Patent ID: 12231661

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 picture that is being encoded or decoded can be referred to as a current picture for clarity of discussion. A network abstraction layer (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 emulation prevention bytes, which are interspersed as desired. A video coding layer (VCL) NAL unit is a NAL unit coded to contain video data, such as a coded slice of a picture. A non-VCL NAL unit is a NAL unit that contains non-video data such as syntax and/or parameters that support decoding the video data, performance of conformance checking, or other operations. An access unit (AU) is a set of NAL units that are associated with each other according to a specified classification rule and pertain to one particular output time. A decoding unit (DU) is an AU or a sub-set of an AU and associated non-VCL NAL units. A layer is a set of VCL NAL units that share a specified characteristic (e.g., a common resolution, frame rate, image size, etc.) and associated non-VCL NAL units. A decoding order is an order in which syntax elements are processed by a decoding process. A video parameter set (VPS) is a data unit that contains parameters related to an entire video.

A temporal scalable bitstream is a bitstream coded in multiple layers providing varying temporal resolution/frame rate (e.g., each layer is coded to support a different frame rate). A sublayer is a temporal scalable layer of a temporal scalable bitstream including VCL NAL units with a particular temporal identifier value and associated non-VCL NAL units. For example, a temporal sublayer is a layer that contains video data associated with a specified frame rate. A sublayer representation is a subset of the bitstream containing NAL units of a particular sublayer and the lower sublayers. Hence, one or more temporal sublayers may be combined to achieve a sublayer representation that can be decoded to result in a video sequence with a specified frame rate. An output layer set (OLS) is a set of layers for which one or more layers are specified as output layer(s). An output layer is a layer that is designated for output (e.g., to a display). An OLS index is an index that uniquely identifies a corresponding OLS. A zeroth (0-th) OLS is an OLS that contains only a lowest layer (layer with a lowest layer identifier) and hence contains only an output layer. A temporal identifier (ID) is a data element that indicates data corresponds to temporal location in a video sequence. A sub-bitstream extraction process is a process that removes NAL units from a bitstream that do not belong to a target set as determined by a target OLS index and a target highest temporal ID. The sub-bitstream extraction process results in an output sub-bitstream containing NAL units from the bitstream that are part of the target set.

An HRD is a decoder model operating on an encoder. The HRD 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. Sequence-level HRD parameters are HRD parameters that apply to an entire coded video sequence, while picture-level HRD parameters are HRD parameters that apply to pictures in a coded video sequence. A maximum HRD temporal ID (Htid) specifies the Temporal ID of the highest sublayer representation for which the HRD parameters are contained in an i-th set of OLS HRD parameters. An operation point (OP) is a temporal subset of an OLS that is identified by an OLS index and a highest temporal ID. A coded picture buffer (CPB) is a first-in first-out buffer in a HRD that contains coded pictures in decoding order for use during bitstream conformance verification. A decoded picture buffer (DPB) is a buffer for holding decoded pictures for reference, output reordering, and/or output delay.

A supplemental enhancement information (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 buffering period (BP) SEI message is a SEI message that contains HRD parameters for initializing an HRD to manage a 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 the 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 CPB removal delay is a period of time that a corresponding current AU can remain in the CPB prior to removal and output to a DPB. An initial CPB removal delay is a default CPB removal delay for each picture, AU, and/or DU in a bitstream, OLS, and/or layer. A CPB removal offset is a location in the CPB used to determine boundaries of a corresponding AU in the CPB. An initial CPB removal offset is a default CPB removal offset associated with each picture, AU, and/or DU in a bitstream, OLS, and/or layer. A decoded picture buffer (DPB) output delay information is a period of time that a corresponding AU can remain in the DPB prior to output. A CPB removal delay information is information related to removal of a corresponding DU from the CPB. 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.

A maximum number of temporal sublayers is a maximum number of sublayers for which the initial CPB removal delay and the initial CPB removal offset are indicated in the BP SEI message. A common CPB removal delay increment specifies the duration, in units of clock sub-ticks, between the nominal CPB removal times of any two consecutive DUs in decoding order in the AU associated with the picture timing SEI message. The common CPB removal delay increment is also used to calculate an earliest possible time of arrival of decoding unit data into the CPB for a hypothetical stream scheduler (HSS).

A number of decoding units specifies the number of DUs in the AU the picture timing SEI message is associated with. A number of NAL units specifies the number of NAL units in the i-th DU of the AU the PT SEI message is associated with. A common CPB removal delay flag specifies whether the syntax elements common CPB removal delay increment are present in the PT SEI message.

A CPB removal delay increment specifies the duration, in units of clock sub-ticks, between the nominal CPB removal times of the (i+1)-th DU and the i-th DU, in decoding order, in the AU associated with the PT SEI message.

A VPS maximum sublayers minus one (vps_max_sublayers_minus1) syntax element is a syntax element that specifies the maximum number of temporal sublayers that may be present in a layer specified by the VPS.

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-02001-v14.

The latest VVC draft provides specifics for picture timing (PT) SEI messages, decoding unit information (DUI) SEI messages, an AU-based HRD operation (e.g., an HRD operation that applies to the entire AU), and a decoding unit (DU)-based HRD operation (e.g., an HRD operation that applies to one decoding unit, or picture, in the AU).

Picture-level coded picture buffer (CPB) parameters needed for the AU-based HRD operations for both layers and sublayers are signaled in the PT SEI messages. Picture-level CPB parameters needed for DU-based HRD operations for layers are signaled in either the PT SEI message or the DUI SEI message. However, picture-level CPB parameters needed for the DU-based HRD operations for sublayers are missing from the PT SEI message and the DUI SEI message.

Disclosed herein are techniques that ensure picture-level CPB parameters corresponding to DU-based HRD operations on sublayers are included in an SEI message. Because the picture-level CPB parameters are included in the SEI message, the HRD can use the DU-based HRD operations to test the sublayers in the bitstream for bitstream conformance, which ensures that the sublayers are properly coded and/or can be properly decoded. Thus, the coder/decoder (a.k.a., “codec”) in video coding is improved relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

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 (PU) containing prediction data and/or a transform unit (TU) containing transformed residual data for the CU. The motion estimation component221generates motion vectors, PUs, 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 PU of a video block in an inter-coded slice by comparing the position of the PU 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 PU 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 an 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 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 schedules561from 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 schedule561specifies 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 schedules561.

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 schedules561are 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 schedules561that 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 schedules561that 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 schedule561to ensure that the resulting sub-bitstream can be correctly decoded under the conditions that are expected for the sub-bitstream. The CPB delivery schedules561are each associated with a schedule index (ScIdx)563. A ScIdx563is an index that identifies a delivery schedule. Accordingly, the HRD parameters in the bitstream551can indicate the CPB delivery schedules561by ScIdx563as well as include sufficient data to allow the HRD500to determine the CPB delivery schedules561and correlate the CPB delivery schedules561to the corresponding OLSs, layers, and/or sublayers.

FIG.6is a schematic diagram illustrating an example multi-layer video sequence600configured for inter-layer prediction621. 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 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/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/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 such, pictures in different layers631-632can share a temporal ID622as long as the pictures are included in the same AU. A temporal ID622is a data element that indicates data corresponds to temporal location in a video sequence. An AU is a set of NAL units that are associated with each other according to a specified classification rule and pertain to one particular output time. For example, an AU may include one or more pictures in different layers, such as picture611and picture615when such pictures are associated with the same temporal ID622. 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 AU and 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.

In order to perform such operations, layers such as layer N631and layer N+1632may be included in an OLS625. An OLS625is a set of layers for which one or more layers are specified as an output layer. An output layer is a layer that is designated for output (e.g., to a display). For example, layer N631may be included solely to support inter-layer prediction621and may never be output. In such a case, layer N+1632is decoded based on layer N631and is output. In such a case, the OLS625includes layer N+1632as the output layer. When an OLS625contains only an output layer, the OLS625is referred to as a 0-th OLS. A 0-th OLS is an OLS that contains only a lowest layer (layer with a lowest layer identifier) and hence contains only an output layer. In other cases, an OLS625may contain many layers in different combinations. For example, an output layer in an OLS625can be coded according to inter-layer prediction621based on a one, two, or many lower layers. Further, an OLS625may contain more than one output layer. Hence, an OLS625may contain one or more output layers and any supporting layers needed to reconstruct the output layers. A multi-layer video sequence600can be coded by employing many different OLSs625that each employ different combinations of the layers. The OLSs625are each associated with an OLS index629, which is an index that uniquely identifies a corresponding OLS625.

Checking a multi-layer video sequence600for standards conformance at a HRD500can become complicated depending on the number of layers631-632and OLSs625. A HRD500may segregate the multi-layer video sequence600into a sequence of operation points627for testing. An operation point627is a temporal subset of an OLS625that is identified by an OLS index629and a highest temporal ID622. As a specific example, a first operation point627could include all pictures in a first OLS625from temporal ID zero to temporal ID two hundred, a second operation point627could include all pictures in the first OLS625from temporal ID two hundred and one to temporal ID four hundred, etc. The operation point627selected for testing at a specified instant is referred to as an OP under test (targetOp). Hence, a targetOp is an operation point627that is selected for conformance testing at a HRD500.

FIG.7is a schematic diagram illustrating an example multi-layer video sequence700configured for temporal scalability. The multi-layer video sequence700may 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 sequence700can be checked for standard conformance by a HRD, such as HRD500. The multi-layer video sequence700is included to depict another example application for layers in a coded video sequence. For example, the multi-layer video sequence700may be employed as a separate embodiment or may be combined with the techniques described with respect to the multi-layer video sequence600.

The multi-layer video sequence700includes sublayers710,720, and730. A sublayer is a temporal scalable layer of a temporal scalable bitstream that includes VCL NAL units (e.g., pictures) with a particular temporal identifier value as well as associated non-VCL NAL units (e.g., supporting parameters). The sublayer710may be referred to as a base layer and sublayers720and730may be referred to as enhancement layers. As shown, the sublayer710includes pictures711at a first frame rate, such as thirty frames per second. The sublayer710is a base layer because the sublayer710includes the base/lowest frame rate. The sublayer720contains pictures721that are temporally offset from the pictures711of sublayer710. The result is that sublayer710and sublayer720can be combined, which results in a frame rate that is collectively higher than the frame rate of the sublayer710alone. For example, sublayer710and720may have a combined frame rate of sixty frames per second. Accordingly, the sublayer720enhances the frame rate of the sublayer710. Further, sublayer730contains pictures731that are also temporally offset from the pictures721and711of sublayers720and710. As such, the sublayer730can be combined with sublayers720and710to further enhance the sublayer710. For example, the sublayers710,720, and730may have a combined frame rate of ninety frames per second.

A sublayer representation740can be dynamically created by combining sublayers710,720, and/or730. A sublayer representation740is a subset of a bitstream containing NAL units of a particular sublayer and the lower sublayers. In the example shown, the sublayer representation740contains pictures741, which are the combined pictures711,721, and731of sublayers710,720, and730. Accordingly, the multi-layer video sequence700can be temporally scaled to a desired frame rate by selecting a sublayer representation740that includes a desired set of sublayers710,720, and/or730. A sublayer representation740may be created by employing an OLS that includes sublayer710,720, and/or730as layers. In such a case, the sublayer representation740is selected as an output layer. As such, temporal scalability is one of several mechanisms that can be accomplished using multi-layer mechanisms.

FIG.8is a schematic diagram illustrating an example bitstream800. For example, the bitstream800can be generated by a codec system200and/or an encoder300for decoding by a codec system200and/or a decoder400according to method100. Further, the bitstream800may include a multi-layer video sequence600and/or700. In addition, the bitstream800may include various parameters to control the operation of an HRD, such as HRD500. Based on such parameters, the HRD can check the bitstream800for conformance with standards prior to transmission toward a decoder for decoding.

The bitstream800includes a VPS811, one or more SPSs813, a plurality of picture parameter sets (PPSs)815, a plurality of slice headers817, image data820, a BP SEI message819, a PT SEI message818, and a DUI SEI message816. A VPS811contains data related to the entire bitstream800. For example, the VPS811may contain data related OLSs, layers, and/or sublayers used in the bitstream800. An SPS813contains sequence data common to all pictures in a coded video sequence contained in the bitstream800. For example, each layer may contain one or more coded video sequences, and each coded video sequence may reference a SPS813for corresponding parameters. The parameters in a SPS813can include picture sizing, bit depth, coding tool parameters, bit rate restrictions, etc. It should be noted that, while each sequence refers to a SPS813, a single SPS813can contain data for multiple sequences in some examples. The PPS815contains parameters that apply to an entire picture. Hence, each picture in the video sequence may refer to a PPS815. It should be noted that, while each picture refers to a PPS815, a single PPS815can 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 PPS815may contain data for such similar pictures. The PPS815can indicate coding tools available for slices in corresponding pictures, quantization parameters, offsets, etc.

The slice header817contains parameters that are specific to each slice in a picture. Hence, there may be one slice header817per slice in the video sequence. The slice header817may contain slice type information, POCs, reference picture lists, prediction weights, tile entry points, deblocking parameters, etc. It should be noted that in some examples, a bitstream800may also include a picture header, which is a syntax structure that contains parameters that apply to all slices in a single picture. For this reason, a picture header and a slice header817may be used interchangeably in some contexts. For example, certain parameters may be moved between the slice header817and a picture header depending on whether such parameters are common to all slices in a picture.

The image data820contains video data encoded according to inter-prediction and/or intra-prediction as well as corresponding transformed and quantized residual data. For example, the image data820may include AUs821, DUs822, and/or pictures823. An AU821is a set of NAL units that are associated with each other according to a specified classification rule and pertain to one particular output time. A DU822is an AU or a sub-set of an AU and associated non-VCL NAL units. A picture823is an array of luma samples and/or an array of chroma samples that create a frame or a field thereof. In plain language, an AU821contains various video data that may be displayed at a specified instant in a video sequence as well as supporting syntax data. Hence, an AU821may contain a single picture823in a single layer bitstream or multiple pictures from multiple layers that are all associated with the same instant in a multi-layer bitstream. Meanwhile, a picture823is a coded image that may be output for display or used to support coding of other picture(s)823for output. A DU822may contain one or more pictures823and any supporting syntax data needed for decoding. For example, a DU822and an AU821may be used interchangeably in simple bitstreams (e.g., when an AU contains a single picture). However, in more complex multi-layer bitstreams (e.g., the bitstream containing the multi-layer video sequence600), a DU822may only contain a portion of the video data from an AU821. For example, an AU821may contain pictures823at several layers (e.g., layers631,632) and/or sublayers (e.g., sublayers710,720,730) where some of the pictures823are associated with different OLSs. In such a case, a DU822may only contain picture(s)823from a specified OLS and/or a specified layer/sublayer.

A picture823contains one or more slices825. A slice825may 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 picture823that are exclusively contained in a single NAL unit829. The slices825are 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 bitstream800is a sequence of NAL units829. A NAL unit829is a container for video data and/or supporting syntax. A NAL unit829can be a VCL NAL unit or a non-VCL NAL unit. A VCL NAL unit is a NAL unit829coded to contain video data, such as a coded slice825and an associated slice header817. A non-VCL NAL unit is a NAL unit829that contains non-video data such as syntax and/or parameters that support decoding the video data, performance of conformance checking, or other operations. For example, a non-VCL NAL unit can contain a VPS811, a SPS813, a PPS815, a BP SEI message819, a PT SEI message818, a DUI SEI message816, or other supporting syntax.

The bitstream800can include one or more SEI messages that support conformance testing by an HRD, such as HRD500. An SEI message is a syntax structure with specified semantics that conveys information 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 data to support HRD processes or other supporting data that is not directly relevant to decoding the bitstream800at a decoder. For example, bitstream800may include a BP SEI message819, a PT SEI message818, and a DUI SEI message816.

A BP SEI message819is a SEI message that contains HRD parameters870for initializing a HRD to manage a CPB. For example, the BP SEI message819may contain data describing the CPB delivery schedules, such as CPB delivery schedule561, that may be employed when performing conformance tests on the bitstream800. A delivery schedule may be described by a pair of values describing the timing of the delivery schedule (e.g., how often to remove data) and describing the amount of data to be transferred (e.g., how much data to remove at each occurrence). The BP SEI message819indicates the AU or DU that should be the starting point of the conformance check (e.g., an AU821or a DU822) and a data pair indicating the default schedule to use for each data unit. In a specific example, the BP SEI message819may include an initial CPB removal delay837and an initial CPB removal offset839. An initial CPB removal delay837is a default CPB removal delay for each picture, AU, and/or DU in a bitstream, OLS, and/or layer. An initial CPB removal offset839is a default CPB removal offset associated with each picture, AU, and/or DU in a bitstream, OLS, and/or layer. By employing the initial CPB removal delay837and the initial CPB removal offset839pair, a HRD can determine a CPB delivery schedule to use when removing data units (AUs or DUs) from the CPB during conformance testing.

In an embodiment, the BP SEI message819includes a maximum number of temporal sublayers841for which the initial CPB removal delay837and the initial CPB removal offset839are indicated in the BP SEI message819. This maximum number of temporal sublayers841is designated bp_max_sublayers_minus1. The value of bp_max_sublayers_minus1 shall be in the range of 0 to a maximum number of sublayers843specified in the VPS811, which is designated vps_max_sublayers_minus1, inclusive. vps_max_sublayers_minus1 plus 1 specifies the maximum number of temporal sublayers that may be present in a layer specified by the VPS811. The value of vps_max_sublayers_minus1 shall be in the range of 0 to 6, inclusive.

A PT SEI message818is a SEI message that contains HRD parameters880(a.k.a., picture level CPB parameters) for managing delivery information for AUs at the CPB and/or the DPB. For example, a PT SEI message818may contain additional parameters for use in performing a HRD conformance test on a corresponding AU. In a specific example, the PT SEI message818may contain a CPB removal delay835and a DPB output delay833. A CPB removal delay835is period of time that a corresponding current AU can remain in the CPB prior to removal and output to a DPB. For example, the CPB removal delay835may be used to calculate the number of clock ticks between the removal of the current AU and a preceding AU in decoding order where the preceding AU is associated with a BP SEI message819. Accordingly, the CPB removal delay835indicates that a removal delay for a current AU is different than the default removal delay described by the initial CPB removal delay837in the BP SEI message819. Further, the CPB removal delay835contains a value of the difference of the removal delay for a current AU from the default value. A DPB output delay833is information describing a period of time that a corresponding AU can remain in the DPB prior to output. Specifically, the DPB output delay833may be employed to determine an output time of a picture from the DPB, and hence the amount of time the picture/AU can remain in the DPB after removal from the CPB. The output time at the HRD corresponds with an expected output of a picture for display at a decoder.

In an embodiment, the PT SEI message818includes a common CPB removal delay increment845, which is designated pt_du_common_cpb_removal_delay_increment_minus1. The common CPB removal delay increment845plus 1 specifies the duration, in units of clock sub-ticks, between the nominal CPB removal times of any two consecutive DUs (e.g., DUs822) in decoding order in the AU (e.g., AU821) associated with the picture timing SEI message818when Htid i is equal to i, where Htid identifies the highest temporal sublayer to be decoded. This value is also used to calculate an earliest possible time of arrival of decoding unit data into the CPB for a hypothetical stream scheduler (HSS). The length of this syntax element is du_cpb_removal_delay_increment_length_minus1+1 bits.

In an embodiment, the PT SEI message818includes a number of decoding units847, which is designated pt_num_decoding_units_minus1. The number of decoding units847plus 1 specifies the number of DUs (e.g., DUs822) in the AU (e.g., AU821) the picture timing SEI message818is associated with. The value of num_decoding_units_minus1 shall be in the range of 0 to PicSizeInCtbsY−1, inclusive. In an embodiment, the PicSizeInCtbsY syntax element represents a size of a picture measured in CTBs (e.g., a width of the picture measured in CTBs x a height of the picture measured in CTBs).

In an embodiment, the PT SEI message818includes a number of NAL units849in the i-th DU of the AU the PT SEI message818is associated with. The number of NAL units849is designated as pt_num_nalus_in_du_minus1[i]. The value of pt_num_nalus_in_du_minus1[i] shall be in the range of 0 to PicSizeInCtbsY−1, inclusive.

In an embodiment, the PT SEI message818includes a common CPB removal delay flag851, which is designated as pt_du_common_cpb_removal_delay_flag. The common CPB removal delay flag851equal to 1 specifies that the syntax elements common CPB removal delay increment845, which are designated as pt_du_common_cpb_removal_delay_increment_minus1[i]), are present in the PT SEI message818. The DU common CPB removal delay flag851equal to 0 specifies that the syntax elements common CPB removal delay increment845are not present. When not present in the PT SEI message818, the common CPB removal delay flag851is inferred to be equal to 0.

In an embodiment, the first DU of the AU is the first pt_num_nalus_in_du_minus1[0]+1 consecutive NAL units in decoding order in the AU. The i-th (with i greater than 0) DU of the AU is the pt_num_nalus_in_du_minus1[i]+1 consecutive NAL units immediately following the last NAL unit in the previous DU of the AU, in decoding order. In an embodiment, there is at least one VCL NAL unit in each DU, and all non-VCL NAL units associated with a VCL NAL unit are included in the same DU as the VCL NAL unit.

In an embodiment, the PT SEI message818includes a CPB removal delay increment853, which is designated pt_du_cpb_removal_delay_increment_minus1. The CPB removal delay increment853plus 1 specifies the duration, in units of clock sub-ticks, between the nominal CPB removal times of the (i+1)-th DU and the i-th DU, in decoding order, in the AU associated with the PT SEI message818when Htid is equal to j. This value is also used to calculate an earliest possible time of arrival of DU data into the CPB for the HSS. The length of this syntax element is bp_du_cpb_removal_delay_increment_length_minus1+1 bits.

In an embodiment, the PT SEI message818includes the maximum number of sublayers843instead of, or in addition to, the VPS811.

A DUI SEI message816is a SEI message that contains HRD parameters890(a.k.a., picture level CPB parameters) for managing delivery information for DUs at the CPB and/or the DPB. For example, the DUI SEI message816may contain additional parameters for use in performing a HRD conformance test on a corresponding DU. As noted above, an AU may contain one or more DUs. Hence, information for checking a DU may be different than information for checking an AU. As a specific example, the DUI SEI message816may contain CPB removal delay information831. A CPB removal delay information831is information related to removal of a corresponding DU from the CPB. For example, the CPB removal delay information831may be used to calculate the number of clock ticks between the removal of the current DU and a preceding DU in decoding order.

In an embodiment, the DUI SEI message816includes the maximum number of temporal sublayers841for which the initial CPB removal delay837and the initial CPB removal offset839are indicated in the BP SEI message819. This maximum number of temporal sublayers841is designated bp_max_sublayers_minus1. The value of bp_max_sublayers_minus1 shall be in the range of 0 to a maximum number of sublayers843specified in the VPS811, which is designated vps_max_sublayers_minus1, inclusive. vps_max_sublayers_minus1 plus 1 specifies the maximum number of temporal sublayers that may be present in a layer specified by the VPS811. The value of vps_max_sublayers_minus1 shall be in the range of 0 to 6, inclusive.

In an embodiment, the DUI SEI message816includes the maximum number of sublayers843instead of, or in addition to, the VPS811.

As can be appreciated by the preceding description, the BP SEI message819, the PT SEI message818, and the DUI SEI message816contain a significant amount of information. In an embodiment, the HRD parameters880and/or890(a.k.a., picture-level CPB parameters) in the PT SEI message818and/or the DUI SEI message816are used to perform DU-based HRD operations on sublayers to test for bitstream conformance.

By way of example, an HRD determines, for each layer, whether the duration, as specified in the PT SEI message818and/or the DUI SEI message816, between the nominal CPB removal times of any two consecutive decoding units in decoding order in the access unit associated with the picture timing SEI message is exceeded. When the duration is exceeded, the bitstream does not conform and a new bitstream with revised CPB parameters is generated and tested by the encoder. That process may repeat until the duration is not exceeded, which means that the bitstream conforms to the standard (e.g., the VVC standard).

The HRD may also determine, for each layer, whether the duration, as specified in the PT SEI message818and/or the DUI SEI message816, between the CPB removal times of the (i+1)-th decoding unit and the i-th decoding unit, in decoding order, in the access unit associated with the picture timing SEI message is exceeded. When the duration is exceeded, the bitstream does not conform and a new bitstream with revised CPB parameters is generated and tested by the encoder. That process may repeat until the duration is not exceeded, which means that the bitstream conforms to the standard (e.g., the VVC standard).

Once a conforming bitstream is obtained, that bitstream may be stored and communicated toward the decoder. In an embodiment, the BP SEI message819, the PT SEI message818, and the DUI SEI message816remain included in the bitstream even though the decoder may not use this information in decoding any of the pictures included in the bitstream.

An example implementation of the HRD using the DU-based HRD operations to test the sublayers in the bitstream for bitstream conformance is provided in the following syntax and semantics.

A picture timing SEI message syntax is as follows.

Descriptorpic_timing( payloadSize ) {pt_max_sub_layers_minus1u(3)cpb_removal_delay_minus1[ pt_max_sub_layers_minus1 ]u(v)for( i = TemporalId; i < pt_max_sub_layers_minus1; i++ ) {sub_layer_delays_present_flag[ i ]u(1)if( sub_layer_delays_present_flag[ i ] ) {cpb_removal_delay_delta_enabled_flag[ i ]u(1)if( cpb_removal_delay_delta_enabled_flag[ i ] )cpb_removal_delay_delta_idx[ i ]u(v)elsecpb_removal_delay_minus1[ i ]u(v)}}dpb_output_delayu(v)if( decoding_unit_hrd_params_present_flag )pic_dpb_output_du_delayu(v)if( decoding_unit_hrd_params_present_flag &&decoding_unit_cpb_params_in_pic_timing_sei_flag ) {num_decoding_units_minus1ue(v)du_common_cpb_removal_delay_flagu(1)if( du_common_cpb_removal_delay_flag )for( i = TemporalId; i < pt_max_sub_layers_minus1; i++ )du_common_cpb_removal_delay_increment_minus1[ i ]u(v)for( i = 0; i <= num_decoding_units_minus1; i++ ) {num_nalus_in_du_minus1[ i ]ue(v)if( !du_common_cpb_removal_delay_flag && i <num_decoding_units_minus1 )for( j = TemporalId; j < pt_max_sub_layers_minus1; j++ )du_cpb_removal_delay_increment_minus1[ i ][ j ]u(v)}}}

An example of picture timing SEI message semantics is as follows.

The picture timing SEI message provides CPB removal delay and DPB output delay information for the access unit associated with the SEI message.

num_decoding_units_minus1 plus 1 specifies the number of decoding units in the access unit the picture timing SEI message is associated with. The value of num_decoding_units_minus1 shall be in the range of 0 to PicSizeInCtbsY−1, inclusive.

du_common_cpb_removal_delay_flag equal to 1 specifies that the syntax elements du_common_cpb_removal_delay_increment_minus1 [i] are present. du_common_cpb_removal_delay_flag equal to 0 specifies that the syntax elements du_common_cpb_removal_delay_increment_minus1[i] are not present.

du_common_cpb_removal_delay_increment_minus1[i] plus 1 specifies the duration, in units of clock sub-ticks (see clause C.1), between the nominal CPB removal times of any two consecutive decoding units in decoding order in the access unit associated with the picture timing SEI message when Htid i equal to i. This value is also used to calculate an earliest possible time of arrival of decoding unit data into the CPB for the HSS, as specified in Annex C of the VVC standard. The length of this syntax element is du_cpb_removal_delay_increment_length_minus1+1 bits.

num_nalus_in_du_minus1[i] plus 1 specifies the number of NAL units in the i-th decoding unit of the access unit the picture timing SEI message is associated with. The value of num_nalus_in_du_minus1[i] shall be in the range of 0 to PicSizeInCtbsY−1, inclusive.

The first decoding unit of the access unit consists of the first num_nalus_in_du_minus1[0]+1 consecutive NAL units in decoding order in the access unit. The i-th (with i greater than 0) decoding unit of the access unit consists of the num_nalus_in_du_minus1[i]+1 consecutive NAL units immediately following the last NAL unit in the previous decoding unit of the access unit, in decoding order. There shall be at least one VCL NAL unit in each decoding unit. All non-VCL NAL units associated with a VCL NAL unit shall be included in the same decoding unit as the VCL NAL unit.

du_cpb_removal_delay_increment_minus1[i][j] plus 1 specifies the duration, in units of clock sub-ticks, between the nominal CPB removal times of the (i+1)-th decoding unit and the i-th decoding unit, in decoding order, in the access unit associated with the picture timing SEI message when Htid i equal to j. This value is also used to calculate an earliest possible time of arrival of decoding unit data into the CPB for the HSS, as specified in Annex C of the VVC standard. The length of this syntax element is du_cpb_removal_delay_increment_length_minus1+1 bits.

An example decoding unit information SEI message syntax is as follows.

Descriptordecoding_unit_info( payloadSize ) {decoding_unit_idxue(v)dui_max_sub_layers_minus1u(3)if( !decoding_unit_cpb_params_in_pic_timing_sei_flag )for( i = TemporalId; i < dui_max_sub_layers_minus1; i++ )du_spt_cpb_removal_delay_increment[ i ]u(v)dpb_output_du_delay_present_flagu(1)if( dpb_output_du_delay_present_flag )pic_spt_dpb_output_du_delayu(v)}

An example of picture timing SEI message semantics is as follows.

The decoding unit information SEI message provides CPB removal delay information for the decoding unit associated with the SEI message.

The following applies for the decoding unit information SEI message syntax and semantics.The syntax elements decoding_unit_hrd_params_present_flag, decoding_unit_cpb_params_in_pic_timing_sei_flag and dpb_output_delay_du_length_minus1, and the variable CpbDpbDelaysPresentFlag are found in or derived from syntax elements in the general_hrd_parameters( ) syntax structure that is applicable to at least one of the operation points to which the decoding unit information SEI message applies.The bitstream (or a part thereof) refers to the bitstream subset (or a part thereof) associated with any of the operation points to which the decoding unit information SEI message applies.

The presence of decoding unit information SEI messages for an operation point is specified as follows.If CpbDpbDelaysPresentFlag is equal to 1, decoding_unit_hrd_params_present_flag is equal to 1 and decoding_unit_cpb_params_in_pic_timing_sei_flag is equal to 0, one or more decoding unit information SEI messages applicable to the operation point shall be associated with each decoding unit in the CVS.Otherwise, if CpbDpbDelaysPresentFlag is equal to 1, decoding_unit_hrd_params_present_flag is equal to 1 and decoding_unit_cpb_params_in_pic_timing_sei_flag is equal to 1, one or more decoding unit information SEI messages applicable to the operation point may or may not be associated with each decoding unit in the CVS.Otherwise (CpbDpbDelaysPresentFlag is equal to 0 or decoding_unit_hrd_params_present_flag is equal to 0), in the CVS there shall be no decoding unit that is associated with a decoding unit information SEI message applicable to the operation point.

The set of NAL units associated with a decoding unit information SEI message consists, in decoding order, of the SEI NAL unit containing the decoding unit information SEI message and all subsequent NAL units in the access unit up to but not including any subsequent SEI NAL unit containing a decoding unit information SEI message with a different value of decoding_unit_idx. Each decoding unit shall include at least one VCL NAL unit. All non-VCL NAL units associated with a VCL NAL unit shall be included in the decoding unit containing the VCL NAL unit.

The TemporalId in the decoding unit information SEI message syntax is the TemporalId of the SEI NAL unit containing the decoding unit information SEI message.

decoding_unit_idx specifies the index, starting from 0, to the list of decoding units in the current access unit, of the decoding unit associated with the decoding unit information SEI message. The value of decoding_unit_idx shall be in the range of 0 to PicSizeInCtbsY−1, inclusive.

A decoding unit identified by a particular value of duIdx includes and only includes all NAL units associated with all decoding unit information SEI messages that have decoding_unit_idx equal to duIdx. Such a decoding unit is also referred to as associated with the decoding unit information SEI messages having decoding_unit_idx equal to duIdx.

For any two decoding units duA and duB in one access unit with decoding_unit_idx equal to duIdxA and duIdxB, respectively, where duIdxA is less than duIdxB, duA shall precede duB in decoding order.

A NAL unit of one decoding unit shall not be present, in decoding order, between any two NAL units of another decoding unit.

dui_max_sub_layers_minus1 plus 1 specifies the the TemporalId of the highest sub-layer representation for which the CPB removal delay information is contained in the decoding unit information SEI message. The value of dui_max_sub_layers_minus1 shall be in the range of 0 to vps_max_sub_layers_minus1, inclusive.

du_spt_cpb_removal_delay_increment[i] specifies the duration, in units of clock sub-ticks, between the nominal CPB times of the last decoding unit in decoding order in the current access unit and the decoding unit associated with the decoding unit information SEI message when Htid i equal to i. This value is also used to calculate an earliest possible time of arrival of decoding unit data into the CPB for the HSS, as specified in Annex C. The length of this syntax element is du_cpb_removal_delay_increment_length_minus1+1. When the decoding unit associated with the decoding unit information SEI message is the last decoding unit in the current access unit, the value of du spt_cpb_removal_delay_increment[i] shall be equal to 0.

dpb_output_du_delay_present_flag equal to 1 specifies the presence of the pic_spt_dpb_output_du_delay syntax element in the decoding unit information SEI message. dpb_output_du_delay_present_flag equal to 0 specifies the absence of the pic_spt_dpb_output_du_delay syntax element in the decoding unit information SEI message.

pic_spt_dpb_output_du_delay is used to compute the DPB output time of the picture when DecodingUnitHrdFlag is equal to 1. It specifies how many sub clock ticks to wait after removal of the last decoding unit in an access unit from the CPB before the decoded picture is output from the DPB. When not present, the value of pic_spt_dpb_output_du_delay is inferred to be equal to pic_dpb_output_du_delay. The length of the syntax element pic_spt_dpb_output_du_delay is given in bits by dpb_output_delay_du_length_minus1+1.

It is a requirement of bitstream conformance that all decoding unit information SEI messages that are associated with the same access unit, apply to the same operation point, and have dpb_output_du_delay_present_flag equal to 1 shall have the same value of pic_spt_dpb_output_du_delay.

The output time derived from the pic_spt_dpb_output_du_delay of any picture that is output from an output timing conforming decoder shall precede the output time derived from the pic_spt_dpb_output_du_delay of all pictures in any subsequent CVS in decoding order.

The picture output order established by the values of this syntax element shall be the same order as established by the values of PicOrderCntVal.

For pictures that are not output by the “bumping” process because they precede, in decoding order, a CLVSS picture that has no_output_of_prior_pics_flag equal to 1 or inferred to be equal to 1, the output times derived from pic_spt_dpb_output_du_delay shall be increasing with increasing value of PicOrderCntVal relative to all pictures within the same CVS.

For any two pictures in the CVS, the difference between the output times of the two pictures when DecodingUnitHrdFlag is equal to 1 shall be identical to the same difference when DecodingUnitHrdFlag is equal to 0.

FIG.9is an embodiment of a method900of decoding implemented by a video decoder (e.g., video decoder400). The method900may be performed after a bitstream has been directly or indirectly received from a video encoder (e.g., video encoder300). The method900improves the decoding process by ensuring picture-level coded picture buffer (CPB) parameters used to perform DU-based HRD operations on sublayers are included in a supplemental enhancement information (SEI) message. Because the picture-level CPB parameters are included in the SEI message, the HRD can use the DU-based HRD operations to test the sublayers in the bitstream for bitstream conformance, which ensures that the sublayers are properly coded and/or can be properly decoded. Thus, the coder/decoder (a.k.a., “codec”) in video coding is improved relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

In block902, the video decoder receives a bitstream comprising a coded picture and an SEI message. The SEI message includes CPB parameters (e.g., the HRD parameters880and/or890referred to as picture-level CPB parameters) used to perform DU-based HRD operations on sublayers (e.g., sublayers710,720,730). The DU-based HRD operations, which correspond to a DU such as DU822, are different from AU-based HRD operations, which correspond to an AU such as AU821. As noted above, the DU-based HRD operations are implemented by an HRD (e.g., HRD500) for the purpose of testing for a bitstream such as bitstream800, which includes a multi-layer video sequence600and/or a multi-layer video sequence700, for bitstream conformance.

In an embodiment, the CPB parameters specify a duration between CPB removal times of two decoding units. In an embodiment, the SEI message is a picture timing (PT) SEI message. In an embodiment, the CPB parameters comprise a common CPB removal delay and a CPB removal delay for AU associated with the PT SEI message.

In an embodiment, the SEI message is a PT SEI message that specifies a number of decoding units in the AU associated with the PT SEI message. In an embodiment, the SEI message is a PT SEI message that specifies a number of NAL units in a DU of the AU associated with the PT SEI message. As used herein, the highest sublayer is the enhancement layer (e.g., sublayer730) furthest away from the base layer (e.g., sublayer710).

In an embodiment, the SEI message is a decoding unit information (DUI) SEI message that provides a temporal ID of an SEI NAL unit containing the DUI SEI message. In an embodiment, the temporal ID specifies a highest sublayer for which CPB removal delay information is contained in the DUI SEI message.

In block904, the video decoder decodes the coded picture from the bitstream to obtain a decoded picture. Thereafter, the decoded picture may be used to generate or produce an image or video sequence for display to a user on the display or screen of an electronic device (e.g., a smart phone, tablet, laptop, personal computer, etc.). In an embodiment, the picture-level CPB parameters contained in the PT SEI message818and/or the DUI SEI message816are not used in decoding the coded picture.

FIG.10is an embodiment of a method1000of encoding a video bitstream implemented by a video encoder (e.g., video encoder300). The method1000may be performed when a picture (e.g., from a video) is to be encoded into a video bitstream and then transmitted toward a video decoder (e.g., video decoder400). The method1000improves the encoding process by ensuring picture-level coded picture buffer (CPB) parameters used to perform DU-based HRD operations on sublayers are included in a supplemental enhancement information (SEI) message. Because the picture-level CPB parameters are included in the SEI message, the HRD can use the DU-based HRD operations to test the sublayers in the bitstream for bitstream conformance, which ensures that the sublayers are properly coded and/or can be properly decoded. Thus, the coder/decoder (a.k.a., “codec”) in video coding is improved relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

In block1002, the video encoder generates a bitstream comprising a coded picture and an SEI message. The SEI message includes CPB parameters (e.g., the HRD parameters880and/or890referred to as picture-level CPB parameters) used to perform DU-based HRD operations on sublayers (e.g., sublayers710,720,730). The DU-based HRD operations, which correspond to a DU such as DU822, are different from AU-based HRD operations, which correspond to an AU such as AU821. As noted above, the DU-based HRD operations are implemented by an HRD (e.g., HRD500) for the purpose of testing for a bitstream such as bitstream800, which includes a multi-layer video sequence600and/or a multi-layer video sequence700, for bitstream conformance.

In an embodiment, the CPB parameters specify a duration between CPB removal times of two decoding units. In an embodiment, the SEI message is a picture timing (PT) SEI message. In an embodiment, the CPB parameters comprise a common CPB removal delay and a CPB removal delay for an access unit (AU) associated with the PT SEI message. In an embodiment, the PT SEI message specifies a number of decoding units in the AU associated with the PT SEI message and a number of network abstraction layer (NAL) units in a decoding unit (DU) of the AU associated with the PT SEI message.

In an embodiment, the SEI message is a decoding unit information (DUI) SEI message that provides a temporal identifier (ID) of an SEI NAL unit containing the DUI SEI message. In an embodiment, the DUI SEI message specifies a temporal identifier (ID) of a highest sublayer for which CPB removal delay information is contained in the DUI SEI message.

In block1004, the video encoder performs the DU-based HRD operations on the sublayers using the CPB parameters to determine whether the bitstream is conforming.

In an embodiment, the bitstream is conforming when the duration between the CPB removal times is not exceeded.

In block1006, the video encoder stores the bitstream for communication toward a video decoder when the bitstream is conforming based on performance of the DU-based HRD operations. The bitstream may be stored in memory until the bitstream is transmitted toward the video decoder. Once received by the video decoder, the encoded bitstream may be decoded (e.g., as described above) to generate or produce an image or video sequence for display to a user on the display or screen of an electronic device (e.g., a smart phone, tablet, laptop, personal computer, etc.).

FIG.11is a schematic diagram of a video coding device1100(e.g., a video encoder300or a video decoder400) according to an embodiment of the disclosure. The video coding device1100is suitable for implementing the disclosed embodiments as described herein. The video coding device1100comprises ingress ports1110and receiver units (Rx)1120for receiving data; a processor, logic unit, or central processing unit (CPU)1130to process the data; transmitter units (Tx)1140and egress ports1150for transmitting the data; and a memory1160for storing the data. The video coding device1100may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports1110, the receiver units1120, the transmitter units1140, and the egress ports1150for egress or ingress of optical or electrical signals.

The processor1130is implemented by hardware and software. The processor1130may 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 processor1130is in communication with the ingress ports1110, receiver units1120, transmitter units1140, egress ports1150, and memory1160. The processor1130comprises a coding module1170. The coding module1170implements the disclosed embodiments described above. For instance, the coding module1170implements, processes, prepares, or provides the various codec functions. The inclusion of the coding module1170therefore provides a substantial improvement to the functionality of the video coding device1100and effects a transformation of the video coding device1100to a different state. Alternatively, the coding module1170is implemented as instructions stored in the memory1160and executed by the processor1130.

The video coding device1100may also include input and/or output (I/O) devices1180for communicating data to and from a user. The I/O devices1180may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I/O devices1180may also include input devices, such as a keyboard, mouse, trackball, etc., and/or corresponding interfaces for interacting with such output devices.

The memory1160comprises one or more disks, tape drives, and solid-state drives and may 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. The memory1160may be volatile and/or non-volatile and may be read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM).

FIG.12is a schematic diagram of an embodiment of a means for coding1200. In an embodiment, the means for coding1200is implemented in a video coding device1202(e.g., a video encoder300or a video decoder400). The video coding device1202includes receiving means1201. The receiving means1201is configured to receive a picture to encode or to receive a bitstream to decode. The video coding device1202includes transmission means1207coupled to the receiving means1201. The transmission means1207is configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means (e.g., one of the I/O devices1180).

The video coding device1202includes a storage means1203. The storage means1203is coupled to at least one of the receiving means1201or the transmission means1207. The storage means1203is configured to store instructions. The video coding device1202also includes processing means1205. The processing means1205is coupled to the storage means1203. The processing means1205is configured to execute the instructions stored in the storage means1203to perform the methods disclosed herein.

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 should 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, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.