Specifying layout in video pictures

A method for specifying layout of subpictures in video pictures is provided. A video decoder receives data from a bitstream to be decoded as a current picture of a video. For a current subpicture of a set of subpictures of the current picture, the video decoder determines a position of the current subpicture based on a width and a height of the current picture and a previously determined width and height of a particular subpicture in the set of subpictures. The video decoder reconstructs the current picture and the current subpicture based on the determined position.

TECHNICAL FIELD

The present disclosure relates generally to video coding. In particular, the present disclosure relates to methods of specifying subpicture layout, slice structure, and picture identification.

BACKGROUND

High-efficiency video coding (HEVC) is the latest international video coding standard developed by the Joint Collaborative Team on Video Coding (JCT-VC). The input video signal is predicted from the reconstructed signal, which is derived from the coded picture regions. The prediction residual signal is processed by a linear transform. The transform coefficients are quantized and entropy coded together with other side information in the bitstream. The reconstructed signal is generated from the prediction signal and the reconstructed residual signal after inverse transform on the de-quantized transform coefficients. The reconstructed signal is further processed by in-loop filtering for removing coding artifacts. The decoded pictures are stored in the frame buffer for predicting the future pictures in the input video signal.

In HEVC, a coded picture is partitioned into non-overlapped square block regions represented by the associated coding tree units (CTUs). A coded picture can be represented by a collection of slices, each comprising an integer number of CTUs. The individual CTUs in a slice are processed in a raster scanning order. A bi-predictive (B) slice may be decoded using intra prediction or inter prediction using at most two motion vectors and reference indices to predict the sample values of each block. A predictive (P) slice is decoded using intra prediction or inter prediction using at most one motion vector and reference index to predict the sample values of each block. An intra (I) slice is decoded using intra prediction only.

A CTU can be partitioned into multiple non-overlapped coding units (CUs) using the recursive quadtree (QT) structure to adapt to various local motion and texture characteristics. A CTU may also be partitioned into one or multiple smaller size CUs by a quadtree with nested multi-type tree using binary and ternary split. The resulting CU partitions can be in square or rectangular shapes.

One or more prediction units (PU) are specified for each CU. The prediction unit, together with the associated CU syntax, works as a basic unit for signaling the predictor information. The specified prediction process is employed to predict the values of the associated pixel samples inside the PU. A CU can be further partitioned using the residual quadtree (RQT) structure for representing the associated prediction residual signal. The leaf nodes of the RQT correspond to the transform units (TUs). A transform unit is comprised of a transform block (TB) of luma samples of size 8×8, 16×16, or 32×32 or four transform blocks of luma samples of size 4×4, and two corresponding transform blocks of chroma samples of a picture in 4:2:0 color format. An integer transform is applied to a transform block and the level values of quantized coefficients together with other side information are entropy coded in the bitstream.

The terms coding tree block (CTB), coding block (CB), prediction block (PB), and transform block (TB) are defined to specify the 2-D sample array of one color component associated with CTU, CU, PU, and TU, respectively. Thus, a CTU consists of one luma CTB, two chroma CTBs, and associated syntax elements. A similar relationship is valid for CU, PU, and TU. The tree partitioning is generally applied simultaneously to both luma and chroma, although exceptions apply when certain minimum sizes are reached for chroma.

SUMMARY

Some embodiments of the disclosure provide a method for specifying layout of subpictures in video pictures. A video decoder receives data from a bitstream to be decoded as a current picture of a video. For a current subpicture of a set of subpictures of the current picture, the video decoder determines a position of the current subpicture based on a width of the current picture and a previously determined width of a particular subpicture in the set of subpictures. The video decoder reconstructs the current picture and the current subpicture based on the determined position.

The decoder determines a position of the current subpicture based on a size (width or height) of the current picture and a previously determined size (width or height) of a particular subpicture in the set of subpictures. The size of the current subpicture is inferred and not signaled in the bitstream. The decoder may determine the horizontal or x-position of the current subpicture based on the width of the current picture and a previously determined width of the particular subpicture.

The position of the current subpicture may be determined based on the width of the current subpicture, and the width of the current subpicture may be determined based on the width of the particular subpicture in the set of subpictures and a width of the current picture. In some embodiments, the width of the current subpicture may be determined by subtracting from the width of the current picture, widths of all subpictures in the set of subpictures except the current subpicture.

In some embodiments, the determined position of the subpicture is expressed as an index of a coded tree block (CTB) at a corner of the current subpicture, and the width of the particular picture is expressed in terms of a number of coded tree bocks (CTBs).

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. Any variations, derivatives and/or extensions based on teachings described herein are within the protective scope of the present disclosure. In some instances, well-known methods, procedures, components, and/or circuitry pertaining to one or more example implementations disclosed herein may be described at a relatively high level without detail, in order to avoid unnecessarily obscuring aspects of teachings of the present disclosure.

I. Signaling Picture Order Count in Picture Header

In coded video, the picture header (PH) of a picture may be used as the start of the picture. Unlike a picture parameter set (PPS) that store information common to several pictures that refers to the PPS, a picture header of a picture store information unique to the picture. The picture header of a picture may store parameters of the picture that remain the same for different slices of the picture. Table 1 shows a picture header.

In some embodiments, the sequence parameter set (SPS) includes a syntax element sps_ph_repetition_enabled_flag that is a flag for enabling picture header repetition. Table 2 shows a SPS that includes a flag for enabling picture header repetition.

In some embodiments, a flag for enabling picture header repetition is present as a syntax element in general constraint info (GCI) in the bitstream. Table 3 shows a GCI that includes a flag no_ph_repetition_constraint_flag for allowing picture header repetition.

The value of syntax element no_ph_repetition_constraint_flag being equal to 1 indicates that there is no picture header repetitions present in OlsInScope and the value of sps_ph_repetition_enabled_flag is constrained to be 0. The value of no_ph_repetition_constraint_flag being equal to 0 does not impose such a constraint.

The value of the syntax element sps_ph_repetition_enabled_flag being equal to 1 specifies that picture header repetitions may be present in CLVSs for pictures associated to the PHs and referring to the SPS. The value of sps_ph_repetition_enabled_flag being equal to 0 specifies that picture header repetitions are not present in CLVSs for pictures referring to the SPS. The sps_ph_repetition_enabled_flag flag may be used as a general picture header repetition feature enabler for pictures in CLVSs, or furtherly as a gate signal to control the actual feature presence in CLVSs. Table 4 shows a picture header that use the SPS picture header repetition enable flag (sps_ph_repetition_enabled_flag).

In some embodiments, the picture order count of the picture is specified in the picture header of the picture. Picture order count of a picture may be used to encode or decode the picture, e.g., for creating interpolated or extrapolated motion vectors for merge candidates for inter prediction. The picture order count may also be used as the identifier of the picture when the picture header is repeated as a loss detection mechanism.

The syntax element ph_pic_order_cnt_Isb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the syntax element ph_pic_order_cnt_Isb is log 2_max_pic_order_cnt_Isb_minus4+4 bits. The value of ph_pic_order_cnt_Isb is constrained to be in the range of 0 to MaxPicOrderCntLsb−1, inclusive. In some embodiments, the value of ph_pic_order_cnt_Isb is the same in all repetitive picture headers.

In some embodiments, each slice of a picture has a syntax element slice_pic_order_cnt_Isb for indicating the picture order count of the picture. The first slice with slice_pic_order_cnt_Isb having same value equal to ph_pic_order_cnt_Isb of the first picture header is the first slice of the picture associated with the picture header. In some embodiments, when present, the value of the slice header syntax element slice_pic_order_cnt_Isb is the same in all slice headers of a coded picture. Table 5 shows a slice header having the syntax element slice_pic_order_cnt_Isb.

The variable CuQpDeltaVal, specifying the difference between a luma quantization parameter for the coding unit containing cu_qp_delta_abs and its prediction, is set equal to 0. The variables CuQpOffsetb, CuQpOffsetCr, and CuQpOffsetCbCr, specifying values to be used when determining the respective values of the Qp′Cb, Qp′Cr, and Qp′CbCrquantization parameters for the coding unit containing cu_chroma_qp_offset_flag, are all set equal to 0.

In some embodiments, when ph_pic_order_cnt_Isb is not present, the syntax element slice_pic_order_cnt_Isb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the slice_pic_order_cnt_Isb syntax element is log 2_max_pic_order_cnt_Isb_minus4+4 bits. The value of the slice_pic_order_cnt_Isb shall be in the range of 0 to MaxPicOrderCntLsb−1, inclusive. When ph_pic_order_cnt_Isb is present, slice_pic_order_cnt_Isb shall be equal to ph_pic_order_cnt_Isb for the slices associated with the picture header.

In some embodiments, when the current picture is a gradual decoding refresh (GDR) picture, the variable RpPicOrderCntVal is derived according to RpPicOrderCntVal=PicOrderCntVal+recovery_poc_cnt.

In some embodiments, the SPS picture header repetition enable flag is used to determine whether to signal a picture header repetition enable flag at the picture level. Table 6 shows a picture header in which the SPS picture header repetition enable flag is used to determine whether to signal a picture header repetition enable flag.

The syntax element ph_repetition_present_flag being equal to 1 specifies that ph_pic_order_cnt_Isb is present for the coded picture associated with the picture header. The picture header repetition may or may not occur for the coded picture associated with the picture header. The syntax element ph_repetition_flag being equal to 0 specifies that ph_pic_order_cnt_Isb is not present.

II. Signaling Subpicture and Slice Layout

A subpicture is a secondary or subsidiary picture or frame of a main video picture, or defined as a rectangular region in a picture. A subpicture may display images, video, texts, or other types of data that are separately coded from the video data of the main video picture. Multiple subpictures may be associated with a video picture, and the associated subpictures are positioned within the picture according to a layout. In some embodiments, rectangular slices may form subpictures that may be used to support sub-bitstream extraction, spatial random access, and bitstream editing etc. The subpicture layout may be specified in a sequence parameter set (SPS) of a sequence that includes the video picture. Table 7 below is an example syntax table for SPS that includes specification for subpicture layout.

In some embodiments, slice layout information of a video picture is signaled in a picture parameter set (PPS) of the video picture. A video picture in a slice-in-tile case is a video picture in which tiles are partitioned into slices. In some embodiments, for rectangular slices in the slice-in-tile picture, the layout of the slices is also specified in the PPS applicable to the picture. When the slice size is equal to the tile size, only the slice height in units of CTU is signaled since the width is the tile width. Table 8 below is an example syntax table for PPS that includes tile and slice syntax structure, for both uniform and non-uniform tile columns and rows for the slice layout specification.

Some embodiments of the disclosure provide a method to improve the signaling for the subpicture layout in the SPS at a video coder (encoder or decoder). In some embodiments, for signaling the subpicture layout in the SPS, the video coder may infer the size information when there is only one subpicture in the picture. When no subpicture is signaled or where there is only one subpicture within a picture, the picture is the subpicture with known position and size information. In some embodiments, the video coder may infer the top-left position for the first subpicture and infer the last subpicture position when there are more than one subpicture in the picture. The top-left position for the first subpicture is [0, 0] and the last subpicture is the right and bottom area of the picture. Table 9 shows modified SPS syntax for specifying subpicture layout.

In other words, when two or more subpictures are coded in the current picture, a size (e.g., width indicated by subpic_width_minus1 or height indicated by subpic_height_minus1) of the first subpicture (i=0) of the current picture are specified in the bitstream, but a position (e.g., top-left position indicated by subpic_ctu_top_left) of the first subpicture, a position and a size of the last subpicture (i=sps_num_subpics_minus1) are not specified in the bitstream. As for each subpicture other than the first and last subpicture (e.g., the second subpicture), both size and position of the subpicture are specified in the bitstream. In some embodiments, the position of the first subpicture, the position and the size of the last subpicture of the current picture are inferred by the video encoder or decoder and not signaled in the bitstream. When there is only one subpicture in the current picture, a position and a size of the only subpicture of the current picture are inferred by the video encoder or decoder and not signaled in the bitstream.

The syntax element subpic_ctu_top_left_x[i] specifies horizontal position of top left CTU of i-th subpicture in unit of CtbSizeY The length of the syntax element is Ceil(Log 2(pic_width_max_in_luma_samples÷CtbSizeY)) bits. When sps_num_subpics_minus1 is greater than 0 (i.e., there are multiple subpictures in the current picture), for i equal to sps_num_subpics_minus1, the value of subpic_width_minus1[i] is derived as follows:

The syntax element subpic_ctu_top_left_y[i] specifies vertical position of top left CTU of i-th subpicture in unit of CtbSizeY The length of the syntax element is Ceil(Log 2(pic_height_max_in_luma_samples÷CtbSizeY)) bits. When sps_num_subpics_minus1 is greater than 0, for i equal to sps_num_subpics_minus1, the value of subpic_height_minus1[i] is derived as follows.

The syntax element subpic_width_minus1[i] plus 1 specifies the width of the i-th subpicture in units of CtbSizeY The length of the syntax element is Ceil(Log 2(pic_width_max_in_luma_samples CtbSizeY)) bits. For i equal to sps_num_subpics_minus1, when sps_num_subpics_minus1 is greater than 0, the value of subpic_width_minus1[i], is derived as follows. Otherwise, the value of subpic_width_minus1[i], when not present, is inferred to be equal to Ceil(pic_width_max_in_luma_samples CtbSizeY)−1.

The syntax element subpic_height_minus1[i] plus 1 specifies the height of the i-th subpicture in units of CtbSizeY The length of the syntax element is Ceil(Log 2(pic_height_max_in_luma_samples÷CtbSizeY)) bits. When sps_num_subpics_minus1 is greater than 0, for i equal to sps_num_subpics_minus1, the value of subpic_height_minus1[i] is derived as follows. Otherwise when not present, the value of subpic_height_minus1[i] is inferred to be equal to Ceil(pic_height_max_in_luma_samples÷CtbSizeY)−1.

In some embodiments, the above two loop processing steps may be modified according to the following:

For some embodiments,FIG.1conceptually illustrates determining the position of a subpicture of a current picture100when there are multiple subpictures in the current picture100. As illustrated, the current picture100includes multiple subpictures111-199that are arranged in one or more rows and one or more columns. When encoding or decoding the current picture100, the positions and the sizes (widths and heights) of the subpictures111-199are determined in sequence. The position and the size of the subpicture111is determined first, and the position and the size of the subpicture199is determined last.

The subpicture111corresponds to the first index (i=0) and the subpicture199correspond to the last index (i=sps_num_subpics_minus1). The position of subpicture111is not signaled in the bitstream but inferred based on the top-left corner of the current picture at (0, 0). The size and position of the subpicture199are not signaled in the bitstream but inferred by the encoder or decoder according to the following.

The x-position (horizontal position) of the subpicture199is determined based on the width of the current picture and previously determined width or widths of the other subpictures in the current picture. Specifically, the position of the subpicture199is determined based on a width of the subpicture199. The width of the subpicture199is determined based on the width of the other subpictures (e.g., the first subpicture191in a same row direction as the last subpicture199), and the width of the current picture100(pic_width_max_in_luma_samples). In some embodiments, the width of the subpicture199is determined by subtracting the widths of the subpictures191-198from the width of the current picture100.

The y-position (vertical position) of the subpicture199is determined based on the height of the current picture and previously determined height or heights of the other subpictures in the current picture. Specifically, the position of the subpicture199is determined based on a height of the subpicture119. The height of the subpicture199is determined based on the height of the other subpictures (e.g., the first subpicture119in a same column direction as the last subpicture199), and the height of the current picture100(pic_height_max_in_luma_samples). In some embodiments, the height of the subpicture199is determined by subtracting the heights of the subpictures119-198from the height of the current picture100.

In some embodiments, the determined position of a subpicture is expressed as an index of a coded tree block (CTB) at a corner (e.g., top-left corner) of that subpicture. The width and height of the current picture is expressed in terms of a number of coded tree bocks (CTBs).

III. Signaling Raster Scan Slice and Tile Layout

Slices may be tile-based or non-tile based. Non-tile slices are slices in a picture that is not partitioned into tiles such that the slices are not bound by tile boundaries. Tile slices are slices in a picture that is partitioned into tiles such that the slices are bound by tile boundaries. A raster scan slice is a slice defined by a sequence of CTUs in raster scan order, and therefore may not be rectangular.

For tile-based raster scan slices, tile partitioning is used as an intermediate data grouping layer for specifying slices. However, some coding tools may not be allowed across tile partition boundaries (e.g., spatial merge mode, affine merge mode, intra-prediction, etc.) such that the coding efficiency to some extent may be decreased. It may be advantageous for some applications to use a reasonable number of tile partitions or no tile partitions.

In some embodiments, tile partitioning for the raster scan slice is optional while the slice partition is specified in units of CTU. In some embodiments, a syntax element no_pic_partition_flag being equal to 1 specifies that no picture partitioning is applied to each picture referring to the PPS. This may imply that there is only a single tile or there is no tile partitioning in the picture. The tile partition parameters, though not present, may be inferred based on a set of inference rules. This is referred to as the slice-in-picture case. In some embodiments, in the slice-in-picture case, the slice is specified in units of CTUs based on raster scan.

FIG.2illustrates slices in a video picture200having only one tile or no tile partition, or the slice-in-pictrue case. The video picture200can be regarded as having only one tile or no tile partitioning at all, and the slices within are non-tile based slices. As illustrated, the layout of the slices are limited by boundaries of the picture and not of any tiles, such that the slices are considered to be partitions of a picture rather than partitions of a tile. The slice in the video picture200are specified in units of CTUs in raster scan.

In some embodiments, when the current picture is partitioned into multiple non-tile based raster scan slices (or non-rectangular slices), whether multiple slices are coded in the current picture (slice-in-picture case) is specified in the bitstream. When the current picture is partitioned into multiple non-tile based raster scan slices and multiple slices are coded in the current picture, the size of a slice is specified in terms of CTUs. Specifically, the number of CTUs in a slice is specified in the bitstream. Tables 10A and 10B respectively show a PPS and a slice header for the slice-in-picture case.

The value of the syntax element subpics_present_flag being 1 specifies that one or more subpictures are present in each coded picture in the coded layer-wise video sequence (CLVS) and subpicture parameters are present in in the SPS raw byte sequence payload (RBSP) syntax. The value of subpics_present_flag being equal to 0 specifies that no subpictures are present in each coded picture in the CLVS and subpicture parameters are not present in the SPS RBSP syntax. In some embodiments, when a bitstream is the result of a sub-bitstream extraction process and the bitstream contains only a subset of the subpictures of the input bitstream to the sub-bitstream extraction process, the value of subpics_present_flag is set to 1 in the RBSP of the SPSs. When subpics_present_flag is equal to 0, each coded picture in the CLVS may be considered as a subpicture in a bitstream extraction and merging process.

The value of the syntax element sps_num_subpics_minus1 plus 1 specifies the number of subpictures. The range of sps_num_subpics_minus1 is constrained to be 0 to 254 in some embodiments. When not present, the value of sps_num_subpics_minus1 is inferred to be equal to 0. The value of sps_num_subpics_minus1 being equal to 0 indicates that each coded picture in the CLVS is the subpicture.

The value of the syntax element rect_slice_flag equal to 0 specifies that tiles or CTUs within each slice are in raster scan order and the slice information is not signalled in PPS. The value of rect_slice_flag being equal to 1 specifies that tiles or CTUs within each slice cover a rectangular region of the picture and the slice information is signaled in the PPS. When not present, rect_slice_flag is inferred to be equal to 1. When subpics_present_flag is equal to 1, the value of rect_slice_flag is inferred to be equal to 1. When raster_scan_slice_in_pic_enabled_flag is equal to 1, the value of rect_slice_flag is inferred to be equal to 0.

The value of the syntax element no_pic_partition_flag being equal to 1 specifies that tile partitioning is not applied to pictures that refer to the PPS. The value of no_pic_partition_flag being equal to 0 specifies that each picture referring to the PPS may be partitioned into more than one tile or slice.

The value of the syntax element raster_scan_slice_in_pic_enabled_flag being equal to 0 specifies that no raster scan slice partitioning is applied to each picture referring to the PPS. The value of raster_scan_slice_in_pic_enabled_flag being equal to 1 specifies that, when no_pic_partition_flag is equal to 1, each picture referring to the PPS may be partitioned into more than one raster scan slice. When not present, the value of raster_scan_slice_in_pic_enabled_flag is inferred to be equal to 0.

The value of the syntax element single_slice_per_subpic_flag being equal to 1 specifies that each subpicture includes one and only one rectangular slice. The value of single_slice_per_subpic_flag being 0 specifies that each subpicture may consist one or more rectangular slices. When single_slice_per_subpic_flag is equal to 1, num_slices_in_pic_minus1 is inferred to be equal to sps_num_subpics_minus1. When single_slice_per_subpic_flag is equal to 1 and sps_num_subpics_minus1 is equal to 0, num_slices_in_pic_minus1 is inferred to be equal to 0 (i.e. the current picture is the subpicture and includes only one rectangular slice).

The value of the syntax element slices_in_pic_present_flag being equal to 1 specifies that multiple slices are present in the current picture. The value of slices_in_pic_present_flag equal to 0 specifies no multiple slices is present in the current picture. When not present, slices_in_pic_present_flag is inferred to be equal to 0.

The value of the syntax element num_ctus_in_slice_minus1 plus 1 specifies the number of CTUs in the current slice. When slices_in_pic_present_flag is equal to 1, the value of num_ctus_in_slice_minus1 in constrained to be in the range of 0 to PicSizeInCtbsY−1, inclusive. When not present, num_ctus_in_slice_minus1 is inferred to be equal to PicSizeInCtbsY−1.

The syntax element slice_address specifies the slice address of the slice. When not present, the value of slice_address is inferred to be 0.

If slices_in_pic_present_flag is equal to 1, the following applies:The slice address is the first CTB in the slice, in CTB raster scan of a picture.The length of slice_address is Ceil(Log 2 (PicSizeInCtbsY)) bits.The value of slice_address shall be in the range of 0 to PicSizeInCtbsY−1, inclusive, and the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.

Otherwise, if rect_slice_flag is equal to 0, the following applies:The slice address is the raster scan tile index.The length of slice_address is Ceil(Log 2 (NumTilesInPic)) bits.The value of slice_address shall be in the range of 0 to NumTilesInPic−1, inclusive.

Otherwise (rect_slice_flag is equal to 1), the following applies:The slice address is the slice index of the slice within the SubPicIdx-th subpicture.The length of slice_address is Ceil(Log 2(NumSlicesInSubpic[SubPicIdx])) bits.The value of slice_address shall be in the range of 0 to NumSlicesInSubpic[SubPicIdx]−1, inclusive.

In some embodiments, for bitstream conformance, the following constraints apply:If rect_slice_flag is equal to 0 or subpics_present_flag is equal to 0, the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.Otherwise, the pair of slice_subpic_id and slice_address values shall not be equal to the pair of slice_subpic_id and slice_address values of any other coded slice NAL unit of the same coded picture.When rect_slice_flag is equal to 0, the slices of a picture shall be in increasing order of their slice_address values.The shapes of the slices of a picture shall be such that each CTU, when decoded, shall have its entire left boundary and entire top boundary consisting of a picture boundary or consisting of boundaries of previously decoded CTU(s).

The value of the syntax element num_tiles_in_slice_minus1 plus 1, when present, specifies the number of tiles in the slice. The value of num_tiles_in_slice_minus1 shall be in the range of 0 to NumTilesInPic−1, inclusive.

The variable NumCtuInCurrSlice, which specifies the number of CTUs in the current slice, and the list CtbAddrInCurrSlice[i], for i ranging from 0 to NumCtuInCurrSlice−1, inclusive, specifying the picture raster scan address of the i-th CTB within the slice, are derived as follows:

In some embodiments, the slice-in-tile case for the raster scan slice is allowed, and the slice may or may not be rectangular. In some embodiments, a syntax element no_pic_partition_flag being equal to 0 specifies that each picture referring to the PPS may be partitioned into more than one tile or slice. In some embodiments, for raster scan slice-in-tile cases, each slice is specified in units of CTUs in raster scan within a tile.

FIG.3illustrates slices in a video picture300having slices in tiles in raster scan (or raster scan slice-in-tile case.) The video picture300has two tiles311and312that are separated by a tile boundary. Each tile includes slices in raster scan that are limited by tile boundaries, such as non-rectangular slices321and322in tile311, and non-rectangular slice323in tile312. In some embodiments, when the current picture is partitioned into non-rectangular slices (or raster scan slices), whether multiple slices are coded in a tile is specified in the bitstream. When multiple slices are coded in a tile, the number of CTUs in a slice is specified in the bitstream. Table 11 show slice header syntax for the raster scan slice-in-tile case.

The value of the syntax element slices_in_tile_present_flag being equal to 1 specifies that the multiple slices are present in the tile. The value of slices_in_tile_present_flag being equal to 0 specifies that no multiple slices is present in the current tile. When not present, slices_in_tile_present_flag is inferred to be equal to 0.

The value of the syntax element num_ctus_in_slice_minus1 plus 1 specifies the number of CTUs in the current slice. When the value of slices_in_tile_present_flag is equal to 1, the value of num_ctus_in_slice_minus1 shall be in the range of 0 to TileSizeInCtbsY−1, inclusive, where TileSizeInCtbsY=RowHeight[tileY] *RowWidth[tileX], tileX is the tile column index containing the current slice, and tileY is the tile row index containing the current slice. When not present, num_ctus_in_slice_minus1 is inferred to be equal to PicSizeInCtbsY−1.

The value of the syntax element slice_address specifies the slice address of the slice. When not present, the value of slice_address is inferred to be equal to 0.

If slices_in_tile_present_flag is equal to 1, the following applies:The slice address is the first CTB in the slice, in CTB raster scan of a picture.The length of slice_address is Ceil(Log 2 (TileSizeInCtbsY)) bits.The value of slice_address shall be in the range of 0 to TileSizeInCtbsY−1, inclusive, and the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.

Otherwise, if rect_slice_flag is equal to 0, the following applies:The slice address is the raster scan tile index.The length of slice_address is Ceil(Log 2 (NumTilesInPic)) bits.The value of slice_address shall be in the range of 0 to NumTilesInPic−1, inclusive.

Otherwise (rect_slice_flag is equal to 1), the following applies:The slice address is the slice index of the slice within the SubPicIdx-th subpicture.The length of slice_address is Ceil(Log 2(NumSlicesInSubpic[SubPicIdx])) bits.The value of slice_address shall be in the range of 0 to NumSlicesInSubpic[SubPicIdx]−1, inclusive.

In some embodiments, for bitstream conformance, the following constraints apply:If rect_slice_flag is equal to 0 or subpics_present_flag is equal to 0, the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.Otherwise, the pair of slice_subpic_id and slice_address values shall not be equal to the pair of slice_subpic_id and slice_address values of any other coded slice NAL unit of the same coded picture.When rect_slice_flag is equal to 0, the slices of a picture shall be in increasing order of their slice_address values.The shapes of the slices of a picture shall be such that each CTU, when decoded, shall have its entire left boundary and entire top boundary consisting of a picture boundary or consisting of boundaries of previously decoded CTU(s).

The value of the syntax element num_tiles_in_slice_minus1 plus 1, when present, specifies the number of tiles in the slice. The value of num_tiles_in_slice_minus1 shall be in the range of 0 to NumTilesInPic−1, inclusive.

The variable NumCtuInCurrSlice, which specifies the number of CTUs in the current slice, and the list CtbAddrInCurrSlice[i], for i ranging from 0 to NumCtuInCurrSlice−1, inclusive, specifying the picture raster scan address of the i-th CTB within the slice, are derived as follows:

In some embodiments, raster scan slices in units of CTU may be based on subpictures. Table 12 illustrates a PPS that includes syntax elements related to subpicture-based slices. Table 13 illustrates a slice header that includes syntax elements related to subpicture-based slices.

The syntax element subpics_present_flag being equal to 1 specifies that one or more subpictures are present in each coded picture in the CLVS and subpicture parameters are present in in the SPS RBSP syntax. The syntax element subpics_present_flag being equal to 0 specifies that no subpictures are present in each coded picture in the CLVS and subpicture parameters are not present in the SPS RBSP syntax. In some embodiments, when a bitstream is the result of a sub-bitstream extraction process and contains only a subset of the subpictures of the input bitstream to the sub-bitstream extraction process, the value of subpics_present_flag is set equal to 1 in the RBSP of the SPSs. When subpics_present_flag is equal to 0, each coded picture in the CLVS may be considered as a subpicture in a bitstream extraction and merging process.

The syntax element rect_slice_flag being equal to 0 specifies that tiles or CTUs within each slice are in raster scan order and the slice information is not signaled in PPS. The value of rect_slice_flag being equal to 1 specifies that tiles or CTUs within each slice cover a rectangular region of the picture and the slice information is signalled in the PPS. When not present, rect_slice_flag is inferred to be equal to 1. When subpics_present_flag is equal to 1, the value of rect_slice_flag shall be equal to 1. When raster_scan_slice_in_pic_enabled_flag is equal to 1, the value of rect_slice_flag is inferred to be equal to 0.

The syntax element no_pic_partition_flag being equal to 1 specifies that no picture tile partitioning is applied to the picture(s) that refer to the PPS. The value of no_pic_partition_flag being equal to 0 specifies that the picture(s) referring to the PPS may be partitioned into more than one tile or slice.

The syntax element raster_scan_slice_in_pic_enabled_flag being equal to 0 specifies that no raster scan slice partitioning is applied to the picture(s) that refer to the PPS. raster_scan_slice_in_pic_enabled_flag equal to 1 specifies that, when no_pic_partition_flag is equal to 1, each picture referring to the PPS may be partitioned into more then one raster scan slice, and when subpics_present_flag is equal to 1, one or more subpictures in each picture referring to the PPS may be partitioned into more than one raster scan slice. When not present, the value of raster_scan_slice_in_pic_enabled_flag is inferred to be equal to 0.

The syntax element single_slice_per_subpic_flag being equal to 1 specifies that each subpicture consists of one and only one rectangular slice. The value of single_slice_per_subpic_flag being equal to 0 specifies that each subpicture may consist one or more rectangular slices. When single_slice_per_subpic_flag is equal to 1, num_slices_in_pic_minus1 is inferred to be equal to sps_num_subpics_minus1. When single_slice_per_subpic_flag is equal to 1 and sps_num_subpics_minus1 is equal to 0, num_slices_in_pic_minus1 is inferred to be equal to 0 (i.e. the current picture is the subpicture and consists only one rectangular slice).

The syntax element slices_in_pic_present_flag being equal to 1 specifies that multiple slices are present in the current picture. The value of slices_in_pic_present_flag equal to 0 specifies no multiple slices is present in the current picture. When not present, the value of slices_in_pic_present_flag is inferred to be equal to 0.

The syntax element num_ctus_in_slice_minus1 plus 1 specifies the number of CTUs in the current slice. When slices_in_pic_present_flag is equal to 1, the value of num_ctus_in_slice_minus1 shall be in the range of 0 to PicSizeInCtbsY−1, inclusive. When not present, the value of num_ctus_in_slice_minus1 is inferred to be equal to PicSizeInCtbsY−1.

The syntax element slice_address specifies the slice address of the slice. When not present, the value of slice_address is inferred to be equal to 0. In some embodiments, If slices_in_pic_present_flag is equal to 1, and subpics_present_flag is equal to 1, the following applies:The slice address is the first CTB in the slice, in CTB raster scan of a subpicture.The length of slice_address is Ceil(Log 2 (PicSizeInCtbsY)) bits.The value of slice_address shall be in the range of 0 to PicSizeInCtbsY−1, inclusive, and the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded subpicture.

Otherwise, if slices_in_pic_present_flag is equal to 1, and subpics_present_flag is equal to 0, the following applies:The slice address is the first CTB in the slice, in CTB raster scan of a picture.The length of slice_address is Ceil(Log 2 (PicSizeInCtbsY)) bits.The value of slice_address shall be in the range of 0 to PicSizeInCtbsY−1, inclusive, and the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.

Otherwise, if rect_slice_flag is equal to 0, the following applies:The slice address is the raster scan tile index.The length of slice_address is Ceil(Log 2 (NumTilesInPic)) bits.The value of slice_address shall be in the range of 0 to NumTilesInPic−1, inclusive

Otherwise (rect_slice_flag is equal to 1), the following applies:The slice address is the slice index of the slice within the SubPicIdx-th subpicture.The length of slice_address is Ceil(Log 2(NumSlicesInSubpic[SubPicIdx])) bits.The value of slice_address shall be in the range of 0 to NumSlicesInSubpic[SubPicIdx]−1, inclusive

It is a requirement of bitstream conformance that the following constraints apply:If rect_slice_flag is equal to 0 or subpics_present_flag is equal to 0, the value of slice_address shall not be equal to the value of slice_address of any other coded slice NAL unit of the same coded picture.Otherwise, the pair of slice_subpic_id and slice_address values shall not be equal to the pair of slice_subpic_id and slice_address values of any other coded slice NAL unit of the same coded picture.When rect_slice_flag is equal to 0, the slices of a picture shall be in increasing order of their slice_address values.The shapes of the slices of a picture shall be such that each CTU, when decoded, shall have its entire left boundary and entire top boundary consisting of a picture boundary or consisting of boundaries of previously decoded CTU(s).

The syntax element num_tiles_in_slice_minus1 plus 1, when present, specifies the number of tiles in the slice. The value of num_tiles_in_slice_minus1 shall be in the range of 0 to NumTilesInPic−1, inclusive.

The variable NumCtuInCurrSlice, which specifies the number of CTUs in the current slice, and the list CtbAddrInCurrSlice[i], for i ranging from 0 to NumCtuInCurrSlice−1, inclusive, specifying the picture raster scan address of the i-th CTB within the slice, are derived as follows:

The foregoing proposed method can be implemented in encoders and/or decoders. For example, the proposed method can be implemented in a header parsing module of an encoder, and/or a header parsing module of a decoder. Video encoders have to follow the foregoing syntax design so as to generate the legal bitstream, and video decoders are able to decode the bitstream correctly only if the parsing process is complied with the foregoing syntax design. When the syntax is skipped in the bitstream, encoders and decoders should set the syntax value as the inferred value to guarantee the encoding and decoding results are matched.

V. Example Video Encoder

FIG.4illustrates an example video encoder400. As illustrated, the video encoder400receives input video signal from a video source405and encodes the signal into bitstream495. The video encoder400has several components or modules for encoding the signal from the video source405, at least including some components selected from a transform module410, a quantization module411, an inverse quantization module414, an inverse transform module415, an intra-picture estimation module420, an intra-prediction module425, a motion compensation module430, a motion estimation module435, an in-loop filter445, a reconstructed picture buffer450, a MV buffer465, and a MV prediction module475, and an entropy encoder490. The motion compensation module430and the motion estimation module435are part of an inter-prediction module440.

In some embodiments, the modules410-490are modules of software instructions being executed by one or more processing units (e.g., a processor) of a computing device or electronic apparatus. In some embodiments, the modules410-490are modules of hardware circuits implemented by one or more integrated circuits (ICs) of an electronic apparatus. Though the modules410-490are illustrated as being separate modules, some of the modules can be combined into a single module.

The video source405provides a raw video signal that presents pixel data of each video frame without compression. A subtractor408computes the difference between the raw video pixel data of the video source405and the predicted pixel data413from the motion compensation module430or intra-prediction module425. The transform module410converts the difference (or the residual pixel data or residual signal409) into transform coefficients (e.g., by performing Discrete Cosine Transform, or DCT). The quantization module411quantizes the transform coefficients into quantized data (or quantized coefficients)412, which is encoded into the bitstream495by the entropy encoder490.

The inverse quantization module414de-quantizes the quantized data (or quantized coefficients)412to obtain transform coefficients, and the inverse transform module415performs inverse transform on the transform coefficients to produce reconstructed residual419. The reconstructed residual419is added with the predicted pixel data413to produce reconstructed pixel data417. In some embodiments, the reconstructed pixel data417is temporarily stored in a line buffer (not illustrated) for intra-picture prediction and spatial MV prediction. The reconstructed pixels are filtered by the in-loop filter445and stored in the reconstructed picture buffer450. In some embodiments, the reconstructed picture buffer450is a storage external to the video encoder400. In some embodiments, the reconstructed picture buffer450is a storage internal to the video encoder400.

The intra-picture estimation module420performs intra-prediction based on the reconstructed pixel data417to produce intra prediction data. The intra-prediction data is provided to the entropy encoder490to be encoded into bitstream495. The intra-prediction data is also used by the intra-prediction module425to produce the predicted pixel data413.

The motion estimation module435performs inter-prediction by producing MVs to reference pixel data of previously decoded frames stored in the reconstructed picture buffer450. These MVs are provided to the motion compensation module430to produce predicted pixel data.

Instead of encoding the complete actual MVs in the bitstream, the video encoder400uses MV prediction to generate predicted MVs, and the difference between the MVs used for motion compensation and the predicted MVs is encoded as residual motion data and stored in the bitstream495.

The MV prediction module475generates the predicted MVs based on reference MVs that were generated for encoding previously video frames, i.e., the motion compensation MVs that were used to perform motion compensation. The MV prediction module475retrieves reference MVs from previous video frames from the MV buffer465. The video encoder400stores the MVs generated for the current video frame in the MV buffer465as reference MVs for generating predicted MVs.

The MV prediction module475uses the reference MVs to create the predicted MVs. The predicted MVs can be computed by spatial MV prediction or temporal MV prediction. The difference between the predicted MVs and the motion compensation MVs (MC MVs) of the current frame (residual motion data) are encoded into the bitstream495by the entropy encoder490.

The entropy encoder490encodes various parameters and data into the bitstream495by using entropy-coding techniques such as context-adaptive binary arithmetic coding (CABAC) or Huffman encoding. The entropy encoder490encodes various header elements, flags, along with the quantized transform coefficients412, and the residual motion data as syntax elements into the bitstream495. The bitstream495is in turn stored in a storage device or transmitted to a decoder over a communications medium such as a network.

The in-loop filter445performs filtering or smoothing operations on the reconstructed pixel data417to reduce the artifacts of coding, particularly at boundaries of pixel blocks. In some embodiments, the filtering operation performed includes sample adaptive offset (SAO). In some embodiment, the filtering operations include adaptive loop filter (ALF).

FIG.5illustrates portions of the video encoder400that implements specification of subpicture layout, slice structure, and picture identification. Specifically, a picture partition engine510generates a set of picture partitioning specifications520for the entropy encoder490based on a set of hardware and rate/distortion information515. These picture partitioning specifications520include slice layout information, subpicture layout information, and slice layout information. The picture partition engine may infer the sizes and the positions of some of the subpictures by referencing widths and positions of other subpictures as described in Section II andFIG.1above.

The entropy encoder490correspondingly signals flags or parameters such as positions and sizes of subpictures (with positions and sizes of some subpicture(s) inferred and not signaled), slice-in-tile or slice-in-picture indications, raster scan slice or rectangular slice indications in SPSs, PPSs, or slice headers of the bitstream495. The entropy encoder490may further signal picture order counts and picture header repeat indications in picture headers in the bitstream495. The picture partition engine510also provide corresponding picture partitioning layout530to the transform module410, intra-picture estimation module420, Intra-picture prediction module425, inter-prediction module440, etc., so these modules may encode the current picture according to the subpicture, tile, and slice layout.

FIG.6conceptually illustrates a process600for determining sizes (widths and/or heights) and positions of subpictures in a picture. In some embodiments, one or more processing units (e.g., a processor) of a computing device implements the encoder400performs the process600by executing instructions stored in a computer readable medium. In some embodiments, an electronic apparatus implementing the encoder400performs the process600.

The encoder receives (at block610) raw pixel data to be encoded as a current picture of a video. The encoder determines (at block615) whether the current picture is associated with a set of subpictures. If so, the process proceeds to block617. If the current picture is not associated with any subpicture, the process proceeds to block660.

At block617, the encoder determines whether there are multiple subpictures associated with the current picture. If so, the process proceeds to620. If there is only one subpicture associated with the current picture, the encoder determines (at block635) the size (width and/or height) and position of the only subpicture and proceeds to650.

At block620, the encoder determines whether the current subpicture is the last subpicture in the set of subpictures, i.e., when the current subpicture is processed after all other subpictures in the set of subpictures. In some embodiments, the subpictures in the set of subpictures are indexed and the current subpicture is the last indexed subpicture in the set indexed subpictures. If the current subpicture is the last picture, the process proceeds to640. If the current subpicture is not the last subpicture in the set of subpictures, the process proceeds to block630.

At block630, the encoder determines the size (width and/or height) and position of the current subpicture. The encoder may receive a specification of the size (width and/or height) of the current subpicture from the encoding configuration. The process then returns to block620to process a next subpicture as the current subpicture.

At640, the encoder determines a position of the current subpicture (the last subpicture) based on a size (width and/or height) of the current picture and a previously determined size (width and/or height) of a particular subpicture in the set of subpictures. The size of the current subpicture is inferred and not signaled in the bitstream. For example, the encoder may determine the horizontal or x-position of the current subpicture based on the width of the current picture and a previously determined width of the particular subpicture. The encoder may also determine the vertical or y-position of the current subpicture based on the height of the current picture and a previously determined height of the particular subpicture. The process then proceeds to block650.

The position of the current subpicture may be determined based on the width and/or the height of the current subpicture. The width of the current subpicture may be determined based on the width of the particular subpictures in the set of subpictures and a width of the current picture. The height of the current subpicture may be determined based on the height of the particular subpictures in the set of subpictures and a height of the current picture. In some embodiments, the width of the current subpicture may be determined by subtracting from the width of the current picture, widths of all subpictures in the row of the set of subpictures except the current subpicture; and the height of the current subpicture may be determined by subtracting from the height of the current picture, heights of all subpictures in the column of the set of subpictures except the current subpicture. In some embodiments, the determined position of the subpicture is expressed as an index of a coded tree block (CTB) at a corner of the current subpicture, and the width and/or height of the particular picture are expressed in terms of a number of coded tree bocks (CTBs).

The encoder encodes (at block650) the set of subpictures based on the determined positions and sizes of the subpictures into the bitstream. The encoder also encodes (at block660) the current picture into the bitstream.

VI. Example Video Decoder

FIG.7illustrates an example video decoder700. As illustrated, the video decoder700is an image-decoding or video-decoding circuit that receives a bitstream795and decodes the content of the bitstream into pixel data of video frames for display. The video decoder700has several components or modules for decoding the bitstream795, including some components selected from an inverse quantization module711, an inverse transform module710, an intra-prediction module725, a motion compensation module730, an in-loop filter745, a decoded picture buffer750, a MV buffer765, a MV prediction module775, and a parser790. The motion compensation module730is part of an inter-prediction module740.

In some embodiments, the modules710-790are modules of software instructions being executed by one or more processing units (e.g., a processor) of a computing device. In some embodiments, the modules710-790are modules of hardware circuits implemented by one or more ICs of an electronic apparatus. Though the modules710-790are illustrated as being separate modules, some of the modules can be combined into a single module.

The parser790(or entropy decoder) receives the bitstream795and performs initial parsing according to the syntax defined by a video-coding or image-coding standard. The parsed syntax element includes various header elements, flags, as well as quantized data (or quantized coefficients)712. The parser790parses out the various syntax elements by using entropy-coding techniques such as context-adaptive binary arithmetic coding (CABAC) or Huffman encoding.

The inverse quantization module711de-quantizes the quantized data (or quantized coefficients)712to obtain transform coefficients, and the inverse transform module710performs inverse transform on the transform coefficients716to produce reconstructed residual signal719. The reconstructed residual signal719is added with predicted pixel data713from the intra-prediction module725or the motion compensation module730to produce decoded pixel data717. The decoded pixels data are filtered by the in-loop filter745and stored in the decoded picture buffer750. In some embodiments, the decoded picture buffer750is a storage external to the video decoder700. In some embodiments, the decoded picture buffer750is a storage internal to the video decoder700.

The intra-prediction module725receives intra-prediction data from bitstream795and according to which, produces the predicted pixel data713from the decoded pixel data717stored in the decoded picture buffer750. In some embodiments, the decoded pixel data717is also stored in a line buffer (not illustrated) for intra-picture prediction and spatial MV prediction.

In some embodiments, the content of the decoded picture buffer750is used for display. A display device755either retrieves the content of the decoded picture buffer750for display directly, or retrieves the content of the decoded picture buffer to a display buffer. In some embodiments, the display device receives pixel values from the decoded picture buffer750through a pixel transport.

The motion compensation module730produces predicted pixel data713from the decoded pixel data717stored in the decoded picture buffer750according to motion compensation MVs (MC MVs). These motion compensation MVs are decoded by adding the residual motion data received from the bitstream795with predicted MVs received from the MV prediction module775.

The MV prediction module775generates the predicted MVs based on reference MVs that were generated for decoding previous video frames, e.g., the motion compensation MVs that were used to perform motion compensation. The MV prediction module775retrieves the reference MVs of previous video frames from the MV buffer765. The video decoder700stores the motion compensation MVs generated for decoding the current video frame in the MV buffer765as reference MVs for producing predicted MVs.

The in-loop filter745performs filtering or smoothing operations on the decoded pixel data717to reduce the artifacts of coding, particularly at boundaries of pixel blocks. In some embodiments, the filtering operation performed includes sample adaptive offset (SAO). In some embodiment, the filtering operations include adaptive loop filter (ALF).

FIG.8illustrates portions of the video decoder700that receives and applies specifications of subpicture layout, slice structure, and picture identification. Specifically, the entropy decoder790parses the bitstream795for syntax elements related to picture partitioning, including flags or parameters such as positions and sizes of subpictures (with positions and sizes of some subpicture(s) inferred and not signaled), slice-in-tile or slice-in-picture indications, raster scan slice or rectangular slice indications in SPSs, PPSs, or slice headers of the bitstream795. The entropy decoder790also parses picture order counts and picture header repeat indications in picture headers. Based on the parsed syntax elements, the entropy decoder790generates a set of picture partitioning information820for a picture partition engine810. The picture partition engine810provides corresponding picture partitioning layout830to the inverse transform module710, Intra-picture prediction module725, inter-prediction module740, etc., so these modules may reconstruct the current picture according to the subpicture, tile, and slice layout. The picture partition engine may also infer the sizes and the positions of some of the subpictures by referencing widths and positions of other subpictures as described in Section II andFIG.1above.

FIG.9conceptually illustrates a process900for determining sizes (width and/or height) and positions of subpictures in a picture. In some embodiments, one or more processing units (e.g., a processor) of a computing device implements the decoder700performs the process900by executing instructions stored in a computer readable medium. In some embodiments, an electronic apparatus implementing the decoder700performs the process900.

The decoder receives (at block910) data from a bitstream to be decoded as a current picture of a video. The decoder determines (at block915) whether the current picture is associated with a set of subpictures. If so, the process proceeds to block917. If the current picture is not associated with any subpicture, the process proceeds to block960.

At block917, the decoder determines whether there are multiple subpictures associated with the current picture. If so, the process proceeds to920. If the there is only one subpicture associated with the current picture, the decoder determines (at block935) the size (width and/or height) and position of the only subpicture and proceeds to950.

At block920, the decoder determines whether the current subpicture is the last subpicture in the set of subpictures, i.e., when the current subpicture is processed after all other subpictures in the set of subpictures. In some embodiments, the subpictures in the set of subpictures are indexed and the current subpicture is the last indexed subpicture in the set indexed subpictures. If the current subpicture is the last subpicture, the process proceeds to940. If the current subpicture is not the last subpicture in the set of subpictures, the process proceeds to block930.

At block930, the decoder determines the size (width and/or height) and position of the current subpicture. The decoder may receive a specification of the size (width and/or height) of the current subpicture from the bitstream. The process then returns to block920to process a next subpicture as the current subpicture.

At940, the decoder determines a position of the current subpicture (the last subpicture) based on a size (width and/or height) of the current picture and a previously determined size (width and/or height) of a particular subpicture in the set of subpictures. The size of the current subpicture is inferred and not parsed from the bitstream. For example, the decoder may determine the horizontal or x-position of the current subpicture based on the width of the current picture and a previously determined width of the particular subpictures. The decoder may also determine the vertical or y-position of the current subpicture based on the height of the current picture and a previously determined height of the particular subpictures. The process then proceeds to block950.

The position of the current subpicture may be determined based on the width and/or the height of the current subpicture. The width of the current subpicture may be determined based on the width of the particular subpictures in the set of subpictures and a width of the current picture. The height of the current subpicture may be determined based on the height of the particular subpictures in the set of subpictures. In some embodiments, the width of the current subpicture may be determined by subtracting from the width of the current picture, widths of all subpictures in the row of the set of subpictures except the current subpicture; and the height of the current subpicture may be determined by subtracting from the height of the current picture, heights of all subpictures in the column of the set of subpictures except the current subpicture. In some embodiments, the determined position of the subpicture is expressed as an index of a coded tree block (CTB) at a corner of the current subpicture, and the width and/or the height of the particular picture are expressed in terms of a number of coded tree bocks (CTBs).

The decoder reconstructs (at block950) the set of subpictures based on the determined positions and sizes of the subpictures. The decoder also reconstructs (at block960) the current picture.

In some embodiments, an encoder may signal (or generate) one or more syntax element in a bitstream, such that a decoder may parse said one or more syntax element from the bitstream.

VII. Example Electronic System

FIG.10conceptually illustrates an electronic system1000with which some embodiments of the present disclosure are implemented. The electronic system1000may be a computer (e.g., a desktop computer, personal computer, tablet computer, etc.), phone, PDA, or any other sort of electronic device. Such an electronic system includes various types of computer readable media and interfaces for various other types of computer readable media. Electronic system1000includes a bus1005, processing unit(s)1010, a graphics-processing unit (GPU)1015, a system memory1020, a network1025, a read-only memory1030, a permanent storage device1035, input devices1040, and output devices1045.

The bus1005collectively represents all system, peripheral, and chipset buses that communicatively connect the numerous internal devices of the electronic system1000. For instance, the bus1005communicatively connects the processing unit(s)1010with the GPU1015, the read-only memory1030, the system memory1020, and the permanent storage device1035.

From these various memory units, the processing unit(s)1010retrieves instructions to execute and data to process in order to execute the processes of the present disclosure. The processing unit(s) may be a single processor or a multi-core processor in different embodiments. Some instructions are passed to and executed by the GPU1015. The GPU1015can offload various computations or complement the image processing provided by the processing unit(s)1010.

The read-only-memory (ROM)1030stores static data and instructions that are used by the processing unit(s)1010and other modules of the electronic system. The permanent storage device1035, on the other hand, is a read-and-write memory device. This device is a non-volatile memory unit that stores instructions and data even when the electronic system1000is off. Some embodiments of the present disclosure use a mass-storage device (such as a magnetic or optical disk and its corresponding disk drive) as the permanent storage device1035.

Other embodiments use a removable storage device (such as a floppy disk, flash memory device, etc., and its corresponding disk drive) as the permanent storage device. Like the permanent storage device1035, the system memory1020is a read-and-write memory device. However, unlike storage device1035, the system memory1020is a volatile read-and-write memory, such a random access memory. The system memory1020stores some of the instructions and data that the processor uses at runtime. In some embodiments, processes in accordance with the present disclosure are stored in the system memory1020, the permanent storage device1035, and/or the read-only memory1030. For example, the various memory units include instructions for processing multimedia clips in accordance with some embodiments. From these various memory units, the processing unit(s)1010retrieves instructions to execute and data to process in order to execute the processes of some embodiments.

The bus1005also connects to the input and output devices1040and1045. The input devices1040enable the user to communicate information and select commands to the electronic system. The input devices1040include alphanumeric keyboards and pointing devices (also called “cursor control devices”), cameras (e.g., webcams), microphones or similar devices for receiving voice commands, etc. The output devices1045display images generated by the electronic system or otherwise output data. The output devices1045include printers and display devices, such as cathode ray tubes (CRT) or liquid crystal displays (LCD), as well as speakers or similar audio output devices. Some embodiments include devices such as a touchscreen that function as both input and output devices.

Finally, as shown inFIG.10, bus1005also couples electronic system1000to a network1025through a network adapter (not shown). In this manner, the computer can be a part of a network of computers (such as a local area network (“LAN”), a wide area network (“WAN”), or an Intranet, or a network of networks, such as the Internet. Any or all components of electronic system1000may be used in conjunction with the present disclosure.

While the present disclosure has been described with reference to numerous specific details, one of ordinary skill in the art will recognize that the present disclosure can be embodied in other specific forms without departing from the spirit of the present disclosure. In addition, a number of the figures (includingFIG.6andFIG.9) conceptually illustrate processes. The specific operations of these processes may not be performed in the exact order shown and described. The specific operations may not be performed in one continuous series of operations, and different specific operations may be performed in different embodiments. Furthermore, the process could be implemented using several sub-processes, or as part of a larger macro process. Thus, one of ordinary skill in the art would understand that the present disclosure is not to be limited by the foregoing illustrative details, but rather is to be defined by the appended claims.

Additional Notes