Abstract: A method is provided for decoding an encoded video stream on a processor having a plurality of processing cores includes receiving and examining a video stream to identify any macroscopic constructs present therein that support parallel processing. Decoding of the video stream is divided into a plurality of decoding functions. The plurality of decoding functions is scheduled for decoding the video stream in a dynamic manner based on availability of any macroscopic constructs that have been identified and then based on a number of bytes used to encode each block into which each picture of the video stream is partitioned. Each of the decoding functions is dispatched to the plurality of processing cores in accordance with the scheduling.

Abstract: A loop filtering method based on an adaptive self-guided filtering is mainly an adaptive self-guided filtering technology considering local structure information of an image, wherein a regularization coefficient is adjusted by calculating a weight coefficient of the regularization coefficient to realize the adaptive self-guide filtering, and then a region-level subspace mapping iterative optimization implemented on each region enables a mapping result of the each region to be optimal, wherein the mapping result of a whole image is closer to an original image. Beneficial effects of the loop filtering method are as follows: a filtering effect of a loop filtering is improved, a distortion effect of a reconstruction image is reduced and a reconstruction quality of a video frame is improved, wherein the reconstruction image is more favorable for a subsequent reference and a subjective and objective quality of the video is further improved.

Abstract: The present invention relates to efficient signaling of an intra prediction mode for predicting a current block in intra prediction coding. According to an aspect of the present invention, a video encoding apparatus divides dozens of intra modes into groups, selects a group to which an actual intra mode of the current block to be encoded belongs, and signals a value corresponding to the group. The video decoding apparatus acquires information on the group to which the actual intra mode of the current block belongs from a bit-stream and then evaluates intra modes belonging to the group to select a final intra mode.

Abstract: Embodiments of this application provide a data transmission method and apparatus and a storage medium. The method includes: After obtaining a first identifier and a second identifier that uniquely identify a first device, the first device scrambles, by using the first identifier, checked data obtained through CRC check. After performing channel coding on to-be-transmitted data and scrambled checked data, the first device scrambles, by using the second identifier, coded data obtained through channel coding, and finally sends scrambled data. In this way, after receiving the scrambled data, a second device may perform descrambling by using the second identifier, and then perform CRC check, to determine whether the received data is correct and determine the first identifier of the first device.

Abstract: A method, computer program, and computer system is provided for signaling output layer sets in a coded video stream. Video data having multiple layers is received. One or more syntax elements are identified. The syntax elements specify one or more output layer sets corresponding to output layers from among the multiple layers of the received video data. The one or more output layers corresponding to the specified output layer sets are decoded and displayed.

Abstract: A video image processing method includes dividing a coding unit into one or more sub-block, constructing first and second motion vector candidate lists, and performing prediction for the coding unit according to the first and second motion vector candidate lists. The first motion vector candidate list includes a motion vector of a sub-block of the coding unit, and the second motion vector candidate list includes a motion vector of the coding unit. Constructing the first motion vector candidate list includes determining a reference motion vector of the coding unit, determining a related reference block of the sub-block of the coding unit in a co-located reference image of the coding unit according to the reference motion vector, determining a scaling factor of the motion vector of the related reference block, adding the scaled motion vector into the first motion vector candidate list.

Abstract: Disclosed are a colour component prediction method, an encoder, a decoder, and a storage medium. The method includes: determining adjacent reference pixels of a current block in a picture; constructing a subset of adjacent reference pixels according to the adjacent reference pixels, wherein the subset of adjacent reference pixels contains a part of the adjacent reference pixels; and calculating model parameters of a prediction model according to the subset of adjacent reference pixels, wherein the prediction model includes N prediction sub-models, the N prediction sub-models correspond to N groups of model parameters, and the prediction sub-models are used to perform, through corresponding model parameters, cross-component prediction of colour components to be predicted, and N is a positive integer greater than or equal to 2.

Abstract: Disclosed herein is a method for decoding a video including determining a coding unit to be decoded by block partitioning, decoding prediction syntaxes for the coding unit, the prediction syntaxes including a skip flag indicating whether the coding unit is encoded in a skip mode, after the decoding of the prediction syntaxes, decoding transform syntaxes including a transformation/quantization skip flag and a coding unit cbf, wherein the transformation/quantization skip flag indicates whether inverse transformation, inverse quantization, and at least part of in-loop filterings are skipped, and the coding unit cbf indicates whether all coefficients in a luma block and two chroma blocks constituting the coding unit are zero, and reconstructing the coding unit based on the prediction syntaxes and the transform syntaxes.

Abstract: A video processing apparatus and a processing method of video stream are provided. In the method, at least one encoding unit is formed in an image frame, sub-encoding units in multiple encoding units of an image sequence are encoded according to a correlation between a first sub-encoding unit and a second sub-encoding unit in the sub-encoding units, and a video stream is generated according to an encoded result of the image sequence. The image frame is an image of the image sequence, and each of the encoding units records encoding information of a belonging block.

Abstract: A method for decoding a video according to the present invention may comprise: determining whether to divide a current block with quad tree partitioning, determining whether to divide the current block with binary tree partitioning when the current block is not divided with the quad tree partitioning, determining a binary tree partition type for the current block when it is determined to divide the current block with the binary tree partitioning, and dividing the current block into two partitions according to the determined binary tree partition type.

Abstract: A method of extracting a sub-bitstream from an encoded video bitstream using at least one processor includes: obtaining an encoded video bitstream, the encoded video bitstream including a plurality of Network Abstraction Layer (NAL) units; obtaining an output layer set list; comparing the NAL units with the output layer set list; and removing NAL units that are not included in the output layer set list.

Abstract: Method and apparatus for constrained de-blocking filter are disclosed. According to one method, a current block is partitioned into a plurality of sub-blocks using SDIP (Short Distance Intra Prediction mod). A first Bs (boundary strength) for an internal block boundary of the plurality of sub-blocks is determined by setting the first Bs to a second Bs of an Intra-coded boundary block of the current block. De-blocking process is applied, using the first Bs, to reconstructed samples across the internal block boundary of the plurality of sub-blocks to generate filtered-reconstructed samples. In another method, the current block is partitioned into two sub-blocks using SBT (sub-block transform) horizontally or vertically and the first Bs (boundary strength) is determined for an internal block boundary between the two sub-blocks by setting the first Bs to a second Bs of a non-zero cbf (coded block flag) block of the two sub-blocks in step.

Abstract: A method for decoding a video according to the present invention may comprise: determining whether to divide a current block with quad tree partitioning, determining whether to divide the current block with binary tree partitioning when the current block is not divided with the quad tree partitioning, determining a binary tree partition type for the current block when it is determined to divide the current block with the binary tree partitioning, and dividing the current block into two partitions according to the determined binary tree partition type.

Abstract: A method for decoding a video according to the present invention may comprise: determining whether to divide a current block with quad tree partitioning, determining whether to divide the current block with binary tree partitioning when the current block is not divided with the quad tree partitioning, determining a binary tree partition type for the current block when it is determined to divide the current block with the binary tree partitioning, and dividing the current block into two partitions according to the determined binary tree partition type.

Abstract: The present disclosure aims to provide a method for detecting a GOP boundary of an encoded bit stream of each layer and associating GOPs of the layers for hierarchical transmission in a video transmission device that transmits a hierarchically encoded bit stream. The present disclosure provides a video transmission device and a video transmission method that detect a GOP head access unit in a base layer of a hierarchically encoded bit stream by analyzing the base layer and detect a head access unit of an enhancement layer of an identical GOP to that of the aforementioned access unit from a decoding time stamp of the access unit by using the relationship between a decoding time stamp of the base layer and a decoding time stamp of the enhancement layer.

Abstract: The image decoding method includes determining a context for use in a current block to be processed, from among a plurality of contexts, wherein in the determining: the context is determined under a condition that control parameters of a left block and an upper block are used, when the signal type is a first type; and the context is determined under a third condition that the control parameter of the upper block is not used and a hierarchical depth of a data unit to which the control parameter of the current block belongs is used, when the signal type is a third type, and the third type is one or more of (i) “merge_flag”, (ii) “ref_idx_l0” or “ref_idx_l1”, (iii) “inter_pred_flag”, (iv) “mvd_l0” or “mvd_l1”, (v) “intra_chroma_pred_mode”, (vi) “cbf_luma”, and (vii) “cbf_cb” or “cbf_cr”.

Abstract: A method for video processing is provided to include: performing a conversion between a current video block of a video that is a chroma block and a coded representation of the video, wherein, during the conversion, the current video block is constructed based on a first domain and a second domain, and wherein the conversion further includes applying a forward reshaping process and/or an inverse reshaping process to one or more chroma components of the current video block.

Abstract: A video decoder can be configured to determine a threshold number of regular coded bins for a first decoding pass; for a first set of coefficients, context decode syntax elements of a coefficient group until the threshold number of regular coded bins is reached; and in response to reaching the threshold number of regular coded bins, for a second set of coefficients, bypass decode additional syntax elements, wherein to bypass decode the additional syntax elements the video decoder, for a coefficient of the second set of coefficients, derives a value for a Rice parameter based on a sum of absolute values of neighboring coefficients to the coefficient; determine values for the first set of coefficients of the transform unit based on the context decoded syntax elements; and determine values for the second set of coefficients of the transform unit based on the additional syntax elements.

Abstract: An example device for coding video data includes a memory configured to store video data; and one or more processors implemented in circuitry and configured to: determine a size of a dimension of a current block of the video data; calculate a context for entropy coding a last significant coefficient coordinate along the dimension, wherein to calculate the context, the one or more processors are configured to: calculate a context shift value according to ((log 2TrafoSize+1)>>2)<<1, wherein log 2TrafoSize represents a logarithmic value of the size of the dimension, ‘>>’ represents a bitwise right shift operator, and ‘<<’ represents a bitwise left shift operator; and calculate the context using the context shift value; and entropy code the last significant coefficient coordinate using the calculated context.

Abstract: Methods for performing palette coding of video data may include: determining whether a luma component of a coding unit (CU) and chroma components of the CU are coded jointly or separately in a palette mode; and in response to the luma component and the chroma components being coded jointly in the palette mode, determining a first maximum palette-table size for the CU; determining a first maximum palette-predictor size for the CU; and predicting the CU based on the first maximum palette-table size and the first maximum palette-predictor size.

Abstract: A method comprises obtaining a first weight for a first probability associated with a first probability update window; obtaining a second weight for a second probability associated with a second probability update window, wherein the first weight and the second weight are unequal; and coding, using the first weight and the second weight, a portion of a video.

Abstract: A method for decoding a video signal based on reduced transform includes the steps of: obtaining, from the video signal, a transform index indicating transform kernels applied to horizontal and vertical directions of a current block; determining a region in which a transform is applied to the current block based on the transform kernels indicated by the transform index and a size of the current block; deriving, as zero, coefficients of a remaining region other than the region to which the transform is applied within the current block; and performing an inverse transform on the region to which the transform is applied using the transform kernels indicated by the transform index.

Abstract: A method of encoding a video frame into a bitstream is described including: applying a downsampling scheme to an original video frame of a first resolution for determining a first low-resolution, LR, original frame and one or more second original LR frames, the first LR original frame and the one or more second LR original frames being of a second resolution that is lower than the first resolution; partitioning the first LR original frame into first original blocks and partitioning the one or more second LR frames into second original blocks; using a prediction method for determining first predicted blocks, the first predicted blocks defining predictions for the first original blocks of the first LR original frame; determining first residual blocks based on the first predicted blocks and the first original blocks and, subsequently, determining first reconstructed blocks based on the first residual blocks and the first predicted blocks; determining second predicted blocks based on the first reconstructed block

Abstract: An encoding method includes a counting process of dividing a gray-scale range of pixels of a coding unit block into a plurality of classes each having a predetermined number of gray-scale levels, and counting a number of pixels belonging to each of the plurality of classes, a class addition process of selecting top n classes (n: an integer greater than or equal to 1) having a largest number of counted pixels, and adding offset values to pixel values of pixels belonging to the n selected classes; and a first signaling process of signaling SAO parameters including the added offset values.

Abstract: According to the present disclosure, a video decoding method performed by a video decoding device includes parsing remaining intra prediction mode information for a current block, deriving neighboring samples of the current block, deriving MPM list including MPM candidates of the current block, deriving an intra prediction mode of the current block based on the remaining intra prediction mode information, wherein the intra prediction mode is one of remaining intra prediction modes excluding the MPM candidates, deriving a prediction sample of the current block based on the intra prediction mode and the neighboring samples, and deriving a reconstructed picture based on the prediction sample, wherein the remaining intra prediction mode information is coded through a truncated binary (TB) binarization process, and wherein a binarization parameter for the TB binarization process is 60.

Abstract: A method for encoding a video signal includes generating an extension region of a first face of a reference frame, where the extension region includes a plurality of extension samples, and a sample value of each extension sample is based on a sample value of a sample of a second face of the reference frame, determining a use of an extension region, providing, based on the use, picture level extension usage information based on the extension region, and encoding the picture level extension usage information into an encoded video signal.

Abstract: Provided are an encoding method and apparatus, and a decoding method and apparatus for adaptively selecting a context model used to entropy-encode and entropy-decode a syntax element, based on various shapes of coding units. The image decoding method includes: determining a context model based on block shape information including at least one of a shape, direction, width, ratio of width and height, or size of a coding unit; obtaining, from a bitstream based on the context model, information about a split shape mode for splitting the coding unit; and determining a split shape mode of the coding unit, based on the information about the split shape mode.

Abstract: A moving-image encoding device calculates a code amount generated by encoding a moving image including an I picture, a P picture, and a B picture as picture types, and calculates a complexity history of the picture which is encoded on the basis of the code amount and a quantization width used in the encoding. This moving-image encoding device estimates an estimated complexity of an encoding object picture to be encoded on the basis of the complexity history of an encoded picture of the same picture type as a picture type of the encoding object picture and the complexity history of the encoded picture immediately preceding the encoding object picture.

Abstract: A video decoder may receive, in a bitstream that comprises an encoded representation of video data, information indicating whether a residual block is partitioned and information indicating a partition tree type for the residual block based on the residual block being partitioned, wherein the residual block is indicative of a difference between a current block and a prediction block. The video decoder may determine, based on the received information that the residual block is partitioned and the partition tree type for the residual block, a plurality of residual sub-blocks into which the residual block is partitioned according to the partition tree type. The video decoder may produce the residual data for the current block based at least in part on the residual block being partitioned according to the partition tree type into the plurality of residual sub-blocks and may decode the current block using the residual data.

Abstract: Devices and methods for video coding are described. One method comprises receiving a bitstream, wherein the bitstream comprises prediction related information, and wherein the prediction related information includes at least one of: numbers and positions of available primary reference samples, an intra prediction mode index, or a size of the current coding block; determining whether a bidirectional intra prediction (BIP) flag is signaled in the bitstream based on the prediction related information; and reconstructing the picture.

Abstract: A context modeling method and apparatus of a split flag are provided. The method includes: obtaining a height and a width of a current node, a height of a first leaf node in a first direction, and a width of a second leaf node in a second direction; determining whether the current node meets a first preset condition and a second preset condition, where the first preset condition includes the height of the current node is greater than the height of the first leaf node, and the second preset condition includes the width of the current node is greater than the width of the second leaf node; and determining a context model of a split flag of the current node based on whether the first and second preset conditions are met.

Abstract: The present disclosure provides method and systems for signaling information regarding chroma quantization parameter (QP) offsets. According to some disclosed embodiments, the methods include: determining whether a joint CbCr residual coding is enabled; and in response to the joint CbCr residual coding being determined to be enabled, signaling a syntax element for adjusting chroma quantization parameter (QP) for joint CbCr component at coding unit (CU) level.

Abstract: The disclosure relates to a video encoding method and a video encoding apparatus, a computer-readable storage medium, and a computer device. The method includes: acquiring a current video frame and an initial quantization parameter; calculating first historical complexity corresponding to the current video frame at a first time granularity; acquiring a second available bit rate at a second time granularity corresponding to the current video frame and a current first available bit rate at the first time granularity corresponding to the current video frame; adjusting the second available bit rate and the first available bit rate according to complexity of the current video frame and the first historical complexity; updating the initial quantization parameter according to an adjusted second available bit rate to obtain a current quantization parameter; and encoding the current video frame according to the current quantization parameter.

Abstract: The present disclosure describes a method, an apparatus, and a storage medium for dividing a coding unit of a video frame. The method includes determining, by a device, according to a correspondence relationship between a frame type and a coding unit type, a target coding unit type based on a target frame type of a target frame, the target coding unit type indicating a division depth for dividing the target frame. The method further includes determining, by the device, according to coding unit information of a target coding unit during dividing the target coding unit with the target coding unit type in the target frame, whether the target coding unit meets a target condition, to obtain a target result; and performing, by the device, a division operation corresponding to the target result on the target coding unit.

Abstract: Disclosed are a display apparatus, an image providing apparatus, and methods of controlling the same, the display apparatus including: a display; and a processor configured to: decode an encoded video stream, decompress the video stream through a neural network including a plurality of channels and a plurality of layers with a parameter set based on learning, and perform image compensation determined based on learning about the decompression with respect to the video stream.

Abstract: An example device includes a memory and processing circuitry in communication with the memory. The processing circuitry of a device is configured to form a most probable mode (MPM) candidate list for a chroma block of the video data stored to the memory, such that the MPM candidate list includes one or more derived modes (DMs) associated with a luma block of the video data associated with the chroma block, and a plurality of luma prediction modes that can be used for coding luminance components of the video data. The processing circuitry is further configured to select a mode from the MPM candidate list, and to code the chroma block according to the mode selected from the MPM candidate list.

Abstract: An apparatus for encoding a block of a picture includes a convolutional neural network (CNN) for determining a block partitioning of the block, the block having an N×N size and a smallest partition determined by the CNN being of size S×S. The CNN includes feature extraction layers; a concatenation layer that receives, from the feature extraction layers, first feature maps of the block, where each first feature map of the first feature maps is of the smallest possible partition size S×S of the block; and at least one classifier that is configured to infer partition decisions for sub-blocks of size (?S)×(?S) of the block, where ? is a power of 2.

Abstract: The amount of processing is reduced with high coding efficiency maintained. There is provided an arithmetic decoding device including syntax decoding means for decoding each of at least a first syntax element and a second syntax element indicating a transform coefficient using arithmetic decoding with a context or arithmetic decoding without a context. The syntax decoding means performs decoding that at least includes not decoding the first syntax element and decoding the second syntax element using the arithmetic decoding without a context, and decoding the first syntax element using the arithmetic decoding with a context and decoding the second syntax element using the arithmetic decoding without a context.

Abstract: A significance-coefficient flag indicates whether a given quantized transform coefficient is equal to zero or not. To encode the significant-coefficient flags, context-based entropy coding can be used. To adapt to the characteristics of a video sequence, the context model is selected based on the statistics of the transform coefficients. In one embodiment, the non-zero probabilities of transform coefficients are compared to different thresholds to divide a transform block into several context regions, where all coefficients in a context region use the same set of context models. In another embodiment, the transform block is first divided into several context regions based on the positions of the transform coefficients, and the non-zero probabilities of transform coefficients are compared with a threshold to divide each context region into two sub-regions, where all coefficients in a sub-region share the same set of context models.

Abstract: There is included a method and apparatus comprising computer code configured to cause a processor or processors to perform parsing at least one video parameter set comprising at least one syntax element indicating whether at least one layer in the scalable bitstream is one of a dependent layer of the scalable bitstream and an independent layer of the scalable bitstream, decoding a picture in the dependent layer by parsing and interpreting an inter-layer reference picture list, and decoding a picture in an independent layer without parsing and interpreting the inter-layer reference picture list.

Abstract: An example method includes decoding, from an encoded video bitstream, a sequence parameter set (SPS) referred to by one or more pictures of video data, wherein decoding the SPS comprises: parsing, at a first position in the SPS, a syntax element that indicates whether joint coding of chroma residuals is enabled or disabled for the one or more pictures of video data referring to the SPS; and parsing, at a second position in the SPS that is after the first position, one or more syntax elements representing a quantization parameter (QP) mapping table.

Abstract: Aspects of the disclosure provide a method and an apparatus including processing circuitry for video decoding. The processing circuitry decodes, from a coded video bitstream, a first syntax element indicating whether a first component in the coded video bitstream is coded based on a second component in the coded video bitstream. The processing circuitry determines whether to decode one or more second syntax elements for a chroma related coding tool based on the first syntax element. The chroma related coding tool is a luma mapping with chroma scaling coding tool or a cross-component adaptive loop filter. The one or more second syntax elements are decoded when the first syntax element indicates that the first component is coded based on the second component. The one or more second syntax elements are not decoded when the first syntax element indicates that the first component is not coded based on the second component.

Abstract: Systems, methods, and media are provided for loop filtering across raster scan slices. One example includes obtaining the video data comprising one or more pictures and a first block of a picture having a pixel subject to filtering. A second block is determined to be located in the first slice in a particular relation to the second block. A third block that includes pixels for filtering the pixel is determined to be in a second slice at a diagonal corner of the first block, with filtering across slice boundaries disabled. First one or more pixels of the second block are identified as available for performing loop filtering of the pixel and second one or more pixels of the third block identified as unavailable for performing the loop filtering of the pixel of the first block. The first one or more pixels and the second one or more pixels are padded.

Abstract: A video decoder receives data from a bitstream for a block of pixels to be decoded as a current block of a current picture of a video. The current block includes a transform block. The video decoder determines a regular bin budget for the transform block. The video decoder entropy decodes the transform block as either regular bins using context modeling or as bypass bins without context modeling. A number of the regular bins used for entropy coding the transform block is limited by the determined regular bin budget regardless of whether the regular bins represent samples of (i) residual signals used to reconstruct pixel data of the current block or (ii) transform coefficients generated by transform operations of the residual signals. The video decoder reconstructs the current block based on the entropy decoded transform block.

Abstract: A method and apparatus for facilitating a turn-based interaction between a virtual agent and a customer of an enterprise are disclosed. The method includes receiving a conversational input provided by the customer during a turn-based interaction between the customer and the agent. One or more conversational inputs exchanged between the customer and the agent prior to the customer's conversational input are identified by positioning a virtual bounding box of fixed width over textual representation of the turn-based interaction. The conversational input and the one or more conversational inputs configure a set of conversational inputs. At least one context vector representation is generated based on an encoding of the set of conversational inputs. Each word of a virtual agent reply is predicted based on the at least one context vector representation. The virtual agent reply is provided to the customer in response to the conversational input of the customer.

Abstract: A method and apparatus for adaptively processing video samples in a video signal frame, the video samples being arranged in a Largest Coding Unit. The method comprises extracting a plurality of video samples from the Largest Coding Unit, calculating a correction offset for a first video sample of the extracted plurality of video samples upon the basis of a first value of the first video sample and a second value of a second video sample of the extracted plurality of video samples, and weighting the first video sample with the correction offset.

Abstract: Determining the occlusions or shadows for an area light within a scene is difficult, especially realistic shadowing in large and dynamic scenes. The disclosure provides an adaptive occlusion sampling process that uses voxel cone tracing to distribute the voxel tracing cones on the surface of area lights to obtain samples for shadowing in computer generated images or scenes. A method of adaptive occlusion sampling from a rectangular area light is disclosed that can be used to provide realistic shadowing in a computer generated scene. A process to compute a shadow of an area light within a scene is also disclosed herein that includes obtaining samples, employing voxel cone tracing, from a light surface of the area light based on sample points of a sampling grid created from sample patterns that are based on a determined number of cones.

Abstract: A method of partitioning in video coding for JVET, comprising representing a JVET coding tree unit as a root node in a quadtree plus binary tree (QTBT structure that can have quadtree or binary partitioning of the root node and quadtree or binary trees branching from each of the leaf nodes. The partitioning at any depth can use asymmetric binary partitioning to split a child node represented by a leaf node into two child coding units of unequal size, representing the two child coding units as leaf nodes in a binary tree branching from the parent leaf node and coding the child coding units represented by final leaf nodes of the binary tree with JVET. Disclosed is a generalized method of partitioning a block, either square or rectangular, which leads to more flexible block sizes with possible higher coding efficiency.

Abstract: A method of processing a video signal based on inter prediction includes constructing a first merge candidate list of a current block using a spatial merge candidate and temporal merge candidate of the current block, constructing a second merge candidate list by adding a history-based merge candidate indicating motion information of a block coded prior to the current block to the first merge candidate list, obtaining a merge index indicating a merge candidate applied to the current block within the second merge candidate list, and generating a prediction block of the current block using motion information of a merge candidate indicated by the merge index. The history-based merge candidate may be added to the first merge candidate list if the history-based merge candidate has motion information not overlapping motion information of a pre-defined merge candidate among merge candidates included in the first merge candidate list.

Abstract: A video decoding device includes a subpicture decoder(s) configured to decode respective subpictures, and a picture combining unit configured to compose the subpictures decoded into a picture such that the subpictures are allowed to overlap with each other.