be higher than the level signaled in the SPS for the CVS contained within the OlsInScope. Note also that when OlsInScope conforms to multiple profiles, general_profile_idc should indicate the profile that provides the preferred decoded result or preferred bitstream identification, as determined by the encoder. Please also note that when the profile_tier_level( ) syntax structure is included in the DPS and the CVS of OlsInScope conforms to different profiles, the general_profile_idc and level_idc should indicate the profile and level to the decoder that can decode the OlsInScope.

[0147] sub_layer_level_present_flag[i] equal to 1 specifies that level information is present in the profile_tier_level( ) syntax structure for the sub-layer representation with TemporalId equal to i. sub_layer_level_present_flag[i] equal to 0 specifies that level information is not present in the profile_tier_level( ) syntax structure for the sub-layer representation with TemporalId equal to i. ptl_alignment_zero_bits shall be equal to 0. The semantics of the syntax element sub_layer_level_idc[i], apart from the specification of inference for non-present values, is the same as the syntax element general_level_idc, but applies to sub-layer representations with TemporalId equal to i.

[0148] Exemplary DPB parameter semantics are as follows: The dpb_parameters(maxSubLayersMinus1, subLayerInfoFlag) syntax structure provides information on the DPB size, maximum picture reordering number, and maximum latency for each CLVS of the CVS. When the dpb_parameters( ) syntax structure is included in a VPS, the OLS to which the dpb_parameters( ) syntax structure applies is specified by the VPS. When the dpb_parameters( ) syntax structure is included in an SPS, the dpb_parameters( ) syntax structure applies to an OLS that includes only layers that are the lowest layer among the layers that reference the SPS, which shall be independent layers.

[0149] max_dec_pic_buffering_minus1[i]+1 specifies, for each CLVS of the CVS, the maximum required size of the decoded picture buffer in units of the picture storage buffer when Htid is equal to i. The value of max_dec_pic_buffering_minus1[i] should be in the range of 0 to MaxDpbSize-1, inclusive. When i is greater than 0, max_dec_pic_buffering_minus1[i] should be greater than or equal to max_dec_pic_buffering_minus1[i-1]. When max_dec_pic_buffering_minus1[i] is not present for i in the range of 0 to maxSubLayersMinus1-1, inclusive, due to subLayerInfoFlag equal to 0, max_dec_pic_buffering_minus1[i] is inferred to be equal to max_dec_pic_buffering_minus1[maxSubLayersMinus1].

[0150] max_num_reorder_pics[i] specifies, for each CLVS in the CVS, the maximum allowable number of pictures in the CLVS that may precede any picture in the CLVS in decoding order and follow it in output order when Htid is equal to i. The value of max_num_reorder_pics[i] should be in the range from 0 to max_dec_pic_buffering_minus1[i], inclusive. When i is greater than 0, max_num_reorder_pics[i] should be greater than or equal to max_num_reorder_pics[i-1]. When max_num_reorder_pics[i] is not present for i in the range from 0 to maxSubLayersMinus1-1, inclusive, due to subLayerInfoFlag equal to 0, max_num_reorder_pics[i] is inferred to be equal to max_num_reorder_pics[maxSubLayersMinus1].

[0151] max_latency_increase_plus1[i] not equal to 0 is used to calculate the value of MaxLatencyPictures[i], which specifies, for each CLVS in the CVS, the maximum number of pictures in the CLVS that may precede any picture of the CLVS in output order and follow that picture in decoding order when Htid is equal to i. When max_latency_increase_plus1[i] is not equal to 0, the value of MaxLatencyPictures[i] may be specified as follows: MaxLatencyPictures[i]=max_num_reorder_pics[i]+max_latency_increase_plus1[i]-1 When max_latency_increase_plus1[i] is equal to 0, the corresponding limit is not expressed.

[0152] The value of max_latency_increase_plus1[i] shall be in the range of 0 to 2-2, inclusive. When max_latency_increase_plus1[i] is not present for i in the range of 0 to maxSubLayersMinus1-1, inclusive, due to subLayerInfoFlag equal to 0, max_latency_increase_plus1[i] is inferred to be equal to max_latency_increase_plus1[maxSubLayersMinus1].

[0153] Exemplary general HRD parameters semantics are as follows: The general_hrd_parameters() syntax structure specifies the HRD parameters used in HRD operations. num_ols_hrd_params_minus1+1 specifies the number of ols_hrd_parameters() syntax structures present in the general_hrd_parameters() syntax structure. The value of num_ols_hrd_params_minus1 should be in the range of 0 to 63, inclusive. When TotalNumOlss is greater than 1, the value of num_ols_hrd_params_minus1 is inferred to be equal to 0. hrd_cpb_cnt_minus1+1 specifies the number of alternative CPB specifications in the CVS bitstream. The value of hrd_cpb_cnt_minus1 should be in the range of 0 to 31, inclusive. hrd_max_temporal_id[i] specifies the TemporalId of the top-level sublayer representation whose HRD parameters are included in the i-th layer_level_hrd_parameters() syntax structure. The value of hrd_max_temporal_id[i] should be in the range of 0 to vps_max_sub_layers_minus1, inclusive. When vps_max_sub_layers_minus1 is equal to 0, the value of hrd_max_temporal_id[i] is inferred to be equal to 0. ols_hrd_idx[i] specifies the index of the ols_hrd_parameters() syntax structure that applies to the i-th OLS. The value of ols_hrd_idx[[i] should be in the range of 0 to num_ols_hrd_params_minus1, inclusive. When not present, the value of ols_hrd_idx[[i] is inferred to be equal to 0.

[0154] The semantics of an example reference picture list structure are as follows: The ref_pic_list_struct(listIdx, rplsIdx) syntax structure may be present in an SPS or in a slice header. Depending on whether the syntax structure is included in a slice header or an SPS, the following applies: If present in a slice header, the ref_pic_list_struct(listIdx, rplsIdx) syntax structure specifies the reference picture list listIdx of the current picture (the picture that contains the slice). Otherwise (present in the SPS), the ref_pic_list_struct(listIdx, rplsIdx) syntax structure specifies candidates for the reference picture list listIdx, and in the semantics specified in the remainder of this section, the term current picture refers to each picture in the CVS that has one or more slices with ref_pic_list_idx[listIdx] equal to an index into the list of ref_pic_list_struct(listIdx, rplsIdx) syntax structures contained in the SPS and that references the SPS. num_ref_entries[listIdx][rplsIdx] specifies the number of entries in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure. The value of num_ref_entries[listIdx][rplsIdx] should be in the range from 0 to MaxDecPicBuffMinus1+14, inclusive.

[0155] An exemplary general decoding process is as follows: The input to this process is a bitstream BitstreamToDecode. The output of this process is a list of decoded pictures. The decoding process is specified such that all decoders conforming to a specified profile and level will produce numerically identical cropped decoded output pictures when invoking the decoding process associated with that profile on a bitstream conforming to that profile and level. Any decoding process that produces cropped decoded output pictures identical to those produced by the process described herein (with the correct output order or output timing, as specified) conforms to the decoding process requirements.

[0156] For each IRAP AU in the bitstream, the following applies: If the AU is the first AU in the bitstream in decoding order, or the respective picture is an Instantaneous Decoding Refresh (IDR) picture, or the respective picture is the first picture of the layer following the end of the sequence NAL unit in decoding order, then the variable NoIncorrectPicOutputFlag is set equal to 1. Otherwise, if the variable HandleCraAsCvsStartFlag is set to a value for the AU, then HandleCraAsCvsStartFlag is set equal to the value provided by the tan external mechanism and NoIncorrectPicOutputFlag is set equal to HandleCraAsCvsStartFlag. Otherwise, HandleCraAsCvsStartFlag and NoIncorrectPicOutputFlag are both set equal to 0.

[0157] For each Gradual Decoding Refresh (GDR) AU in the bitstream, the following applies: The variable NoIncorrectPicOutputFlag is set equal to 1 if the AU is the first AU in the bitstream in decoding order or the respective picture is the first picture of the layer following the end of the sequence NAL unit in decoding order. Otherwise, if some external mechanism is available to set the variable HandleGdrAsCvsStartFlag to a value for the AU, HandleGdrAsCvsStartFlag is set equal to the value provided by the external mechanism and NoIncorrectPicOutputFlag is set equal to HandleGdrAsCvsStartFlag. Otherwise, HandleGdrAsCvsStartFlag and NoIncorrectPicOutputFlag are both set equal to 0. For both IRAP and GDR pictures, the above operations are used to identify the CVS in the bitstream. Decoding is repeatedly called for each coded picture of BitstreamToDecode in decoding order.

[0158] An exemplary decoding process for reference picture list construction is as follows: This process is invoked at the beginning of the decoding process for each slice of a non-IDR picture. Reference pictures are addressed through a reference index. The reference index is an index into the reference picture list. When decoding an I slice, the reference picture list is not used in decoding the slice data. When decoding a P slice, only reference picture list 0 (e.g., RefPicList[0]) is used in decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (e.g., RefPicList[1]) are used in decoding the slice data.

[0159] The following constraints apply for bitstream conformance: For each i equal to 0 or 1, num_ref_entries[i][RplsIdx[i]] should not be less than NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] should be present in the DPB and should have a TemporalId less than or equal to the TemporalId of the current picture. The picture referenced by each entry in RefPicList[0] or RefPicList[1] should not be the current picture and should have a non_reference_picture_flag equal to 0. A short-term reference picture (STRP) entry in RefPicList[0] or RefPicList[1] of a slice of a picture and a long-term reference picture (LTRP) entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture should not reference the same picture. There should be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by that entry is 224 or more.

[0160] 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 should be less than or equal to MaxDecPicBuffMinus1, and setOfRefPics should be the same for all slices of a picture. When the current picture is a Stepwise Temporal Sub-layer Access (STSA) picture, there should be no active entries in RefPicList[0] or RefPicList[1] with TemporalId equal to the TemporalId of the current picture. When the current picture is a picture that follows, in decoding order, an STSA picture with TemporalId equal to the TemporalId of the current picture, there shall be no picture with TemporalId equal to the TemporalId of the current picture included as an active entry in RefPicList[0] or RefPicList[1] that precedes the STSA picture in decoding order.

[0161] The pictures referenced by each Inter-Layer Reference Picture (ILRP) entry in RefPicList[0] or RefPicList[1] of the slices of the current picture shall be in the same access unit as the current picture. The pictures referenced by each ILRP entry in RefPicList[0] or RefPicList[1] of the slices of the current picture shall be present in the DPB and shall have a nuh_layer_id less than the nuh_layer_id of the current picture. Each ILRP entry in RefPicList[0] or RefPicList[1] of a slice shall be an active entry.

[0162] An example HRD specification is as follows: The HRD is used to check the conformance of bitstreams and decoders. A set of bitstream conformance tests is used to check the conformance of the entire bitstream, denoted as entireBitstream. The set of bitstream conformance tests is for testing the conformance of each OP of each OLS specified by the VPS.

[0163] For each test, the following ordered steps are applied in the order listed, followed by the process described after these steps in this section: An operation point to be tested, denoted targetOp, is selected by selecting a target OLS with OLS index opOlsIdx and highest TemporalId value opTid. The value of opOlsIdx is in the range from 0 to TotalNumOlss-1, inclusive. The value of opTid is in the range from 0 to vps_max_sub_layers_minus1, inclusive. For each pair of selected values ​​of opOlsIdx and opTid, such that the sub-bitstream output by invoking the sub-bitstream extraction process with entireBitstream, opOlsIdx, and opTid as inputs satisfies the following conditions: There is at least one VCL NAL unit with nuh_layer_id equal to each of the values ​​of nuh_layer_id in LayerIdInOls[opOlsIdx] in BitstreamToDecode. There is at least one VCL NAL unit with TemporalId equal to opTid in BitstreamToDecode.

[0164] If the layers in targetOp include all layers in the entireBitstream and opTid is greater than or equal to the highest TemporalId value among all NAL units in the entireBitstream, then BitstreamToDecode is set to be identical to the entireBitstream. Otherwise, BitstreamToDecode is set to be output by invoking a sub-bitstream extraction process with entireBitstream, opOlsIdx, and opTid as input. The values ​​of TargetOlsIdx and Htid are set equal to the opOlsIdx and opTid of targetOp, respectively. A value of ScIdx is selected. The selected ScIdx shall be in the range from 0 to hrd_cpb_cnt_minus1, inclusive. The access unit in BitstreamToDecode associated with the buffering period SEI message applicable to TargetOlsIdx (present in TargetLayerBitstream or available through an external mechanism) is selected as the HRD initialization point and is referred to as access unit 0 for each layer in the target OLS.

[0165] The following steps are applied to each layer with OLS layer index TargetOlsLayerIdx in the target OLS. The ols_hrd_parameters() syntax structures and sub_layer_hrd_parameters() syntax structures applicable to BitstreamToDecode are selected as follows: The ols_hrd_idx[TargetOlsIdx]th ols_hrd_parameters() syntax structure in the VPS (or provided through an external mechanism) is selected. Within the selected ols_hrd_parameters( ) syntax structure, if BitstreamToDecode is a type I bitstream, then the sub_layer_hrd_parameters(Htid) syntax structure immediately following the condition if(general_vcl_hrd_params_present_flag) is selected and the variable NalHrdModeFlag is set equal to 0, otherwise (BitstreamToDecode is a type II bitstream), then the sub_layer_hrd_parameters(Htid) syntax structure immediately following either the condition if(general_vcl_hrd_params_present_flag) (in which case the variable NalHrdModeFlag is set equal to 0) or the condition if(general_nal_hrd_params_present_flag) (in which case the variable NalHrdModeFlag is set equal to 1) is selected. When BitstreamToDecode is a Type II bitstream and NalHrdModeFlag is equal to 0, all non-VCL NAL units except filler data NAL units, as well as all leading_zero_8bits, zero_byte, start_code_prefix_one_3bytes, and trailing_zero_8bits syntax elements that form a byte stream from the NAL unit stream, when present, are discarded from BitstreamToDecode and the remaining bitstream is assigned to BitstreamToDecode.

[0166] When decoding_unit_hrd_params_present_flag is equal to 1, the CPB is scheduled to operate either at the access unit level (in this case the variable DecodingUnitHrdFlag is set equal to 0) or at the decoding unit level (in this case the variable DecodingUnitHrdFlag is set equal to 1). Otherwise, DecodingUnitHrdFlag is set equal to 0 and the CPB is scheduled to operate at the access unit level.

[0167] For each access unit in BitstreamToDecode starting with access unit 0, a buffering period SEI message (present in BitstreamToDecode or available through an external mechanism) associated with the access unit and applied to TargetOlsIdx is selected, a picture timing period SEI message (present in BitstreamToDecode or available through an external mechanism) associated with the access unit and applied to TargetOlsIdx is selected, and when DecodingUnitHrdFlag is equal to 1 and decoding_unit_cpb_params_in_pic_timing_sei_flag is equal to 0, a decoding unit information SEI message (present in BitstreamToDecode or available through an external mechanism) associated with a decoding unit in the access unit and applied to TargetOlsIdx is selected.

[0168] Each conformance test includes a combination of one option in each of the above steps. When there is more than one option for a step, only one option is selected for any particular conformance test. All possible combinations of all steps form the entire set of conformance tests. For each operating point under test, the number of bitstream conformance tests to be performed is equal to n0*n1*n2*n3, where the values ​​of n0, n1, n2, and n3 are specified as follows: n1 is equal to hrd_cpb_cnt_minus1+1. n1 is the number of access units in BitstreamToDecode associated with the buffering period SEI message. n2 is derived as follows: If BitstreamToDecode is a Type I bitstream, then n0 is equal to 1. Otherwise (BitstreamToDecode is a Type II bitstream), then n0 is equal to 2. n3 is derived as follows: If decoding_unit_hrd_params_present_flag is equal to 0, then n3 is equal to 1. Otherwise, n3 is equal to 2.

[0169] The HRD includes a bitstream extractor (optionally present), a coded picture buffer (CPB), an instantaneous decoding process, a decoded picture buffer (DPB) that conceptually contains sub-DPBs for each layer, and output cropping. For each bitstream conformance test, the CPB size (in bits) is CpbSize[Htid][ScIdx], and the DPB parameters max_dec_pic_buffering_minus1[Htid], max_num_reorder_pics[Htid], and MaxLatencyPictures[Htid] for each layer are found in or derived from the dpb_parameters( ) syntax structure that applies to that layer depending on whether the layer is an independent layer and whether the layer is an output layer of the target OLS.

[0170] The HRD may operate as follows: The HRD is initialized at decoding unit 0, and both the CPB and each sub-DPB of the DPB are set to empty (the sub-DPB fullness for each sub-DPB is set to be equal to 0). After initialization, the HRD may not be initialized again by a subsequent buffering period SEI message. The data associated with each decoding unit that flows into each CPB according to a specified arrival schedule is delivered by a virtual stream scheduler (HSS). The data associated with each decoding unit is removed and decoded instantly by an instantaneous decoding process at the CPB removal time of the decoding unit. Each decoded picture is placed in the DPB. A decoded picture is removed from the DPB when the decoded picture is no longer needed for inter-prediction reference and no longer needed for output.

[0171] An exemplary operation of the decoded picture buffer is as follows: These specifications may be applied independently to each set of selected decoded picture buffer (DPB) parameters. The decoded picture buffer conceptually includes sub-DPBs, each of which includes a picture storage buffer for storage of decoded pictures of one layer. Each of the picture storage buffers may include decoded pictures that are marked as used for reference or are retained for later output. The processes described herein are applied sequentially, and are applied independently for each layer starting from the lowest layer in the OLS, in order of increasing values ​​of the nuh_layer_id of the layers in the OLS. When these processes are applied to a particular layer, only the sub-DPB for the particular layer is affected. In the description of these processes, DPB refers to the sub-DPB for a particular layer, and that particular layer is referred to as the current layer.

[0172] In the operation of the Output Timing DPB, decoded pictures in the same access unit with PicOutputFlag equal to 1 are output consecutively in ascending order of the value of the decoded pictures' nuh_layer_id. Let picture n and the current picture be the coded or decoded pictures of access unit n for a particular value of nuh_layer_id, where n is a non-negative integer. Removal of a picture from the DPB before the decoding of the current picture occurs as follows: Removal of a picture from the DPB before the decoding of the current picture (but after parsing the slice header of the first slice of the current picture) occurs substantially instantaneously at the CPB removal time of the first decoding unit of access unit n (containing the current picture) and proceeds as follows:

[0173] The decoding process for reference picture list construction is invoked, and the decoding process for reference picture marking is invoked. The following ordered steps are applied when the current AU is a Coded Video Sequence Start (CVSS) AU that is not AU0. The variable NoOutputOfPriorPicsFlag is derived for the decoder under test as follows: If the values ​​of pic_width_max_in_luma_samples, pic_height_max_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8, or max_dec_pic_buffering_minus1[Htid] derived for any picture in the current AU differ from the values ​​of pic_width_in_luma_samples, pic_height_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8, or max_dec_pic_buffering_minus1[Htid] respectively derived for a preceding picture in the same CLVS, NoOutputOfPriorPicsFlag may be set to 1 by the decoder under test, regardless of the value of no_output_of_prior_pics_flag. Although setting NoOutputOfPriorPicsFlag equal to no_output_of_prior_pics_flag may be preferable under these conditions, the decoder under test is permitted to set NoOutputOfPriorPicsFlag to 1 in this case. Otherwise, NoOutputOfPriorPicsFlag is set equal to no_output_of_prior_pics_flag.

[0174] The derived value of NoOutputOfPriorPicsFlag for the decoder under test is applied to the HRD such that when the value of NoOutputOfPriorPicsFlag is equal to 1, all picture storage buffers in the DPB are emptied without output of the pictures they contain and the DPB fullness is set equal to 0. When both of the following conditions are true for any picture k in the DPB, all such pictures k in the DPB are removed from the DPB: Picture k may be marked as unused for reference, or picture k may have PictureOutputFlag equal to 0, or the DPB output time is less than or equal to the CPB removal time of the first decoding unit (denoted as decoding unit m) of the current picture n, and DpbOutputTime[k] is less than or equal to DuCpbRemovalTime[m]. For each picture removed from the DPB, the DPB fullness is decremented by 1.

[0175] The operation of the output order DPB may be as follows. These processes may be applied independently for each set of selected decoded picture buffer DPB parameters. The decoded picture buffer conceptually contains sub-DPBs, each of which contains a picture storage buffer for storage of decoded pictures of one layer. Each of the picture storage buffers contains decoded pictures that are marked as being used for reference or are kept for future output. The process for output and removal of a picture from the DPB is invoked before the decoding of the current picture, followed by the invocation of a process for marking and storage of the current decoded picture, and finally the invocation of a process for additional bumping. These processes are applied independently for each layer, starting with the lowest layer in the OLS, in order of increasing values ​​of the nuh_layer_id of the layers in the OLS. When these processes are applied for a particular layer, only the sub-DPB for the particular layer is affected.

[0176] In the operation of the Output Order DPB, similar to the operation of the Output Timing DPB, decoded pictures with PicOutputFlag equal to 1 within the same access unit are also output consecutively in ascending order of the value of nuh_layer_id of the decoded pictures. Let picture n and current picture be the coded or decoded pictures of access unit n for a particular value of nuh_layer_id, where n is a non-negative integer. The output and removal of pictures from the DPB are described as follows:

[0177] Output and removal of a picture from the DPB before the decoding of the current picture (but after parsing the slice header of the first slice of the current picture) occurs substantially instantaneously when the first decoding unit of the access unit containing the current picture is removed from the CPB, and proceeds as follows: The decoding process for reference picture list construction and the decoding process for reference picture marking are invoked. If the current AU is a CVSS AU that is not AU0, the following ordered steps are applied: The variable NoOutputOfPriorPicsFlag is derived for the decoder under test as follows: If the values ​​of pic_width_max_in_luma_samples, pic_height_max_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8, or max_dec_pic_buffering_minus1[Htid] derived for any picture in the current AU differ from the values ​​of pic_width_in_luma_samples, pic_height_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8, or max_dec_pic_buffering_minus1[Htid] respectively derived for a preceding picture in the same CLVS, NoOutputOfPriorPicsFlag may be set to 1 by the decoder under test, regardless of the value of no_output_of_prior_pics_flag.

[0178] Although setting NoOutputOfPriorPicsFlag equal to no_output_of_prior_pics_flag may be preferable under these conditions, the decoder under test is allowed to set NoOutputOfPriorPicsFlag to 1 in this case. Otherwise, NoOutputOfPriorPicsFlag is set equal to no_output_of_prior_pics_flag. The value of NoOutputOfPriorPicsFlag derived for the decoder under test is applied for the HRD as follows: If NoOutputOfPriorPicsFlag is equal to 1, all picture storage buffers in the DPB are emptied without output of the pictures they contain and the DPB fullness is set equal to 0. Otherwise (NoOutputOfPriorPicsFlag is equal to 0), all picture storage buffers containing pictures marked as not needed for output and not used for reference are emptied (without output), all non-empty picture storage buffers in the DPB are emptied by repeatedly calling bumping, and the DPB fullness is set equal to 0.

[0179] Otherwise (the current picture is not a CLVSS picture), all picture storage buffers containing pictures marked as not needed for output and not used for reference are emptied (without output). For each picture storage buffer emptied, the DPB fullness is decremented by one. When one or more of the following conditions are true, the bumping process is repeatedly invoked while further decrementing the DPB fullness by one for each additional picture storage buffer emptied until none of the following conditions are true: The number of pictures in the DPB that are marked as needed for output is greater than max_num_reorder_pics[Htid]; max_latency_increase_plus1[Htid] is not equal to 0 and there is at least one picture in the DPB that is marked as needed for output whose associated variable PicLatencyCount is greater than or equal to MaxLatencyPictures[Htid]; The number of pictures in the DPB is greater than or equal to max_dec_pic_buffering_minus1[Htid]+1.

[0180] In one example, the additional bumping may occur as follows: The specified process may occur substantially instantaneously when the last decoding unit of access unit n, which contains the current picture, is removed from the CPB. When the current picture has PictureOutputFlag equal to 1, for each picture in the DPB that is marked as needed for output and follows the current picture in output order, the associated variable PicLatencyCount is set equal to PicLatencyCount+1. The following also applies: If the current decoded picture has PictureOutputFlag equal to 1, the current decoded picture is marked as needed for output and the associated variable PicLatencyCount is set equal to 0. Otherwise (the current decoded picture has PictureOutputFlag equal to 0), the current decoded picture is marked as not needed for output.

[0181] The bumping process is repeatedly called when one or more of the following conditions are true, until none of the following conditions are true: The number of pictures in the DPB that are marked as needed for output is greater than max_num_reorder_pics[Htid]. max_latency_increase_plus1[Htid] is not equal to 0 and there is at least one picture in the DPB that is marked as needed for output whose associated variable PicLatencyCount is greater than or equal to MaxLatencyPictures[Htid].

[0182] The bumping process includes the following ordered steps: The picture or pictures that are first for output are selected as those with the minimum value of PicOrderCntVal of all pictures in the DPB marked as needed for output. Each of these pictures is cropped using the conformance cropping window for pictures in ascending nuh_layer_id order, the cropped picture is output, and the picture is marked as not needed for output. Each picture storage buffer, including pictures marked as unused for reference, that was one of the cropped and output pictures is emptied and the fullness of the associated sub-DPB is decremented by one. For any two pictures picA and picB that belong to the same CVS and are output by the bumping process, when picA is output earlier than picB, the value of PicOrderCntVal of picA is less than the value of PicOrderCntVal of picB.

[0183] An exemplary sub-bitstream extraction process is as follows: The inputs to this process are the bitstream inBitstream, a target OLS index targetOlsIdx, and a target highest TemporalId value tIdTarget. The output of this process is the sub-bitstream outBitstream. Bitstream conformance may require that for any input bitstream, the output from this process having as input the bitstream, targetOlsIdx equal to an index into a list of OLSs specified by the VPS, and tIdTarget equal to any value in the range from 0 to 6, inclusive, and that an output sub-bitstream that satisfies the following conditions shall be a conforming bitstream: The output sub-bitstream contains at least one VCL NAL unit with nuh_layer_id equal to each of the values ​​of nuh_layer_id in LayerIdInOls[targetOlsIdx]. The output sub-bitstream contains at least one VCL NAL unit with TemporalId equal to tIdTarget. A conforming bitstream contains one or more coded slice NAL units with TemporalId equal to 0, but may not contain any coded slice NAL units with nuh_layer_id equal to 0.

[0184] The output sub-bitstream OutBitstream is derived as follows: The bitstream outBitstream is set to be identical to the bitstream inBitstream. All NAL units with TemporalId greater than tIdTarget are removed from outBitstream. All NAL units with nuh_layer_id that are not included in the list LayerIdInOls[targetOlsIdx] are removed from outBitstream. All SEI NAL units that contain a scalable nesting SEI message with nesting_ols_flag equal to 1 such that NestingOlsIdx[i] is equal to targetOlsIdx and for no value of i in the range from 0 to nesting_num_olss_minus1, inclusive, are removed from outBitstream. When targetOlsIdx is greater than 0, all SEI NAL units, including non-scalable nested SEI messages with payloadType equal to 0 (buffering duration), 1 (picture timing), or 130 (decoding unit information), are removed from outBitstream.

[0185] The syntax of an exemplary scalable nesting SEI message is as follows:

[0186] [Table 7]

[0187] Exemplary general SEI payload semantics are as follows: For the applicable layers or OLSs of a non-scalable nested SEI message, the following applies: For a non-scalable nested SEI message, when payloadType is equal to 0 (buffering duration), 1 (picture timing), or 130 (decoding unit information), the non-scalable nested SEI message applies only to the 0th OLS. For a non-scalable nested SEI message, when payloadType is equal to any value in VclAssociatedSeiList, the non-scalable nested SEI message applies only to layers whose VCL NAL unit has nuh_layer_id equal to the nuh_layer_id of the SEI NAL unit that contains the SEI message.

[0188] Bitstream conformance may require that the following restrictions apply to the value of nuh_layer_id of an SEI NAL unit: When a non-scalable nested SEI message has payloadType equal to 0 (buffering duration), 1 (picture timing), or 130 (decoding unit information), the SEI NAL unit that contains the non-scalable nested SEI message should have nuh_layer_id equal to vps_layer_id[0]. When a non-scalable nested SEI message has payloadType equal to any value in VclAssociatedSeiList, the SEI NAL unit that contains the non-scalable nested SEI message should have nuh_layer_id equal to the value of nuh_layer_id of the VCL NAL unit associated with the SEI NAL unit. An SEI NAL unit containing a scalable nesting SEI message should have a nuh_layer_id equal to the minimum of nuh_layer_id of all layers to which the scalable nesting SEI message applies (when nesting_ols_flag of the scalable nesting SEI message is equal to 0) or the minimum of nuh_layer_id of all layers in the OLS to which the scalable nesting SEI message applies (when nesting_ols_flag of the scalable nesting SEI message is equal to 1).

[0189] The semantics of an exemplary scalable nesting SEI message are as follows: The scalable nesting SEI message provides a mechanism to associate an SEI message with a particular OLS or with a particular layer. The scalable nesting SEI message contains one or more SEI messages. An SEI message contained in a scalable nesting SEI message is also referred to as a scalable nest SEI message. Bitstream conformance may require that the following restrictions apply to the inclusion of SEI messages within a scalable nesting SEI message:

[0190] An SEI message with payloadType equal to 132 (decoded picture hash) or 133 (scalable nesting) may not be included in a scalable nesting SEI message. When a scalable nesting SEI message contains a buffering period, picture timing, or decoding unit information SEI message, the scalable nesting SEI message should not contain any other SEI message with payloadType not equal to 0 (buffering period), 1 (picture timing), or 130 (decoding unit information).

[0191] Bitstream conformance may require that the following restrictions apply to the value of nal_unit_type of SEI NAL units that contain scalable nesting SEI messages: When a scalable nesting SEI message contains an SEI message with payloadType equal to 0 (buffering duration), 1 (picture timing), 130 (decoding unit information), 145 (dependent RAP indication), or 168 (frame field information), the SEI NAL unit that contains the scalable nesting SEI message should have nal_unit_type equal to PREFIX_SEI_NUT.

[0192] nesting_ols_flag equal to 1 specifies that the scalable nesting SEI message applies to a specific OLS. nesting_ols_flag equal to 0 specifies that the scalable nesting SEI message applies to a specific layer. Bitstream conformance may require that the following restrictions on the value of nesting_ols_flag apply: When the scalable nesting SEI message contains an SEI message with payloadType equal to 0 (buffering duration), 1 (picture timing), or 130 (decoding unit information), the value of nesting_ols_flag should be equal to 1. When the scalable nesting SEI message contains an SEI message with payloadType equal to a value in VclAssociatedSeiList, the value of nesting_ols_flag should be equal to 0. nesting_num_olss_minus1+1 specifies the number of OLSs to which the scalable nesting SEI message applies. The value of nesting_num_olss_minus1 should be in the range 0 to TotalNumOlss-1, inclusive.

[0193] nesting_ols_idx_delta_minus1[i] is used to derive the variable NestingOlsIdx[i], which specifies the OLS index of the ith OLS to which the scalable nesting SEI message applies when nesting_ols_flag is equal to 1. The value of nesting_ols_idx_delta_minus1[i] should be in the range from 0 to TotalNumOlss-2, inclusive. The variable NestingOlsIdx[i] may be derived as follows: if(i==0) NestingOlsIdx[i]=nesting_ols_idx_delta_minus1[i] else NestingOlsIdx[i]=NestingOlsIdx[i-1]+nesting_ols_idx_delta_minus1[i]+1

[0194] nesting_all_layers_flag equal to 1 specifies that the scalable nesting SEI message applies to all layers with nuh_layer_id greater than or equal to the nuh_layer_id of the current SEI NAL unit. nesting_all_layers_flag equal to 0 specifies that the scalable nesting SEI message may or may not apply to all layers with nuh_layer_id greater than or equal to the nuh_layer_id of the current SEI NAL unit. nesting_num_layers_minus1+1 specifies the number of layers to which the scalable nesting SEI message applies. The value of nesting_num_layers_minus1 should be in the range from 0 to vps_max_layers_minus1-GeneralLayerIdx[nuh_layer_id], inclusive, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit. nesting_layer_id[i] specifies the value of nuh_layer_id of the i-th layer to which the scalable nesting SEI message applies when nesting_all_layers_flag is equal to 0. The value of nesting_layer_id[i] should be greater than nuh_layer_id, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit.

[0195] The variable NestingNumLayers, which specifies the number of layers to which the scalable nesting SEI message applies when nesting_ols_flag is equal to 0, and the list NestingLayerId[i], for i in the range from 0 to NestingNumLayers-1, inclusive, which specifies a list of values ​​of nuh_layer_id of the layers to which the scalable nesting SEI message applies, may be derived as follows, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit: if(nesting_all_layers_flag) { NestingNumLayers=vps_max_layers_minus1+1-GeneralLayerIdx[nuh_layer_id] for(i=0; i <NestingNumLayers; i++) NestingLayerId[i]=vps_layer_id[GeneralLayerIdx[nuh_layer_id]+i] } else { NestingNumLayers=nesting_num_layers_minus1+1 for(i=0; i <NestingNumLayers; i++) NestingLayerId[i]=(i==0) ? nuh_layer_id: nesting_layer_id[i] }

[0196] nesting_num_seis_minus1+1 specifies the number of scalable nested SEI messages. The value of nesting_num_seis_minus1 should be in the range of 0 to 63, inclusive. nesting_zero_bit should be equal to 0.

[0197] FIG. 8 is a schematic diagram of an exemplary video coding device 800. The video coding device 800 is suitable for implementing the disclosed examples / embodiments as described herein. The video coding device 800 comprises a downstream port 820, an upstream port 850, and / or a transceiver unit (Tx / Rx) 810 including a transmitter and / or a receiver for communicating data upstream and / or downstream across a network. The video coding device 800 also includes a processor 830 including a logic unit and / or a central processing unit (CPU) for processing data, and a memory 832 for storing data. The video coding device 800 may also comprise electrical, optical-electrical (OE) components, electrical-optical (EO) components, and / or wireless communication components coupled to the upstream port 850 and / or the downstream port 820 for communication of data over an electrical, optical, or wireless communication network. The video coding device 800 may also include input and / or output (I / O) devices 860 for communicating data to and from a user. The I / O devices 860 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I / O devices 860 may also include input devices such as a keyboard, mouse, trackball, etc., and / or corresponding interfaces for interacting with such output devices.

[0198] The processor 830 is implemented by hardware and software. The processor 830 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor 830 communicates with the downstream port 820, the Tx / Rx 810, the upstream port 850, and the memory 832. The processor 830 comprises a coding module 814. The coding module 814 implements the disclosed embodiments described herein, such as the methods 100, 900, and 1000, which may employ the multi-layer video sequence 600, the bitstream 700, and / or the sub-bitstream 701. The coding module 814 may also implement any other method / mechanism described herein. Furthermore, the coding module 814 may implement the codec system 200, the encoder 300, the decoder 400, and / or the HRD 500. For example, the coding module 814 may be employed to encode, extract, and / or decode a bitstream that includes a simulcast layer and is without a VPS. Furthermore, the coding module 814 may be employed to set and / or infer various syntax elements and / or variables to avoid errors based on a reference to a VPS extracted as part of the sub-bitstream extraction. Thus, the coding module 814 may be configured to execute mechanisms to address one or more of the problems described above. Thus, the coding module 814 causes the video coding device 800 to provide additional functionality and / or coding efficiency when coding video data. Hence, the coding module 814 improves the functionality of the video coding device 800 and also addresses problems specific to video coding techniques. Furthermore, the coding module 814 performs conversions to different states of the video coding device 800.Alternatively, the coding module 814 may be implemented as instructions stored in memory 832 and executed by the processor 830 (eg, as a computer program product stored on a non-transitory medium).

[0199] Memory 832 includes one or more memory types such as a disk, a tape drive, a solid state drive, a read only memory (ROM), a random access memory (RAM), a flash memory, a ternary content addressable memory (TCAM), a static random access memory (SRAM), etc. Memory 832 stores programs when such programs are selected for execution, and may be used as an overflow data storage device to store instructions and data retrieved during execution of the programs.

[0200] 9 is a flowchart of an example method 900 of encoding a multi-layer video sequence into a bitstream, such as bitstream 700, to support VPS 711 removal during sub-bitstream extraction process 729 for simulcast layers. Method 900 may be employed by an encoder, such as codec system 200, encoder 300, and / or video coding device 800, when performing method 100. Additionally, method 900 may operate on HRD 500 and thus perform conformance tests on multi-layer video sequence 600 and / or its extracted layers.

[0201] The method 900 may start when an encoder receives a video sequence and determines, for example, based on user input, to encode the video sequence into a multi-layer bitstream. In step 901, the encoder encodes coded pictures in a set of VCL NAL units into a bitstream. For example, the encoder may encode pictures in the video sequence into one or more layers and encode the layers into a multi-layer bitstream. Thus, the bitstream includes one or more layers. A layer may include a set of VCL NAL units and associated non-VCL NAL units having the same layer Id. As a specific example, a VCL NAL unit may be associated with a layer identified by / with nuh_layer_id. Specifically, a set of VCL NAL units is part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id. A layer may include a set of VCL NAL units that contain video data of an encoded picture as well as any parameter set used to code such a picture. Such parameters may be included in a VPS, SPS, PPS, picture header, slice header, or other parameter set or syntax structure. As a specific example, an encoder may encode an SPS including sps_video_parameter_set_id into a bitstream. One or more of the layers may be output layers. Layers that are not output layers are referred to as reference layers and are encoded to support reconstructing output layers, but such supporting layers are not intended for output at a decoder. In this manner, an encoder can encode various combinations of layers for transmission to a decoder upon request. Layers may be transmitted as desired to allow a decoder to obtain different representations of a video sequence depending on network conditions, hardware capabilities, and / or user settings.In this example, at least one of the layers is a simulcast layer that does not use inter-layer prediction.

[0202] In step 903, the HRD operating in the encoder can perform a set of bitstream conformance tests on the layer to ensure conformance with VVC or other standards. For example, the HRD can obtain sps_video_parameter_set_id from the SPS. sps_video_parameter_set_id specifies the value of vps_video_parameter_set_id of the VPS referenced by the SPS when sps_video_parameter_set_id is greater than 0. Furthermore, when sps_video_parameter_set_id is equal to 0, the SPS does not reference the VPS, and the VPS is not referenced when decoding each pre-coded layer video sequence that references the SPS. Thus, sps_video_parameter_set_id is set to 0 and / or inferred to be 0 when sps_video_parameter_set_id is obtained from an SPS referenced by a pre-coded layer video sequence included in the simulcast layer.

[0203] The HRD may set GeneralLayerIdx[nuh_layer_id] to be equal to 0 and / or infer that it is equal to 0 when sps_video_parameter_set_id is equal to 0. GeneralLayerIdx[nuh_layer_id] is equal to the current layer index for the corresponding layer and thus indicates the current layer index. Hence, the current layer index for the simulcast layer is set / inferred to be 0. Furthermore, the HRD may infer that the value of vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1 when sps_video_parameter_set_id is equal to 0. Specifically, vps_independent_layer_flag[i] may be included in the VPS and set to 0 to indicate that the i-th layer uses inter-layer prediction, or set to 1 to indicate that the i-th layer does not use inter-layer prediction. Hence, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the current layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. When the current layer is a simulcast layer, the VPS is omitted and inter-layer prediction is not employed. Thus, the inference of a value of 1 when sps_video_parameter_set_id is equal to 0 ensures that the simulcast layer works properly during decoding in the HRD while avoiding references to the VPS, which is extracted during bitstream extraction for the simulcast layer. Hence, the inference avoids sub-bitstream extraction errors that would otherwise occur when the VPS is removed for the simulcast layer.The HRD may then decode the coded picture from the VCL NAL unit in the simulcast layer based on the SPS, sps_video_parameter_set_id, GeneralLayerIdx[nuh_layer_id], and / or vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] to generate a decoded picture. Thus, the HRD can verify whether the simulcast layer of the multi-layer bitstream conforms to the bitstream without unexpected errors caused by the omission of the VPS for the simulcast layer.

[0204] In step 905, the encoder can store the bitstream for communication to the decoder upon request. The encoder can also perform sub-bitstream extraction to obtain the simulcast layer and transmit the bitstream / sub-bitstream to the encoder when desired.

[0205] 10 is a flowchart of an example method 1000 of decoding a video sequence from a bitstream, such as sub-bitstream 701, that includes a simulcast layer extracted from a multi-layer bitstream, such as bitstream 700, where VPS 711 has been removed during sub-bitstream extraction process 729. Method 1000 may be employed by a decoder, such as codec system 200, decoder 400, and / or video coding device 800, when performing method 100. Additionally, method 1000 may be employed on multi-layer video sequence 600, or an extracted layer thereof, that has been checked for conformance by an HRD, such as HRD 500.

[0206] Method 1000 may start when a decoder begins to receive a bitstream including a coded video sequence of a simulcast layer extracted from a multi-layer bitstream, e.g., as a result of method 900. In step 1001, the decoder receives a bitstream including a simulcast layer extracted from a multi-layer bitstream by an encoder or other intermediate content server. The simulcast layer includes a coded layer video sequence including a set of coded pictures. For example, the bitstream includes coded pictures included in a set of one or more VCL NAL units associated with a simulcast layer, where each coded picture is identified by / has a nuh_layer_id. A layer may include a set of VCL NAL units and associated non-VCL NAL units having the same layer Id. For example, a layer may include a set of VCL NAL units that contain the video data of an encoded picture as well as any parameter set used to code such a picture. Hence, a set of VCL NAL units is part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id. A simulcast layer is also an output layer and does not employ inter-layer prediction. The bitstream also includes an SPS that includes sps_video_parameter_set_id, which specifies the value of vps_video_parameter_set_id of the VPS referenced by the SPS when sps_video_parameter_set_id is greater than 0. Additionally, when sps_video_parameter_set_id is equal to 0, the SPS does not reference the VPS, and the VPS is not referenced when decoding each coded layer video sequence that references the SPS.Thus, sps_video_parameter_set_id is set to and / or inferred to be 0 when sps_video_parameter_set_id is obtained from an SPS referenced by a precoded layer video sequence included in a simulcast layer. Additionally, a bitstream does not include a VPS when the bitstream includes only a simulcast layer.

[0207] In step 1003, the decoder may set GeneralLayerIdx[nuh_layer_id] equal to 0 and / or infer that it is equal to 0 when sps_video_parameter_set_id is equal to 0. GeneralLayerIdx[nuh_layer_id] is equal to the current layer index for the corresponding layer and thus indicates the current layer index. Hence, the current layer index for the received simulcast layer is set / inferred to be 0.

[0208] In step 1005, the decoder may set / infer that the value of vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] is equal to 1 when sps_video_parameter_set_id is equal to 0. Specifically, vps_independent_layer_flag[i] may be included in the VPS and set to 0 to indicate that the i-th layer uses inter-layer prediction, or set to 1 to indicate that the i-th layer does not use inter-layer prediction. Hence, vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the current layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction. When the current layer is a simulcast layer, the VPS is omitted from the bitstream and inter-layer prediction is not employed. Thus, the inference of a value of 1 when sps_video_parameter_set_id is equal to 0 ensures that the simulcast layer operates properly during decoding while avoiding references to the VPS, which is extracted during bitstream extraction for the simulcast layer and therefore not received at the decoder. The inference therefore avoids sub-bitstream extraction errors that would otherwise occur when the VPS is removed for the simulcast layer.

[0209] In step 1007, the decoder may decode coded pictures from VCL NAL units in the simulcast layer based on the SPS, sps_video_parameter_set_id, GeneralLayerIdx[nuh_layer_id], and / or vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] to generate decoded pictures. The decoder may then forward the decoded pictures for display as part of a decoded video sequence in step 1009.

[0210] 11 is a schematic diagram of an example system 1100 for coding a multi-layer video sequence into a bitstream 700 to support removal of the VPS 711 during the sub-bitstream extraction process 729 for the simulcast layer. The system 1100 may be implemented by an encoder and a decoder, such as the codec system 200, the encoder 300, the decoder 400, and / or the video coding device 800. Furthermore, the system 1100 may employ the HRD 500 to perform conformance tests on the multi-layer video sequence 600, the bitstream 700, and / or the sub-bitstream 701. In addition, the system 1100 may be employed when implementing the methods 100, 900, and / or 1000.

[0211] The system 1100 includes a video encoder 1102. The video encoder 1102 comprises an encoding module 1103 for encoding a coded picture and an SPS into a bitstream, where the coded picture is encoded into a set of VCL NAL units, where the VCL NAL units are associated with a layer having nuh_layer_id, and where the SPS includes sps_video_parameter_set_id. The video encoder 1102 further comprises an HRD module 1105 for performing a set of bitstream conformance tests on the bitstream by setting GeneralLayerIdx[nuh_layer_id] equal to 0 when sps_video_parameter_set_id is equal to 0, and decoding the coded picture from the VCL NAL units based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture. The video encoder 1102 further comprises a storage module 1106 for storing the bitstream for communication to a decoder. The video encoder 1102 further comprises a transmission module 1107 for transmitting the bitstream towards the video decoder 1110. The video encoder 1102 may be further configured to perform any of the steps of the method 900.

[0212] The system 1100 also includes a video decoder 1110. The video decoder 1110 comprises a receiving module 1111 for receiving a bitstream including an SPS and a coded picture, where the SPS includes sps_video_parameter_set_id and the coded picture is in a set of VCL NAL units associated with a layer having nuh_layer_id. The video decoder 1110 further comprises a setting module 1113 for setting GeneralLayerIdx[nuh_layer_id] equal to 0 when sps_video_parameter_set_id is equal to 0. The video decoder 1110 further comprises a decoding module 1115 for decoding the coded picture from the VCL NAL unit based on GeneralLayerIdx[nuh_layer_id] to generate a decoded picture. The video decoder 1110 further comprises a forwarding module 1117 for forwarding the decoded picture for display as part of a decoded video sequence. The video decoder 1110 may be further configured to perform any of the steps of the method 1000.

[0213] A first component is directly coupled to a second component when there are no intervening components, other than a line, trace, or another medium between the first and second components. A first component is indirectly coupled to a second component when there are intervening components, other than a line, trace, or another medium between the first and second components. The term "coupled" and variations thereof include both directly coupled and indirectly coupled. Also, use of the term "about" means a range that includes ±10% of the following number, unless otherwise stated.

[0214] It should also be understood that the steps of the exemplary methods described herein do not necessarily have to be performed in the order described, and the order of steps of such methods should be understood to be merely exemplary. Similarly, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present disclosure.

[0215] Although several embodiments are provided in this disclosure, it can be understood that the disclosed systems and methods can be embodied in many other specific forms without departing from the spirit or scope of the disclosure. The examples should be considered illustrative and not restrictive, and the invention should not be limited to the details set forth in the specification. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0216] In addition, the techniques, systems, subsystems, and methods described and illustrated in various embodiments as discrete or separate may be combined or integrated with other systems, components, techniques, or methods without departing from the scope of the present disclosure. Other examples of changes, substitutions, and alterations will be ascertainable by those skilled in the art and could be made without departing from the spirit and scope disclosed herein. [Explanation of symbols]

[0217] 100 How it works 200 Coding and Decoding (Codec) Systems 201 Segmented Video Signal 211 General Coder Control Component 213 Transform Scaling and Quantization Components 215 In-Picture Estimation Component 217 Intra-Picture Prediction Component 219 Motion Compensation Component 221 Motion Estimation Component 223 Decoded Picture Buffer Component 225 In-Loop Filter Components 227 Filter Control Analysis Component 229 Scaling and Inverse Transformation Components 231 Header Formatting and Context-Adaptive Binary Arithmetic Coding (CABAC) Components 300 Video Encoder 301 Segmented Video Signal 313 Transform and Quantize Components 317 In-Picture Prediction Component 321 Motion Compensation Component 323 Decoded Picture Buffer Component 325 In-Loop Filter Components 329 Inverse Transform and Quantization Components 331 Entropy Coding Component 400 Video Decoder 417 In-Picture Prediction Component 421 Motion Compensation Component 423 Decoded Picture Buffer Component 425 In-Loop Filter Components 429 Inverse Transform and Quantization Components 433 Entropy Decoding Component 500HRD 541 Virtual Stream Scheduler (HSS) 543 CPB 545 Decoding Process Components 547 DPB 549 Output Cropping Component 551 Bitstream 553 Decoding Unit (DU) 555 Decoded DUs 556 Reference Pictures 557 Pictures 559 Output Cropped Picture 600 Multi-layer Video Sequences 621 Inter-layer Prediction 611, 612, 613, 614 Pictures 615, 616, 617, 618 Pictures 621 Inter-layer Prediction 623 Inter Prediction 631 Upper Layer N 632 Lower Layer N+1 700 bitstream 701 Sub-Bitstream 711 VPS 713 SPS 715 Picture Parameter Set (PPS) 717 Slice Header 720 Image data 723 Layer 724 Layer 725 Pictures 726 Pictures 727 Slice 728 slices 729 Sub-Bitstream Extraction Process 731 sps_video_parameter_set_id 732 nuh_layer_id 733 VPS independent layer flag (vps_independent_layer_flag) 735 vps_video_parameter_set_id 741 VCL NAL Units 742 non-VCL NAL units 800 Video Coding Device 810 Transceiver Unit (Tx / Rx) 814 Coding Module 820 Downstream Port 830 Processor 832 Memory 850 Upstream Port 860 Input and / or Output (I / O) Devices 900 ways 1000 ways 1100 System 1102 Video Encoder 1103 Encoding Module 1105 HRD Module 1106 Memory Module 1107 Transmission Module 1110 Video Decoder 1111 Receiver Module 1113 Configuration Module 1115 Decoding Module 1117 Transfer Module

Claims

1. A method implemented by a decoder, comprising: receiving, by the decoder, a bitstream including a sequence parameter set (SPS), a coded layer video sequence (CLVS) that references the SPS for a layer, and a coded picture, the SPS including an SPS video parameter set identifier (sps_video_parameter_set_id), the coded picture being within a set of video coding layer (VCL) NAL units associated with a layer having a network abstraction layer (NAL) unit header layer identifier (nuh_layer_id), and when the layer does not use inter-layer prediction, the SPS has a value of nuh_layer_id equal to the value of nuh_layer_id of the CLVS; setting, by the decoder, a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to the nuh_layer_id equal to 0 when the sps_video_parameter_set_id is equal to 0; and decoding, by the decoder, the coded picture from the VCL NAL unit based on the GeneralLayerIdx[nuh_layer_id] to generate a decoded picture.

2. The method of claim 1 , wherein GeneralLayerIdx[nuh_layer_id] is equal to the current layer index.

3. 3. The method of claim 1 or 2, further comprising the step of inferring, by the decoder, that a value of a video parameter set (VPS) independent layer flag (vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) for GeneralLayerIdx[nuh_layer_id] is equal to 1 when sps_video_parameter_set_id is equal to 0.

4. 4. The method of claim 1, wherein vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction.

5. 5. The method of claim 1, wherein the sps_video_parameter_set_id specifies a value of a VPS parameter set identifier (vps_video_parameter_set_id) when the sps_video_parameter_set_id is greater than 0.

6. A method according to any one of claims 1 to 5, wherein when the sps_video_parameter_set_id is equal to 0, the SPS does not reference a VPS and the VPS is not referenced when decoding each coded layer video sequence that references the SPS.

7. The method of claim 1 , wherein the set of VCL NAL units is part of the layer when the set of VCL NAL units all have a particular value of nuh_layer_id.

8. A method implemented by an encoder, comprising: encoding, by the encoder, into a bitstream a coded picture, a sequence parameter set (SPS), and a coded layered video sequence (CLVS) that references the SPS for a layer, the coded picture being encoded into a set of video coding layer (VCL) network abstraction layer (NAL) units, the VCL NAL units being associated with a layer having a NAL unit header layer identifier (nuh_layer_id), when the layer does not use inter-layer prediction, the SPS has a value of nuh_layer_id equal to the value of nuh_layer_id of the CLVS, and the SPS includes an SPS video parameter set identifier (sps_video_parameter_set_id); setting, by a hypothetical reference decoder operating in the encoder, a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to the nuh_layer_id equal to 0 when the sps_video_parameter_set_id is equal to 0; A hypothetical reference decoder (HRD) running on the encoder decodes the coded picture from the VCL NAL unit based on the GeneralLayerIdx[nuh_layer_id] to generate a decoded picture. performing a set of bitstream conformance tests on the bitstream by the HRD on the encoder; storing, at the encoder, the bitstream for communication to a decoder.

9. The method of claim 8, wherein GeneralLayerIdx[nuh_layer_id] is equal to the current layer index.

10. 10. The method of claim 8 or 9, further comprising a step of inferring, by the HRD running on the encoder, that a value of a video parameter set (VPS) independent layer flag (vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]]) for the GeneralLayerIdx[nuh_layer_id] is equal to 1 when sps_video_parameter_set_id is equal to 0.

11. 11. The method of any one of claims 8 to 10, wherein vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id]] specifies whether the layer with index GeneralLayerIdx[nuh_layer_id] uses inter-layer prediction.

12. 12. A method according to claim 8, wherein the sps_video_parameter_set_id specifies a value of a VPS parameter set identifier (vps_video_parameter_set_id) when the sps_video_parameter_set_id is greater than 0.

13. A method according to any one of claims 8 to 12, wherein when the sps_video_parameter_set_id is equal to 0, the SPS does not reference a VPS and the VPS is not referenced when decoding each coded layer video sequence that references the SPS.

14. The method of any one of claims 8 to 13, wherein the set of VCL NAL units is part of the layer when the set of VCL NAL units all have a particular value of nuh_layer_id.

15. 1. A video coding device, comprising:

15. A video coding device comprising: a processor; a receiver coupled to the processor; a memory coupled to the processor; and a transmitter coupled to the processor, wherein the processor, the receiver, the memory, and the transmitter are configured to perform the method of any one of claims 1 to 14.

16. A non-transitory computer-readable medium comprising a computer program for use by a video coding device, the computer program comprising computer-executable instructions stored on the non-transitory computer-readable medium that, when executed by a processor, causes the video coding device to perform a method according to any one of claims 1 to 14.

17. receiving means for receiving a bitstream including a sequence parameter set (SPS), a coded layer video sequence (CLVS) that references the SPS for a layer, and a coded picture, the SPS including an SPS video parameter set identifier (sps_video_parameter_set_id), the coded picture being within a set of video coding layer (VCL) NAL units associated with a layer having a network abstraction layer (NAL) unit header layer identifier (nuh_layer_id), and when the layer does not use inter-layer prediction, the SPS has a value of nuh_layer_id equal to the value of nuh_layer_id of the CLVS; a setting means for setting a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to the nuh_layer_id to be equal to 0 when the sps_video_parameter_set_id is equal to 0; and decoding means for decoding the coded picture from the VCL NAL unit based on the GeneralLayerIdx[nuh_layer_id] to generate a decoded picture.

18. 18. The decoder of claim 17, further configured to perform a method according to any one of claims 1 to 7.

19. encoding means for encoding into a bitstream a coded picture, a sequence parameter set (SPS), and a coded layered video sequence (CLVS) that references the SPS for a layer, the coded picture being encoded into a set of video coding layer (VCL) network abstraction layer (NAL) units, the VCL NAL units being associated with a layer having a NAL unit header layer identifier (nuh_layer_id), when the layer does not use inter-layer prediction, the SPS having a value of nuh_layer_id equal to the value of nuh_layer_id of the CLVS, and the SPS including an SPS video parameter set identifier (sps_video_parameter_set_id); When the sps_video_parameter_set_id is equal to 0, a general layer index (GeneralLayerIdx[nuh_layer_id]) corresponding to the nuh_layer_id is set equal to 0; Decode the coded picture from the VCL NAL unit based on the GeneralLayerIdx[nuh_layer_id] to generate a decoded picture. a hypothetical reference decoder (HRD) means for performing a set of bitstream conformance tests on said bitstream by and storage means for storing said bitstream for communication to a decoder.

20. 20. The encoder of claim 19, further configured to perform a method according to any one of claims 8 to 14.

Images