Patent ID: 12192502

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

The following terms are defined as follows unless used in a contrary context herein. Specifically, the following definitions are intended to provide additional clarity to the present disclosure. However, terms may be described differently in different contexts. Accordingly, the following definitions should be considered as a supplement and should not be considered to limit any other definitions of descriptions provided for such terms herein.

A bitstream is a sequence of bits including video data that is compressed for transmission between an encoder and a decoder. An encoder is a device that is configured to employ encoding processes to compress video data into a bitstream. A decoder is a device that is configured to employ decoding processes to reconstruct video data from a bitstream for display. A picture is an array of luma samples and/or an array of chroma samples that create a frame or a field thereof. A slice is an integer number of complete tiles or an integer number of consecutive complete coding tree unit (CTU) rows (e.g., within a tile) of a picture that are exclusively contained in a single network abstraction layer (NAL) unit. A picture that is being encoded or decoded can be referred to as a current picture for clarity of discussion. A coded picture is a coded representation of a picture comprising video coding layer (VCL) NAL units with a particular value of NAL unit header layer identifier (nuh_layer_id) within an access unit (AU) and containing all coding tree units (CTUs) of the picture. A decoded picture is a picture produced by applying a decoding process to a coded picture.

An AU is a set of coded pictures that are included in different layers and are associated with the same time for output from a decoded picture buffer (DPB). A NAL unit is a syntax structure containing data in the form of a Raw Byte Sequence Payload (RBSP), an indication of the type of data, and interspersed as desired with emulation prevention bytes. 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, performance of conformance checking, or other operations. A NAL unit type (nal_unit_type) is a syntax element contained in a NAL unit that indicates a type of data contained in the NAL unit. A layer is a set of VCL NAL units that share a specified characteristic (e.g., a common resolution, frame rate, image size, etc.) as indicated by layer ID and associated non-VCL NAL units. A NAL unit header layer identifier (nuh_layer_id) is a syntax element that specifies an identifier of a layer that includes a NAL unit. A temporal identifier (TemporalId) is a derived identifier that indicates the relative position of a NAL unit in a video sequence. A NAL unit header temporal identifier plus one (nuh_temporal_id_plus1) is a signaled identifier that indicates the relative position of a NAL unit in a video sequence.

A hypothetical reference decoder (HRD) is a decoder model operating on an encoder that checks the variability of bitstreams produced by an encoding process to verify conformance with specified constraints. A bitstream conformance test is a test to determine whether an encoded bitstream complies with a standard, such as Versatile Video Coding (VVC). HRD parameters are syntax elements that initialize and/or define operational conditions of an HRD. HRD parameters may be included in supplemental enhancement information (SEI) messages and/or in a video parameter set (VP S). A SEI message is a syntax structure with specified semantics that conveys information that is not needed by the decoding process in order to determine the values of the samples in decoded pictures. A SEI NAL unit is a NAL unit that contains one or more SEI messages. A specific SEI NAL unit may be referred to as a current SEI NAL unit. A scalable nesting SEI message is a message that contains a plurality of SEI messages that correspond to one or more output layer sets (OLSs) or one or more layers. A buffering period (BP) SEI message is a SEI message that contains HRD parameters for initializing an HRD to manage a coded picture buffer (CPB). A picture timing (PT) SEI message is a SEI message that contains HRD parameters for managing delivery information for AUs at the CPB and/or a decoded picture buffer (DPB). A decoding unit information (DUI) SEI message is a SEI message that contains HRD parameters for managing delivery information for DUs at the CPB and/or the DPB. A scalable nesting SEI message is a set of scalable-nested SEI messages. A scalable-nested SEI message is a SEI message that is nested inside a scalable nesting SEI message. A prefix SEI message is a SEI message that applies to one or more subsequent NAL units. A suffix SEI message is a SEI message that applies to one or more preceding NAL units.

A picture parameter set (PPS) is a syntax structure containing syntax elements that apply to entire coded pictures as determined by a syntax element found in each picture header. A picture header is a syntax structure containing syntax elements that apply to all slices of a coded picture. A slice header is a part of a coded slice containing data elements pertaining to all tiles or CTU rows within a tile represented in the slice. A coded video sequence is a set of one or more coded pictures. A decoded video sequence is a set of one or more decoded pictures.

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

Many video compression techniques can be employed to reduce the size of video files with minimal loss of data. For example, video compression techniques can include performing spatial (e.g., intra-picture) prediction and/or temporal (e.g., inter-picture) prediction to reduce or remove data redundancy in video sequences. 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 treeblocks, 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 unidirectional prediction (P) or bidirectional prediction (B) slice of a picture may be coded by employing spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames and/or images, and reference pictures may be referred to as reference frames and/or reference images. Spatial or temporal prediction results in a predictive block representing an image block. Residual data represents pixel differences between the original image block and the predictive block. Accordingly, an inter-coded block is encoded according to a motion vector that points to a block of reference samples forming the predictive block and the residual data indicating the difference between the coded block and the predictive block. An intra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain. These result in residual transform coefficients, which may be quantized. The quantized transform coefficients may initially be arranged in a two-dimensional array. The quantized transform coefficients may be scanned in order to produce a one-dimensional vector of transform coefficients. Entropy coding may be applied to achieve even more compression. Such video compression techniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encoded and decoded according to corresponding video coding standards. Video coding standards include International Telecommunication Union (ITU) Standardization Sector (ITU-T) H.261, International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IEC MPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding (AVC), also known as 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), and three dimensional (3D) AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T and ISO/IEC has begun developing a video coding standard referred to as Versatile Video Coding (VVC). VVC is included in a Working Draft (WD), which includes JVET-O2001-v14.

A video sequence can include many pictures. To ensure the pictures are displayed in the correct order, video coding systems may assign the pictures a temporal identifier (TemporalId). Some video coding systems employ layers of pictures, where each layer includes substantially the same video at different resolutions, picture sizes, frame rates, etc. Pictures in different layers may be displayed in the alternative, depending conditions at the decoder. Accordingly, pictures in different layers that are positioned at the same point in the video sequence share the same TemporalId. Further, pictures in different layers that share the same TemporalId make up an access unit (AU). For example, a decoder may display a single picture selected from a single layer at each AU to display a video sequence.

Some video coding systems employ SEI messages. An SEI message contains information that is not needed by the decoding process in order to determine the values of the samples in decoded pictures. For example, the SEI messages may contain parameters used by a HRD operating at an encoder to check a bitstream for conformance with standards. Further, the video coding systems may code a video sequence into the bitstream as layers of pictures. The SEI messages may be related to varying pictures and/or varying combinations of layers. Accordingly, ensuring that the proper SEI message is associated with the proper pictures/layers can become challenging in complex multi-layer bitstreams. In the event that an SEI message is not associated with the correct layer/picture, the HRD may be unable to properly check the layer/picture for conformance. This may result in encoding errors.

Disclosed herein is a mechanism for correctly associating SEI messages to corresponding pictures/layers. Multilayer bitstreams may organize pictures and associated parameters into AUs. An AU is a set of coded pictures that are included in different layers and are associated with the same output time. An SEI message may be positioned in the same AU as the first picture associated with the SEI message. Further, the SEI message is assigned a TemporalId. A TemporalId is an identifier that indicates the relative position of a network abstraction layer (NAL) unit in a video sequence. The TemporalId of the SEI message is constrained to be equal to the TemporalId of the AU that contains the SEI message. Stated differently, the pictures are included in video coding layer (VCL) NAL units and parameters are included in non-VCL NAL units. When the non-VCL NAL unit is an SEI NAL unit containing an SEI message, the TemporalId of the non-VCL NAL unit is constrained to be equal to the TemporalId of the AU containing the non-VCL NAL unit. This approach ensures that the SEI messages are correctly associated with corresponding pictures in the AUs. Hence, various errors may be avoided. As a result, the functionality of the encoder and the decoder is improved. Further, coding efficiency may be increased, which reduces processor, memory, and/or network signaling resource usage at both the encoder and the decoder.

FIG.1is a flowchart of an example operating method100of coding a video signal. Specifically, a video signal is encoded at an encoder. The encoding process compresses the video signal by employing various mechanisms to reduce the video file size. A smaller file size allows the compressed video file to be transmitted toward a user, while reducing associated bandwidth overhead. The decoder then decodes the compressed video file to reconstruct the original video signal for display to an end user. The decoding process generally mirrors the encoding process to allow the decoder to consistently reconstruct the video signal.

At step101, the video signal is input into the 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 contains a series of image frames that, when viewed in a sequence, gives the visual impression of motion. The frames contain pixels that are expressed in terms of light, referred to herein as luma components (or luma samples), and color, which is referred to as chroma components (or color samples). In some examples, the frames may also contain depth values to support three dimensional viewing.

At step103, the video is partitioned into blocks. Partitioning includes subdividing the pixels in each frame into square and/or rectangular blocks for compression. For example, in High Efficiency Video Coding (HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first be divided into coding tree units (CTUs), which are blocks of a predefined size (e.g., sixty-four pixels by sixty-four pixels). The CTUs contain both luma and chroma samples. Coding trees may be employed to divide the CTUs into blocks and then recursively subdivide the blocks until configurations are achieved that support further encoding. For example, luma components of a frame may be subdivided until the individual blocks contain relatively homogenous lighting values. Further, chroma components of a frame may be subdivided until the individual blocks contain relatively homogenous color values. Accordingly, partitioning mechanisms vary depending on the content of the video frames.

At step105, various compression mechanisms are employed to compress the image blocks partitioned at step103. For example, inter-prediction and/or intra-prediction may be employed. Inter-prediction is designed to take advantage of the fact that objects in a common scene tend to appear in successive frames. Accordingly, a block depicting an object in a reference frame need not be repeatedly described in adjacent frames. Specifically, an object, such as a table, may remain in a constant position over multiple frames. Hence the table is described once and adjacent frames can refer back to the reference frame. Pattern matching mechanisms may be employed to match objects over multiple frames. Further, moving objects may be represented across multiple frames, for example due to object movement or camera movement. As a particular example, a video may show an automobile that moves across the screen over multiple frames. Motion vectors can be employed to describe 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. As such, inter-prediction can encode an image block in a current frame as a set of motion vectors indicating an offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-prediction takes advantage of the fact that luma and chroma components tend to cluster in a frame. For example, a patch of green in a portion of a tree tends to be positioned adjacent to similar patches of green. Intra-prediction employs multiple directional prediction modes (e.g., thirty-three in HEVC), a planar mode, and a direct current (DC) mode. The directional modes indicate that a current block is similar/the same as samples of a neighbor block in a corresponding direction. Planar mode indicates that a series of blocks along a row/column (e.g., a plane) can be interpolated based on neighbor blocks at the edges of the row. Planar mode, in effect, indicates a smooth transition of light/color across a row/column by employing a relatively constant slope in changing values. DC mode is employed for boundary smoothing and indicates that a block is similar/the same as an average value associated with samples of all the neighbor blocks associated with the angular directions of the directional prediction modes. Accordingly, intra-prediction blocks can represent image blocks as various relational prediction mode values instead of the actual values. Further, inter-prediction blocks can represent image blocks as motion vector values instead of the actual values. In either case, the prediction blocks may not exactly represent the image blocks in some cases. Any differences are stored in residual blocks. Transforms may be applied to the residual blocks to further compress the file.

At step107, various filtering techniques may be applied. In HEVC, the filters are applied according to an in-loop filtering scheme. The block based prediction discussed above may result in the creation of blocky images at the decoder. Further, the block based prediction scheme may encode a block and then reconstruct the encoded block for later use as a reference block. The in-loop filtering scheme iteratively applies noise suppression filters, de-blocking filters, adaptive loop filters, and sample adaptive offset (SAO) filters to the blocks/frames. These filters mitigate such blocking artifacts so that the encoded file can be accurately reconstructed. Further, these filters mitigate artifacts in the reconstructed reference blocks so that artifacts are less likely to create additional artifacts in subsequent blocks that are encoded based on the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered, the resulting data is encoded in a bitstream at step109. The bitstream includes the data discussed above as well as any signaling data desired to support proper video signal reconstruction at the decoder. For example, such data may include partition data, prediction data, residual blocks, and various flags providing coding instructions to the decoder. The bitstream may be stored in memory for transmission toward a decoder upon request. The bitstream may also be broadcast and/or multicast toward a plurality of decoders. The creation of the bitstream is an iterative process. Accordingly, steps101,103,105,107, and109may occur continuously and/or simultaneously over many frames and blocks. The order shown inFIG.1is presented for clarity and ease of discussion, and is not intended to limit the video coding process to a particular order.

The decoder receives the bitstream and begins the decoding process at step111. Specifically, the decoder employs an entropy decoding scheme to convert the bitstream into corresponding syntax and video data. The decoder employs the syntax data from the bitstream to determine the partitions for the frames at step111. The partitioning should match the results of block partitioning at step103. Entropy encoding/decoding as employed in step111is now described. The encoder makes many choices during the compression process, such as selecting block partitioning schemes from several possible choices based on the spatial positioning of values in the input image(s). Signaling the exact choices may employ a large number of bins. As used herein, a bin is a binary value that is treated as a variable (e.g., a bit value that may vary depending on context). Entropy coding allows the encoder to discard any options that are clearly not viable for a particular case, leaving a set of allowable options. Each allowable option is then assigned a code word. The length of the code words is based on the number of allowable options (e.g., one bin for two options, two bins for three to four options, etc.) The encoder then encodes the code word for the selected option. This scheme reduces the size of the code words as the code words are as big as desired to uniquely indicate a selection from a small sub-set of allowable options as opposed to uniquely indicating the selection from a potentially large set of all possible options. The decoder then decodes the selection by determining the set of allowable options in a similar manner to the encoder. By determining the set of allowable options, the decoder can read the code word and determine the selection made by the encoder.

At step113, the decoder performs block decoding. Specifically, the decoder employs reverse transforms to generate residual blocks. Then the decoder employs the residual blocks and corresponding prediction blocks to reconstruct the image blocks according to the partitioning. The prediction blocks may include both intra-prediction blocks and inter-prediction blocks as generated at the encoder at step105. The reconstructed image blocks are then positioned into frames of a reconstructed video signal according to the partitioning data determined at step111. Syntax for step113may also be signaled in the bitstream via entropy coding as discussed above.

At step115, filtering is performed on the frames of the reconstructed video signal in a manner similar to step107at the encoder. For example, noise suppression filters, de-blocking filters, adaptive loop filters, and SAO filters may be applied to the frames to remove blocking artifacts. Once the frames are filtered, the video signal can be output to a display at step117for viewing by an end user.

FIG.2is a schematic diagram of an example coding and decoding (codec) system200for video coding. Specifically, codec system200provides functionality to support the implementation of operating method100. Codec system200is generalized to depict components employed in both an encoder and a decoder. Codec system200receives and partitions a video signal as discussed with respect to steps101and103in operating method100, which results in a partitioned video signal201. Codec system200then compresses the partitioned video signal201into a coded bitstream when acting as an encoder as discussed with respect to steps105,107, and109in method100. When acting as a decoder, codec system200generates an output video signal from the bitstream as discussed with respect to steps111,113,115, and117in operating method100. The codec system200includes a general coder control component211, a transform scaling and quantization component213, an intra-picture estimation component215, an intra-picture prediction component217, a motion compensation component219, a motion estimation component221, a scaling and inverse transform component229, a filter control analysis component227, an in-loop filters component225, a decoded picture buffer component223, and a header formatting and context adaptive binary arithmetic coding (CABAC) component231. Such components are coupled as shown. InFIG.2, black lines indicate movement of data to be encoded/decoded while dashed lines indicate movement of control data that controls the operation of other components. The components of codec system200may all be present in the encoder. The decoder may include a subset of the components of codec system200. For example, the decoder may include the intra-picture prediction component217, the motion compensation component219, the scaling and inverse transform component229, the in-loop filters component225, and the decoded picture buffer component223. These components are now described.

The partitioned video signal201is a captured video sequence that has been partitioned into blocks of pixels by a coding tree. A coding tree employs various split modes to subdivide a block of pixels into smaller blocks of pixels. These blocks can then be further subdivided into smaller blocks. The blocks may be referred to as nodes on the coding tree. Larger parent nodes are split into smaller child nodes. The number of times a node is subdivided is referred to as the depth of the node/coding tree. The divided blocks can be included in coding units (CUs) in some cases. For example, a CU can be a sub-portion of a CTU that contains a luma block, red difference chroma (Cr) block(s), and a blue difference chroma (Cb) block(s) along with corresponding syntax instructions for the CU. The split modes may include a binary tree (BT), triple tree (TT), and a quad tree (QT) employed to partition a node into two, three, or four child nodes, respectively, of varying shapes depending on the split modes employed. The partitioned video signal201is forwarded to the general coder control component211, the transform scaling and quantization component213, the intra-picture estimation component215, the filter control analysis component227, and the motion estimation component221for compression.

The general coder control component211is configured to make decisions related to coding of the images of the video sequence into the bitstream according to application constraints. For example, the general coder control component211manages optimization of bitrate/bitstream size versus reconstruction quality. Such decisions may be made based on storage space/bandwidth availability and image resolution requests. The general coder control component211also manages buffer utilization in light of transmission speed to mitigate buffer underrun and overrun issues. To manage these issues, the general coder control component211manages partitioning, prediction, and filtering by the other components. For example, the general coder control component211may dynamically increase compression complexity to increase resolution and increase bandwidth usage or decrease compression complexity to decrease resolution and bandwidth usage. Hence, the general coder control component211controls the other components of codec system200to balance video signal reconstruction quality with bit rate concerns. The general coder control component211creates control data, which controls the operation of the other components. The control data is also forwarded to the header formatting and CABAC component231to be encoded in the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal201is also sent to the motion estimation component221and the motion compensation component219for inter-prediction. A frame or slice of the partitioned video signal201may be divided into multiple video blocks. Motion estimation component221and the motion compensation component219perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal prediction. Codec system200may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

Motion estimation component221and motion compensation component219may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a coded object relative to a predictive block. A predictive block is a block that is found to closely match the block to be coded, in terms of pixel difference. A predictive block may also be referred to as a reference block. Such pixel difference may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. HEVC employs several coded objects including a CTU, coding tree blocks (CTBs), and CUs. For example, a CTU can be divided into CTBs, which can then be divided into CBs for inclusion in CUs. A CU can be encoded as a prediction unit containing prediction data and/or a transform unit (TU) containing transformed residual data for the CU. The motion estimation component221generates motion vectors, prediction units, and TUs by using a rate-distortion analysis as part of a rate distortion optimization process. For example, the motion estimation component221may determine multiple reference blocks, multiple motion vectors, etc. for a current block/frame, and may select the reference blocks, motion vectors, etc. having the best rate-distortion characteristics. The best rate-distortion characteristics balance both quality of video reconstruction (e.g., amount of data loss by compression) with coding efficiency (e.g., size of the final encoding).

In some examples, codec system200may calculate values for sub-integer pixel positions of reference pictures stored in decoded picture buffer component223. For example, video codec system200may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation component221may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision. The motion estimation component221calculates a motion vector for a prediction unit of a video block in an inter-coded slice by comparing the position of the prediction unit to the position of a predictive block of a reference picture. Motion estimation component221outputs the calculated motion vector as motion data to header formatting and CABAC component231for encoding and motion to the motion compensation component219.

Motion compensation, performed by motion compensation component219, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation component221. Again, motion estimation component221and motion compensation component219may be functionally integrated, in some examples. Upon receiving the motion vector for the prediction unit of the current video block, motion compensation component219may locate the predictive block to which the motion vector points. A residual video block is then formed by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values. In general, motion estimation component221performs motion estimation relative to luma components, and motion compensation component219uses motion vectors calculated based on the luma components for both chroma components and luma components. The predictive block and residual block are forwarded to transform scaling and quantization component213.

The partitioned video signal201is also sent to intra-picture estimation component215and intra-picture prediction component217. As with motion estimation component221and motion compensation component219, intra-picture estimation component215and intra-picture prediction component217may be highly integrated, but are illustrated separately for conceptual purposes. The intra-picture estimation component215and intra-picture prediction component217intra-predict a current block relative to blocks in a current frame, as an alternative to the inter-prediction performed by motion estimation component221and motion compensation component219between frames, as described above. In particular, the intra-picture estimation component215determines an intra-prediction mode to use to encode a current block. In some examples, intra-picture estimation component215selects an appropriate intra-prediction mode to encode a current block from multiple tested intra-prediction modes. The selected intra-prediction modes are then forwarded to the header formatting and CABAC component231for encoding.

For example, the intra-picture estimation component215calculates rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and selects the intra-prediction mode having the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original unencoded block that was encoded to produce the encoded block, as well as a bitrate (e.g., a number of bits) used to produce the encoded block. The intra-picture estimation component215calculates ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block. In addition, intra-picture estimation component215may be configured to code depth blocks of a depth map using a depth modeling mode (DMM) based on rate-distortion optimization (RDO).

The intra-picture prediction component217may generate a residual block from the predictive block based on the selected intra-prediction modes determined by intra-picture estimation component215when implemented on an encoder or read the residual block from the bitstream when implemented on a decoder. The residual block includes the difference in values between the predictive block and the original block, represented as a matrix. The residual block is then forwarded to the transform scaling and quantization component213. The intra-picture estimation component215and the intra-picture prediction component217may operate on both luma and chroma components.

The transform scaling and quantization component213is configured to further compress the residual block. The transform scaling and quantization component213applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block, producing a video block comprising residual transform coefficient values. Wavelet transforms, integer transforms, sub-band transforms or other types of transforms could also be used. The transform may convert the residual information from a pixel value domain to a transform domain, such as a frequency domain. The transform scaling and quantization component213is also configured to scale the transformed residual information, for example based on frequency. Such scaling involves applying a scale factor to the residual information so that different frequency information is quantized at different granularities, which may affect final visual quality of the reconstructed video. The transform scaling and quantization component213is also configured to quantize the transform coefficients to further reduce 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 component213may then perform a scan of the matrix including the quantized transform coefficients. The quantized transform coefficients are forwarded to the header formatting and CABAC component231to be encoded in the bitstream.

The scaling and inverse transform component229applies a reverse operation of the transform scaling and quantization component213to support motion estimation. The scaling and inverse transform component229applies inverse scaling, transformation, and/or quantization to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block which may become a predictive block for another current block. The motion estimation component221and/or motion compensation component219may calculate a reference block by adding the residual block back to a corresponding predictive block for use in motion estimation of a later block/frame. Filters are applied to the reconstructed reference blocks to mitigate artifacts created during scaling, quantization, and transform. Such artifacts could otherwise cause inaccurate prediction (and create additional artifacts) when subsequent blocks are predicted.

The filter control analysis component227and the in-loop filters component225apply the filters to the residual blocks and/or to reconstructed image blocks. For example, the transformed residual block from the scaling and inverse transform component229may be combined with a corresponding prediction block from intra-picture prediction component217and/or motion compensation component219to reconstruct the original image block. The filters may then be applied to the reconstructed image block. In some examples, the filters may instead be applied to the residual blocks. As with other components inFIG.2, the filter control analysis component227and the in-loop filters component225are highly integrated and may be implemented together, but are depicted separately for conceptual purposes. Filters applied to the reconstructed reference blocks are applied to particular spatial regions and include multiple parameters to adjust how such filters are applied. The filter control analysis component227analyzes the reconstructed reference blocks to determine where such filters should be applied and sets corresponding parameters. Such data is forwarded to the header formatting and CABAC component231as filter control data for encoding. The in-loop filters component225applies such filters based on the filter control data. The filters may include a deblocking filter, a noise suppression filter, a SAO filter, and an adaptive loop filter. Such filters may be applied in the spatial/pixel domain (e.g., on a reconstructed pixel block) or in the frequency domain, depending on the example.

When operating as an encoder, the filtered reconstructed image block, residual block, and/or prediction block are stored in the decoded picture buffer component223for later use in motion estimation as discussed above. When operating as a decoder, the decoded picture buffer component223stores and forwards the reconstructed and filtered blocks toward a display as part of an output video signal. The decoded picture buffer component223may be any memory device capable of storing prediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component231receives the data from the various components of codec system200and encodes such data into a coded bitstream for transmission toward a decoder. Specifically, the header formatting and CABAC component231generates various headers to encode control data, such as general control data and filter control data. Further, prediction data, including intra-prediction and motion data, as well as residual data in the form of quantized transform coefficient data are all encoded in the bitstream. The final bitstream includes all information desired by the decoder to reconstruct the original partitioned video signal201. Such information may also include intra-prediction mode index tables (also referred to as codeword mapping tables), definitions of encoding contexts for various blocks, indications of most probable intra-prediction modes, an indication of partition information, etc. Such data may be encoded by employing entropy coding. For example, the information may be encoded by employing context adaptive variable length coding (CAVLC), CABAC, syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy coding technique. Following the entropy coding, the coded bitstream may be transmitted to another device (e.g., a video decoder) or archived for later transmission or retrieval.

FIG.3is a block diagram illustrating an example video encoder300. Video encoder300may be employed to implement the encoding functions of codec system200and/or implement steps101,103,105,107, and/or109of operating method100. Encoder300partitions an input video signal, resulting in a partitioned video signal301, which is substantially similar to the partitioned video signal201. The partitioned video signal301is then compressed and encoded into a bitstream by components of encoder300.

Specifically, the partitioned video signal301is forwarded to an intra-picture prediction component317for intra-prediction. The intra-picture prediction component317may be substantially similar to intra-picture estimation component215and intra-picture prediction component217. The partitioned video signal301is also forwarded to a motion compensation component321for inter-prediction based on reference blocks in a decoded picture buffer component323. The motion compensation component321may be substantially similar to motion estimation component221and motion compensation component219. The prediction blocks and residual blocks from the intra-picture prediction component317and the motion compensation component321are forwarded to a transform and quantization component313for transform and quantization of the residual blocks. The transform and quantization component313may be substantially similar to the transform scaling and quantization component213. The transformed and quantized residual blocks and the corresponding prediction blocks (along with associated control data) are forwarded to an entropy coding component331for coding into a bitstream. The entropy coding component331may be substantially similar to the header formatting and CABAC component231.

The transformed and quantized residual blocks and/or the corresponding prediction blocks are also forwarded from the transform and quantization component313to an inverse transform and quantization component329for reconstruction into reference blocks for use by the motion compensation component321. The inverse transform and quantization component329may be substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component325are also applied to the residual blocks and/or reconstructed reference blocks, depending on the example. The in-loop filters component325may be substantially similar to the filter control analysis component227and the in-loop filters component225. The in-loop filters component325may include multiple filters as discussed with respect to in-loop filters component225. The filtered blocks are then stored in a decoded picture buffer component323for use as reference blocks by the motion compensation component321. The decoded picture buffer component323may be substantially similar to the decoded picture buffer component223.

FIG.4is a block diagram illustrating an example video decoder400. Video decoder400may be employed to implement the decoding functions of codec system200and/or implement steps111,113,115, and/or117of operating method100. Decoder400receives a bitstream, for example from an encoder300, and generates a reconstructed output video signal based on the bitstream for display to an end user.

The bitstream is received by an entropy decoding component433. The entropy decoding component433is configured to implement an entropy decoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or other entropy coding techniques. For example, the entropy decoding component433may employ header information to provide a context to interpret additional data encoded as codewords in the bitstream. The decoded information includes any desired information to decode the video signal, such as general control data, filter control data, partition information, motion data, prediction data, and quantized transform coefficients from residual blocks. The quantized transform coefficients are forwarded to an inverse transform and quantization component429for reconstruction into residual blocks. The inverse transform and quantization component429may be similar to inverse transform and quantization component329.

The reconstructed residual blocks and/or prediction blocks are forwarded to intra-picture prediction component417for reconstruction into image blocks based on intra-prediction operations. The intra-picture prediction component417may be similar to intra-picture estimation component215and an intra-picture prediction component217. Specifically, the intra-picture prediction component417employs prediction modes to locate a reference block in the frame and applies a residual block to the result to reconstruct intra-predicted image blocks. The reconstructed intra-predicted image blocks and/or the residual blocks and corresponding inter-prediction data are forwarded to a decoded picture buffer component423via an in-loop filters component425, which may be substantially similar to decoded picture buffer component223and in-loop filters component225, respectively. The in-loop filters component425filters the reconstructed image blocks, residual blocks and/or prediction blocks, and such information is stored in the decoded picture buffer component423. Reconstructed image blocks from decoded picture buffer component423are forwarded to a motion compensation component421for inter-prediction. The motion compensation component421may be substantially similar to motion estimation component221and/or motion compensation component219. Specifically, the motion compensation component421employs motion vectors from a reference block to generate a prediction block and applies a residual block to the result to reconstruct an image block. The resulting reconstructed blocks may also be forwarded via the in-loop filters component425to the decoded picture buffer component423. The decoded picture buffer component423continues to store additional reconstructed image blocks, which can be reconstructed into frames via the partition information. Such frames may also be placed in a sequence. The sequence is output toward a display as a reconstructed output video signal.

FIG.5is a schematic diagram illustrating an example HRD500. A HRD500may be employed in an encoder, such as codec system200and/or encoder300. The HRD500may check the bitstream created at step109of method100before the bitstream is forwarded to a decoder, such as decoder400. In some examples, the bitstream may be continuously forwarded through the HRD500as the bitstream is encoded. In the event that a portion of the bitstream fails to conform to associated constraints, the HRD500can indicate such failure to an encoder to cause the encoder to re-encode the corresponding section of the bitstream with different mechanisms.

The HRD500includes a hypothetical stream scheduler (HSS)541. A HSS541is a component configured to perform a hypothetical delivery mechanism. The hypothetical delivery mechanism is used for checking the conformance of a bitstream or a decoder with regards to the timing and data flow of a bitstream551input into the HRD500. For example, the HSS541may receive a bitstream551output from an encoder and manage the conformance testing process on the bitstream551. In a particular example, the HSS541can control the rate that coded pictures move through the HRD500and verify that the bitstream551does not contain non-conforming data.

The HSS541may forward the bitstream551to a CPB543at a predefined rate. The HRD500may manage data in decoding units (DU)553. A DU553is an Access Unit (AU) or a sub-set of an AU and associated non-video coding layer (VCL) network abstraction layer (NAL) units. Specifically, an AU contains one or more pictures associated with an output time. For example, an AU may contain a single picture in a single layer bitstream, and may contain a picture for each layer in a multi-layer bitstream. Each picture of an AU may be divided into slices that are each included in a corresponding VCL NAL unit. Hence, a DU553may contain one or more pictures, one or more slices of a picture, or combinations thereof. Also, parameters used to decode the AU, pictures, and/or slices can be included in non-VCL NAL units. As such, the DU553contains non-VCL NAL units that contain data needed to support decoding the VCL NAL units in the DU553. The CPB543is a first-in first-out buffer in the HRD500. The CPB543contains DUs553including video data in decoding order. The CPB543stores the video data for use during bitstream conformance verification.

The CPB543forwards the DUs553to a decoding process component545. The decoding process component545is a component that conforms to the VVC standard. For example, the decoding process component545may emulate a decoder400employed by an end user. The decoding process component545decodes the DUs553at a rate that can be achieved by an example end user decoder. If the decoding process component545cannot decode the DUs553fast enough to prevent an overflow of the CPB543, then the bitstream551does not conform to the standard and should be re-encoded.

The decoding process component545decodes the DUs553, which creates decoded DUs555. A decoded DU555contains a decoded picture. The decoded DUs555are forwarded to a DPB547. The DPB547may be substantially similar to a decoded picture buffer component223,323, and/or423. To support inter-prediction, pictures that are marked for use as reference pictures556that are obtained from the decoded DUs555are returned to the decoding process component545to support further decoding. The DPB547outputs the decoded video sequence as a series of pictures557. The pictures557are reconstructed pictures that generally mirror pictures encoded into the bitstream551by the encoder.

The pictures557are forwarded to an output cropping component549. The output cropping component549is configured to apply a conformance cropping window to the pictures557. This results in output cropped pictures559. An output cropped picture559is a completely reconstructed picture. Accordingly, the output cropped picture559mimics what an end user would see upon decoding the bitstream551. As such, the encoder can review the output cropped pictures559to ensure the encoding is satisfactory.

The HRD500is initialized based on HRD parameters in the bitstream551. For example, the HRD500may read HRD parameters from a VPS, a SPS, and/or SEI messages. The HRD500may then perform conformance testing operations on the bitstream551based on the information in such HRD parameters. As a specific example, the HRD500may determine one or more CPB delivery schedules from the HRD parameters. A delivery schedule specifies timing for delivery of video data to and/or from a memory location, such as a CPB and/or a DPB. Hence, a CPB delivery schedule specifies timing for delivery of AUs, DUs553, and/or pictures, to/from the CPB543. It should be noted that the HRD500may employ DPB delivery schedules for the DPB547that are similar to the CPB delivery schedules.

Video may be coded into different layers and/or OLSs for use by decoders with varying levels of hardware capabilities as well for varying network conditions. The CPB delivery schedules are selected to reflect these issues. Accordingly, higher layer sub-bitstreams are designated for optimal hardware and network conditions and hence higher layers may receive one or more CPB delivery schedules that employ a large amount of memory in the CPB543and short delays for transfers of the DUs553toward the DPB547. Likewise, lower layer sub-bitstreams are designated for limited decoder hardware capabilities and/or poor network conditions. Hence, lower layers may receive one or more CPB delivery schedules that employ a small amount of memory in the CPB543and longer delays for transfers of the DUs553toward the DPB547. The OLSs, layers, sublayers, or combinations thereof can then be tested according to the corresponding delivery schedule to ensure that the resulting sub-bitstream can be correctly decoded under the conditions that are expected for the sub-bitstream. Accordingly, the HRD parameters in the bitstream551can indicate the CPB delivery schedules as well as include sufficient data to allow the HRD500to determine the CPB delivery schedules and correlate the CPB delivery schedules to the corresponding OLSs, layers, and/or sublayers.

FIG.6is a schematic diagram illustrating an example multi-layer video sequence600. The multi-layer video sequence600may be encoded by an encoder, such as codec system200and/or encoder300and decoded by a decoder, such as codec system200and/or decoder400, for example according to method100. Further, the multi-layer video sequence600can be checked for standard conformance by a HRD, such as HRD500. The multi-layer video sequence600is included to depict an example application for layers in a coded video sequence. A multi-layer video sequence600is any video sequence that employs a plurality of layers, such as layer N631and layer N+1632.

In an example, the multi-layer video sequence600may employ inter-layer prediction621. Inter-layer prediction621is applied between pictures611,612,613, and614and pictures615,616,617, and618in different layers. In the example shown, pictures611,612,613, and614are part of layer N+1632and pictures615,616,617, and618are part of layer N631. A layer, such as layer N631and/or layer N+1632, is a group of pictures that are all associated with a similar value of a characteristic, such as a similar size, quality, resolution, signal to noise ratio, capability, etc. A layer may be defined formally as a set of VCL NAL units that share the same layer ID and associated non-VCL NAL units. 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, performance of conformance checking, or other operations.

In the example shown, layer N+1632is associated with a larger image size than layer N631. Accordingly, pictures611,612,613, and614in layer N+1632have a larger picture size (e.g., larger height and width and hence more samples) than pictures615,616,617, and618in layer N631in this example. However, such pictures can be separated between layer N+1632and layer N631by other characteristics. While only two layers, layer N+1632and layer N631, are shown, a set of pictures can be separated into any number of layers based on associated characteristics. Layer N+1632and layer N631may also be denoted by a layer ID. A layer ID is an item of data that is associated with a picture and denotes the picture is part of an indicated layer. Accordingly, each picture611-618may be associated with a corresponding layer ID to indicate which layer N+1632or layer N631includes the corresponding picture. For example, a layer ID may include a NAL unit header layer identifier (nuh_layer_id), which is a syntax element that specifies an identifier of a layer that includes a NAL unit (e.g., that include slices and/or parameters of the pictures in a layer). A layer associated with a lower quality/smaller image size/smaller bitstream size, such as layer N631, is generally assigned a lower layer ID and is referred to as a lower layer. Further, a layer associated with a higher quality/larger image size/larger bitstream size, such as layer N+1632, is generally assigned a higher layer ID and is referred to as a higher layer.

Pictures611-618in different layers631-632are configured to be displayed in the alternative. As a specific example, a decoder may decode and display picture615at a current display time if a smaller picture is desired or the decoder may decode and display picture611at the current display time if a larger picture is desired. As such, pictures611-614at higher layer N+1632contain substantially the same image data as corresponding pictures615-618at lower layer N631(notwithstanding the difference in picture size). Specifically, picture611contains substantially the same image data as picture615, picture612contains substantially the same image data as picture616, etc.

Pictures611-618can be coded by reference to other pictures611-618in the same layer N631or N+1632. Coding a picture in reference to another picture in the same layer results in inter-prediction623. Inter-prediction623is depicted by solid line arrows. For example, picture613may be coded by employing inter-prediction623using one or two of pictures611,612, and/or614in layer N+1632as a reference, where one picture is referenced for unidirectional inter-prediction and/or two pictures are referenced for bidirectional inter-prediction. Further, picture617may be coded by employing inter-prediction623using one or two of pictures615,616, and/or618in layer N631as a reference, where one picture is referenced for unidirectional inter-prediction and/or two pictures are referenced for bidirectional inter-prediction. When a picture is used as a reference for another picture in the same layer when performing inter-prediction623, the picture may be referred to as a reference picture. For example, picture612may be a reference picture used to code picture613according to inter-prediction623. Inter-prediction623can also be referred to as intra-layer prediction in a multi-layer context. As such, inter-prediction623is a mechanism of coding samples of a current picture by reference to indicated samples in a reference picture that is different from the current picture where the reference picture and the current picture are in the same layer.

Pictures611-618can also be coded by reference to other pictures611-618in different layers. This process is known as inter-layer prediction621, and is depicted by dashed arrows. Inter-layer prediction621is a mechanism of coding samples of a current picture by reference to indicated samples in a reference picture where the current picture and the reference picture are in different layers and hence have different layer IDs. For example, a picture in a lower layer N631can be used as a reference picture to code a corresponding picture at a higher layer N+1632. As a specific example, picture611can be coded by reference to picture615according to inter-layer prediction621. In such a case, the picture615is used as an inter-layer reference picture. An inter-layer reference picture is a reference picture used for inter-layer prediction621. In most cases, inter-layer prediction621is constrained such that a current picture, such as picture611, can only use inter-layer reference picture(s) that are included in the same AU627and that are at a lower layer, such as picture615. When multiple layers (e.g., more than two) are available, inter-layer prediction621can encode/decode a current picture based on multiple inter-layer reference picture(s) at lower levels than the current picture.

A video encoder can employ a multi-layer video sequence600to encode pictures611-618via many different combinations and/or permutations of inter-prediction623and inter-layer prediction621. For example, picture615may be coded according to intra-prediction. Pictures616-618can then be coded according to inter-prediction623by using picture615as a reference picture. Further, picture611may be coded according to inter-layer prediction621by using picture615as an inter-layer reference picture. Pictures612-614can then be coded according to inter-prediction623by using picture611as a reference picture. As such, a reference picture can serve as both a single layer reference picture and an inter-layer reference picture for different coding mechanisms. By coding higher layer N+1632pictures based on lower layer N631pictures, the higher layer N+1632can avoid employing intra-prediction, which has much lower coding efficiency than inter-prediction623and inter-layer prediction621. As such, the poor coding efficiency of intra-prediction can be limited to the smallest/lowest quality pictures, and hence limited to coding the smallest amount of video data. The pictures used as reference pictures and/or inter-layer reference pictures can be indicated in entries of reference picture list(s) contained in a reference picture list structure.

The pictures611-618may also be included in access units (AUs)627. An AU627is a set of coded pictures that are included in different layers and are associated with the same output time during decoding. Accordingly, coded pictures in the same AU627are scheduled for output from a DPB at a decoder at the same time. For example, pictures614and618are in the same AU627. Pictures613and617are in a different AU627from pictures614and618. Pictures614and618in the same AU627may be displayed in the alternative. For example, picture618may be displayed when a small picture size is desired and picture614may be displayed when a large picture size is desired. When the large picture size is desired, picture614is output and picture618is used only for interlayer prediction621. In this case, picture618is discarded without being output once interlayer prediction621is complete.

An AU627can be further divided into one or more picture units (PUs)628. A PU628is a subset of an AU627that contains a single coded picture. A PU628can be formally defined as a set of NAL units that are associated with each other according to a specified classification rule, are consecutive in decoding order, and contain exactly one coded picture. It should be noted that a PU628can be referred to as a decoding unit (DU) when discussed in terms of a HRD and/or associated conformance tests.

It should also be noted that pictures611-618, and hence AUs627and PUs628, are each associated with a temporal identifier (TemporalId)629. A TemporalId629is a derived identifier that indicates the relative position of a NAL unit in a video sequence. Pictures and/or PUs628in the same AU627are associated with the same value of TemporalId629. For example, a first AU627in a sequence may include a TemporalId629of zero, with subsequent AUs627including consecutively increasing TemporalIds629. Non-VCL NAL units may also be associated with TemporalIds629. For example, a parameter set may be included in an AU627and may be associated with one or more pictures in the AU627. In such a case, the TemporalId629of the parameter set may be less than or equal to the TemporalId629of the AU627.

FIG.7is a schematic diagram illustrating an example bitstream700. For example, the bitstream700can be generated by a codec system200and/or an encoder300for decoding by a codec system200and/or a decoder400according to method100. Further, the bitstream700may include a multi-layer video sequence600. In addition, the bitstream700may include various parameters to control the operation of a HRD, such as HRD500. Based on such parameters, the HRD can check the bitstream700for conformance with standards prior to transmission toward a decoder for decoding.

The bitstream700includes a VPS711, one or more SPSs713, a plurality of picture parameter sets (PPSs)715, a plurality of adaptation parameter sets (APSs)716, a plurality of picture headers718, a plurality of slice headers717, image data720, and SEI messages719. A VPS711contains data related to the entire bitstream700. For example, the VPS711may contain data related OLSs, layers, and/or sublayers used in the bitstream700. An SPS713contains sequence data common to all pictures in a coded video sequence contained in the bitstream700. For example, each layer may contain one or more coded video sequences, and each coded video sequence may reference a SPS713for corresponding parameters. The parameters in a SPS713can include picture sizing, bit depth, coding tool parameters, bit rate restrictions, etc. It should be noted that, while each sequence refers to a SPS713, a single SPS713can contain data for multiple sequences in some examples. The PPS715contains parameters that apply to an entire picture. Hence, each picture in the video sequence may refer to a PPS715. It should be noted that, while each picture refers to a PPS715, a single PPS715can contain data for multiple pictures in some examples. For example, multiple similar pictures may be coded according to similar parameters. In such a case, a single PPS715may contain data for such similar pictures. The PPS715can indicate coding tools available for slices in corresponding pictures, quantization parameters, offsets, etc.

An APS716is syntax structure containing syntax elements/parameters that apply to one or more slices727in one or more pictures725. Such correlations can be determined based on syntax elements found in slice headers717associated with the slices727. For example, an APS716may apply to at least one, but less than all, slices727in a first picture721, to at least one, but less than all, slices727in a second picture725, etc. An APS716can be separated into multiple types based on the parameters contained in the APS716. Such types may include adaptive loop filter (ALF) APS, luma mapping with chroma scaling (LMCS) APS, and scaling list (Scaling) APS. An ALF is an adaptive block based filter that includes a transfer function controlled by variable parameters and employs feedback from a feedback loop to refine the transfer function. Further, the ALF is employed to correct coding artifacts (e.g., errors) that occur as a result of block based coding, such as blurring and ringing artifacts. As such, ALF parameters included in an ALF APS may include parameters selected by the encoder to cause an ALF to remove block based coding artifacts during decoding at the decoder. LMCS is a process that is applied as part of the decoding process that maps luma samples to particular values and in some cases also applies a scaling operation to the values of chroma samples. The LMCS tool may reshapes luma components based on mappings to corresponding chroma components in order to reduce rate distortion. As such, a LMCS APS includes parameters selected by the encoder to cause a LMCS tool to reshape luma components. A scaling list APS contains coding tool parameters associated with quantization matrices used by specified filters. As such, an APS716may contain parameters used to apply various filters to coded slices727during conformance testing at a HRD and/or upon decoding at a decoder.

A picture header718is a syntax structure containing syntax elements that apply to all slices727of a coded picture725. For example, a picture header718may contain picture order count information, reference picture data, data relating in intra-random access point (IRAP) pictures, data related to filter application for a picture725, etc. A PU may contain exactly one picture header718and exactly one picture725. As such, the bitstream700may include exactly one picture header718per picture725. A slice header717contains parameters that are specific to each slice727in a picture725. Hence, there may be one slice header717per slice727in the video sequence. The slice header717may contain slice type information, filtering information, prediction weights, tile entry points, deblocking parameters, etc. In some instances, syntax elements may be the same for all slices727in a picture725. In order to reduce redundancy, the picture header718and slice header717may share certain types of information. For example, certain parameters (e.g., filtering parameters) may be included in the picture header718when they apply to an entire picture725or included in a slice header717when they apply to a group of slices727that are a subset of the entire picture725.

The image data720contains video data encoded according to inter-prediction and/or intra-prediction as well as corresponding transformed and quantized residual data. For example, the image data720may include layers723, pictures725, and/or slices727. A layer723is a set of VCL NAL units745that share a specified characteristic (e.g., a common resolution, frame rate, image size, etc.) as indicated by a layer ID, such as a nuh_layer_id, and associated non-VCL NAL units741. For example, a layer723may include a set of pictures725that share the same nuh_layer_id. A layer723may be substantially similar to layers631and/or632. A nuh_layer_id is a syntax element that specifies an identifier of a layer723that includes at least one NAL unit. For example, the lowest quality layer723, known as a base layer, may include the lowest value of nuh_layer_id with increasing values of nuh_layer_id for layers723of higher quality. Hence, a lower layer is a layer723with a smaller value of nuh_layer_id and a higher layer is a layer723with a larger value of nuh_layer_id.

A picture725is an array of luma samples and/or an array of chroma samples that create a frame or a field thereof. For example, a picture725is a coded image that may be output for display or used to support coding of other picture(s)725for output. A picture725contains one or more slices727. A slice727may be defined as an integer number of complete tiles or an integer number of consecutive complete coding tree unit (CTU) rows (e.g., within a tile) of a picture725that are exclusively contained in a single NAL unit. The slices727are 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 luma components or chroma components of the CTU. The CTUs/CTBs are further divided into coding blocks based on coding trees. The coding blocks can then be encoded/decoded according to prediction mechanisms.

A SEI message719is a syntax structure with specified semantics that conveys information that is not needed by the decoding process in order to determine the values of the samples in decoded pictures. For example, the SEI messages719may contain data to support HRD processes or other supporting data that is not directly relevant to decoding the bitstream700at a decoder. A set of SEI messages719may be implemented as a scalable nesting SEI message. The scalable nesting SEI message provides a mechanism to associate SEI messages719with specific layers723. A scalable nesting SEI message is a message that contains a plurality of scalable-nested SEI messages. A scalable-nested SEI message is an SEI message719that correspond to one or more OLSs or one or more layers723. An OLS is a set of layers723where at least one of the layers723is an output layer. Accordingly, a scalable nesting SEI message can be said to include a set of scalable-nested SEI messages or said to include a set of SEI messages719, depending on context. Further, a scalable nesting SEI message contains a set of scalable-nested SEI messages of the same type. SEI messages719may include a BP SEI message that contains HRD parameters for initializing an HRD to manage a CPB for testing corresponding OLSs and/or layers723. SEI messages719may also include a PT SEI message that contains HRD parameters for managing delivery information for AUs at the CPB and/or the DPB for testing corresponding OLSs and/or layers723. SEI messages719may also include a DUI SEI message that contains HRD parameters for managing delivery information for DUs at the CPB and/or the DPB for testing corresponding OLSs and/or layers723.

A bitstream700can be coded as a sequence of NAL units. A NAL unit is a container for video data and/or supporting syntax. ANAL unit can be a VCL NAL unit745or a non-VCL NAL unit741. A VCL NAL unit745is a NAL unit coded to contain video data. Specifically, a VCL NAL unit745contains a slice727and an associated slice header717. A non-VCL NAL unit741is a NAL unit that contains non-video data such as syntax and/or parameters that support decoding the video data, performance of conformance checking, or other operations. Non-VCL NAL units741may include a VPS NAL unit, a SPS NAL unit, a PPS NAL unit, an APS NAL unit, picture header (PH) NAL unit, and an SEI NAL unit, which contain a VPS711, a SPS713, a PPS715, a APS716, a picture header718, and a SEI message719, respectively. It should be noted that the preceding list of NAL units is exemplary and not exhaustive.

Each NAL unit is associated with a NAL unit header temporal identifier plus one (nuh_temporal_id_plus1)731. The nuh_temporal_id_plus1731is a signaled identifier that indicates the relative position of a corresponding NAL unit in a video sequence. A decoder and/or a HRD can determine a TemporalId for the corresponding NAL unit based on the value of nuh_temporal_id_plus1731. Specifically, the nuh_temporal_id_plus1731is signaled in a header of the NAL unit. The TemporalId for the NAL unit can be determined by the decoder/HRD by subtracting one from the value of nuh_temporal_id_plus1731. As such, the value of nuh_temporal_id_plus1731should not be set to zero as this would result in a TemporalId with a negative value.

Further, SEI messages719can be employed as prefix SEI messages and/or suffix SEI messages. A prefix SEI message is a SEI message719that applies to one or more subsequent NAL units. A suffix SEI message is a SEI message719that applies to one or more preceding NAL units. A prefix SEI message is included in a prefix SEI NAL unit type (PREFIX_SEI_NUT)742and a suffix SEI message is included in a suffix SEI NAL unit type (SUFFIX_SEI_NUT)743. A PREFIX_SEI_NUT742is a non-VCL NAL unit with a type value set to indicate the non-VCL NAL unit contains a prefix SEI message. A SUFFIX_SEI_NUT743is a non-VCL NAL unit with a type value set to indicate the non-VCL NAL unit contains a suffix SEI message.

As noted above, the SEI messages719may contain parameters used by a HRD operating at an encoder to check a bitstream for conformance with standards. The SEI messages719may be related to varying pictures725and/or varying combinations of layers723. Accordingly, ensuring that the proper SEI message719is associated with the proper pictures725and/or layers723can become challenging in complex multi-layer bitstreams. Further, a prefix SEI message should be included in the bitstream700prior to the first NAL unit associated with the prefix SEI message, while a suffix SEI message should be included in the bitstream700immediately after the first NAL unit associated with the suffix SEI message. In the event that an SEI message719is not positioned correctly in the bitstream700and/or is not associated with the correct layer723and/or picture725, the HRD may be unable to properly check the layer723and/or picture725for conformance. This may result in encoding errors caused by the HRD and/or errors when decoding at a decoder. For example, the HRD may filter the picture improperly and/or fail to detect standards violations. Further, a decoder may fail to detect transmission related coding errors and/or improperly return an indication of a transmission related coding error when no such errors exist.

Bitstream700is modified to ensure the SEI messages719are correctly associated with corresponding layers723, pictures725, slices727, and/or NAL units. As described with respect toFIG.6, multilayer bitstreams may organize pictures and associated parameters into AUs. An AU is a set of coded pictures that are included in different layers and are associated with the same output time. In bitstream700, each SEI message719is positioned in the same AU as the first picture725associated with the SEI message719. Further, the SEI message719is assigned a TemporalId. The TemporalId of the SEI message719is constrained to be equal to the TemporalId of the AU that contains the SEI message719. In a particular example, each picture725in an AU shares the same value of TemporalId and hence share the same value of nuh_temporal_id_plus1731. Thus, the nuh_temporal_id_plus1731of the SEI message719is the same as the nuh_temporal_id_plus1731of each of the pictures725that correspond to which the SEI message719applies.

Stated differently, the pictures725are included in VCL NAL units745and parameters are included in non-VCL NAL units741. When the non-VCL NAL unit741is an SEI NAL unit of type PREFIX_SEI_NUT742or SUFFIX_SEI_NUT743that contains an SEI message719, the TemporalId/nuh_temporal_id_plus1731of the non-VCL NAL unit741is constrained to be equal to the TemporalId/nuh_temporal_id_plus1731of the AU containing the non-VCL NAL unit741. This approach ensures that the SEI messages719are correctly associated with corresponding pictures725in the AUs. Hence, various errors may be avoided. As a result, the functionality of the encoder and the decoder is increased. Further, coding efficiency may be increased, which reduces processor, memory, and/or network signaling resource usage at both the encoder and the decoder.

The preceding information is now described in more detail herein below. Layered video coding is also referred to as scalable video coding or video coding with scalability. Scalability in video coding may be supported by using multi-layer coding techniques. A multi-layer bitstream comprises a base layer (BL) and one or more enhancement layers (ELs). Example of scalabilities includes spatial scalability, quality/signal to noise ratio (SNR) scalability, multi-view scalability, frame rate scalability, etc. When a multi-layer coding technique is used, a picture or a part thereof may be coded without using a reference picture (intra-prediction), may be coded by referencing reference pictures that are in the same layer (inter-prediction), and/or may be coded by referencing reference pictures that are in other layer(s) (inter-layer prediction). A reference picture used for inter-layer prediction of the current picture is referred to as an inter-layer reference picture (ILRP).FIG.6illustrates an example of multi-layer coding for spatial scalability in which pictures in different layers have different resolutions.

Some video coding families provide support for scalability in separated profile(s) from the profile(s) for single-layer coding. Scalable video coding (SVC) is a scalable extension of the advanced video coding (AVC) that provides support for spatial, temporal, and quality scalabilities. For SVC, a flag is signaled in each macroblock (MB) in EL pictures to indicate whether the EL MB is predicted using the collocated block from a lower layer. The prediction from the collocated block may include texture, motion vectors, and/or coding modes. Implementations of SVC may not directly reuse unmodified AVC implementations in their design. The SVC EL macroblock syntax and decoding process differs from the AVC syntax and decoding process.

Scalable HEVC (SHVC) is an extension of HEVC that provides support for spatial and quality scalabilities. Multiview HEVC (MV-HEVC) is an extension of HEVC that provides support for multi-view scalability. 3D HEVC (3D-HEVC) is an extension of HEVC that provides support for 3D video coding that is more advanced and more efficient than MV-HEVC. Temporal scalability may be included as an integral part of a single-layer HEVC codec. In the multi-layer extension 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 the reference picture list(s) along with other temporal reference pictures in the current layer. Inter-layer prediction (ILP) is achieved at the prediction unit level by setting the value of the reference index to refer to the inter-layer reference picture(s) in the reference picture list(s). Spatial scalability resamples a reference picture or part thereof when an ILRP has a different spatial resolution than the current picture being encoded or decoded. Reference picture resampling can be realized at either picture level or coding block level.

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

The preceding aspects contain certain problems. For example, the nuh_layer_id values for SPS, PPS, and APS NAL units may not be properly constrained. Further, the TemporalId value for SEI NAL units may not be properly constrained. In addition, setting of NoOutputOfPriorPicsFlag may not be properly specified when reference picture resampling is enabled and pictures within a CLVS have different spatial resolutions. Also, in some video coding systems suffix SEI messages cannot be contained in a scalable nesting SEI message. As another example, buffering period, picture timing, and decoding unit information SEI messages may include parsing dependencies on VPS and/or SPS.

In general, this disclosure describes video coding improvement approaches. The descriptions of the techniques are based on VVC. However, the techniques also apply to layered video coding based on other video codec specifications.

One or more of the abovementioned problems may be solved as follows. The nuh_layer_id values for SPS, PPS, and APS NAL units are properly constrained herein. The TemporalId value for SEI NAL units is properly constrained herein. Setting of the NoOutputOfPriorPicsFlag is properly specified when reference picture resampling is enabled and pictures within a CLVS have different spatial resolutions. Suffix SEI messages are allowed to be contained in a scalable nesting SEI message. Parsing dependencies of BP, PT, and DUI SEI messages on VPS or SPS may be removed by repeating the syntax element decoding_unit_hrd_params_present_flag in the BP SEI message syntax, the syntax elements decoding_unit_hrd_params_present_flag and decoding_unit_cpb_params_in_pic_timing_sei_flag in the PT SEI message syntax, and the syntax element decoding_unit_cpb_params_in_pic_timing_sei_flag in the DUI SEI message.

An example implementation of the preceding mechanisms is as follows. An example general NAL unit semantics is as follows.

A nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for the NAL unit. The value of nuh_temporal_id_plus1 should not be equal to zero. The variable TemporalId may be derived as follows:

TemporalId=nuh_temporal⁢_id⁢_plus1-1
When nal_unit_type is in the range of IDR_W_RADL to RSV_IRAP_13, inclusive, TemporalId should be equal to zero. When nal_unit_type is equal to STSA_NUT, TemporalId should not be equal to zero.

The value of TemporalId should be the same for all VCL NAL units of an access unit. The value of TemporalId of a coded picture, a layer access unit, or an access unit may be the value of the TemporalId of the VCL NAL units of the coded picture, the layer access unit, or the access unit. The value of TemporalId of a sub-layer representation may be the greatest value of TemporalId of all VCL NAL units in the sub-layer representation.

The value of TemporalId for non-VCL NAL units is constrained as follows. If nal_unit_type is equal to DPS_NUT, VPS_NUT, or SPS_NUT, TemporalId is equal to zero and the TemporalId of the access unit containing the NAL unit should be equal to zero. Otherwise if nal_unit_type is equal to EOS_NUT or EOB_NUT, TemporalId should be equal to zero. Otherwise, if nal_unit_type is equal to AUD_NUT, FD_NUT, PREFIX_SEI_NUT, or SUFFIX_SEI_NUT, TemporalId should be equal to the TemporalId of the access unit containing the NAL unit. Otherwise, when nal_unit_type is equal to PPS_NUT or APS_NUT, TemporalId should be greater than or equal to the TemporalId of the access unit containing the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId should be equal to the minimum value of the TemporalId values of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT or APS_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit. This is because all PPSs and APSs may be included in the beginning of a bitstream. Further, the first coded picture has TemporalId equal to zero.

An example sequence parameter set RBSP semantics is as follows. An SPS RBSP should be available to the decoding process prior to being referenced. The SPS may be included in at least one access unit with TemporalId equal to zero or provided through external mechanism. The SPS NAL unit containing the SPS may be constrained to have a nuh_layer_id equal to the lowest nuh_layer_id value of PPS NAL units that refer to the SPS.

An example picture parameter set RBSP semantics is as follows. A PPS RBSP should be available to the decoding process prior to being referenced. The PPS should be included in at least one access unit with TemporalId less than or equal to the TemporalId of the PPS NAL unit or provided through external mechanism. The PPS NAL unit containing the PPS RBSP should have a nuh_layer_id equal to the lowest nuh_layer_id value of the coded slice NAL units that refer to the PPS.

An example adaptation parameter set semantics is as follows. Each APS RBSP should be available to the decoding process prior to being referenced. The APS should also be included in at least one access unit with TemporalId less than or equal to the TemporalId of the coded slice NAL unit that refers the APS or provided through an external mechanism. An APS NAL unit is allowed to be shared by pictures/slices of multiple layers. The nuh_layer_id of an APS NAL unit should be equal to the lowest nuh_layer_id value of the coded slice NAL units that refer to the APS NAL unit. Alternatively, an APS NAL unit may not be shared by pictures/slices of multiple layers. The nuh_layer_id of an APS NAL unit should be equal to the nuh_layer_id of slices referring to the APS.

In an example, removal of pictures from the DPB before decoding of the current picture is discussed as follows. The removal of pictures from the DPB before decoding of the current picture (but after parsing the slice header of the first slice of the current picture) may occur at the CPB removal time of the first decoding unit of access unit n (containing the current picture). This proceeds as follows. The decoding process for reference picture list construction is invoked and the decoding process for reference picture marking is invoked.

When the current picture is a coded layer video sequence start (CLVSS) picture that is not picture zero, the following ordered steps are applied. The variable NoOutputOfPriorPicsFlag is derived for the decoder under test as follows. If the value of pic_width_max_in_luma_samples, pic_height_max_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid] derived from the SPS is different from the value of pic_width_in_luma_samples, pic_height_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid], respectively, derived from the SPS referred to by the preceding picture, NoOutputOfPriorPicsFlag may be set to one by the decoder under test, regardless of the value of no_output_of_prior_pics_flag. It should be noted that, although setting NoOutputOfPriorPicsFlag equal to no_output_of_prior_pics_flag may be preferred under these conditions, the decoder under test is allowed to set NoOutputOfPriorPicsFlag to one in this case. Otherwise, NoOutputOfPriorPicsFlag may be set equal to no_output_of_prior_pics_flag.

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

In an example, output and removal of pictures from the DPB is discussed as follows. The output and removal of pictures from the DPB before the decoding of the current picture (but after parsing the slice header of the first slice of the current picture) may occur when the first decoding unit of the access unit containing the current picture is removed from the CPB and proceeds as follows. The decoding process for reference picture list construction and decoding process for reference picture marking are invoked.

If the current picture is a CLVSS picture that is not picture zero, the following ordered steps are applied. The variable NoOutputOfPriorPicsFlag can be derived for the decoder under test as follows. If the value of pic_width_max_in_luma_samples, pic_height_max_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1[Htid] derived from the SPS is different from the value of pic_width_in_luma_samples, pic_height_in_luma_samples, chroma_format_idc, separate_colour_plane_flag, bit_depth_luma_minus8, bit_depth_chroma_minus8 or sps_max_dec_pic_buffering_minus1 [Htid], respectively, derived from the SPS referred to by the preceding picture, NoOutputOfPriorPicsFlag may be set to one by the decoder under test, regardless of the value of no_output_of_prior_pics_flag. It should be noted that although setting NoOutputOfPriorPicsFlag equal to no_output_of_prior_pics_flag is preferred under these conditions, the decoder under test can set NoOutputOfPriorPicsFlag to one in this case. Otherwise, NoOutputOfPriorPicsFlag can be set equal to no_output_of_prior_pics_flag.

The value of NoOutputOfPriorPicsFlag derived for the decoder under test can be applied for the HRD as follows. If NoOutputOfPriorPicsFlag is equal to one, all picture storage buffers in the DPB are emptied without output of the pictures they contain and the DPB fullness is set equal to zero. Otherwise (NoOutputOfPriorPicsFlag is equal to zero), all picture storage buffers containing a picture that is marked as not needed for output and unused for reference are emptied (without output) and all non-empty picture storage buffers in the DPB are emptied by repeatedly invoking a bumping process and the DPB fullness is set equal to zero.

Otherwise (the current picture is not a CLVSS picture), all picture storage buffers containing a picture which are marked as not needed for output and unused for reference are emptied (without output). For each picture storage buffer that is emptied, the DPB fullness is decremented by one. When one or more of the following conditions are true, the bumping process is invoked repeatedly while further decrementing the DPB fullness by one for each additional picture storage buffer that is emptied until none of the following conditions are true. A condition is that the number of pictures in the DPB that are marked as needed for output is greater than sps_max_num_reorder_pics[Htid]. Another condition is that a sps_max_latency_increase_plus1 [Htid] is not equal to zero and there is at least one picture in the DPB that is marked as needed for output for which the associated variable PicLatencyCount is greater than or equal to SpsMaxLatencyPictures[Htid]. Another condition is that the number of pictures in the DPB is greater than or equal to SubDpbSize[Htid].

An example general SEI message syntax is as follows.

Descriptorsei_payload( payloadType, payloadSize ) {if( nal_unit_type = = PREFIX_SEI_NUT )if( payloadType = = 0 )buffering_period( payloadSize )else if( payloadType = = 1 )pic_timing( payloadSize )else if( payloadType = = 3 )filler_payload( payloadSize )else if( payloadType = = 130 )decoding_unit_info( payloadSize )else if( payloadType = = 133 )scalable_nesting( payloadSize )else if( payloadType = = 145 )dependent_rap_indication( payloadSize )// Specified in ITU-T H.SEI | ISO/IEC 23002-7.else if( payloadType = = 168 )frame_field_info( payloadSize )elsereserved_sei_message( payloadSize )else /* nal_unit_type = = SUFFIX_SEI_NUT */if( payloadType = = 3 )filler_payload( payloadSize )if( payloadType = = 132 )decoded_picture_hash( payloadSize )// Specified in ITU-T H.SEI | ISO/IEC 23002-7.else if( payloadType = = 133 )scalable_nesting( payloadSize )elsereserved_sei_message( payloadSize )if( more_data_in_payload( ) ) {if( payload_extension_present( ) )reserved_payload_extension_datau(v)payload_bit_equal_to_one /* equal to 1 */f(1)while( !byte_aligned( ) )payload_bit_equal_to_zero /* equal to 0 */f(1)}}

An example scalable nesting SEI message syntax is as follows.

Descriptorscalable_nesting( payloadSize ) {nesting_ols_flagu(1)if( nesting_ols_flag ) {nesting_num_olss_minus1ue(v)for( i = 0; i <= nesting_num_olss_minus1; i++ ) {nesting_ols_idx_delta_minus1[ i ]ue(v)if( NumLayersInOls[ NestingOlsIdx[ i ] ] > 1 ) {nesting_num_ols_layers_minus1[ i ]ue(v)for( j = 0; j <= nesting_num_ols_layers_minus1[ i ]; j++ )nesting_ols_layer_idx_delta_minus1[ i ][ j ]ue(v)}}} else {nesting_all_layers_flagu(1)if( !nesting_all_layers_flag ) {nesting_num_layers_minus1ue(v)for( i = 1; i <= nesting_num_layers_minus1; i++ )nesting_layer_id[ i ]u(6)}}nesting_num_seis_minus1ue(v)while( !byte_aligned( ) )nesting_zero_bit /* equal to 0 */u(1)for(i = 0; i <= nesting_num_seis_minus1; i++ )sei_message( )}

An example scalable nesting SEI message semantics is as follows. A scalable nesting SEI message provides a mechanism to associate SEI messages with specific layers in the context of specific OLSs or with specific layers not in the context of an OLS. A scalable nesting SEI message contains one or more SEI messages. The SEI messages contained in the scalable nesting SEI message are also referred to as the scalable-nested SEI messages. Bitstream conformance may require that the following restrictions apply when SEI messages are contained in a scalable nesting SEI message.

An SEI message that has payloadType equal to one hundred thirty two (decoded picture hash) or one hundred thirty three (scalable nesting) should not be contained in a scalable nesting SEI message. When a scalable nesting SEI message contains a buffering period, picture timing, or decoding unit information SEI message, the scalable nesting SEI message should not contain any other SEI message with payloadType not equal to zero (buffering period), one (picture timing), or one hundred thirty (decoding unit information).

Bitstream conformance may also require that the following restrictions apply on the value of the nal_unit_type of the SEI NAL unit containing a scalable nesting SEI message. When a scalable nesting SEI message contains an SEI message that has payloadType equal to zero (buffering period), one (picture timing), one hundred thirty (decoding unit information), one hundred forty five (dependent RAP indication), or one hundred sixty eight (frame-field information), the SEI NAL unit containing the scalable nesting SEI message should have a nal_unit_type set equal to PREFIX_SEI_NUT. When a scalable nesting SEI message contains an SEI message that has payloadType equal to one hundred thirty two (decoded picture hash), the SEI NAL unit containing the scalable nesting SEI message should have a nal_unit_type set equal to SUFFIX_SEI_NUT.

A nesting_ols_flag may be set equal to one to specify that the scalable-nested SEI messages apply to specific layers in the context of specific OLSs. The nesting_ols_flag may be set equal to zero to specify that that the scalable-nested SEI messages generally apply (e.g., not in the context of an OLS) to specific layers.

Bitstream conformance may require that the following restrictions are applied to the value of nesting_ols_flag. When the scalable nesting SEI message contains an SEI message that has payloadType equal to zero (buffering period), one (picture timing), or one hundred thirty (decoding unit information), the value of nesting_ols_flag should be equal to one. When the scalable nesting SEI message contains an SEI message that has payloadType equal to a value in VclAssociatedSeiList, the value of nesting_ols_flag should be equal to zero.

A nesting_num_olss_minus1 plus one specifies the number of OLSs to which the scalable-nested SEI messages apply. The value of nesting_num_olss_minus1 should be in the range of zero to TotalNumOlss−1, inclusive. The nesting_ols_idx_delta_minus1[i] is used to derive the variable NestingOlsIdx[i] that specifies the OLS index of the i-th OLS to which the scalable-nested SEI messages apply when nesting_ols_flag is equal to one. The value of nesting_ols_idx_delta_minus1[i] should be in the range of zero to TotalNumOlss−2, inclusive. The variable NestingOlsIdx[i] may be derived as follows:

if( i = = 0 )NestingOlsIdx[ i ] = nesting_ols_idx_delta_minus1[ i ]elseNestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] +nesting_ols_idx_delta_minus1[ i ] + 1

The nesting_num_ols_layers_minus1[i] plus one specifies the number of layers to which the scalable-nested SEI messages apply in the context of the NestingOlsIdx[i]-th OLS. The value of nesting_num_ols_layers_minus1 [i] should be in the range of zero to NumLayersInOls[NestingOlsIdx[i]]−1, inclusive.

The nesting_ols_layer_idx_delta_minus1[i][j] is used to derive the variable NestingOlsLayerIdx[i][j] that specifies the OLS layer index of the j-th layer to which the scalable-nested SEI messages apply in the context of the NestingOlsIdx[i]-th OLS when nesting_ols_flag is equal to one. The value of nesting_ols_layer_idx_delta_minus1 [i] should be in the range of zero to NumLayersInOls[nestingOlsIdx[i]]−two, inclusive.

The variable NestingOlsLayerIdx[i][j] may be derived as follows:

if( j = = 0 )NestingOlsLayerIdx[ i ][ j ] =nesting_ols_layer_idx_delta_minus1[ i ][ j ]elseNestingOlsLayerIdx[ i ][ j ] =NestingOlsLayerIdx[ i ][ j − 1 ] +nesting_ols_layer_idx_delta_minus1[ i ][ j ] + 1

The lowest value among all values of LayerIdInOls[NestingOlsIdx[i]][NestingOlsLayerIdx[i][0]] for i in the range of zero to nesting_num_olss_minus1, inclusive, should be equal to nuh_layer_id of the current SEI NAL unit (e.g., the SEI NAL unit containing the scalable nesting SEI message). The nesting_all_layers_flag may be set equal to one to specify that the scalable-nested SEI messages generally apply to all layers that have nuh_layer_id greater than or equal to the nuh_layer_id of the current SEI NAL unit. The nesting_all_layers_flag may be set equal to zero to specify that the scalable-nested SEI messages may or may not generally apply to all layers that have nuh_layer_id greater than or equal to the nuh_layer_id of the current SEI NAL unit.

The nesting_num_layers_minus1 plus one specifies the number of layers to which the scalable-nested SEI messages generally apply. The value of nesting_num_layers_minus1 should be in the range of zero to vps_max_layers_minus1−GeneralLayerIdx[nuh_layer_id], inclusive, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit. The nesting_layer_id[i] specifies the nuh_layer_id value of the i-th layer to which the scalable-nested SEI messages generally apply when nesting_all_layers_flag is equal to zero. The value of nesting_layer_id[i] should be greater than nuh_layer_id, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit.

When the nesting_ols_flag is equal to one, the variable NestingNumLayers, specifying the number of layer to which the scalable-nested SEI messages generally apply, and the list NestingLayerId[i] for i in the range of zero to NestingNumLayers−1, inclusive, specifying the list of nuh_layer_id value of the layers to which the scalable-nested SEI messages generally apply, are derived as follows, where nuh_layer_id is the nuh_layer_id of the current SEI NAL unit:

if( nesting_all_layers_flag ) {NestingNumLayers =vps_max_layers_minus1 + 1 − GeneralLayerIdx[ nuh_layer_id ]for( i = 0; i < NestingNumLayers; i ++)NestingLayerId[ i ] =vps_layer_id[ GeneralLayerIdx[ nuh_layer_id ] + i ] (D-2)} else {NestingNumLayers = nesting_num_layers_minus1 + 1for( i = 0; i < NestingNumLayers; i ++)NestingLayerId[ i ] = ( i = = 0 ) ?nuh_layer_id : nesting_layer_id[ i ]}

The nesting_num_seis_minus1 plus one specifies the number of scalable-nested SEI messages. The value of nesting_num_seis_minus1 should be in the range of zero to sixty three, inclusive. The nesting_zero_bit should be set equal to zero.

FIG.8is a schematic diagram of an example video coding device800. The video coding device800is suitable for implementing the disclosed examples/embodiments as described herein. The video coding device800comprises downstream ports820, upstream ports850, and/or transceiver units (Tx/Rx)810, including transmitters and/or receivers for communicating data upstream and/or downstream over a network. The video coding device800also includes a processor830including a logic unit and/or central processing unit (CPU) to process the data and a memory832for storing the data. The video coding device800may also comprise electrical, optical-to-electrical (OE) components, electrical-to-optical (EO) components, and/or wireless communication components coupled to the upstream ports850and/or downstream ports820for communication of data via electrical, optical, or wireless communication networks. The video coding device800may also include input and/or output (I/O) devices860for communicating data to and from a user. The I/O devices860may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I/O devices860may also include input devices, such as a keyboard, mouse, trackball, etc., and/or corresponding interfaces for interacting with such output devices.

The processor830is implemented by hardware and software. The processor830may 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 processor830is in communication with the downstream ports820, Tx/Rx810, upstream ports850, and memory832. The processor830comprises a coding module814. The coding module814implements the disclosed embodiments described herein, such as methods100,900, and1000, which may employ a multi-layer video sequence600and/or a bitstream700. The coding module814may also implement any other method/mechanism described herein. Further, the coding module814may implement a codec system200, an encoder300, a decoder400, and/or a HRD500. For example, the coding module814may be employed signal and/or read various parameters as described herein. Further, the coding module may be employed to encode and/or decode a video sequence based on such parameters. As such, the signaling changes described herein may increase the efficiency and/or avoid errors in the coding module814. Accordingly, the coding module814may be configured to perform mechanisms to address one or more of the problems discussed above. Hence, coding module814causes the video coding device800to provide additional functionality and/or coding efficiency when coding video data. As such, the coding module814improves the functionality of the video coding device800as well as addresses problems that are specific to the video coding arts. Further, the coding module814effects a transformation of the video coding device800to a different state. Alternatively, the coding module814can be implemented as instructions stored in the memory832and executed by the processor830(e.g., as a computer program product stored on a non-transitory medium).

The memory832comprises one or more memory types such as disks, tape drives, solid-state drives, read only memory (ROM), random access memory (RAM), flash memory, ternary content-addressable memory (TCAM), static random-access memory (SRAM), etc. The memory832may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution.

FIG.9is a flowchart of an example method900of encoding a video sequence into a bitstream, such as bitstream700, by constraining TemporalIds for SEI messages in the bitstream. Method900may be employed by an encoder, such as a codec system200, an encoder300, and/or a video coding device800when performing method100. Further, the method900may operate on a HRD500and hence may perform conformance tests on a multi-layer video sequence600.

Method900may begin when an encoder receives a video sequence and determines to encode that video sequence into a multi-layer bitstream, for example based on user input. At step901, the encoder encodes a coded picture in one or more VCL NAL units in a bitstream. For example, the coded picture may be included in an AU in a layer. Further, the encoder can encode one or more layers including the coded picture into a multi-layer bitstream. A layer may include a set of VCL NAL units with the same layer ID and associated non-VCL NAL units. For example, the set of VCL NAL units are part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id. A layer may include a set of VCL NAL units that contain video data of encoded pictures as well as any parameter sets used to code such pictures. One or more of the layers may be output layers. Layers that are not an output layer are encoded to support reconstructing the output layer(s), but such supporting layers are not intended for output at a decoder. In this way, the encoder can encode various combinations of layers for transmission to a decoder upon request. The layer can be transmitted as desired to allow the decoder to obtain different representations of the video sequence depending on network conditions, hardware capabilities, and/or user settings.

At step903, the encoder can encode one or more a non-VCL NAL units into the bitstream. For example, the layer and/or set of layers also include various non-VCL NAL units. The non-VCL NAL units are associated with the set of VCL NAL units that all have a particular value of nuh_layer_id. Specifically, a non-VCL NAL unit is encoded such that a TemporalId for the non-VCL NAL unit is constrained to be equal to a TemporalId of an AU containing the non-VCL NAL unit when a nal_unit_type of the non-VCL NAL indicates a SEI message is included in the non-VCL NAL. Stated differently, a SEI message may be included in the same AU as the picture to which the SEI applies. Accordingly, the TemporalId of the SEI message contained in a non-VCL NAL unit is constrained to be equal to the TemporalId of the AU that contains the SEI message/non-VCL NAL unit. In some examples, the SEI message is a prefix SEI message, and hence the nal_unit_type of the non-VCL NAL is equal to a PREFIX_SEI_NUT. In some examples, the SEI message is a suffix SEI message, and hence the nal_unit_type of the non-VCL NAL is equal to a SUFFIX_SEI_NUT. The

The TemporalId for the non-VCL NAL unit may be specified by a nuh_temporal_id_plus1 syntax element in the non-VCL NAL unit. Likewise, the TemporalId for the AU may be specified by a nuh_temporal_id_plus1 syntax element in a VCL NAL unit containing a slice of the coded picture in the AU. A TemporalId of the VCL NAL units is constrained to be the same for all VCL NAL units in a same AU. Accordingly, a nuh_temporal_id_plus1 syntax element of the VCL NAL units is constrained to be the same for all VCL NAL units in a same AU. Hence, the value of the nuh_temporal_id_plus1 syntax element in the non-VCL NAL unit containing the SEI message is the same as the value of the nuh_temporal_id_plus1 syntax element in any VCL NAL unit in the same AU as the SEI message. The TemporalId for the non-VCL NAL unit is derived as follows:

TemporalId=nuh_temporal⁢_id⁢_plus1-1.
In addition, the value of the nuh_temporal_id_plus1 for the non-VCL NAL unit and the VCL NAL unit in the AU may not be set to zero as this would result in a negative value of TemporalId. The preceding constraints and/or requirements ensure that the bitstream conforms with, for example, VVC or some other standard, modified as indicated herein. However, the encoder may also be capable of operating in other modes where it is not so constrained, such as when operating under a different standard or a different version of the same standard.

At step905, the encoder employs a HRD to perform a set of bitstream conformance tests on the bitstream based on the SEI message. The set may include one or more conformance tests. For example, the HRD can employ the TemporalIds and/or nuh_temporal_id_plus1 values to correlate SEI messages to the pictures. Hence, the HRD can employ the parameters from the SEI message to perform one or more conformance tests on the coded picture in the same AU as the SEI message. The encoder can then store the bitstream for communication toward a decoder at step907. The encoder can also transmit the bitstream toward the decoder as desired.

FIG.10is a flowchart of an example method1000of decoding a video sequence from a bitstream, such as bitstream700, where TemporalIds for the SEI messages in the bitstream are constrained. Method1000may be employed by a decoder, such as a codec system200, a decoder400, and/or a video coding device800when performing method100. Further, method1000may be employed on a multi-layer video sequence600that has been checked for conformance by a HRD, such as HRD500.

Method1000may begin when a decoder begins receiving a bitstream of coded data representing a multi-layer video sequence, for example as a result of method900and/or in response to a request by the decoder. At step1001, the decoder receives a bitstream a bitstream comprising a coded picture in one or more VCL NAL units and a non-VCL NAL unit. For example, the coded picture may be included in an AU. Further, the bitstream may include one or more layers including the coded picture. A layer may include a set of VCL NAL units with the same layer ID and associated non-VCL NAL units. For example, the set of VCL NAL units are part of a layer when the set of VCL NAL units all have a particular value of nuh_layer_id. A layer may include a set of VCL NAL units that contain video data of coded pictures as well as any parameter sets used to code such pictures. One or more of the layers may be output layers. Layers that are not an output layer are encoded to support reconstructing the output layer(s), but such supporting layers are not intended for output. In this way, the decoder can obtain different representations of the video sequence depending on network conditions, hardware capabilities, and/or user settings. The layer also includes various non-VCL NAL units. The non-VCL NAL units are associated with the set of VCL NAL units that all have a particular value of nuh_layer_id.

Specifically, a non-VCL NAL unit is coded in the bitstream such that a TemporalId for the non-VCL NAL unit is constrained to be equal to a TemporalId of an AU containing the non-VCL NAL unit when a nal_unit_type of the non-VCL NAL indicates a SEI message is included in the non-VCL NAL. Stated differently, a SEI message may be included in the same AU as the picture to which the SEI applies. Accordingly, the TemporalId of the SEI message contained in a non-VCL NAL unit is constrained to be equal to the TemporalId of the AU that contains the SEI message/non-VCL NAL unit. In some examples, the SEI message is a prefix SEI message, and hence the nal_unit_type of the non-VCL NAL is equal to a PREFIX_SEI_NUT. In some examples, the SEI message is a suffix SEI message, and hence the nal_unit_type of the non-VCL NAL is equal to a SUFFIX_SEI_NUT.

The TemporalId for the non-VCL NAL unit may be specified by a nuh_temporal_id_plus1 syntax element in the non-VCL NAL unit. Accordingly, the decoder can derive the TemporalId for the non-VCL NAL unit based on the nuh_temporal_id_plus1 syntax element in the non-VCL NAL unit at step1002. Likewise, the TemporalId for the AU may be specified by a nuh_temporal_id_plus1 syntax element in a VCL NAL unit containing a slice of the coded picture in the AU. A TemporalId of the VCL NAL units is constrained to be the same for all VCL NAL units in a same AU. Accordingly, a nuh_temporal_id_plus1 syntax element of the VCL NAL units is constrained to be the same for all VCL NAL units in a same AU. Hence, the value of the nuh_temporal_id_plus1 syntax element in the non-VCL NAL unit containing the SEI message is the same as the value of the nuh_temporal_id_plus1 syntax element in any VCL NAL unit in the same AU as the SEI message. The TemporalId for the non-VCL NAL unit is derived as follows:

TemporalId=nuh_temporal⁢_id⁢_plus1-1.
In addition, the value of the nuh_temporal_id_plus1 for the non-VCL NAL unit and the VCL NAL unit in the AU may not be set to zero as this would result in a negative value of TemporalId.

In an embodiment, the video decoder expects a TemporalId for the non-VCL NAL unit to be equal to a TemporalId of an AU containing the non-VCL NAL unit when a nal_unit_type of the non-VCL NAL is a SEI message as described above based on VVC or some other standard. If, however, the decoder determines that this condition is not true, the decoder may detect an error, signal an error, request that a revised bitstream (or a portion thereof) be resent, or take some other corrective measures to ensure that a conforming bitstream is received.

At step1003, the decoder can decode the coded picture from the VCL NAL units to produce a decoded picture. For example, the decoder can employ the TemporalIds and/or nuh_temporal_id_plus1 values to correlate SEI messages to the pictures. The decoder can then employ the SEI messages as desired when decoding the coded picture. At step1005, the decoder can forward the decoded picture for display as part of a decoded video sequence.

FIG.11is a schematic diagram of an example system1100for coding a video sequence using a bitstream where TemporalIds for the SEI messages in the bitstream are constrained. System1100may be implemented by an encoder and a decoder such as a codec system200, an encoder300, a decoder400, and/or a video coding device800. Further, the system1100may employ a HRD500to perform conformance tests on a multi-layer video sequence600and/or a bitstream700. In addition, system1100may be employed when implementing method100,900, and/or1000.

The system1100includes a video encoder1102. The video encoder1102comprises an encoding module1103for encoding a coded picture in one or more VCL NAL units in a bitstream. The encoding module1103is further for encoding into the bitstream a non-VCL NAL unit such that a TemporalId for the non-VCL NAL unit is constrained to be equal to a TemporalId of an AU containing the non-VCL NAL unit when a nal_unit_type of the non-VCL NAL is a SEI message. The video encoder1102further comprises a HRD module1105for performing a set of bitstream conformance tests on the bitstream based on the SEI message. The video encoder1102further comprises a storing module1106for storing the bitstream for communication toward a decoder. The video encoder1102further comprises a transmitting module1107for transmitting the bitstream toward a video decoder1110. The video encoder1102may be further configured to perform any of the steps of method900.

The system1100also includes a video decoder1110. The video decoder1110comprises a receiving module1111for receiving a bitstream comprising a coded picture in one or more VCL NAL units and a non-VCL NAL unit, wherein a TemporalId for the non-VCL NAL unit is constrained to be equal to a TemporalId of an AU containing the non-VCL NAL unit when a nal_unit_type of the non-VCL NAL is a SEI message. The video decoder1110further comprises a decoding module1113for decoding the coded picture from the VCL NAL units to produce a decoded picture. The video decoder1110further comprises a forwarding module1115for forwarding the decoded picture for display as part of a decoded video sequence. The video decoder1110may be further configured to perform any of the steps of method1000.

A first component is directly coupled to a second component when there are no intervening components, except for a line, a trace, or another medium between the first component and the second component. The first component is indirectly coupled to the second component when there are intervening components other than a line, a trace, or another medium between the first component and the second component. The term “coupled” and its variants include both directly coupled and indirectly coupled. The use of the term “about” means a range including ±10% of the subsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, 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.

While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

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