OLS for spatial and snr scalability

Abstract

To provide improved compression and decompression techniques that improve compression ratio without sacrificing image quality.SOLUTION: A video coding mechanism is disclosed. The mechanism includes encoding a bitstream comprising one or more layers of coded pictures. A video parameter set (VPS) is also encoded into the bitstream. The VPS includes an output layer set (OLS) mode identification code (ols_mode_idc) specifying that a total number of OLSs specified by the VPS is equal to a number of layers specified by the VPS. The bitstream is stored for communication toward a decoder.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 905,128, entitled "Signalling Of Output Layer Sets For Spatial And SNR Scalabilities," filed September 24, 2019 by Ye-Kui Wang, which is incorporated herein by reference.

[0002] FIELD This disclosure relates generally to video coding, and more particularly to configuring output layer sets (OLS) in multi-layer bitstreams to support spatial and signal-to-noise (SNR) scalability. [Background technology]

[0003] The amount of video data required to render even a relatively short video can be significant, which can create difficulties when the data is to be streamed or otherwise transmitted over communication networks with limited bandwidth capacity. Therefore, video data is generally compressed before being transmitted over modern telecommunications networks. Video size can also be an issue when the video is stored on a storage device, as memory resources may be limited. Often, video compression devices use software and / or hardware at the source to code the video data before transmission or storage, thereby reducing the amount of data needed 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. With limited network resources and an ever-increasing demand for higher video quality, improved compression and decompression techniques that increase compression ratios with little or no sacrifice in image quality are desirable. Summary of the Invention [Means for solving the problem]

[0004] In an embodiment, the present disclosure includes a method implemented in a decoder, the method including the steps of: receiving, by a receiver of the decoder, a bitstream including one or more layers of a coded picture and a video parameter set (VPS), wherein the VPS includes an OLS mode identification code (ols_mode_idc) that specifies that the total number of output layer sets (OLS) specified by the VPS is equal to the number of layers specified by the VPS; determining, by a processor of the decoder, an output layer based on the ols_mode_idc of the VPS; and decoding, by the processor of the decoder, the coded picture from the output layer to generate a decoded picture.

[0005] To support scalability, layers of pictures may be used. For example, video may be coded into multiple layers. A layer may be coded without reference to other layers. Such a layer is called a simulcast layer. Thus, a simulcast layer may be decoded without reference to other layers. As another example, a layer may be coded using inter-layer prediction, which allows a current layer to be coded by including only the differences between the current layer and a reference layer. For example, the current layer and the reference layer may comprise the same video sequence coded by varying characteristics such as the signal-to-noise ratio (SNR), picture size, frame rate, etc. Some video coding systems are configured to simply decode and output the topmost coded layer, indicated by a layer identifier (ID), along with one or more indicated lower layers. This can create problems with scalability, as a decoder may not want to decode the topmost layer. This causes errors when video scalability is attempted in such systems. This can be a significant problem, as requiring the decoder to always support the top layer results in a system that cannot scale to intermediate layers based on different hardware and network requirements.

[0006] This example includes a mechanism for using OLS to support scalability. This includes both spatial scalability and SNR scalability. This example uses the ols_mode_idc syntax element for use in conjunction with OLS. The ols_mode_idc syntax element can be included in a VPS and can be set to 0 to indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layers 0 and i, and that only the top layer is output for each OLS. This supports scalability because a decoder can quickly determine, for example, that the third OLS includes layers 0 through 3 and that the third layer should be decoded and output based on layers 0 through 2. Thus, the decoder may receive only the layers needed to decode the received top layer, which can be decoded and displayed. In this way, the total number of coded layers may not affect the decoding process, and errors may be prevented. Thus, the disclosed mechanisms enhance the capabilities of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder. In certain embodiments, ols_mode_idc saves bits in encoded bitstreams that include multiple OLSs where much data is shared, thus providing savings in streaming servers and bandwidth savings for the transmission of such bitstreams.

[0007] Optionally, in any of the above-described aspects, another implementation of the aspect provides that ols_mode_idc specifies that the i-th OLS includes layers having layer indices from 0 to i, inclusive.

[0008] Optionally, in any of the above-described aspects, another implementation of the aspect provides that ols_mode_idc specifies, for each OLS, that only the top layer of each OLS is the output layer.

[0009] Optionally, in any of the above aspects, another implementation of the aspect provides that ols_mode_idc is equal to 0.

[0010] Optionally, in any of the above-described aspects, another implementation of the aspect provides that the VPS includes a VPS maximum layers minus one (vps_max_layers_minus1) that specifies the number of layers specified by the VPS, which is the maximum allowed number of layers in each coded video sequence (CVS) that references the VPS.

[0011] Optionally, in any of the above-described aspects, another implementation of the aspect specifies that when ols_mode_idc is equal to 0 or when ols_mode_idc is equal to 1, the total number of OLSs (TotalNumOlss) is equal to vps_max_layers_minus1 plus 1.

[0012] Optionally, in any of the above-described aspects, another implementation of the aspect comprises deriving a number of layers in the ith OLS (NumLayersInOls[i]) and a layer identifier (ID) in the OLS (LayerIdInOLS[i][j]) that specifies a value of a network abstraction layer (NAL) unit header layer identifier (nuh_layer_id) of the jth layer of the ith OLS as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 ] Specifies that vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each_layer_is_an_ols_flag is an OLS flag that specifies whether at least one OLS contains two or more layers.

[0013] In an embodiment, the present disclosure includes a method implemented by an encoder, the method including the steps of: encoding, by a processor of the encoder, a bitstream including one or more layers of a coded picture; encoding, by the processor, a VPS into the bitstream, wherein the VPS includes an ols_mode_idc that specifies that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS; and storing, by a memory coupled to the processor, the bitstream for transmission to a decoder.

[0014] To support scalability, layers of a picture may be used. For example, video may be coded into multiple layers. A layer may be coded without reference to other layers. Such a layer is called a simulcast layer. Thus, a simulcast layer may be decoded without reference to other layers. As another example, a layer may be coded using inter-layer prediction. This allows a current layer to be coded by including only the differences between the current layer and a reference layer. For example, the current layer and the reference layer may comprise the same video sequence coded by varying characteristics such as SNR, picture size, frame rate, etc. Some video coding systems are configured to simply decode and output the top-most coded layer indicated by a layer ID along with one or more indicated lower layers. This can create problems with scalability because a decoder may not want to decode the top layer. This can cause errors when video scalability is attempted in such systems. This can be a significant problem, as requiring a decoder to always support the top layer results in a system that cannot scale to intermediate layers based on different hardware and network requirements.

[0015] This example includes a mechanism for using OLS to support scalability. This includes both spatial scalability and SNR scalability. This example uses the ols_mode_idc syntax element for use in conjunction with OLS. The ols_mode_idc syntax element can be included in a VPS and can be set to 0 to indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layers 0 and i, and that only the top layer is output for each OLS. This supports scalability because a decoder can quickly determine, for example, that the third OLS includes layers 0 through 3 and that the third layer should be decoded and output based on layers 0 through 2. Thus, the decoder may receive only the layers needed to decode the received top layer, which can be decoded and displayed. In this way, the total number of coded layers may not affect the decoding process, and errors may be prevented. Thus, the disclosed mechanisms enhance the capabilities of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder. In certain embodiments, ols_mode_idc saves bits in encoded bitstreams that include multiple OLSs where much data is shared, thus providing savings in streaming servers and bandwidth savings for the transmission of such bitstreams.

[0016] Optionally, in any of the above-described aspects, another implementation of the aspect provides that ols_mode_idc specifies that the i-th OLS includes layers having layer indices from 0 to i, inclusive.

[0017] Optionally, in any of the above-described aspects, another implementation of the aspect provides that ols_mode_idc specifies, for each OLS, that only the top layer of each OLS is the output layer.

[0018] Optionally, in any of the above aspects, another implementation of the aspect provides that ols_mode_idc is equal to 0.

[0019] Optionally, in any of the above-described aspects, another implementation of the aspect provides that the VPS includes a vps_max_layers_minus1 that specifies the number of layers specified by the VPS, which is the maximum allowed number of layers in each CVS that references the VPS.

[0020] Optionally, in any of the above-described aspects, another implementation of the aspect provides that when ols_mode_idc is equal to 0 or when ols_mode_idc is equal to 1, TotalNumOlss is equal to vps_max_layers_minus1 plus 1.

[0021] Optionally, in any of the above-described aspects, another implementation of the aspect is to derive NumLayersInOls[i] and LayerIdInOLS[i][j], which specifies a value of nuh_layer_id of the jth layer of the ith OLS, as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 ] Specifies that vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each_layer_is_an_ols_flag is an OLS flag specifying whether at least one OLS contains two or more layers.

[0022] In an embodiment, the present disclosure includes a video coding device including 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 above aspects.

[0023] In an 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 above aspects.

[0024] In an embodiment, the present disclosure includes a decoder including receiving means for receiving a bitstream including one or more layers of a coded picture and a VPS, where the VPS includes an ols_mode_idc that specifies that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS; determining means for determining an output layer based on the ols_mode_idc of the VPS; decoding means for decoding the coded picture from the output layer to generate a decoded picture; and forwarding means for forwarding the decoded picture for display as part of a decoded video sequence.

[0025] To support scalability, layers of a picture may be used. For example, video may be coded into multiple layers. A layer may be coded without reference to other layers. Such a layer is called a simulcast layer. Thus, a simulcast layer may be decoded without reference to other layers. As another example, a layer may be coded using inter-layer prediction. This allows a current layer to be coded by including only the differences between the current layer and a reference layer. For example, the current layer and the reference layer may comprise the same video sequence coded by varying characteristics such as SNR, picture size, frame rate, etc. Some video coding systems are configured to simply decode and output the top-most coded layer indicated by a layer ID along with one or more indicated lower layers. This can create problems with scalability because a decoder may not want to decode the top layer. This can cause errors when video scalability is attempted in such systems. This can be a significant problem, as requiring a decoder to always support the top layer results in a system that cannot scale to intermediate layers based on different hardware and network requirements.

[0026] This example includes a mechanism for using OLS to support scalability. This includes both spatial scalability and SNR scalability. This example uses the ols_mode_idc syntax element for use in conjunction with OLS. The ols_mode_idc syntax element can be included in a VPS and can be set to 0 to indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layers 0 and i, and that only the top layer is output for each OLS. This supports scalability because a decoder can quickly determine, for example, that the third OLS includes layers 0 through 3 and that the third layer should be decoded and output based on layers 0 through 2. Thus, the decoder may receive only the layers needed to decode the received top layer, which can be decoded and displayed. In this way, the total number of coded layers may not affect the decoding process, and errors may be prevented. Thus, the disclosed mechanisms enhance the capabilities of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder. In certain embodiments, ols_mode_idc saves bits in encoded bitstreams that include multiple OLSs where much data is shared, thus providing savings in streaming servers and bandwidth savings for the transmission of such bitstreams.

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

[0028] In an embodiment, the present disclosure includes an encoder including encoding means for encoding a bitstream including one or more layers of a coded picture and encoding a VPS into the bitstream, where the VPS includes an ols_mode_idc that specifies that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS; and storage means for storing the bitstream for transmission to a decoder.

[0029] To support scalability, layers of a picture may be used. For example, video may be coded into multiple layers. A layer may be coded without reference to other layers. Such a layer is called a simulcast layer. Thus, a simulcast layer may be decoded without reference to other layers. As another example, a layer may be coded using inter-layer prediction. This allows a current layer to be coded by including only the differences between the current layer and a reference layer. For example, the current layer and the reference layer may comprise the same video sequence coded by varying characteristics such as SNR, picture size, frame rate, etc. Some video coding systems are configured to simply decode and output the top-most coded layer indicated by a layer ID along with one or more indicated lower layers. This can create problems with scalability because a decoder may not want to decode the top layer. This can cause errors when video scalability is attempted in such systems. This can be a significant problem, as requiring a decoder to always support the top layer results in a system that cannot scale to intermediate layers based on different hardware and network requirements.

[0030] This example includes a mechanism for using OLS to support scalability. This includes both spatial scalability and SNR scalability. This example uses the ols_mode_idc syntax element for use in conjunction with OLS. The ols_mode_idc syntax element can be included in a VPS and can be set to 0 to indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layers 0 and i, and that only the top layer is output for each OLS. This supports scalability because a decoder can quickly determine, for example, that the third OLS includes layers 0 through 3 and that the third layer should be decoded and output based on layers 0 through 2. Thus, the decoder may receive only the layers needed to decode the received top layer, which can be decoded and displayed. In this way, the total number of coded layers may not affect the decoding process, and errors may be prevented. Thus, the disclosed mechanisms enhance the capabilities of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder. In certain embodiments, ols_mode_idc saves bits in encoded bitstreams that include multiple OLSs where much data is shared, thus providing savings in streaming servers and bandwidth savings for the transmission of such bitstreams.

[0031] Optionally, in any of the above aspects, another implementation of the aspect provides that the encoder is further configured to perform the method of any of the above aspects.

[0032] For purposes of clarity, any one of the above-described embodiments may be combined with any one or more of the other above-described embodiments to create new embodiments within the scope of the present disclosure.

[0033] These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

[0034] 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 reference numerals represent like parts. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a flow diagram of an exemplary method for coding a video signal. [Figure 2] 1 is a schematic diagram of an example coding and decoding (codec) system for video coding. [Figure 3] FIG. 1 is a schematic diagram illustrating an exemplary video encoder. [Figure 4] FIG. 1 is a schematic diagram illustrating an exemplary video decoder. [Figure 5] 1 is a schematic diagram illustrating an example multi-layer video sequence configured for inter-layer prediction. [Figure 6] FIG. 1 is a schematic diagram illustrating an example video sequence with OLS configured for spatial and / or SNR scalability. [Figure 7] FIG. 1 is a schematic diagram illustrating an example bitstream including an OLS configured for scalability. [Figure 8] 1 is a schematic diagram of an exemplary video coding device. [Figure 9] 1 is a flow diagram of an example method for encoding a video sequence with OLS configured for scalability. [Figure 10]1 is a flow diagram of an example method for decoding a video sequence that includes an OLS configured for scalability. [Figure 11] 1 is a schematic diagram of an example system for coding a video sequence with OLS configured for scalability. DETAILED DESCRIPTION OF THE INVENTION

[0036] While example implementations of one or more embodiments are provided below, it should be understood at the outset that the disclosed systems and / or methods may be implemented using any number of technologies, whether currently known or in existence. The present disclosure should in no way be limited to the example implementations, drawings, and technologies shown below, including the example designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims, along with their full range of equivalents.

[0037] Unless used herein in a contradictory context, the following terms are defined as follows. In particular, 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 supplemental and not limiting of any other definitions given for such terms herein.

[0038] A bitstream is a sequence of bits containing 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 from the bitstream for display using a decoding process. A picture is an array of luma samples and an array of chroma samples that make up a frame or a field thereof. The picture being encoded or decoded may be referred to as the current picture for clarity of discussion.

[0039] A Network Abstraction Layer (NAL) unit is a syntax structure that contains data in the form of a Raw Byte Sequence Payload (RBSP), an indication of the type of data, and optionally interspersed with emulation prevention bytes. A video coding layer (VCL) NAL unit is a NAL unit 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 related non-VCL NAL units that share specified characteristics (e.g., a common resolution, frame rate, picture size, etc.). The VCL NAL units of a layer may share a specific value of the NAL unit header layer identifier (nuh_layer_id). A coded picture is a coded representation of a picture, including VCL NAL units with a specific value of the NAL unit header layer identifier (nuh_layer_id) in the access unit (AU), and including all coding tree units (CTUs) of the picture. A decoded picture is a picture generated by applying a decoding process to a coded picture. A coded video sequence (CVS) is a sequence of AUs that, in decoding order, includes one or more coded video sequence start (CVSS) AUs and, optionally, one more AU that is not a CVSS AU. A CVSS AU is an AU that includes prediction units (PUs) for each layer specified by a video parameter set (VPS), and a coded picture within each PU is the start picture of the CVS / coded layer video sequence (CLVS).

[0040] An output layer set (OLS) is a set of layers in which one or more layers are designated as output layers. An output layer is a layer designated for output (e.g., to a display). The top layer is the layer in the OLS with the highest layer identifier (ID) among all layers in the OLS. In some exemplary OLS modes, the top layer may always be the output layer. A video parameter set (VPS) is a data unit that contains parameters related to the entire video. Inter-layer prediction is a mechanism for coding a current picture in a current layer by referencing a reference picture in a reference layer, where the current picture and the reference picture are included in the same AU and the reference layer contains a lower nuh_layer_id than the current layer.

[0041] The OLS mode identification code (ols_mode_idc) is a syntax element that indicates information related to the number of OLSs, the layers of the OLS, and the output layers of the OLS. The VPS maximum layers minus 1 (vps_max_layers_minus1) is a syntax element that signals the number of layers specified by the VPS and, therefore, the maximum number of layers allowed in the corresponding CVS. The each layer is an OLS flag (each_layer_is_an_ols_flag) is a syntax element that indicates whether each OLS in the bitstream contains a single layer. The total number of OLSs (TotalNumOLss) is a variable that specifies the total number of OLSs specified by the VPS. The number of layers in the i-th OLS (NumLayersInOLS[i]) is a variable that specifies the number of layers in the particular OLS indicated by the OLS index value i. The layer ID in an OLS (LayerIdInOLS[i][j]) is a variable that specifies the nuh_layer_id value of the jth layer of the ith OLS indicated by the layer index j and OLS index i. The vps_layer_id[i] is a syntax element that indicates the layer ID of the ith layer.

[0042] The following acronyms are used in this specification: Coding Tree Block (CTB), Coding Tree Unit (CTU), Coding Unit (CU), Coded Video Sequence (CVS), Joint Video Experts Team (JVET), Motion Constrained Tile Set (MCTS), Maximum Transmission Unit (MTU), Network Abstraction Layer (NAL), Output Layer Set (OLS), Picture Order Count (POC), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set (SPS), Video Parameter Set (VPS), and Versatile Video Coding (VVC).

[0043] Many video compression techniques may be used to reduce the size of video files with minimal loss of data. For example, video compression techniques may include performing spatial (e.g., intra-picture) prediction and / or temporal (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 using 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 that represents an image block. Residual data represents pixel differences between the original image block and the predictive block. Thus, inter-coded blocks are coded by motion vectors that point to blocks of reference samples that form the predictive block, and residual data that indicates the difference between the coded block and the predictive block. Intra-coded blocks are coded by intra-coding modes and residual data. For further compression, the residual data may be transformed from the pixel domain to the transform domain, resulting in residual transform coefficients, which may be quantized. First, the quantized transform coefficients may 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 further compression. Such video compression techniques are discussed in more detail below.

[0044] To ensure that the encoded video can be accurately decoded, the video is encoded and decoded according to a corresponding video coding standard, including International Telecommunication Union (ITU) Standardization Sector (ITU-T) H.261, International Organization for Standardization / International Electrotechnical Commission (ISO / IEC) Moving 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), and Multiview Video Coding plus Depth (MVC+D), as well as three-dimensional (3D) AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC). The Joint Video Experts Team (JVET) of ITU-T and ISO / IEC has begun development of a video coding standard called Versatile Video Coding (VVC). VVC is included in the WDs including JVET-O2001-v14.

[0045] To support scalability, layers of pictures may be used. For example, video may be coded into multiple layers. A layer may be coded without reference to other layers. Such a layer is called a simulcast layer. Thus, a simulcast layer can be decoded without reference to other layers. As another example, a layer may be coded using inter-layer prediction, which allows a current layer to be coded by including only the differences between the current layer and a reference layer. For example, the current layer and the reference layer may contain the same video sequence coded by varying characteristics such as signal-to-noise ratio (SNR), picture size, frame rate, etc.

[0046] Some video coding systems are configured to only decode and output the highest coded layer indicated by a layer identifier (ID) along with one or more indicated lower layers. This can create problems with scalability because a decoder may not want to decode the highest layer. In particular, a decoder generally requests the highest layer it can support, but the decoder generally cannot decode layers higher than the requested layer. As a specific example, a decoder may want to receive and decode the third layer of a total of 15 coded layers. Because layers 4 through 15 are not necessary to decode the third layer, the third layer may be transmitted to the decoder without such layers. However, because the top layer (layer 15) is not present and the video system is instructed to always decode and display the top layer, the decoder may not be able to properly decode and display the third layer. This causes errors when video scalability is attempted in such systems. This can be a significant problem, as requiring the decoder to always support the top layer results in a system that cannot scale to intermediate layers based on different hardware and network requirements.

[0047] Disclosed herein is a system that uses output layer sets (OLS) to support scalability, including both spatial scalability and signal-to-noise ratio (SNR) scalability. Spatial scalability allows a video sequence to be coded into layers such that the layers are placed into OLSs such that each OLS contains enough data to decode the video sequence for a corresponding output screen size. Thus, spatial scalability may include a set of layers for decoding video for smartphone screens, a set of layers for decoding video for large television screens, and a set of layers for intermediate screen sizes. SNR scalability allows a video sequence to be coded into layers such that the layers are placed into OLSs such that each OLS contains enough data to decode the video sequence at different SNRs. Thus, SNR scalability may include sets of layers that may be decoded for low-quality video, high-quality video, and various intermediate video qualities based on network conditions. This disclosure uses the OLS mode identification code (ols_mode_idc) syntax element for use in conjunction with OLS. The ols_mode_idc syntax element may be included in a video parameter set (VPS) and may be set to 0 to indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layer 0 and layer i, and that only the top layer is output for each OLS. This supports scalability because a decoder can quickly determine, for example, that the third OLS includes layers 0 through 3 and that the third layer should be decoded and output based on layers 0 through 2. Thus, the decoder may receive only the layers needed to decode the received top layer, which can be decoded and displayed. In this way, the total number of coded layers may not affect the decoding process, and errors may be prevented.Thus, the disclosed mechanisms enhance the functionality of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder.

[0048] 1 is a flow diagram of an exemplary operational method 100 for coding a video signal. In particular, a video signal is encoded in an encoder. The encoding process compresses the video signal by reducing the video file size using various mechanisms. 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 to reconstruct the original video signal for display to the end user. Generally, the decoding process faithfully mimics the encoding process to allow the decoder to consistently reconstruct the video signal.

[0049] In 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 an audio component and a video component. The video component includes a series of image frames that, when viewed in sequence, create the visual impression of movement. A frame includes pixels represented by 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 frame may also include depth values ​​to support three-dimensional viewing.

[0050] In step 103, the video is partitioned into blocks. Partitioning involves subdividing the pixels of 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 divided into coding tree units (CTUs), which are blocks of a predefined size (e.g., 64 pixels by 64 pixels). CTUs contain both luma samples and chroma samples. A coding tree may be used to divide the CTUs into blocks and then iteratively 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 uniform lighting values. For example, the chroma component of a frame may be subdivided until each block contains relatively uniform color values. Thus, the partitioning mechanism varies depending on the content of the video frame.

[0051] In step 105, various compression mechanisms are used to compress the image blocks partitioned in step 103. For example, inter-prediction and / or intra-prediction may be used. Inter-prediction is designed to take advantage of the fact that objects in a typical scene tend to appear in consecutive frames. Therefore, a block depicting an object in a reference frame need not be repeatedly shown in neighboring frames. In particular, an object such as a table may remain in a constant position across multiple frames. Thus, the table may be shown once, and adjacent frames may look back to the reference frame. A pattern matching mechanism may be used to match objects across multiple frames. Furthermore, a moving object may be depicted across multiple frames, for example, due to object movement or camera movement. As a specific example, a video may show a car moving across the screen over multiple frames. A motion vector may be used to indicate such movement. A motion vector is a two-dimensional vector that provides an offset from the coordinates of an object in a frame to the coordinates of the object in a reference frame. Thus, 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 a reference frame.

[0052] Intra prediction encodes blocks within a common frame. Intra prediction takes advantage of the fact that luma and chroma components tend to cluster within a frame. For example, a green area in a part of a tree tends to be located near similar green areas. Intra prediction uses multiple directional prediction modes (e.g., 33 in HEVC), planar mode, and direct current (DC) mode. Directional mode indicates that the current block is similar / the same as samples of neighboring blocks in the corresponding direction. Planar mode indicates that a series of blocks (e.g., planes) along a row / column can be interpolated based on neighboring blocks at the end of the row. In effect, planar mode indicates a smooth transition of light / color between rows / columns by using a relatively constant gradient of changing values. DC mode is used for boundary smoothing and indicates that the block is similar / the same as the average value associated with samples of all neighboring blocks related to the angular direction of the directional prediction mode. Therefore, intra-predicted blocks may represent image blocks as values ​​of various related prediction modes instead of actual values. Furthermore, inter-predicted blocks may represent image blocks as values ​​of motion vectors instead of actual values. In either case, the prediction block may not exactly represent the image block in some cases. Any differences are stored in a residual block. To further compress the file, a transform may be applied to the residual block.

[0053] Various filtering techniques may be applied in step 107. In HEVC, filters are applied by an in-loop filtering scheme. The block-based prediction discussed above may result in the generation of blocky images at the decoder. Furthermore, block-based prediction schemes may encode blocks and then reconstruct the encoded blocks for later use as reference blocks. In-loop filtering schemes iteratively apply noise suppression filters, deblocking filters, adaptive loop filters, and sample adaptive offset (SAO) filters to blocks / frames. These filters mitigate such blocking artifacts so that the encoded file can be accurately reconstructed. Furthermore, these filters mitigate artifacts in the reconstructed reference blocks so that the artifacts are less likely to cause further artifacts in subsequent blocks that are coded based on the reconstructed reference blocks.

[0054] Once the video signal has been segmented, compressed, and filtered, the resulting data is encoded into a bitstream in step 109. The bitstream includes the data discussed above and any signaling data desired to support proper video signal reconstruction at a decoder. For example, such data may include segmentation data, prediction data, residual blocks, and various flags that provide 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. Generating the bitstream is an iterative process. Thus, steps 101, 103, 105, 107, and 109 may occur continuously and / or simultaneously across many frames and blocks. The order depicted in FIG. 1 is presented for clarity and ease of discussion and is not intended to limit the video coding process to any particular order.

[0055] The decoder receives the bitstream and begins the decoding process in step 111. In particular, the decoder uses an entropy decoding scheme to convert the bitstream into corresponding syntax and video data. In step 111, the decoder uses syntax data from the bitstream to determine partitions for the frame. The partitioning should match the result of the block partitioning in step 103. The entropy encoding / decoding used in step 111 is described below. The encoder makes many choices during the compression process, such as selecting a block partitioning scheme from several possible options based on the spatial location of values ​​in the input image. Signaling a strict raw selection may use a large number of bins. As used herein, a bin is a binary value (e.g., a bit value that can change depending on the situation) treated as a variable. Entropy coding allows the encoder to discard all options that clearly do not work 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 choices (e.g., one bin for two choices, two bins for three to four choices, etc.). The encoder then encodes the codeword for the selected choice. This scheme reduces the size of the codeword because the codeword is only as large as desired to uniquely indicate a choice from a small subset of allowable choices, as opposed to uniquely indicating a choice from a potentially large set of all possible choices. The decoder then decodes the choices by determining the set of allowable choices in the same manner as the encoder. By determining the set of allowable choices, the decoder can read the codeword and determine the choice made by the encoder.

[0056] In step 113, the decoder performs decoding of the block. In particular, the decoder generates a residual block using an inverse transform. The decoder then uses the residual block and the corresponding prediction block to reconstruct an image block according to the partitioning. The prediction block may include both intra-predicted blocks and inter-predicted blocks generated by the encoder in step 105. The reconstructed image block is 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 by entropy coding as discussed above.

[0057] In step 115, filtering is performed on the frames of the reconstructed video signal, similar to step 107 of 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. Once the frames have been filtered, the video signal may be output to a display in step 117 for viewing by an end user.

[0058] 2 is a schematic diagram of an exemplary coding and decoding (codec) system 200 for video coding. In particular, codec system 200 provides functionality to support the implementation of operational method 100. Codec system 200 is generalized to depict components used in both encoders and decoders. Codec system 200 receives and segments a video signal as discussed in connection with steps 101 and 103 of operational method 100, resulting in a segmented video signal 201. Then, when acting as an encoder, codec system 200 compresses segmented video signal 201 into a coded bitstream as discussed in connection with steps 105, 107, and 109 of method 100. When acting as a decoder, codec system 200 generates an output video signal from the bitstream as discussed in connection with steps 111, 113, 115, and 117 of 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 format and context adaptive binary arithmetic coding (CABAC) component 231. Such components are coupled as shown. In FIG. 2, black lines indicate the movement of data to be coded / decoded, while 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 described below.

[0059] The partitioned video signal 201 is a captured video sequence that has been partitioned into blocks of pixels by a coding tree. The coding tree uses 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 divided 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 coding units (CUs). For example, a CU may be a subpart of a CTU that includes a luma block, a red-difference (Cr) block, and a blue-difference (Cb) block, along with corresponding syntax instructions for the CU. Partitioning modes may include a binary tree (BT), a ternary tree (TT), and a quad tree (QT), each of which is used to partition a node into two, three, or four child nodes of varying shapes depending on the partitioning mode used. 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.

[0060] 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 made based on storage space / bandwidth availability and image resolution requirements. The general coder control component 211 also manages buffer utilization in light of transmission rates to mitigate buffer underrun and overrun 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 increase bandwidth usage, or dynamically decrease compression complexity to decrease resolution and decrease bandwidth usage. Thus, the general coder control component 211 controls other components of the codec system 200 to balance the quality of reconstruction of the video signal and bitrate concerns. The general coder control component 211 generates control data that controls the operation of the other components. Control data is also forwarded to the header format and CABAC component 231 to be encoded into the bitstream to signal parameters for decoding at the decoder.

[0061] The partitioned video signal 201 is also transmitted 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 relative to one or more blocks in one or more reference frames to provide temporal prediction. The codec system 200 may, for example, perform multiple coding passes to select an appropriate coding mode for each block of video data.

[0062] The motion estimation component 221 and the motion compensation component 219 may be highly integrated but are shown separately for conceptual purposes. Motion estimation, performed by the motion estimation component 221, is the process of generating motion vectors that estimate motion with respect to a video block. A motion vector may indicate, for example, the displacement of an object being coded relative to a predictive block. A predictive block is a block known to closely match a block being coded in terms of 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 uses 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 for inclusion in CUs. A CU may be coded as a prediction unit (PU) containing predictive data for the CU and / or a transform unit (TU) containing transformed residual data. The motion estimation component 221 generates motion vectors, PUs, and TUs by using 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 the current block / frame, and may 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 loss due to compression) and the coding efficiency (e.g., the size of the final encoding).

[0063] In some examples, the codec system 200 may calculate values ​​for sub-integer pixel positions of a reference picture 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 a reference picture. Accordingly, the motion estimation component 221 may perform motion searches related to full-pixel 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 an inter-coded slice by comparing the positions of the PUs with the positions of predictive blocks in the reference picture. The motion estimation component 221 outputs the calculated motion vectors as motion data to the header format and CABAC component 231 for encoding and outputs motion to the motion compensation component 219.

[0064] The motion compensation performed by the motion compensation component 219 may include retrieving 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 find 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. Generally, the motion estimation component 221 performs motion estimation related 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.

[0065] The partitioned video signal 201 is also sent to an intra-picture estimation component 215 and an intra-picture prediction component 217. Like 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 shown separately for conceptual purposes. The intra-picture estimation component 215 and the intra-picture prediction component 217 intra-predict the current block relative to blocks within the 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 the 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 for encoding the current block from multiple tested intra-prediction modes. The selected intra-prediction mode is then forwarded to the header format and CABAC component 231 for encoding.

[0066] For example, the intra picture estimation component 215 calculates a rate-distortion value using a rate-distortion analysis for various tested intra prediction modes and selects an intra prediction mode with the best rate-distortion characteristics among the tested modes. The rate-distortion analysis generally determines the amount of distortion (or error) between a coded block and the original uncoded block coded to generate the coded block, and the bit rate (e.g., number of bits) used to generate the coded block. The intra picture estimation component 215 calculates a ratio from the distortion and rate for the various coded blocks to determine which intra prediction mode exhibits the best rate-distortion value for the block. Furthermore, 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 rate-distortion optimization (RDO).

[0067] The intra-picture prediction component 217, when implemented in an encoder, may generate a residual block from the prediction block based on the selected intra-prediction mode determined by the intra-picture estimation component 215, or, when implemented in a decoder, may read the residual block from the bitstream. The residual block contains the 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.

[0068] 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, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a similar transform, to the residual block to generate a video block containing residual transform coefficient values. Wavelet transforms, integer transforms, subband transforms, or other types of transforms may 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 further configured to scale the transformed residual information, for example, based on frequency. Such scaling may include applying a scale factor to the residual information so that different frequency information is quantized with different granularities, which may affect the final visual quality of the reconstructed video. The transform, scaling, and quantization component 213 is further 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 modified by adjusting a quantization parameter. In some examples, the transform, scaling, and quantization component 213 may then perform a scan of the matrix containing the quantized transform coefficients, which are forwarded to the header format and CABAC component 231 to be encoded into the bitstream.

[0069] 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, for example, inverse scaling, inverse transform, and / or inverse quantization to reconstruct a residual block in the pixel domain for later use as a reference block, which may become a prediction block for another current block. The motion estimation component 221 and / or motion compensation component 219 may calculate a reference block by adding the residual block back to the corresponding prediction block for use in motion estimation of a subsequent block / frame. A filter is applied to the reconstructed reference block to mitigate artifacts introduced during scaling, quantization, and transformation. Otherwise, such artifacts may result in inaccurate predictions (and further artifacts) when subsequent blocks are predicted.

[0070] The filter control analysis component 227 and the in-loop filter component 225 apply filters to residual blocks and / or reconstructed image blocks. For example, a 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, a filter may be applied to the residual block instead. Like the other components in 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 shown separately for conceptual purposes. The filters applied to the reconstructed reference blocks are applied to specific spatial regions and include multiple parameters for adjusting how such filters are applied. The filter control analysis component 227 analyzes the reconstructed reference blocks to determine where such filters should be applied and sets the corresponding parameters. Such data is forwarded as filter control data to the header format and CABAC component 231 for encoding. The in-loop filter component 225 applies such filters based on the filter control data. The filters may include a deblocking filter, a noise suppression filter, an SAO filter, and an adaptive loop filter. Such filters may be applied in the spatial / pixel domain (e.g., to the reconstructed pixel blocks) or in the frequency domain, depending on the example.

[0071] 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 discussed 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.

[0072] The header format and CABAC component 231 receives data from various components of the codec system 200 and encodes such data into a coded bitstream for transmission to a decoder. In particular, the header format and CABAC component 231 generates various headers for encoding control data, such as general control data and filter control data. Additionally, prediction data, including intra-prediction and motion data, and residual data in the form of quantized transform coefficient data are all coded into the bitstream. The final bitstream contains all information desired by a decoder to reconstruct the original segmented video signal 201. Such information may also include an index table of intra-prediction modes (also called a codeword mapping table), definitions of coding contexts for various blocks, an indication of the most likely intra-prediction mode, an indication of segmentation information, and so on. Such data may be coded using entropy coding. For example, the information may be encoded using 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. After entropy coding, the coded bitstream may be transmitted to another device (e.g., a video decoder) or archived for later transmission or retrieval.

[0073] 3 is a block diagram illustrating an example video encoder 300. Video encoder 300 may be used to perform the encoding functions of codec system 200 and / or to perform steps 101, 103, 105, 107, and / or 109 of method of operation 100. Encoder 300 segments an input video signal, resulting in a segmented video signal 301 that is substantially similar to segmented video signal 201. Segmented video signal 301 is then compressed and encoded into a bitstream by components of encoder 300.

[0074] In particular, 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 reference blocks 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 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 block and the corresponding prediction block are forwarded (together with associated control data) to an entropy coding component 331 for coding into a bitstream. The entropy coding component 331 may be substantially similar to the header format and CABAC component 231 .

[0075] The transformed and quantized residual block and / or the corresponding prediction block are also transferred from the transform and quantization component 313 to the inverse transform and quantization component 329 for reconstruction into a reference block 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 of 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 include multiple filters as discussed in connection with 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.

[0076] 4 is a block diagram illustrating an exemplary video decoder 400. Video decoder 400 may be used to perform the decoding functionality of codec system 200 and / or to perform steps 111, 113, 115, and / or 117 of method of operation 100. Decoder 400 receives a bitstream from, for example, encoder 300 and generates a reconstructed output video signal based on the bitstream for display to an end user.

[0077] The bitstream is received by the entropy decoding component 433. The entropy decoding component 433 is configured to perform an entropy decoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or other entropy coding techniques. For example, the entropy decoding component 433 may use header information to provide context for interpreting additional data encoded as codewords in the bitstream. The decoded information includes any desired information for decoding the video signal, such as general control data, filter control data, partitioning information, motion data, prediction data, and quantized transform coefficients from residual blocks. The quantized transform coefficients are forwarded to the inverse transform and quantization component 429 for reconstruction into residual blocks. The inverse transform and quantization component 429 may be similar to the inverse transform and quantization component 329.

[0078] The reconstructed residual block and / or predictive block are forwarded to the intra-picture prediction component 417 for reconstruction into an image block based on an intra-prediction operation. The intra-picture prediction component 417 may be substantially similar to the intra-picture estimation component 215 and the intra-picture prediction component 217. In particular, the intra-picture prediction component 417 identifies a reference block within a frame using the prediction mode and applies the residual block to the result to reconstruct an intra-predicted image block. The reconstructed intra-predicted image block and / or residual block and corresponding inter-prediction data are forwarded to the decoded picture buffer component 423 via an 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, residual block, and / or predictive block, and such information is stored in the decoded picture buffer component 423. The reconstructed image blocks from the decoded picture buffer component 423 are 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. In particular, the motion compensation component 421 generates a prediction block using a motion vector from a reference 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 an in-loop filter component 425. The decoded picture buffer component 423 continues to store additional reconstructed image blocks, which may be reconstructed into frames according to the partitioning information. Such frames may also be arranged in a sequence. The sequence is output to a display as a reconstructed output video signal.

[0079] 5 is a schematic diagram illustrating an example multi-layer video sequence 500 configured for inter-layer prediction 521. The multi-layer video sequence 500 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, in accordance with method 100, for example. The multi-layer video sequence 500 is included to illustrate an example application of layers in a coded video sequence. The multi-layer video sequence 500 is any video sequence that uses multiple layers, such as layer N 531 and layer N+1 532.

[0080] In an example, multi-layer video sequence 500 may use inter-layer prediction 521. Inter-layer prediction 521 is applied between pictures 511, 512, 513, and 514 and pictures 515, 516, 517, and 518 of different layers. In the shown example, pictures 511, 512, 513, and 514 are part of layer N+1 532, and pictures 515, 516, 517, and 518 are part of layer N 531. A layer, such as layer N 531 and / or layer N+1 532, 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 formally be defined as a set of VCL NAL units and associated non-VCL NAL units that share the same nuh_layer_id. A VCL NAL unit is a NAL unit 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.

[0081] In the shown example, layer N+1 532 is associated with a larger image size than layer N 531. Thus, pictures 511, 512, 513, and 514 of layer N+1 532 have a larger picture size (e.g., larger height and width, and therefore more samples) than pictures 515, 516, 517, and 518 of layer N 531 in this example. However, such pictures may be divided between layer N+1 532 and layer N 531 by other characteristics. Although only two layers, layer N+1 532 and layer N 531, are shown, a set of pictures may be divided into any number of layers based on relevant characteristics. Also, layer N+1 532 and layer N 531 may be indicated 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 indicated layer. Thus, each picture 511-518 may be associated with a corresponding layer ID to indicate whether layer N+1 532 or layer N 531 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 the identifier of the layer that contains the NAL unit (e.g., containing slices and / or parameters of a picture within the layer). Layers associated with lower quality / bitstream sizes, such as layer N 531, are generally assigned lower layer IDs and are referred to as lower layers. Furthermore, layers associated with higher quality / bitstream sizes, such as layer N+1 532, are generally assigned higher layer IDs and are referred to as upper layers.

[0082] Pictures 511-518 in different layers 531-532 are configured to be displayed alternatively. As a particular example, a decoder may decode and display picture 515 at the current display time if a smaller picture is desired, or may decode and display picture 511 at the current display time if a larger picture is desired. Thus, pictures 511-514 in higher layer N+1 532 contain substantially the same image data as corresponding pictures 515-518 in lower layer N 531 (despite differences in picture size). In particular, picture 511 contains substantially the same image data as picture 515, picture 512 contains substantially the same image data as picture 516, and so on.

[0083] Pictures 511-518 may be coded by referencing other pictures 511-518 in the same layer N 531 or N+1 532. Coding a picture with reference to another picture in the same layer results in inter-prediction 523. Inter-prediction 523 is indicated by a solid arrow. For example, picture 513 may be coded using inter-prediction 523 using one or two of pictures 511, 512, and / or 514 in layer N+1 532 as references, with one picture referenced for unidirectional inter-prediction and / or two pictures referenced for bidirectional inter-prediction. Furthermore, picture 517 may be coded using inter-prediction 523 using one or two of pictures 515, 516, and / or 518 in layer N 531 as references, with one picture referenced for unidirectional inter-prediction and / or two pictures referenced for bidirectional inter-prediction. When a picture is used as a reference for another picture of the same layer when performing inter prediction 523, the picture may be called a reference picture. For example, picture 512 may be a reference picture used to code picture 513 by inter prediction 523. Inter prediction 523 may also be called intra-layer prediction in a multi-layer context. Thus, inter prediction 523 is a mechanism for coding samples of a current picture by referring 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.

[0084] Pictures 511-518 may also be coded by referencing other pictures 511-518 in different layers. This process is known as inter-layer prediction 521 and is indicated by the dashed arrows. Inter-layer prediction 521 is a mechanism for coding samples of a current picture by referencing indicated samples in a reference picture when 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 531 may be used as a reference picture for coding a corresponding picture in an upper layer N+1 532. As a specific example, picture 511 may be coded by inter-layer prediction 521 with reference to picture 515. In such a case, picture 515 is used as an inter-layer reference picture. An inter-layer reference picture is a reference picture used for inter-layer prediction 521. In most cases, inter-layer prediction 521 is constrained so that a current picture, such as picture 511, may use only inter-layer reference pictures that are included in the same AU and are in a lower layer, such as picture 515. An AU is a set of pictures associated with a particular output time in a video sequence, and thus an AU may contain as many as one picture per layer. When multiple layers (e.g., three or more) are available, inter-layer prediction 521 may encode / decode the current picture based on multiple inter-layer reference pictures that are at a lower level than the current picture.

[0085] A video encoder can use the multi-layer video sequence 500 to encode pictures 511-518 with many different combinations and / or permutations of inter-prediction 523 and inter-layer prediction 521. For example, picture 515 may be coded with intra-prediction. Then, pictures 516-518 may be coded with inter-prediction 523 by using picture 515 as a reference picture. Furthermore, picture 511 may be coded with inter-layer prediction 521 by using picture 515 as an inter-layer reference picture. Then, pictures 512-514 may be coded with inter-prediction 523 by using picture 511 as a reference picture. Thus, a reference picture may serve as both a single-layer reference picture and an inter-layer reference picture for different coding mechanisms. By coding pictures of the upper layer N+1 532 based on pictures of the lower layer N 531, the upper layer N+1 532 can avoid using intra prediction, which has much lower coding efficiency than inter prediction 523 and inter-layer prediction 521. Thus, the poor coding efficiency of intra prediction may be limited to pictures of the smallest / lowest quality, and thus to the coding of 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.

[0086] To perform such operations, layers such as layer N 531 and layer N+1 532 may be included in OLS 525. OLS 525 is a set of layers in which one or more layers are designated as output layers. An output layer is a layer designated for output (e.g., to a display). For example, layer N 531 may be included only to support inter-layer prediction 521 and may not be output. In such a case, layer N+1 532 is decoded and output based on layer N 531. In such a case, OLS 525 includes layer N+1 532 as an output layer. OLS 525 may include many layers in different combinations. For example, the output layer of OLS 525 may be coded by inter-layer prediction 521 based on one, two, or many lower layers. Furthermore, OLS 525 may include two or more output layers. Thus, OLS 525 may include one or more output layers and any support layers required to reconstruct the output layer. A multi-layer video sequence 500 can be coded by using many different OLSs 525, each using a different combination of layers.

[0087] As a particular example, inter-layer prediction 521 may be used to support scalability. For example, a video may be coded into a base layer, such as layer N 531, and several enhancement layers, such as layer N+1 532, layer N+2, and layer N+3, that are coded by inter-layer prediction 521. The video sequence may be coded with respect to scalable features, such as signal-to-noise ratio (SNR), frame rate, picture size, etc. An OLS 525 may then be generated for each allowable feature. For example, the OLS 525 for a first resolution may include only layer N 531, the OLS 525 for a second resolution may include layer N 531 and layer N+1 532, and the OLS for a third resolution may include layer N 531, layer N+1 532, layer N+2, etc. In this manner, the OLS 525 may be transmitted to allow a decoder to decode whatever version of the multi-layer video sequence 500 is desired based on network conditions, hardware constraints, etc.

[0088] 6 is a schematic diagram illustrating an example video sequence 600 with OLS configured for spatial and / or SNR scalability. Video sequence 600 is a particular example of multi-layer video sequence 500. Thus, 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, in accordance with method 100, for example. Video sequence 600 is useful for scalability.

[0089] The exemplary video sequence 600 includes OLSs 620, 621, and 622, which may be substantially similar to OLS 525. Although three OLSs are shown, any number of OLSs may be used. Each OLS 620, 621, and 622 is referenced by an OLS index and includes one or more layers. In particular, OLSs 620, 621, and 622 include layer 630, layers 630 and 631, and layers 630, 631, and 632, respectively. Layers 630, 631, and 632 may be substantially similar to layer N 531 and layer N+1 532. Layers 630, 631, and 632 are referenced by layer indexes. The video sequence 600 includes the same number of layers as the number of OLSs. In particular, OLS 620 with the lowest OLS index includes layer 630 with the lowest layer index. Each other OLS includes all the layers of the previous OLS with a lower OLS index plus one more layer. For example, OLS 621 has a higher OLS index than OLS 620 and includes all the layers of OLS 620 plus one more layer: layers 630 and 631. Similarly, OLS 622 has a higher OLS index than OLS 621 and includes all the layers of OLS 621 plus one more layer: layers 630, 631, and 632. This pattern can continue until the layer with the highest layer index and the OLS with the highest OLS index are reached.

[0090] Furthermore, layer 630 is a base layer. All other layers 631 and 632 are enhancement layers that are coded by inter-layer prediction based on all layers with lower layer indices. In particular, layer 630 is a base layer and is not coded by inter-layer prediction. Layer 631 is an enhancement layer that is coded by inter-layer prediction based on layer 630. Furthermore, layer 632 is an enhancement layer that is coded by inter-layer prediction based on layers 630 and 631. As a result, OLS 620 includes layer 630, which has the lowest quality SNR and / or smallest image size. Because OLS 620 does not use inter-layer prediction, OLS 620 can be completely decoded without reference to any layer other than 630. OLS 621 includes layer 631, which has a higher quality SNR and / or image size than layer 630, and layer 631 can be completely decoded by inter-layer prediction because OLS 621 also includes layer 630. Similarly, OLS 622 includes layer 632, which has a higher quality SNR and / or image size than layers 630 and 631, and layer 632 can be fully decoded by inter-layer prediction because OLS 622 also includes layers 630 and 631. Thus, video sequence 600 is coded to scale to any pre-selected SNR and / or image size by sending the corresponding OLS 622, 621, or 620 to the decoder. As more OLSs 622, 621, and 620 are used, video sequence 600 can be scaled to greater SNR image qualities and / or image sizes.

[0091] Thus, video sequence 600 can support spatial scalability. Spatial scalability allows video sequence 600 to be coded into layers 630, 631, and 632, such that layers 630, 631, and 632 are placed into OLSs 620, 621, and 622 such that each OLS 620, 621, and 622 contains enough data to decode video sequence 600 to a corresponding output screen size. Thus, spatial scalability may include a set of layers (e.g., layer 630) for decoding video for a smartphone screen, a set of layers (e.g., layers 630, 631, and 632) for decoding video for a large television screen, and a set of layers (e.g., layers 630 and 631) for intermediate screen sizes. SNR scalability allows video sequence 600 to be coded into layers 630, 631, and 632 such that layers 630, 631, and 632 are placed into OLSs 620, 621, and 622 such that each OLS 620, 621, and 622 contains enough data to decode video sequence 600 at different SNRs. Thus, SNR scalability may include a set of layers (e.g., layer 630) that may be decoded for low-quality video, high-quality video (e.g., layers 630, 631, and 632), and various intermediate video qualities (e.g., layers 630 and 631) to support network conditions.

[0092] This disclosure provides efficient signaling to enable the video sequence 600 to be used correctly and efficiently. For example, the video sequence 600 may be indicated by an ols_mode_idc syntax element. For example, the ols_mode_idc syntax element may identify the video sequence 600 as OLS mode 0. Thus, the ols_mode_idc syntax element may be set to zero and signaled in the bitstream to indicate that the video sequence 600 is used. Thus, a decoder can receive any OLS and determine, based on the ols_mode_idc, that the received layer with the highest layer index is the output layer of the received OLS, and that the output layer may be decoded by inter-layer prediction based on other lower layers in the OLS.

[0093] 7 is a schematic diagram illustrating an example bitstream 700 including an OLS configured for scalability. For example, bitstream 700 may be generated by codec system 200 and / or encoder 300 for decoding by codec system 200 and / or decoder 400 according to method 100. Furthermore, bitstream 700 may include coded multi-layer video sequence 500 and / or video sequence 600.

[0094] Bitstream 700 includes a VPS 711, one or more sequence parameter sets (SPSs) 713, multiple picture parameter sets (PPSs) 715, multiple slice headers 717, and image data 720. The VPS 711 includes data related to the entire bitstream 700. For example, the VPS 711 may include data related to image sequences, layers, and / or sublayers used in the bitstream 700. The SPS 713 includes sequence data common to all pictures in a coded video sequence included in the bitstream 700. For example, each layer may include one or more coded video sequences, and each coded video sequence may reference the SPS 713 for corresponding parameters. The parameters in the SPS 713 may include picture sizing, bit depth, coding tool parameters, bit rate constraints, etc. Note that while each sequence references an SPS 713, in some examples, a single SPS 713 may include data for multiple sequences. PPS 715 contains parameters that apply to the entire picture. Thus, each picture in a video sequence may reference PPS 715. Note that while each picture references PPS 715, in some examples, a single PPS 715 may contain data for multiple pictures. For example, multiple similar pictures may be coded according to similar parameters. In such cases, a single PPS 715 may contain data for such similar pictures. PPS 715 may indicate available coding tools, quantization parameters, offsets, etc. for slices within the corresponding picture.

[0095] The slice header 717 contains parameters specific to each slice 727 in a picture 725. Thus, there may be one slice header 717 for each slice 727 in a video sequence. The slice header 717 may include slice type information, 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 contains parameters that apply to all slices 727 in a single picture. For this reason, picture header and slice header 717 may be used interchangeably in some contexts. For example, certain parameters may be moved between slice header 717 and picture header depending on whether such parameters are common to all slices 727 in a picture 725.

[0096] Image data 720 includes video data coded by inter-prediction and / or intra-prediction and corresponding transformed and quantized residual data. For example, image data 720 may include layers 723 of a picture 725. The layers 723 may be organized into OLSs 721. OLSs 721 may be substantially similar to OLSs 525, 620, 621, and / or 622. In particular, OLSs 721 are a set of layers 723 in which one or more layers are designated as output layers. For example, bitstream 700 may be coded to include several OLSs 721 such that video is coded at different resolutions, frame rates, picture 725 sizes, etc. Upon request by the decoder, a sub-bitstream extraction process can remove all but the requested OLSs 721 from bitstream 700. The encoder can then send bitstream 700 to the decoder including only the requested OLSs 721, and thus only video that meets the requested criteria.

[0097] Layer 723 may be substantially similar to layer N 531, layer N+1 532, and / or layers 631, 632, and / or 633. Layer 723 is generally a set of coded pictures 725. Formally, layer 723 may be defined as a set of VCL NAL units that, when decoded, share specified characteristics (e.g., a common resolution, frame rate, picture size, etc.). Pictures 725 may be coded as a set of VCL NAL units. Layer 723 also includes associated non-VCL NAL units to support decoding of the VCL NAL units. VCL NAL units of layer 723 may share a particular value of an exemplary layer ID, nuh_layer_id. Layer 723 may be a simulcast layer coded without inter-layer prediction, or may be a layer 723 coded with inter-layer prediction based on other layers.

[0098] A picture 725 is an array of luma samples and chroma samples that generate a frame or a field thereof. For example, a picture 725 may be a coded image that may be output for display or used to support coding of other pictures 725 for output. A picture 725 may include a set of VCL NAL units. A picture 725 includes one or more slices 727. A slice 727 may be defined as an integer number of complete tiles or an integer number of consecutive complete coding tree units (CTUs) (e.g., within a tile) of a picture 725 that are exclusively contained in a single NAL unit, specifically a VCL NAL unit. A slice 727 is further divided into CTUs and / or coding tree blocks (CTBs). A CTU is a group of samples of a predefined size that can be partitioned by a coding tree. A CTB is a subset of a CTU and contains the luma or chroma component of the CTU. A CTU / CTB is further divided into coding blocks based on the coding tree. The coding blocks can then be encoded / decoded by a prediction mechanism.

[0099] This disclosure includes mechanisms for supporting spatial and / or SNR scalability, for example, with video sequence 600. For example, VPS 711 may include ols_mode_idc 735. ols_mode_idc 735 is a syntax element that indicates information related to the number of OLSs 721, the layers 723 of the OLSs 721, and the output layers 723 of the OLSs 721. An output layer 723 is any layer that is specified for output by a decoder, as opposed to being used only for reference-based coding. ols_mode_idc 735 may be set to 1 or 2 for coding other types of video. ols_mode_idc 735 may be set to 0 to support spatial and / or SNR scalability. For example, ols_mode_idc 735 may be set to 0 to indicate that the total number of OLSs 721 in the video sequence is equal to the total number of layers 723 specified in the VPS 711, that the ith OLS 721 includes layers 0 through i, including layer 0 and layer i, and that for each OLS 721, only the top layer is output. This set of conditions may describe a video sequence 600 having any number of OLSs 721. An advantage of using ols_mode_idc 735 is that it saves bits. A decoder in an application system typically receives only a single OLS. However, ols_mode_idc 735 further provides bit savings in coded bitstreams that include multiple OLSs where much data is shared, thus providing savings at the streaming server and providing bandwidth savings for the transmission of such bitstreams.

[0100] In some examples, the VPS 711 also includes a VPS maximum layers minus 1 (vps_max_layers_minus1) 737 syntax element. vps_max_layers_minus1 737 is a syntax element that signals the number of layers 723 specified by the VPS 711 and, therefore, the maximum number of layers 723 allowed in the corresponding coded video sequence in the bitstream 700. ols_mode_idc 735 may reference the vps_max_layers_minus1 737 syntax element. For example, ols_mode_idc 735 may indicate that the total number of OLS 721 is equal to the number of layers 723 specified by vps_max_layers_minus1 737.

[0101] Additionally, the VPS 711 may further include each_layer_is_an_ols_flag 733. Each_layer_is_an_ols_flag 733 is a syntax element that signals whether each OLS 721 in the bitstream 700 includes a single layer 723. For example, when scalability is not used, each OLS 721 may include a single simulcast layer. Thus, each_layer_is_an_ols_flag 733 may be set (e.g., to 0) to indicate that one or more OLSs 721 include two or more layers 723 to support scalability. Thus, each_layer_is_an_ols_flag 733 may be used to support scalability. For example, a decoder may examine each_layer_is_an_ols_flag 733 to determine that some of the OLSs 721 include two or more layers 723. When Each_layer_is_an_ols_flag 733 is set to 0 and ols_mode_idc 735 is set to 0 (or 1, used for a different mode), the total number of OLSs (TotalNumOlss) may be set equal to vps_max_layers_minus1 737. TotalNumOlss is a variable used by both the decoder and the hypothetical reference decoder (HRD) of the encoder. TotalNumOlss is a variable used to store the number of OLSs 721 based on the data in the bitstream 700. TotalNumOlss may then be used for decoding in the decoder or for checking for errors in the bitstream 700 in the HRD of the encoder.

[0102] The VPS 711 may also include a VPS layer identifier (vps_layer_id[i]) 731 syntax element. vps_layer_id[i] 731 is an array that stores the layer ID (e.g., nuh_layer_id) of each layer. Thus, vps_layer_id[i] 731 indicates the layer ID of the i-th layer.

[0103] The decoder or HRD may be able to use the data of the VPS 711 to determine the configuration of the OLS 721 and layers 723. In a particular example, the number of layers in the ith OLS (NumLayersInOls[i]) and the layer ID of the OLS (LayerIdInOLS[i][j]), which specifies the value of nuh_layer_id for the jth layer of the ith OLS, are derived as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 ] vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each_layer_is_an_ols_flag is an OLS flag for each layer that specifies whether at least one OLS contains two or more layers.

[0104] The data of the VPS 711 may be used to support SNR and / or spatially scalable layers 723. The layers 723 may be coded and included in the OLS 721. The encoder may send a bitstream 700 including the required OLS 721 and VPS 711 to the decoder. The decoder may then use the information in the VPS 711 to correctly decode the layers 723 of the OLS 721. This approach supports coding efficiency while supporting scalability. In particular, the decoder may quickly determine the number of layers 723 of the OLS 721, the output layer of the OLS 721, and the layers 723 to be decoded to support decoding of the output layer via inter-layer prediction. Thus, the decoder may receive only the layers 723 needed to decode the highest received layer, which may be decoded and displayed. In this manner, the total number of coded layers 723 may not affect the decoding process, and one or more of the errors discussed above may be prevented. Thus, the disclosed mechanisms enhance the functionality of the encoder and / or decoder. Furthermore, the disclosed mechanisms may reduce the size of the bitstream, thus reducing processor, memory, and / or network resource utilization in both the encoder and decoder.

[0105] Hereafter, the above-mentioned information will be described in more detail below in this specification. Layered video coding is also called 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, multiview scalability, frame rate scalability, etc. When a multi-layer coding technique is used, a picture or a portion thereof may be coded without using a reference picture (intra-prediction), may be coded by referencing a reference picture in the same layer (inter-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 called an inter-layer reference picture (ILRP). FIG. 5 shows an example of multi-layer coding for spatial scalability in which pictures in different layers have different resolutions.

[0106] Some video coding families provide scalability support in profiles separate 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) of an EL picture to indicate whether the EL MB is predicted using collocated blocks from a lower layer. Predictions from collocated blocks may also include texture, motion vectors, and / or coding modes. SVC implementations may not directly reuse unmodified AVC implementations in their design. The syntax and decoding process of EL macroblocks in SVC differ from those of AVC.

[0107] 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 more advanced and efficient 3D video coding than MV-HEVC. Temporal scalability may 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 reference indices in a reference picture list along with other temporal reference pictures of 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 involves resampling a reference picture or part of it when the ILRP has a different spatial resolution than the current picture being coded or decoded. Resampling of the reference picture can be achieved either at the picture level or at the coding block level.

[0108] VVC may also support layered video coding. A VVC bitstream may contain multiple layers. The layers may all be independent of each other. For example, a layer may be coded without using inter-layer prediction. In this case, the layer is also referred to as a simulcast layer. In some cases, some of the layers are coded using ILP. A flag in the VPS may indicate whether a layer is a simulcast layer or whether some layers use 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 contains a specified set of layers, and one or more layers in the set of layers are designated as output layers. An output layer is a layer of the OLS that is output. In some implementations of VVC, when a layer is a simulcast layer, only one layer may be selected for decoding and output. In some implementations of VVC, when any layer uses ILP, the entire bitstream including all layers is specified to be decoded. Additionally, certain of the layers are designated to be output layers, which may be indicated as the top layer only, all layers, or the top layer together with an indicated set of lower layers.

[0109] The above-described aspect involves certain problems. In some video coding systems, when inter-layer prediction is used, the entire bitstream and all layers are designated to be decoded, and a specific layer among the layers is designated to be the output layer. The output layer may be indicated as the top layer only, all layers, or the top layer together with an indicated set of lower layers. To simplify the problem description, two layers may be used, with the upper layer using the lower layer as a reference for inter-layer prediction. For spatial scalability and / or SNR scalability, the system should specify the use of only the lower layer (only decoding and outputting the lower layer). The system should also specify the use of both layers (decoding both layers and outputting the upper layer). Unfortunately, this is not possible in some video coding systems.

[0110] Generally, this disclosure describes techniques for simple and efficient signaling of output layer sets (OLS) for spatial and SNR scalability. The technique description is based on VVC from ITU-T and ISO / IEC JVET. However, the technique is also applicable to layered video coding based on other video codec specifications.

[0111] One or more of the above-mentioned problems may be solved as follows. In particular, the present disclosure includes a simple and efficient method for signaling OLSs for spatial and SNR scalability. A video coding system may use a VPS to indicate that some layers use ILPs, that the total number of OLSs specified by the VPS is equal to the number of layers, that the i-th OLS includes layers with layer indices from 0 to i, inclusive, and that for each OLS, only the top layer in the OLS is output.

[0112] An exemplary implementation of the above mechanism is as follows: An exemplary video parameter set syntax is as follows: [Table 1A] [Table 1B]

[0113] The semantics of an example video parameter set are as follows: The VPS RBSP should be available to the decoding process before being referenced, should be included in at least one access unit with TemporalId equal to 0 or provided through an external mechanism, and the VPS NAL unit containing the VPS RBSP should have nuh_layer_id equal to vps_layer_id

[0000] . All VPS NAL units with a particular value of vps_video_parameter_set_id in a CVS should have the same content. The vps_video_parameter_set_id provides an identifier for the VPS for reference by other syntax elements. The value of vps_max_layers_minus1 plus 1 specifies the maximum allowed number of layers in each CVS that references the VPS. The value of vps_max_sub_layers_minus1 plus 1 specifies the maximum number of temporal sub-layers that may be present in each CVS that references the VPS. The value of [vps_max_sub_layers_minus1] should be in the range 0 to 6 inclusive.

[0114] vps_all_independent_layers_flag may be set equal to 1 to specify that all layers in the CVS are coded independently, without using inter-layer prediction. vps_all_independent_layers_flag may be set equal to 0 to specify 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 is 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

[0000] is inferred to be equal to 1. vps_layer_id[ i ] specifies the value of nuh_layer_id for the i-th layer. For any two non-negative integer values ​​m and n, when m is less than n, the value of vps_layer_id[ m ] should be less than vps_layer_id[ n ]. vps_independent_layer_flag[ i ] may be set equal to 1 to specify that the layer with index i does not use inter-layer prediction. vps_independent_layer_flag[ i ] may be set equal to 0 to specify that the layer with index i may use inter-layer prediction and vps_layer_dependency_flag[ i ] is present in the VPS. When not present, the value of vps_independent_layer_flag[ i ] is inferred to be equal to 1.

[0115] vps_direct_dependency_flag[i][j] may be set equal to 0 to specify that the layer with index j is not a direct reference layer of the layer with index i. vps_direct_dependency_flag[i][j] may be set equal to 1 to specify that the layer with index j is a direct reference layer of the layer with index i. When vps_direct_dependency_flag[i][j] is not present for i and j ranging from 0 to vps_max_layers_minus1, inclusive, vps_direct_dependency_flag[i][j] is inferred to be equal to 0. The variable DirectDependentLayerIdx[i][j], which specifies the jth directly dependent layer of the ith layer, is derived as follows: for( i = 1; i < vps_max_layers_minus1; i++ ) if( !vps_independent_layer_flag[ i ] ) for( j = i, k = 0; j >= 0; j-- ) if( vps_direct_dependency_flag[ i ][ j ] ) DirectDependentLayerIdx[ i ][ k++ ] = j

[0116] The variable GeneralLayerIdx[ i ], which specifies the layer index of the layer with nuh_layer_id equal to vps_layer_id[ i ], is derived as follows: for( i = 0; i <= vps_max_layers_minus1; i++ ) GeneralLayerIdx[ vps_layer_id[ i ] ] = i

[0117] each_layer_is_an_ols_flag may be set equal to 1 to specify 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 may be set equal to 0 to specify that an output layer set may contain two or more layers. 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.

[0118] ols_mode_idc may be set equal to 0 to specify 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 may be set equal to 1 to specify 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 in the OLS are output. ols_mode_idc may be set equal to 2 to specify that the total number of OLSs specified by the VPS is explicitly signaled, and for each OLS, the top layer in the OLS and the explicitly signaled set of lower layers are output. The value of ols_mode_idc should be in the range from 0 to 2, inclusive. The value 3 of ols_mode_idc is reserved. 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.

[0119] The value of num_output_layer_sets_minus1 plus 1 specifies the total number of OLSs specified by the VPS when ols_mode_idc is 2. The variable TotalNumOlss, which specifies the total number of OLSs specified by the VPS, is 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

[0120] 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 ] may be set equal to 1 to specify that the jth layer is included in the ith OLS. layer_included_flag[ i ][ j ] may be set equal to 0 to specify that the jth layer is not included in the ith OLS.

[0121] The variable NumLayersInOls[i] that specifies the number of layers of the i-th OLS and the variable LayerIdInOls[i][j] that specifies the value of nuh_layer_id of the j-th layer of the i-th OLS may be derived as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 } }

[0122] The variable OlsLayeIdx[ i ][ j ], which specifies the OLS layer index of the layer with nuh_layer_id 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

[0123] The lowest layer of each OLS should 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 ]

[0000] ] ] should be equal to 1. Each layer may be included in at least one OLS specified by the VPS. In other words, for each layer with a particular value of nuh_layer_id (e.g., nuhLayerId is equal to one of vps_layer_id[ k ] for k ranging from 0 to vps_max_layers_minus1, inclusive), there should be at least one pair of i and j values ​​such that the value of LayerIdInOls[ i ][ j ] is equal to nuhLayerId, where i is in the range from 0 to TotalNumOlss - 1, inclusive, and j is in the range NumLayersInOls[ i ] - 1. Any layer in an OLS can be either the output layer of the OLS or a reference layer (direct or indirect) of an OLS output layer.

[0124] vps_output_layer_flag[ i ][ j ] specifies whether the jth layer of the ith OLS is output when ols_mode_idc is equal to 2. vps_output_layer_flag[ i ] may be set equal to 1 to specify that the jth layer of the ith OLS is output. vps_output_layer_flag[ i ] may be set equal to 0 to specify that the jth layer of the ith OLS is not output. When vps_all_independent_layers_flag is equal to 1 and each_layer_is_an_ols_flag is equal to 0, the value of vps_output_layer_flag[ i ] may be inferred to be equal to 1.

[0125] The variable OutputLayerFlag[i][j], where a value of 1 specifies that the jth layer of the ith OLS is output and a value of 0 specifies that the jth layer of 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 ] }

[0126] The 0th OLS includes only the lowest layer (e.g., the layer with nuh_layer_id equal to vps_layer_id

[0000] ), and for the 0th OLS, only the included layer is output. vps_constraint_info_present_flag may be set equal to 1 to specify that the general_constraint_info() syntax structure is present in the VPS. vps_constraint_info_present_flag may be set equal to 0 to specify that the general_constraint_info() syntax structure is not present in the VPS. vps_reserved_zero_7bits SHOULD be equal to 0 in a conforming bitstream. Other values ​​of vps_reserved_zero_7bits are reserved. Decoders SHOULD ignore the value of vps_reserved_zero_7bits.

[0127] general_hrd_params_present_flag may be set equal to 1 to specify 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 may be set equal to 0 to specify 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 should be greater than 0. A clock tick in seconds is equal to num_units_in_tick divided by time_scale. For example, when the picture rate of the video signal is 25 Hz, time_scale may be equal to 27000000, num_units_in_tick may be equal to 1080000, and therefore a clock tick may be equal to 0.04 seconds.

[0128] time_scale is the number of time units that elapse in one second. For example, a time coordinate system that measures time using a 27 megahertz (MHz) clock has a time_scale of 27,000,000. The value of time_scale should be greater than 0. vps_extension_flag may be set equal to 0 to specify that the vps_extension_data_flag syntax structure is not present in the VPS RBSP syntax structure. vps_extension_flag may be set equal to 1 to specify 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 do not affect a decoder's conformance to the profile. Conforming decoders should ignore all vps_extension_data_flag syntax elements.

[0129] 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 includes a downstream port 820, an upstream port 850, and / or a transceiver unit (Tx / Rx) 810 including a transmitter and / or receiver for communicating data upstream and / or downstream over a network. The video coding device 800 further includes a processor 830 including a logic unit and / or central processing unit (CPU) for processing data and a memory 832 for storing data. The video coding device 800 may also include electrical, optical-electrical (OE) components, electro-optical (EO) components, and / or wireless communication components coupled to the upstream port 850 and / or downstream port 820 for communicating 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.

[0130] 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 includes a coding module 814. The coding module 814 implements the disclosed embodiments described herein, such as methods 100, 900, and 1000, which may use the multi-layer video sequence 500, the video sequence 600, and / or the bitstream 700. The coding module 814 may also implement any other method / mechanism described herein. Additionally, the coding module 814 may implement the codec system 200, the encoder 300, and / or the decoder 400. For example, the coding module 814 may be used to code a video sequence into layers and / or OLSs to support SNR and / or spatial scalability. For example, the coding module 814 may encode and / or decode an ols_mode_idc syntax element to / from a VPS of a bitstream. The ols_mode_idc syntax element may indicate that the total number of OLSs in a video sequence is equal to the total number of layers specified in the VPS, that the i-th OLS includes layers 0 through i, including layer 0 and layer i, and that for each OLS, only the highest layer is output. Thus, the coding module 814 may use the ols_mode_idc syntax element to indicate / determine that only the highest received layer can be decoded and displayed, and that all other received layers should be decoded to support decoding of the highest received layer.Coding module 814 may be implemented as instructions stored in memory 832 and executed by processor 830 (e.g., as a computer program product stored on a non-transitory medium).

[0131] Memory 832 includes one or more memories such as a disk, tape drive, solid-state drive, read-only memory (ROM), random access memory (RAM), flash memory, ternary content-addressable memory (TCAM), static random access memory (SRAM), etc. Memory 832 may be used to store programs when such programs are selected for execution as well as an overflow data storage device for storing instructions and data read during the execution of programs.

[0132] 9 is a flow diagram of an example method 900 for encoding a video sequence with an OLS configured for scalability, such as multi-layer video sequence 500 and / or video sequence 600 in bitstream 700. Method 900 may be used by an encoder, such as codec system 200, encoder 300, and / or video coding device 800, when performing method 100.

[0133] Method 900 may begin when an encoder receives a video sequence and determines, for example, based on user input, to encode the video sequence as a scalable video sequence within a set of layers and OLSs. The video sequence may be coded to support SNR scalability, spatial scalability, scalability according to other features discussed herein, or a combination thereof. In step 901, the encoder may encode a bitstream including one or more layers of a coded picture. In particular, the encoder may encode a base layer with the lowest layer ID and various enhancement layers with increasing layer IDs. Each enhancement layer with layer ID j may be coded using inter-layer prediction based on the base layer and any enhancement layers with layer IDs less than j. Additionally, layers may be organized into OLSs with OLS IDs, which may be denoted by i to distinguish layer IDs of j. For example, there may be one OLS per layer. Thus, an OLS with OLS ID i may include an output layer with layer ID j, where i is equal to i. An OLS with OLS ID i may include all layers with layer IDs between 0 and j-1 inclusive. For example, an OLS with OLS ID 5 may include layers 0 through 5, with layer 5 being the output layer.

[0134] In step 903, the encoder encodes the VPS into a bitstream. The VPS includes an ols_mode_idc syntax element. ols_mode_idc may be set to specify that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS. Furthermore, ols_mode_idc may be set to specify that the i-th OLS includes layers with layer indices from 0 to i and / or j, inclusive (e.g., in this case, i equals j). ols_mode_idc may be set to specify that, for each OLS, only the top layer of each OLS is the output layer. For example, ols_mode_idc may be set to one of several modes. When ols_mode_idc is set to 0, the above-mentioned modes may be signaled. In some examples, the VPS may also include vps_max_layers_minus1, which specifies the number of layers specified by the VPS. This is also the maximum allowed number of layers in each CVS that references a VPS. ols_mode_idc may reference vps_max_layers_minus1.

[0135] As an example, a video sequence may be decoded in a hypothetical reference decoder of a decoder and / or encoder for purposes of standard verification. When decoding a video sequence when each_layer_is_an_ols_flag of the VPS is set to 0, when ols_mode_idc is set to 0, or when ols_mode_idc is set to 1, the total number of OLSs (TotalNumOlss) variable of the video sequence may be set equal to vps_max_layers_minus1 plus 1. As a specific example, the number of layers of the ith OLS (NumLayersInOls[i]) and the layer ID of the OLS (LayerIdInOLS[i][j]), which specifies the value of nuh_layer_id of the jth layer of the ith OLS, may be derived as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 ] Specifies that vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each_layer_is_an_ols_flag is an OLS flag for each layer that specifies whether at least one OLS contains two or more layers.

[0136] In step 905, the encoder may store the bitstream for transmission to the decoder. For example, the decoder may be aware of available OLSs (e.g., via communication and / or other protocols such as dynamic adaptive streaming over hypertext transfer protocol (DASH)). The decoder may select and request an OLS with the highest ID that can be properly decoded / displayed by the decoder. For example, in the case of spatial scalability, the decoder may request an OLS with a picture size associated with the screen connected to the decoder. In the case of SNR scalability, the decoder may request an OLS with the highest ID that can be decoded in light of current network conditions (e.g., in light of available communication bandwidth). The encoder and / or intermediate cache or content server may then transmit the OLS and associated layers to the decoder for decoding. Thus, the encoder may generate a video sequence that can be scaled up or down based on the decoder's needs.

[0137] 10 is a flow diagram of an example method 1000 for decoding a video sequence including an OLS configured for scalability, such as multi-layer video sequence 500 and / or video sequence 600 in bitstream 700. Method 1000 may be used by a decoder, such as codec system 200, decoder 400, and / or video coding device 800, when performing method 100.

[0138] Method 1000 may begin when a decoder begins receiving a bitstream including an OLS having a set of layers of a scalable video sequence, for example, as a result of method 900. The video sequence may be coded to support SNR scalability, spatial scalability, scalability according to other features discussed herein, or a combination thereof. At step 1001, the decoder may receive a bitstream including one or more layers of a coded picture and a VPS. The layers may be included in the OLS. For example, the layers may include a base layer with the lowest layer ID and various enhancement layers with increasing layer IDs. Each enhancement layer with layer ID j may be coded using inter-layer prediction based on the base layer and any enhancement layers with layer IDs less than j. The OLS may include an OLS ID, which may be denoted by i, to distinguish layer IDs of j. For example, there may be one OLS in the coded bitstream for each layer. Thus, an OLS with OLS ID i may include an output layer with layer ID j, where i is equal to i. A received OLS with OLS ID i may include all layers with layer IDs 0 through j-1 inclusive. As an example, a received OLS with OLS ID 5 may include layers 0 through 5, with layer 5 being the output layer. The configuration of the OLS and layers may be indicated by the VPS.

[0139] For example, a VPS includes an ols_mode_idc syntax element. ols_mode_idc may be set to specify that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS. Furthermore, ols_mode_idc may be set to specify that the i-th OLS includes layers with layer indices from 0 to i and / or j, inclusive (e.g., in this case, i equals j). ols_mode_idc may be set to specify that, for each OLS, only the top layer of each OLS is the output layer. For example, ols_mode_idc may be set to one of several modes. The aforementioned modes may be signaled when ols_mode_idc is set to 0. In some examples, a VPS may also include vps_max_layers_minus1, which specifies the number of layers specified by the VPS. This is the maximum allowed number of layers in each CVS that references the VPS. ols_mode_idc may refer to vps_max_layers_minus1.

[0140] In step 1003, the decoder may determine the output layers based on the ols_mode_idc of the VPS. As an example, when decoding a video sequence when each_layer_is_an_ols_flag of the VPS is set to 0, when ols_mode_idc is set to 0, or when ols_mode_idc is set to 1, the total number of OLSs for the video sequence (TotalNumOlss) variable may be set equal to vps_max_layers_minus1 plus 1. As a specific example, the number of layers for the ith OLS (NumLayersInOls[i]) and the layer ID of the OLS (LayerIdInOLS[i][j]), which specifies the value of nuh_layer_id for the jth layer of the ith OLS, may be derived as follows: NumLayersInOls

[0000] = 1 LayerIdInOls

[0000]

[0000] = vps_layer_id

[0000] for( i = 1, i < TotalNumOlss; i++ ) { if( each_layer_is_an_ols_flag ) { NumLayersInOls[ i ] = 1 LayerIdInOls[ i ]

[0000] = 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 ] Specifies that vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each_layer_is_an_ols_flag is an OLS flag for each layer that specifies whether at least one OLS contains two or more layers. This process allows the decoder to determine the configuration of the OLS as well as the IDs of the output layer and the IDs of the supporting layers.

[0141] Once the ID of the output layer and the ID of the support layer are known, the decoder can begin decoding coded pictures of the output layer based on the support layer by using inter-layer prediction. In step 1005, the decoder can decode coded pictures from the output layer to generate decoded pictures. In step 1007, the decoder can forward the decoded pictures for display as part of the decoded video sequence.

[0142] For example, a decoder may be aware of available OLSs (e.g., via communication and / or other protocols such as Dynamic Adaptive Streaming over Hypertext Transfer Protocol (DASH)). The decoder may select and request an OLS with the highest ID that can be properly decoded / displayed by the decoder. For example, in the case of spatial scalability, the decoder may request an OLS with a picture size associated with the screen connected to the decoder. In the case of SNR scalability, the decoder may request an OLS with the highest ID that can be decoded in light of current network conditions (e.g., in light of available communication bandwidth). The encoder and / or intermediate cache or content server may then transmit the OLS and associated layers to the decoder for decoding. Thus, the encoder can generate a video sequence that can be scaled up or down based on the decoder's needs. The decoder can then decode the requested video sequence upon receipt by using method 1000.

[0143] 11 is a schematic diagram of an example system 1100 for coding a video sequence with an OLS configured for scalability, such as multi-layer video sequence 500 and / or video sequence 600 in bitstream 700. System 1100 may be implemented by an encoder and decoder, such as codec system 200, encoder 300, decoder 400, and / or video coding device 800. Furthermore, system 1100 may be used when performing methods 100, 900, and / or 1000.

[0144] The system 1100 includes a video encoder 1102. The video encoder 1102 includes an encoding module 1105 for encoding a bitstream including one or more layers of a coded picture. The encoding module 1105 is further for encoding a VPS into the bitstream, the VPS including an ols_mode_idc specifying that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS. The video encoder 1102 further includes a storage module 1106 for storing the bitstream for transmission to a decoder. The video encoder 1102 further includes a transmission module 1107 for transmitting the bitstream to a video decoder 1110. The video encoder 1102 may be further configured to perform any of the steps of method 900.

[0145] System 1100 also includes a video decoder 1110. The video decoder 1110 includes a receiving module 1111 for receiving a bitstream including one or more layers of a coded picture and a VPS, where the VPS includes an ols_mode_idc specifying that the total number of OLSs specified by the VPS is equal to the number of layers specified by the VPS. The video decoder 1110 further includes a determining module 1113 for determining an output layer based on the ols_mode_idc of the VPS. The video decoder 1110 further includes a decoding module 1115 for decoding the coded picture from the output layer to generate a decoded picture. The video decoder 1110 further includes a transferring module 1117 for transferring 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 method 1000.

[0146] 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. The use of the term "about" means a range including ±10% of the subsequent number, unless otherwise specified.

[0147] It should also be understood that the steps of the exemplary methods described herein are not necessarily required to be performed in the order described, and that the order of steps of such methods is to be understood as being exemplary only. 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.

[0148] Although several embodiments have been provided in this disclosure, it will be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the disclosure. These examples should be considered illustrative and not limiting, and the intention should not be limited to the details given herein. For example, various elements or components may be combined or integrated into another system, or certain features may be omitted, or not implemented.

[0149] Additionally, techniques, systems, subsystems, and methods described and illustrated in various embodiments as separate or distinct 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 may occur to those skilled in the art and may be made without departing from the spirit and scope of what is disclosed herein. [Explanation of symbols]

[0150] 100 How it works 200 Coding and Decoding (Codec) Systems 201 segmented video signal 211 General Coda Control Components 213 Transformation, Scaling and Quantization Components 215 Intra-picture estimation components 217 Intra-picture prediction components 219 Motion Compensation Components 221 Motion Estimation Components 223 Decoded Picture Buffer Components 225 In-loop filter components 227 Filter Control Analysis Components 229 Scaling and Inverse Transformation Components 231 Header Format and Context-Adaptive Binary Arithmetic Coding (CABAC) Components 300 Video Encoder 301 segmented video signal 313 Transformation and Quantization Components 317 Intra-picture prediction components 321 Motion Compensation Components 323 Decoded Picture Buffer Components 325 In-Loop Filter Components 329 Inverse Transform and Quantization Components 331 Entropy Coding Components 400 Video Decoder 417 Intra-picture prediction components 421 Motion Compensation Components 423 Decoded Picture Buffer Components 425 In-Loop Filter Components 429 Inverse Transform and Quantization Components 433 Entropy Decoding Components 500 multi-layer video sequences 511 Pictures 512 Pictures 513 Pictures 514 Pictures 515 Pictures 516 Pictures 517 Pictures 518 Pictures 521 Inter-layer Prediction 523 Inter Prediction 525 OLS 531 Layer N 532 Layer N+1 600 video sequences 620 OLS 621 OLS 622 OLS 630 Layers 631 Layer 632 Layers 700 bitstream 711 VPS 713 Sequence Parameter Set (SPS) 715 Picture Parameter Set (PPS) 717 Slice Header 720 image data 721 OLS 723 Layer 725 Pictures 727 slices 731 vps_layer_id[i] 733 each_layer_is_an_ols_flag 735 ols_mode_idc 737 vps_max_layers_minus1 800 Video Coding Device 810 Transceiver Unit (Tx / Rx) 814 Coding Module 820 downstream ports 830 processor 832 memory 850 upstream ports 860 Input and / or Output (I / O) Devices 900 ways 1000 ways 1100 System 1102 Video Encoder 1105 Encoding Module 1106 Storage Module 1107 Transmitting Module 1110 Video Decoder 1111 Receiver Module 1113 Decision Module 1115 Decryption Module 1117 Transfer Module

Claims

1. A method implemented by a decoder, comprising: receiving, by a receiver of the decoder, a bitstream including one or more layers of a coded picture and a video parameter set (VPS), the VPS including an output layer set (OLS) mode identification code (ols_mode_idc) specifying that the total number of output layer sets (OLS) specified by the VPS is equal to the number of layers specified by the VPS; determining, by a processor of the decoder, an output layer based on the ols_mode_idc of the VPS; and decoding, by a processor of the decoder, coded pictures from the output layer to generate decoded pictures.

2. The method of claim 1 , wherein the ols_mode_idc specifies that the i-th OLS includes layers having layer indices from 0 to i, inclusive.

3. 3. The method of claim 1 or 2, wherein the ols_mode_idc specifies, for each OLS, that only the top layer of each OLS is the output layer.

4. 4. The method of claim 1, wherein ols_mode_idc is equal to 0.

5. 5. The method of claim 1, wherein the VPS includes a VPS max layers minus 1 (vps_max_layers_minus1) that specifies the number of layers specified by the VPS, which is the maximum allowed number of layers in each coded video sequence (CVS) that references the VPS.

6. 6. The method of claim 1, wherein when the ols_mode_idc is equal to 0 or when the ols_mode_idc is equal to 1, the total number of OLSs (TotalNumOlss) is equal to vps_max_layers_minus1 plus 1.

7. The number of layers in the i-th OLS (NumLayersInOls [i]), and a layer identifier (ID) of the OLS (LayerIdInOLS[i]) that specifies the value of the Network Abstraction Layer (NAL) unit header layer identifier (nuh_layer_id) of the jth layer of the ith OLS. [i][j]) are 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 ] 7. A method according to any one of claims 1 to 6, wherein vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each layer is an OLS flag specifying whether at least one OLS contains two or more layers.

8. 1. A method implemented by an encoder, comprising: encoding, by a processor of the encoder, a bitstream including one or more layers of a coded picture; encoding, by the processor, a video parameter set (VPS) into the bitstream, the VPS including an output layer set (OLS) mode identification code (ols_mode_idc) specifying that the total number of output layer sets (OLS) specified by the VPS is equal to the number of layers specified by the VPS; storing, by a memory coupled to the processor, the bitstream for transmission to a decoder.

9. The method of claim 8 , wherein the ols_mode_idc specifies that the i-th OLS includes layers having layer indices from 0 to i, inclusive.

10. 10. The method of claim 8 or 9, wherein the ols_mode_idc specifies, for each OLS, that only the top layer of each OLS is the output layer.

11. 11. The method of claim 8, wherein ols_mode_idc is equal to 0.

12. 12. The method of claim 8, wherein the VPS includes a VPS max layers minus 1 (vps_max_layers_minus1) that specifies the number of layers specified by the VPS, which is the maximum allowed number of layers in each coded video sequence (CVS) that references the VPS.

13. 13. The method of claim 8, wherein when the ols_mode_idc is equal to 0 or when the ols_mode_idc is equal to 1, the total number of OLSs (TotalNumOlss) is equal to vps_max_layers_minus1 plus 1.

14. The number of layers in the i-th OLS (NumLayersInOls [i]), and a layer identifier (ID) of the OLS (LayerIdInOLS[i]) that specifies the value of the Network Abstraction Layer (NAL) unit header layer identifier (nuh_layer_id) of the jth layer of the ith OLS. [i][j]) are 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 ] 14. A method according to any one of claims 8 to 13, wherein vps_layer_id[i] is the i-th VPS layer identifier, TotalNumOlss is the total number of OLSs specified by the VPS, and each layer is an OLS flag specifying whether at least one OLS contains two or more layers.

15. 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. 15. A non-transitory computer-readable medium comprising a computer program product for use by a video coding device, the computer program product 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 the method of any one of claims 1 to 14.

17. receiving means for receiving a bitstream including one or more layers of a coded picture and a video parameter set (VPS), wherein the VPS includes an output layer set (OLS) mode identification code (ols_mode_idc) specifying that a total number of output layer sets (OLS) specified by the VPS is equal to the number of layers specified by the VPS; determining means for determining an output layer based on the ols_mode_idc of the VPS; decoding means for decoding coded pictures from the output layer to generate decoded pictures; and transferring means for transferring said decoded pictures for display as part of a decoded video sequence.

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

19. An encoding means, encoding a bitstream including one or more layers of the coded picture; and encoding means for encoding a video parameter set (VPS) into the bitstream, the VPS including an output layer set (OLS) mode identification code (ols_mode_idc) specifying that a total number of output layer sets (OLS) specified by the VPS is equal to the number of layers specified by the VPS; and storage means for storing said bitstream for transmission 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.

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