Patent Description:
Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-<NUM> Visual and ITU-T H. <NUM> (also known as ISO/IEC MPEG-<NUM> AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in <NPL>, which is referred to herein as ITU-T H. Extensions and improvements for ITU-T H. <NUM> are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) are studying the potential need for standardization of future video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model <NUM> (JEM <NUM>), Algorithm Description of Joint Exploration Test Model <NUM> (JEM <NUM>), ISO/IEC JTC1/SC29/WG11 Document: <NPL> describes the coding features under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H. It should be noted that the coding features of JEM <NUM> are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM <NUM> and implementations of JEM reference software. Further, in response to a "Joint Call for Proposals on Video Compression with Capabilities beyond HEVC," jointly issued by VCEG and MPEG, multiple descriptions of video coding were proposed by various groups at the <NUM>th Meeting of ISO/IEC <NPL>. As a result of the multiple descriptions of video coding, a draft text of a video coding specification is described in "<NPL>, document <NPL>, document <NPL>, which is referred to as <NPL>, is an update to <NPL>.

Video compression techniques reduce data requirements for storing and transmitting video data by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of frames within a video sequence, a frame within a group of frames, slices within a frame, coding tree units (e.g., macroblocks) within a slice, coding blocks within a coding tree unit, etc.). Intra prediction coding techniques (e.g., intra-picture (spatial)) and inter prediction techniques (i.e., inter-picture (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, motion vectors, and block vectors). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in a compliant bitstream. Compliant bitstreams and associated metadata may be formatted according to data structures.

The present invention is defined by the claimed subject-matter. Embodiments that do not fall under the claimed subject-matter do not form part of the invention.

In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for signaling reference pictures for coded video. Signaling of reference pictures according to the techniques described herein may be particularly useful for improving video distribution system performance by lowering transmission bandwidth. It should be noted that although techniques of this disclosure are described with respect to ITU-T H. <NUM>, ITU-T H. <NUM>, JVET-J1001, and JVET-K1001 the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H. Thus, reference to ITU-T H. <NUM>, ITU-T H. <NUM>, JVET-J1001, and JVET-K1001 is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.

Video content typically includes video sequences comprised of a series of frames. A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may include a one or more slices, where a slice includes a plurality of video blocks. A video block includes an array of pixel values (also referred to as samples) that may be predictively coded. Video blocks may be ordered according to a scan pattern (e.g., a raster scan). A video encoder performs predictive encoding on video blocks and sub-divisions thereof. <NUM> specifies a macroblock including <NUM> x <NUM> luma samples. <NUM> specifies an analogous Coding Tree Unit (CTU) structure (which may be referred to as a Largest Coding Unit (LCU)) where a picture may be split into CTUs of equal size and each CTU may include Coding Tree Blocks (CTB) having <NUM> x <NUM>, <NUM> x <NUM>, or <NUM> x <NUM> luma samples. As used herein, the term video block may generally refer to an area of a picture or may more specifically refer to the largest array of pixel values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, according to ITU-T H. <NUM>, each video frame or picture may be partitioned to include one or more tiles, where a tile is a sequence of coding tree units corresponding to a rectangular area of a picture.

In ITU-T H. <NUM>, a CTU is composed of respective CTBs for each component of video data (e.g., luma (Y) and chroma (Cb and Cr)). Further, in ITU-T H. <NUM>, a CTU may be partitioned according to a quadtree (QT) partitioning structure, which results in the CTBs of the CTU being partitioned into Coding Blocks (CB). That is, in ITU-T H. <NUM>, a CTU may be partitioned into quadtree leaf nodes. According to ITU-T H. <NUM>, one luma CB together with two corresponding chroma CBs and associated syntax elements are referred to as a coding unit (CU). In ITU-T H. <NUM>, a minimum allowed size of a CB may be signaled. In ITU-T H. <NUM>, the smallest minimum allowed size of a luma CB is 8x8 luma samples. In ITU-T H. <NUM>, the decision to code a picture area using intra prediction or inter prediction is made at the CU level.

In ITU-T H. <NUM>, a CU is associated with a prediction unit (PU) structure having its root at the CU. In ITU-T H. <NUM>, PU structures allow luma and chroma CBs to be split for purposes of generating corresponding reference samples. That is, in ITU-T H. <NUM>, luma and chroma CBs may be split into respect luma and chroma prediction blocks (PBs), where a PB includes a block of sample values for which the same prediction is applied. In ITU-T H. <NUM>, a CB may be partitioned into <NUM>, <NUM>, or <NUM> PBs. <NUM> supports PB sizes from 64x64 samples down to 4x4 samples. In ITU-T H. <NUM>, square PBs are supported for intra prediction, where a CB may form the PB or the CB may be split into four square PBs (i.e., intra prediction PB sizes type include MxM or M/ 2xM/<NUM>, where M is the height and width of the square CB). In ITU-T H. <NUM>, in addition to the square PBs, rectangular PBs are supported for inter prediction, where a CB may by halved vertically or horizontally to form PBs (i.e., inter prediction PB types include MxM, M/2xM/<NUM>, M/2xM, or MxM/<NUM>). Further, it should be noted that in ITU-T H. <NUM>, for inter prediction, four asymmetric PB partitions are supported, where the CB is partitioned into two PBs at one quarter of the height (at the top or the bottom) or width (at the left or the right) of the CB (i.e., asymmetric partitions include M/4xM left, M/4xM right, MxM/<NUM> top, and MxM/<NUM> bottom). Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) corresponding to a PB is used to produce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256x256 luma samples. JEM specifies a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree (BT) structure. That is, in JEM, the binary tree structure enables quadtree leaf nodes to be recursively divided vertically or horizontally. Thus, the binary tree structure in JEM enables square and rectangular leaf nodes, where each leaf node includes a CB. As illustrated in <FIG>, a picture included in a GOP may include slices, where each slice includes a sequence of CTUs and each CTU may be partitioned according to a QTBT structure. In JEM, CBs are used for prediction without any further partitioning. That is, in JEM, a CB may be a block of sample values on which the same prediction is applied. Thus, a JEM QTBT leaf node may be analogous a PB in ITU-T H.

Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) may associate PUs with corresponding reference samples. Residual data may include respective arrays of difference values corresponding to each component of video data (e.g., luma (Y) and chroma (Cb and Cr)). Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to pixel difference values to generate transform coefficients. It should be noted that in ITU-T H. <NUM>, CUs may be further sub-divided into Transform Units (TUs). That is, an array of pixel difference values may be sub-divided for purposes of generating transform coefficients (e.g., four <NUM> x <NUM> transforms may be applied to a <NUM> x <NUM> array of residual values corresponding to a <NUM> x16 luma CB), such sub-divisions may be referred to as Transform Blocks (TBs). Transform coefficients may be quantized according to a quantization parameter (QP). Quantized transform coefficients (which may be referred to as level values) may be entropy coded according to an entropy encoding technique (e.g., content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), etc.). Further, syntax elements, such as, a syntax element indicating a prediction mode, may also be entropy coded. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data. A binarization process may be performed on syntax elements as part of an entropy coding process. Binarization refers to the process of converting a syntax value into a series of one or more bits. These bits may be referred to as "bins. "
As described above, intra prediction data or inter prediction data is used to produce reference sample values for a block of sample values. The difference between sample values included in a current PB, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. As described above, intra prediction data or inter prediction data may associate an area of a picture (e.g., a PB or a CB) with corresponding reference samples. For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H. <NUM>, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode (predMode: <NUM>), a DC (i.e., flat overall averaging) prediction mode (predMode: <NUM>), and <NUM> angular prediction modes (predMode: <NUM>-<NUM>). In JEM, defined possible intra-prediction modes include a planar prediction mode (predMode: <NUM>), a DC prediction mode (predMode: <NUM>), and <NUM> angular prediction modes (predMode: <NUM>-<NUM>). It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.

For inter prediction coding, a motion vector (MV) identifies reference samples in a previously coded picture (i.e., picture available when decoding or encoding a current picture) for coding a current video block in a current picture and thereby exploits temporal redundancy in video. For example, a current video block may be predicted from reference block(s) located in previously coded picture(s) and a motion vector may be used to indicate the location of the reference block. A motion vector and associated data may describe, for example, a horizontal component of the motion vector, a vertical component of the motion vector, a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision), a prediction direction and/or a reference picture index value. Further, a coding standard, such as, for example ITU-T H. <NUM>, may support motion vector prediction. Motion vector prediction enables a motion vector to be specified using motion vectors of neighboring blocks. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called "merge" mode, and "skip" and "direct" motion inference. Further, JEM supports advanced temporal motion vector prediction (ATMVP), Spatial-temporal motion vector prediction (STMVP), Pattern matched motion vector derivation (PMMVD) mode, which is a special merge mode based on Frame-Rate Up Conversion (FRUC) techniques, and affine transform motion compensation prediction.

Residual data may include respective arrays of difference values corresponding to each component of video data. Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to an array of difference values to generate transform coefficients. In ITU-T H. <NUM>, a CU is associated with a transform unit (TU) structure having its root at the CU level. That is, in ITU-T H. <NUM>, as described above, an array of difference values may be sub-divided for purposes of generating transform coefficients (e.g., four 8x8 transforms may be applied to a 16x16 array of residual values). It should be noted that in ITU-T H. <NUM>, TBs are not necessarily aligned with PBs.

It should be noted that in JEM, residual values corresponding to a CB are used to generate transform coefficients without further partitioning. That is, in JEM a QTBT leaf node may be analogous to both a PB and a TB in ITU-T H. It should be noted that in JEM, a core transform and a subsequent secondary transforms may be applied (in the video encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed. Further, in JEM, whether a secondary transform is applied to generate transform coefficients may be dependent on a prediction mode.

A quantization process may be performed on transform coefficients. Quantization approximates transform coefficients by amplitudes restricted to a set of specified values. Quantization may be used in order to vary the amount of data required to represent a group of transform coefficients. Quantization may be realized through division of transform coefficients by a scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Quantized transform coefficients may be referred to as coefficient level values. Inverse quantization (or "dequantization") may include multiplication of coefficient level values by the scaling factor. It should be noted that as used herein the term quantization process in some instances may refer to division by a scaling factor to generate level values or multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases.

With respect to the equations used herein, the following arithmetic operators may be used:.

Further, the following mathematical functions may be used:.

With respect to the example syntax used herein, the following definitions of logical operators may be applied:.

Further, the following relational operators may be applied:.

Further, it should be noted that in the syntax descriptors used herein, the following descriptors may be applied:.

As described above, according to ITU-T H. <NUM>, each video frame or picture may be partitioned to include one or more slices and further partitioned to include one or more tiles. <FIG> is a conceptual diagram illustrating an example of a group of pictures including slices. In the example illustrated in <FIG>, Pic<NUM> is illustrated as including two slices (i.e., Slice<NUM> and Slice<NUM>) where each slice includes a sequence of CTUs (e.g., in raster scan order). It should be noted that a slice is a sequence of one or more slice segments starting with an independent slice segment and containing all subsequent dependent slice segments (if any) that precede the next independent slice segment (if any) within the same access unit. A slice segment, like a slice, is a sequence of coding tree units. In the examples described herein, in some cases the terms slice and slice segment may be used interchangeably to indicate a sequence of coding tree units. It should be noted that in ITU-T H. <NUM>, a tile may consist of coding tree units contained in more than one slice and a slice may consist of coding tree units contained in more than one tile. However, ITU-T H. <NUM> provides that one or both of the following conditions shall be fulfilled: (<NUM>) All coding tree units in a slice belong to the same tile; and (<NUM>) All coding tree units in a tile belong to the same slice. Tile sets may be used to define boundaries for coding dependencies (e.g., intra-prediction dependencies, entropy encoding dependencies, etc.,) and as such, may enable parallelism in coding.

In ITU-T H. <NUM>, a coded video sequence (CVS) may be encapsulated (or structured) as a sequence of access units, where each access unit includes video data structured as network abstraction layer (NAL) units. In ITU-T H. <NUM>, a bitstream is described as including a sequence of NAL units forming one or more CVSs. It should be noted that ITU-T H. <NUM> supports multi-layer extensions, including format range extensions (RExt), scalability (SHVC), multi-view (MV-HEVC), and <NUM>-D (3D-HEVC). Multi-layer extensions enable a video presentation to include a base layer and one or more additional enhancement layers. For example, a base layer may enable a video presentation having a basic level of quality (e.g., High Definition rendering) to be presented and an enhancement layer may enable a video presentation having an enhanced level of quality (e.g., an Ultra High Definition rendering) to be presented. In ITU-T H. <NUM>, an enhancement layer may be coded by referencing a base layer. That is, for example, a picture in an enhancement layer may be coded (e.g., using inter prediction techniques) by referencing one or more pictures (including scaled versions thereof) in a base layer. In ITU-T H. <NUM>, each NAL unit may include an identifier indicating a layer of video data the NAL unit is associated with. It should be noted that sub-bitstream extraction may refer to a process where a device receiving a compliant bitstream forms a new compliant bitstream by discarding and/or modifying data in the received bitstream. For example, sub-bitstream extraction may be used to form a new compliant bitstream corresponding to a particular representation of video (e.g., a high quality representation).

Referring to the example illustrated in <FIG>, each slice of video data included in Pic <NUM> (i.e., Slice<NUM> and Slice<NUM>) is illustrated as being encapsulated in a NAL unit. In ITU-T H. <NUM>, each of a video sequence, a GOP, a picture, a slice, and CTU may be associated with metadata that describes video coding properties. <NUM> defines parameters sets that may be used to describe video data and/or video coding properties. In ITU-T H. <NUM>, parameter sets may be encapsulated as a special type of NAL unit or may be signaled as a message. NAL units including coded video data (e.g., a slice) may be referred to as VCL (Video Coding Layer) NAL units and NAL units including metadata (e.g., parameter sets) may be referred to as non-VCL NAL units. Further, ITU-T H. <NUM> enables supplemental enhancement information (SEI) messages to be signaled. In ITU-T H. <NUM>, SEI messages assist in processes related to decoding, display or other purposes, however, SEI messages may not be required for constructing the luma or chroma samples by the decoding process. In ITU-T H. <NUM>, SEI messages may be signaled in a bitstream using non-VCL NAL units. Further, SEI messages may be conveyed by some means other than by being present in the bitstream (i.e., signaled out-of-band).

<FIG> illustrates an example of a bitstream including multiple CVSs, where a CVS is represented by NAL units included in a respective access unit. In the example illustrated in <FIG>, non-VCL NAL units include respective parameter set units (i.e., Video Parameter Sets (VPS), Sequence Parameter Sets (SPS), and Picture Parameter Set (PPS) units) and an access unit delimiter NAL unit. <NUM> defines NAL unit header semantics that specify the type of Raw Byte Sequence Payload (RBSP) data structure included in the NAL unit.

As described above, for inter prediction coding, reference samples in a previously coded picture are used for coding video blocks in a current picture. Previously coded pictures which are available for use as reference when coding a current picture are referred as reference pictures. It should be noted that the decoding order does not necessary correspond with the picture output order, i.e., the temporal order of pictures in a video sequence. In ITU-T H. <NUM>, when a picture is decoded it is stored to a decoded picture buffer (DPB) (which may be referred to as frame buffer, a reference buffer, a reference picture buffer, or the like). In ITU-T H. <NUM>, pictures stored to the DPB are removed from the DPB when they been output and are no longer needed for coding subsequent pictures. In ITU-T H. <NUM>, a determination of whether pictures should be removed from the DPB is invoked once per picture, after decoding a slice header, i.e., at the onset of decoding a picture. For example, referring to <FIG>, Pic<NUM> is illustrated as referencing Pic<NUM>. Similarly, Pic<NUM> is illustrated as referencing Pic<NUM>. With respect to <FIG> assuming the picture number corresponds to the decoding order the DPB would be populated as follows: after decoding Pic<NUM>, the DPB would include {Pic<NUM> }; at the onset of decoding Pic<NUM>, the DPB would include {Pic<NUM>}; after decoding Pic<NUM>, the DPB would include {Pic<NUM>, Pic<NUM>}; at the onset of decoding Pic<NUM>, the DPB would include {Pic<NUM>, Pic<NUM>}. Pic<NUM> would then be decoded with reference to Pic<NUM> and after decoding Pic<NUM>, the DPB would include {Pic<NUM>, Pic<NUM>, Pic<NUM>}. At the onset of decoding Pic<NUM>, pictures Pic<NUM> and Pic<NUM> would be marked for removal from the DPB, as they are not needed for decoding Pic<NUM> (or any subsequent pictures, not shown) and assuming Pic<NUM> and Pic<NUM> have been output, the DPB would be updated to include {Pic<NUM>}. Pic<NUM> would then be decoded with referencing Pic-<NUM>. The process of marking pictures for removal from a DPB may be referred to as reference picture set (RPS) management.

In ITU-T H. <NUM>, the RPS of the current picture consists of five RPS lists: RefPicSetStCurrBefore, RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and RefPicSetLtFoll. RefPicSetStCurrBefore, RefPicSetStCurrAfter and RefPicSetStFoll are collectively referred to as the short-term RPS. RefPicSetLtCurr and RefPicSetLtFoll are collectively referred to as the long-term RPS. It should be noted that in ITU-T H. <NUM> and RefPicSetStCurrBefore, RefPicSetStCurrAfter and RefPicSetLtCurr contain all reference pictures that may be used for inter prediction of the current picture and one or more pictures that follow the current picture in decoding order. RefPicSetStFoll and RefPicSetLtFoll consist of all reference pictures that are not used for inter prediction of the current picture but may be used in inter prediction for one or more pictures that follow the current picture in decoding order. <NUM> provides where each coded picture is associated with a picture order count variable, denoted as PicOrderCntVal. In ITU-T H. <NUM>, picture order counts are used to identify pictures. In ITU-T H. <NUM>, in one CVS, the PicOrderCntVal values for each of the coded pictures is unique. Further, in ITU-T H. <NUM> picture order counts provide the relative output order of pictures (i.e., from a decoded picture buffer, e.g., for display) included in a CVS (i.e., pictures with lower picture order counts are output before pictures with a higher picture order counts). In ITU-T H. <NUM>, the value of PicOrderCntVal is in the range of -<NUM><NUM> to <NUM><NUM> - <NUM>, inclusive. <NUM> provides where syntax explicitly identifies which pictures are to be included in the RPS, as opposed to indicating which pictures are to be included in the RPS implicitly by identifying which pictures are to be removed from the DPB.

As described above, ITU-T H. <NUM> provides two general types of reference pictures sets: long-term reference picture sets and short-term reference picture sets. Thus, ITU-T H. <NUM> provides where pictures in the DPB are marked as follows: "unused for reference," "used for short-term reference," or "used for long-term reference. " In ITU-T H. <NUM>, short-term reference pictures are identified by their PicOrderCntVal values and long-term reference pictures are identified either by their PicOrderCntVal values or their slice_pic_order_cnt_lsb values (described below). <NUM> further provides where the following five lists of picture order count values are constructed to derive the RPS: PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll. The construction of PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll is described in further detail below.

In ITU-T H. <NUM>, a set of long-term RPS may be signaled in an SPS. Further, in ITU-T sets of candidate short-term RPSs may be in signaled in the SPS. Further, one of the candidate short-term RPSs may be indicated by signaling of an index to one of the SPS candidate RPSs in the slice segment header. Further, short-term RPS may be signaled directly in slice segment header.

Table <NUM> illustrates the portion of the sequence parameter set in ITU-T H. <NUM> relating to indicating reference picture sets.

<NUM> provides the following definitions for the respective syntax elements illustrated in Table <NUM>.

With respect to st_ref_pic_set (i), Table <NUM> illustrates the st_ref_pic_set( i ) syntax provided in ITU-T H.

When inter_ref_pic_set_prediction_flag is equal to <NUM>, the variables DeltaPocS0[ stRpsIdx ][ i ], UsedByCurrPicS0[ stRpsIdx ][ i ], NumNegativePics[ stRpsIdx ], DeltaPocS1[ stRpsIdx ][ i ], UsedByCurrPicS1[ stRpsIdx ][ i ] and NumPositivePics[ stRpsIdx ] are derived as follows:
<IMG>
<IMG>.

When inter_ref_pic_set_prediction_flag is equal to <NUM>, the variables NumNegativePics[ stRpsIdx ], NumPositivePics[ stRpsIdx ], UsedByCurrPicS0[ stRpsIdx ][ i ], UsedByCurrPicS1[ stRpsIdx ][ i ], DeltaPocS0[ stRpsIdx ][ i] and DeltaPocS1[ stRpsIdx ][ i ] are derived as follows:
NumNegativePics[ stRpsIdx ] = num_negative_pics
NumPositivePics[ stRpsIdx ] = num_positive_pics
UsedByCurrPicS0[ stRpsIdx ][ i ] = used_by_curr_pic_s0_flag[ i ]
UsedByCurrPicS1[ stRpsIdx ][ i ] = used_by_curr_pic_s1_flag[ i ]
- If i is equal to <NUM>, the following applies:
DeltaPocS0[ stRpsIdx ][ i ] = -( delta_poc_s0_minus1[ i ] + <NUM> )
DeltaPocS1[ stRpsIdx ][ i ] = delta_poc_s1_minus1[ i ] + <NUM>
- Otherwise, the following applies:.

<MAT> <MAT> The variable NumDeltaPocs[ stRpsIdx ] is derived as follows: <MAT>.

As described above, ITU-T H. <NUM> specifies where a st_ref_pic_set( stRpsIdx ) syntax structure may be present in an SPS or in a slice segment header. <NUM> further provides where depending on whether the syntax structure is included in a slice header or an SPS, the following applies:.

Table <NUM> illustrates the portion of the slice segment header in ITU-T H. <NUM> relating to indicating reference picture sets.

The variable DeltaPocMsbCycleLt[ i ] is derived as follows:
<IMG>.

As described above, in ITU-T H. <NUM> PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll are constructed to derive the RPS. <NUM> provides the following with respect to constructing PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll:.

<NUM> further provides where PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr, and PocLtFoll are used to derive the five RPS lists for the current picture (RefPicSetStCurrBefore, RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and RefPicSetLtFoll) as follows:.

Finally, in ITU-T H. <NUM> a decoding process is performed for construction of one or two temporary reference picture list(s) using the five RPS lists. The one or two temporary reference picture list(s) that are constructed may optionally be modified (i.e., re-indexed). The modified or unmodified temporary reference picture list(s) are used to create a final reference picture list(s). The index values of the reference picture list(s) are used to identify a picture during inter prediction.

According to the techniques herein, a simplified process for generating a reference picture lists is described. According to the techniques herein, reference picture lists may be signaled directly. As described in further detail below, in one example, according to the techniques herein, reference picture lists may be signaled directly as follows: a set of candidate picture lists may be signaled in the SPS and one to three indices to the SPS candidate picture lists may be signaled in the slice segment header or new reference picture lists may be signaled directly in slice segment header; the one or two final reference picture lists may be created based on the signaled indices. Additionally, reference pictures are marked based on one, two, or three reference picture lists. The techniques described herein result is a more simplified decoding process compared to the ITU-T H. <NUM> approach. Further, direct signaling of reference picture lists avoids requiring signaling of reference picture list modification syntax on top of reference picture set syntax.

<FIG> is a block diagram illustrating an example of a system that may be configured to code (i.e., encode and/or decode) video data according to one or more techniques of this disclosure. System <NUM> represents an example of a system that may encapsulate video data according to one or more techniques of this disclosure. As illustrated in <FIG>, system <NUM> includes source device <NUM>, communications medium <NUM>, and destination device <NUM>. In the example illustrated in <FIG>, source device <NUM> may include any device configured to encode video data and transmit encoded video data to communications medium <NUM>. Destination device <NUM> may include any device configured to receive encoded video data via communications medium <NUM> and to decode encoded video data. Source device <NUM> and/or destination device <NUM> may include computing devices equipped for wired and/or wireless communications and may include, for example, set top boxes, digital video recorders, televisions, desktop, laptop or tablet computers, gaming consoles, medical imagining devices, and mobile devices, including, for example, smartphones, cellular telephones, personal gaming devices.

Communications medium <NUM> may include any combination of wireless and wired communication media, and/or storage devices. Communications medium <NUM> may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium <NUM> may include one or more networks. For example, communications medium <NUM> may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.

<FIG> is a conceptual drawing illustrating an example of components that may be included in an implementation of system <NUM>. In the example implementation illustrated in <FIG>, system <NUM> includes one or more computing devices 402A-402N, television service network <NUM>, television service provider site <NUM>, wide area network <NUM>, local area network <NUM>, and one or more content provider sites 412A-412N. The implementation illustrated in <FIG> represents an example of a system that may be configured to allow digital media content, such as, for example, a movie, a live sporting event, etc., and data and applications and media presentations associated therewith to be distributed to and accessed by a plurality of computing devices, such as computing devices 402A-402N. In the example illustrated in <FIG>, computing devices 402A-402N may include any device configured to receive data from one or more of television service network <NUM>, wide area network <NUM>, and/or local area network <NUM>. For example, computing devices 402A-402N may be equipped for wired and/or wireless communications and may be configured to receive services through one or more data channels and may include televisions, including so-called smart televisions, set top boxes, and digital video recorders. Further, computing devices 402A-402N may include desktop, laptop, or tablet computers, gaming consoles, mobile devices, including, for example, "smart" phones, cellular telephones, and personal gaming devices.

Television service network <NUM> is an example of a network configured to enable digital media content, which may include television services, to be distributed. For example, television service network <NUM> may include public over-the-air television networks, public or subscription-based satellite television service provider networks, and public or subscription-based cable television provider networks and/or over the top or Internet service providers. It should be noted that although in some examples television service network <NUM> may primarily be used to enable television services to be provided, television service network <NUM> may also enable other types of data and services to be provided according to any combination of the telecommunication protocols described herein. Further, it should be noted that in some examples, television service network <NUM> may enable two-way communications between television service provider site <NUM> and one or more of computing devices 402A-402N. Television service network <NUM> may comprise any combination of wireless and/or wired communication media. Television service network <NUM> may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Television service network <NUM> may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include DVB standards, ATSC standards, ISDB standards, DTMB standards, DMB standards, Data Over Cable Service Interface Specification (DOCSIS) standards, HbbTV standards, W3C standards, and UPnP standards.

Referring again to <FIG>, television service provider site <NUM> may be configured to distribute television service via television service network <NUM>. For example, television service provider site <NUM> may include one or more broadcast stations, a cable television provider, or a satellite television provider, or an Internet-based television provider. For example, television service provider site <NUM> may be configured to receive a transmission including television programming through a satellite uplink/downlink. Further, as illustrated in <FIG>, television service provider site <NUM> may be in communication with wide area network <NUM> and may be configured to receive data from content provider sites 412A-412N. It should be noted that in some examples, television service provider site <NUM> may include a television studio and content may originate therefrom.

Wide area network <NUM> may include a packet based network and operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, <NUM>rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, European standards (EN), IP standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards, such as, for example, one or more of the IEEE <NUM> standards (e.g., Wi-Fi). Wide area network <NUM> may comprise any combination of wireless and/or wired communication media. Wide area network <NUM> may include coaxial cables, fiber optic cables, twisted pair cables, Ethernet cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. In one example, wide area network <NUM> may include the Internet. Local area network <NUM> may include a packet based network and operate according to a combination of one or more telecommunication protocols. Local area network <NUM> may be distinguished from wide area network <NUM> based on levels of access and/or physical infrastructure. For example, local area network <NUM> may include a secure home network.

Referring again to <FIG>, content provider sites 412A-412N represent examples of sites that may provide multimedia content to television service provider site <NUM> and/or computing devices 402A-402N. For example, a content provider site may include a studio having one or more studio content servers configured to provide multimedia files and/or streams to television service provider site <NUM>. In one example, content provider sites 412A-412N may be configured to provide multimedia content using the IP suite. For example, a content provider site may be configured to provide multimedia content to a receiver device according to Real Time Streaming Protocol (RTSP), HTTP, or the like. Further, content provider sites 412A-412N may be configured to provide data, including hypertext based content, and the like, to one or more of receiver devices computing devices 402A-402N and/or television service provider site <NUM> through wide area network <NUM>. Content provider sites 412A-412N may include one or more web servers. Data provided by data provider site 412A-412N may be defined according to data formats.

Referring again to <FIG>, source device <NUM> includes video source <NUM>, video encoder <NUM>, data encapsulator <NUM>, and interface <NUM>. Video source <NUM> may include any device configured to capture and/or store video data. For example, video source <NUM> may include a video camera and a storage device operably coupled thereto. Video encoder <NUM> may include any device configured to receive video data and generate a compliant bitstream representing the video data. A compliant bitstream may refer to a bitstream that a video decoder can receive and reproduce video data therefrom. Aspects of a compliant bitstream may be defined according to a video coding standard. When generating a compliant bitstream video encoder <NUM> may compress video data. Compression may be lossy (discernible or indiscernible to a viewer) or lossless. <FIG> is a block diagram illustrating an example of video encoder <NUM> that may implement the techniques for encoding video data described herein. It should be noted that although example video encoder <NUM> is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video encoder <NUM> and/or sub-components thereof to a particular hardware or software architecture. Functions of video encoder <NUM> may be realized using any combination of hardware, firmware, and/or software implementations.

Video encoder <NUM> may perform intra prediction coding and inter prediction coding of picture areas, and, as such, may be referred to as a hybrid video encoder. In the example illustrated in <FIG>, video encoder <NUM> receives source video blocks. In some examples, source video blocks may include areas of picture that has been divided according to a coding structure. For example, source video data may include macroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalent coding unit. In some examples, video encoder <NUM> may be configured to perform additional sub-divisions of source video blocks. It should be noted that the techniques described herein are generally applicable to video coding, regardless of how source video data is partitioned prior to and/or during encoding. In the example illustrated in <FIG>, video encoder <NUM> includes summer <NUM>, transform coefficient generator <NUM>, coefficient quantization unit <NUM>, inverse quantization and transform coefficient processing unit <NUM>, summer <NUM>, intra prediction processing unit <NUM>, inter prediction processing unit <NUM>, filter unit <NUM>, and entropy encoding unit <NUM>. As illustrated in <FIG>, video encoder <NUM> receives source video blocks and outputs a bitstream.

In the example illustrated in <FIG>, video encoder <NUM> may generate residual data by subtracting a predictive video block from a source video block. The selection of a predictive video block is described in detail below. Summer <NUM> represents a component configured to perform this subtraction operation. In one example, the subtraction of video blocks occurs in the pixel domain. Transform coefficient generator <NUM> applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block or sub-divisions thereof (e.g., four <NUM> x <NUM> transforms may be applied to a <NUM> x <NUM> array of residual values) to produce a set of residual transform coefficients. Transform coefficient generator <NUM> may be configured to perform any and all combinations of the transforms included in the family of discrete trigonometric transforms, including approximations thereof. Transform coefficient generator <NUM> may output transform coefficients to coefficient quantization unit <NUM>. Coefficient quantization unit <NUM> may be configured to perform quantization of the transform coefficients. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may alter the rate-distortion (i.e., bit-rate vs. quality of video) of encoded video data. The degree of quantization may be modified by adjusting a quantization parameter (QP). A quantization parameter may be determined based on slice level values and/or CU level values (e.g., CU delta QP values). QP data may include any data used to determine a QP for quantizing a particular set of transform coefficients. As illustrated in <FIG>, quantized transform coefficients (which may be referred to as level values) are output to inverse quantization and transform coefficient processing unit <NUM>. Inverse quantization and transform coefficient processing unit <NUM> may be configured to apply an inverse quantization and an inverse transformation to generate reconstructed residual data. As illustrated in <FIG>, at summer <NUM>, reconstructed residual data may be added to a predictive video block. In this manner, an encoded video block may be reconstructed and the resulting reconstructed video block may be used to evaluate the encoding quality for a given prediction, transformation, and/or quantization. Video encoder <NUM> may be configured to perform multiple coding passes (e.g., perform encoding while varying one or more of a prediction, transformation parameters, and quantization parameters). The rate-distortion of a bitstream or other system parameters may be optimized based on evaluation of reconstructed video blocks. Further, reconstructed video blocks may be stored and used as reference for predicting subsequent blocks.

Referring again to <FIG>, intra prediction processing unit <NUM> may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit <NUM> may be configured to evaluate a frame and determine an intra prediction mode to use to encode a current block. As described above, possible intra prediction modes may include planar prediction modes, DC prediction modes, and angular prediction modes. Further, it should be noted that in some examples, a prediction mode for a chroma component may be inferred from a prediction mode for a luma prediction mode. Intra prediction processing unit <NUM> may select an intra prediction mode after performing one or more coding passes. Further, in one example, intra prediction processing unit <NUM> may select a prediction mode based on a rate-distortion analysis. As illustrated in <FIG>, intra prediction processing unit <NUM> outputs intra prediction data (e.g., syntax elements) to entropy encoding unit <NUM> and transform coefficient generator <NUM>. As described above, a transform performed on residual data may be mode dependent (e.g., a secondary transform matrix may be determined based on a predication mode).

Referring again to <FIG>, inter prediction processing unit <NUM> may be configured to perform inter prediction coding for a current video block. Inter prediction processing unit <NUM> may be configured to receive source video blocks and calculate a motion vector for PUs of a video block. A motion vector may indicate the displacement of a PU of a video block within a current video frame relative to a predictive block within a reference frame. Inter prediction coding may use one or more reference pictures. Further, motion prediction may be uni-predictive (use one motion vector) or bi-predictive (use two motion vectors). Inter prediction processing unit <NUM> may be configured to select a predictive block by calculating a pixel difference determined by, for example, sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. As described above, a motion vector may be determined and specified according to motion vector prediction. Inter prediction processing unit <NUM> may be configured to perform motion vector prediction, as described above. Inter prediction processing unit <NUM> may be configured to generate a predictive block using the motion prediction data. For example, inter prediction processing unit <NUM> may locate a predictive video block within a frame buffer (not shown in <FIG>). It should be noted that inter prediction processing unit <NUM> may further be configured to apply one or more interpolation filters to a reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Inter prediction processing unit <NUM> may output motion prediction data for a calculated motion vector to entropy encoding unit <NUM>.

Referring again to <FIG>, filter unit <NUM> receives reconstructed video blocks and coding parameters and outputs modified reconstructed video data. Filter unit <NUM> may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering. SAO filtering is a non-linear amplitude mapping that may be used to improve reconstruction by adding an offset to reconstructed video data. It should be noted that as illustrated in <FIG>, intra prediction processing unit <NUM> and inter prediction processing unit <NUM> may receive modified reconstructed video block via filter unit <NUM>. Entropy encoding unit <NUM> receives quantized transform coefficients and predictive syntax data (i.e., intra prediction data and motion prediction data). It should be noted that in some examples, coefficient quantization unit <NUM> may perform a scan of a matrix including quantized transform coefficients before the coefficients are output to entropy encoding unit <NUM>. In other examples, entropy encoding unit <NUM> may perform a scan. Entropy encoding unit <NUM> may be configured to perform entropy encoding according to one or more of the techniques described herein. In this manner, video encoder <NUM> represents an example of a device configured to generate encoded video data according to one or more techniques of this disclose.

Referring again to <FIG>, data encapsulator <NUM> may receive encoded video data and generate a compliant bitstream, e.g., a sequence of NAL units according to a defined data structure. A device receiving a compliant bitstream can reproduce video data therefrom. Further, as described above, sub-bitstream extraction may refer to a process where a device receiving a ITU-T H. <NUM> compliant bitstream forms a new ITU-T H. <NUM> compliant bitstream by discarding and/or modifying data in the received bitstream. It should be noted that the term conforming bitstream may be used in place of the term compliant bitstream. In one example, data encapsulator <NUM> may be configured to generate syntax according to one or more techniques described herein. It should be noted that data encapsulator <NUM> need not necessary be located in the same physical device as video encoder <NUM>. For example, functions described as being performed by video encoder <NUM> and data encapsulator <NUM> may be distributed among devices illustrated in <FIG>.

As described above, in one example, according to the techniques herein, reference picture lists may be signaled directly as follows: a set of candidate picture lists may be signaled in the SPS (or other parameter set, e.g., VPS) and one to three indices to the SPS candidate picture lists may be signaled in the slice segment header or new reference picture lists may be signaled directly in slice segment header. A slice segment header may is some cases be referred to as a segment header. Table <NUM> illustrates an example of relevant syntax that may be included in an SPS and Table <NUM> illustrates an example of relevant syntax in the a slice segment header that may be used for directly signaling reference picture lists according to the techniques herein. It should be noted that syntax included in Table <NUM> is not limited to being included in an SPS (e.g., the syntax may be included in a parameter set) and syntax included in Table <NUM> is not limited to being included in a slice segment header (e.g., the syntax may be included in a header associated with another type of picture region, e.g., a picture header or a tile set header).

In one example, the following definitions may be used for the respective syntax elements illustrated in Table <NUM>.

Table <NUM> illustrates an example of pic_list syntax according to the techniques herein.

Table <NUM> illustrates another example of pic_list syntax according to the techniques herein.

In one example, the following definitions may be used for the respective syntax elements illustrated in Table <NUM> and Table <NUM>.

With respect to the example illustrated in Table <NUM>, in one example, the following definitions may be used for syntax element delta_entries_minus1. delta_entries_minus1[ i ] plus <NUM>,.

The value of delta_entries_minus1[ i ] shall be in the range of <NUM> to <NUM><NUM> - <NUM>, inclusive.

When inv_list_flag is equal to <NUM>, the variables NumNegativePics[ listIdx ], NumPositivePics[ listIdx ], DeltaPocS0[ listIdx ][ i ], and DeltaPocS1[ listIdx ][ i ] are derived as follows: <MAT> <MAT>.

The variable NumDeltaPocs[ listIdx ] is derived as follows: <MAT>.

Based on the syntax provided above in Tables <NUM>-<NUM>, in one example, a process for deriving reference picture lists (RPL)s, i.e., a process performed by a video decoder at the onset of decoding a picture may be performed according to and/or based the following steps:
The following applies:
The variable CurrRPListIdx[j] for j in the range of <NUM> to num_rpl slice header minus1, inclusive,is derived as follows:.

The following applies for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive,
<IMG>
All reference pictures in the DPB that are not included in RefPics[ j ] for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive, are marked as "unused for reference".

In one example, for the case where Otherwise, CurrRPListIdx[j] is set equal to rpl_idx[num_ref_pic_lists_minus1+j+<NUM>] the following may be performed
<IMG>.

Further, based on the syntax provided above in Tables <NUM>-<NUM>, in one example, a process for reference picture lists construction, i.e., a process performed by a video decoder at the beginning of the decoding process for each P or B slice for constructing the reference picture lists RefPicList0 and, for B slices, RefPicListl may be as performed based on the following:.

In another example, constructing the reference picture lists RefPicList0 and, for B slices,
RefPicList1 may be as performed based on the following, where a RPL modification may be present:.

Further, based on the syntax provided above in Tables <NUM>-<NUM>, in one example, a process for generating unavailable reference pictures may be performed according to and/or based the following steps:.

Further, based on the syntax provided above in Tables <NUM>-<NUM>, in one example, a process for generating one unavailable reference pictures may be performed according to and/or based the following steps:
When this process is invoked, an unavailable picture is generated as follows:.

Further, based on the syntax provided above in Tables <NUM>-<NUM>, in one example, a process for selecting a reference picture may be performed according to and/or based the following steps:.

In one example, according to the techniques herein, long-term reference picture lists may be signaled directly, as provided in further detail below. Table <NUM> illustrates an example of relevant syntax that may be included in an SPS for signaling long-term reference picture lists directly. It should be noted that syntax included in Table <NUM> is not limited to being included in an SPS (e.g., the syntax may be included in a parameter set).

Table <NUM> illustrates an example of pic_list syntax that may be used in conjunction with the example syntax illustrated in Table <NUM>.

Based on the syntax provided above in Table <NUM> and Table <NUM>, in one example, a process for deriving reference picture lists (RPL)s may be performed according to and/or based the following steps. The steps may be executed in sequence shown below or in a different order.

Based on the syntax provided above in Table <NUM> and Table <NUM>, in one example, a process for generating unavailable pictures may be performed according to and/or based the following steps:.

Based on the syntax provided above in Table <NUM> and Table <NUM>, in one example, constructing the reference picture lists RefPicList0 and, for B slices, RefPicList1 may be as performed based on the following:.

Table <NUM> illustrates another example of relevant syntax that may be included in an SPS and Table <NUM> illustrates an example of relevant syntax in slice segment header that may be used for signaling long-term reference picture lists directly according to the techniques herein. It should be noted that syntax included in Table <NUM> is not limited to being included in an SPS and syntax included in Table <NUM> is not limited to being included in a slice segment header. In the example illustrated with respect to Table <NUM> and Table <NUM>, the long term reference picture related information is not included in the pic_list(), but instead it is included in a separate long term ltrp_pic_list(). It should be noted that when the long term reference picture related information is included in a separate ltrp_pic_list(), pic_list() may be based on the example illustrated in Table <NUM>.

Table <NUM> illustrates another example of ltrp_pic_list syntax that may be used in conjunction with the example syntax illustrated in Table <NUM> and Table <NUM>.

Based on the syntax provided above in Table <NUM>, Table <NUM> and Table <NUM>, in one example, a process for deriving reference picture lists (RPL)s may be performed according to and/or based the following steps. The steps may be executed in sequence shown below or in a different order. The following applies:
The variable CurrRPListIdx[j] for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive, is derived as follows:.

The following applies for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive,
<IMG>.

The following applies for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive, for n in the range of <NUM> to num_ltrp_rpl_slice_header_minus1, inclusive. :
The variable CurrLTRPRPListIdx[n] for n in the range of <NUM> to num_ltrp_rpl_slice_header_minus1, inclusive, is derived as follows:.

All reference pictures that are included in RefPics[ j ][ k ] for k in the range NumDeltaPocs[ CurrRPListIdx[j] ] to NumDeltaPocs[ CurrRPListIdx[j] ]+ NumPocLt [CurrLTRPRPListIdx[n]]-<NUM>], inclusive, for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive, are marked as "used for long-term reference".

All reference pictures in the DPB that are not included in RefPics[ j ] for j in the range of <NUM> to num_rpl_slice_header_minus1, inclusive, are marked as "unused for reference".

Based on the syntax provided above in Table <NUM>, Table <NUM> and Table <NUM>, in one example, a process for generating unavailable pictures may be performed according to and/or based the following steps:
For each RefPics[ j ][ i ], with i in the range of <NUM> to NumDeltaPocs[ CurrRPListIdx[j] ], inclusive, for j in the range <NUM> to num_rpl_slice_header_minus1, inclusive, that is equal to "no reference picture", a picture is generated as specified in "generation of one unavailable picture", and the following applies:.

Based on the syntax provided above in in Table <NUM>, Table <NUM> and Table <NUM>, in one example, constructing the reference picture lists RefPicList0 and, for B slices, RefPicList1 may be as performed based on the following:.

In one example, a long-term reference picture list may be directly signaled in a slice header. With respect to the example of SPS syntax illustrated in Table <NUM>, Table <NUM> illustrates an example of relevant syntax in slice segment header that may be used for signaling long-term reference picture lists directly according to the techniques herein. Further, Table <NUM> provides an example of a long-term reference picture that may be included in a slice segment header. It should be noted that the example long-term reference picture list illustrated in Table <NUM> is arranged such that first few entries (indicated by a syntax element or variable) in the list signal Long-term reference picture (LTRP) information for the current picture and the remaining entries in the list signal LTRP information for pictures following the current picture in the bitstream order.

If long_term_ref_pics_present_flag is equal to <NUM> NumPocLt is set equal to <NUM>
<IMG>.

Based on the syntax provided above in Table <NUM> and Table <NUM>, in one example, a process for deriving reference picture lists (RPL)s may be performed according to and/or based the following steps. The steps may be executed in sequence shown below or in a different order.

The following applies for j in the range of <NUM> to num_rpl_slice_header_minusl, inclusive,
<IMG>
for j in the range of in the range of <NUM> to <NUM> if current slice is a B slice or for j in the range of <NUM> if current slice is a P slice:
<IMG>
<IMG>.

And for j equal to max(<NUM>, num_rpl_slice_header_minus1) if current slice is a B slice or for j equal to max(<NUM>, num_rpl_slice_header_minus1) if current slice is a P slice :
<IMG>.

All reference pictures that are included in RefPics[ j ][ k ] for k in the range NumDeltaPocs[ CurrRPListIdx[j] ] to NumDeltaPocs[ CurrRPListIdx[j] ]+ NumPocLtCurr-<NUM>], inclusive, for j in the range of in the range of <NUM> to <NUM> if current slice is a B slice or for j in the range of <NUM> if current slice is a P slice
and for k in the range NumDeltaPocs[ CurrRPListIdx[j] ] to NumDeltaPocs[ CurrRPListIdx[j] ]+ NumPocLt -NumPocLtCurr-<NUM>], inclusive, for j equal to max(<NUM>, num_rpl_slice_header_minusl) if current slice is a B slice or for j equal to max(<NUM>, num_rpl_slice_header_minus1) if current slice is a P slice are marked as "used for long-term reference".

Based on the syntax provided above in Table <NUM> and Table <NUM>, in one example, a process for generating unavailable pictures may be performed according to and/or based the following steps:
For each RefPics[ j ][ i ], with i in the range of <NUM> to NumDeltaPocs[ CurrRPListIdx[j] ], inclusive, for j in the range <NUM> to num_rpl_slice_header_minus1, inclusive, that is equal to "no reference picture", a picture is generated as specified in "generation of one unavailable picture", and the following applies:.

In an example the above steps may be performed for j equal to num_rpl_slice_header_minus1 only.

For each RefPics[ j ][ i ] for i in the range NumDeltaPocs[ CurrRPListIdx[j] ] to NumDeltaPocs[ CurrRPListIdx[j] ]+ NumPocLt-NumPocLtCurr ]-<NUM>], inclusive, for equal to max(<NUM>, num_rpl_slice_header_minus1) if current slice is a B slice or for j equal to max(<NUM>, num_rpl_slice_header_minusl) if current slice is a P slice, that is equal to "no reference picture", a picture is generated as specified in "generation of one unavailable picture", and the following applies:.

In one example, the long-term reference picture may be inserted in the reference picture list <NUM> and/ or reference picture list <NUM> according to their PicOrderCntVal value distance compared to the PicOrderCntVal of the current picture.

It should be noted that with respect to the example illustrated in Tables <NUM>-<NUM>, processes the generation of one unavailable picture and reference picture list selection may be similar to that described above with respect Tables <NUM>-<NUM>.

As described above, a process for reference picture lists construction of RefPicList0 and RefPicList1 includes determining respective values for NumRpsCurrList0 and NumRpsCurrList1. As provided above, values for NumRpsCurrList0 and NumRpsCurrList1 are determined based on respective values of num_ref_idx_10_active_minus1 and num_ref_idx_11_active_minus1. In JVET-K1001 values of num_ref_idx_10_active_minus1 and num_ref_idx_l1_active_minus1 may be determined based on the following syntax elements included in the picture parameter set (PPS).

According to the techniques herein, num_ref idx_l0_default_active_minus1, and num_ref_idx_l1_default_active_minus1 may be removed from the PPS in JVET-K1001, and variations of the PPS including num_ref_idx_l0_default_active_minus1, and num_ref_idx_l1_default_active_minus1. num_ref_idx_active_override_flag, num_ref_idx_l0_active_minus1, and num_ref_dx_l1_active_minus1 may be removed from the slice header in JVET-K1001, and variations of the slice header including num_ref_idx_active_override_flag, num_ref_idx_l0_active_minus1, and num_ref_idx_l1_active_minus1. That is, according to the techniques herein values of num_ref_idx_l0_active_minus1, and num_ref_idx_l1_active_minus1 are derived instead of being signaled directly. Further, techniques for deriving values corresponding to num_ref_idx_10_active_minus1 and num_ref_idx_l1_active_minus1 according to techniques herein are described below. It should be noted that the conventions in ITU-T H. <NUM> and JVET-K1001 provide where signaled values in calculations include underscores and derived values, which are called variables, do not include underscores. Thus, in the equations below NumRefIdxL0ActiveMinus is a derived variable, the value of which corresponds to the previously signalled value of num_ref_idx_l0)active_minus1 and NumRefIdxL1ActiveMinus is a derived variable, the value of which corresponds to the previously signalled value num_ref_idx_11_active_minus1. It should be noted that when the techniques described herein are used to modify JVET-K1001 instances of num_ref_idx_10_active_minus1 and num_ref_idx_l1_active_minus1 in JVET-K1001 are replaced with respective instances of NumRefIdxL0ActiveMinus and NumRefIdxL1ActiveMinus. For the sake of brevity, each respective replacement of num_ref_idx_10_active_minus1 and num_ref_idx_l1_active_minus1 with NumRefIdxL0ActiveMinus and NumRefIdxL1ActiveMinus is not described in detail herein.

In one example, according to the techniques herein, NumRefIdxL0ActiveMinus and NumRefIdxL1ActiveMinus may be derived as follows:.

It should be noted that in one example, in the equations above, the step of subtracting <NUM> to derive NumRefIdxL0ActiveMinus and NumRefIdxL1ActiveMinus may be omitted.

Additionally, in this case the reference picture list <NUM> and reference picture list <NUM> creation process will be modified as follows:.

In another example, additionally, in this case the reference picture list <NUM> and reference picture list <NUM> creation process will be modified as follows:.

"On reference picture management for VVC," 12th Meeting of ISO/IEC JTC1/SC29/WG11 <NUM>-<NUM> October <NUM>, Macao, CN, document JVET-L0112-v3, which is referred to herein as JVET-L0112, describes a reference picture management approach based on direct signaling and derivation of reference picture lists <NUM> and <NUM>. In particular, Table <NUM> illustrates the relevant syntax included in the SPS for the reference picture management approach described in JVET-L0112, Table <NUM> illustrates the relevant syntax included in the PPS for the reference picture management approach described in JVET-L0112, and Table <NUM> illustrates the relevant syntax included in the slice header for the reference picture management approach described in JVET-L0112.

JVET-L0112 provides the following definitions for the respective syntax elements illustrated in Table <NUM>:.

In one example, according to the techniques herein, the slice header in JVET-L0112 may be modified to such that when the syntax elements corresponding to the number of active reference pictures are needed to be signaled, they are only signaled when the corresponding reference picture list includes more than one entry. In this case, when not signaled the number of active reference pictures for reference picture list <NUM> and/or reference picture list <NUM> are inferred. This provides bit savings.

In particular, Table <NUM> illustrates an example of the relevant syntax included in the slice header according to the techniques herein.

With respect to the respective syntax elements illustrated in Table <NUM>, the definitions may be based on the definitions provided above. With respect to the syntax element num_ref_idx_active_minus1 the definition may be based on the following:.

For i equal to <NUM> or <NUM>, when the current slice is a B slice and num_ref_idx_active_override_flag is equal to <NUM>, and num_ref_idx_active_minus1[ i ] is not present, num_ref_idx_active_minus1[ i ] is inferred to be equal to <NUM>. In another example a different value may be inferred for num_ref_idx_active_minus1[ i ] for I equal to <NUM> and <NUM>.

When the current slice is a P slice and num_ref_idx_active_override_flag is equal to <NUM>, num_ref_idx_active_minus1[ <NUM> ] is not present, num_ref_idx_active_minus1[ <NUM>] is inferred to be equal to <NUM>. In another example, a different value may be inferred for num_ref_idx_active_minus1[ <NUM>].

When the current slice is a P slice, NumRefIdxActive[ <NUM> ] is inferred to be equal to <NUM>.

When the current slice is an I slice, both NumRefIdxActive[ <NUM> ] and NumRefIdxActive[ <NUM> ] are inferred to be equal to <NUM>.

Further, in one example, according to the techniques herein, in Tables <NUM> num_ref_idx_active_minus1[ i ] may be instead be signaled as num_ref_idx_active[ i ], to allow a reference picture list to have no active reference pictures for a current picture. This may be the case when that reference picture list only includes pictures which are reference pictures for future pictures in the bitstream. Another case where a reference picture list may be empty may be when num_strp_entries[ listIdx ][ rplsIdx ] and num_ltrp_entries[ listIdx ][ rplsIdx ] are signaled in ref_pic_list_struct( listIdx, rplsIdx, ltrpFlag ) such that the value of NumEntriesInList[ listIdx ][ rplsIdx ] shall be in the range of <NUM> to sps_max_dec_pic_buffering_minus1. In one example, num_ref_idx_active [ i ] may be based on the following definition:.

Further, in one example, according to the techniques herein, in Table <NUM> may be modified and signaled as in Table 18A. In this case, num_ref_idx_active_minus1[ i ] may be instead be signaled as num_ref_idx_active[ i ] to allow a reference picture list to have no active reference pictures for a current picture. This may be the case when that reference picture list only includes pictures which are reference pictures for future pictures in the bitstream. Another case where a reference picture list may be empty may be when num_strp_entries[ listIdx ][ rplsIdx ] and num_ltrp_entries[ listIdx ][ rplsIdx ] are signaled in ref_pic_list_struct( listIdx, rplsIdx, ltrpFlag ) such that the value of NumEntriesInList[ listIdx ][ rplsIdx ] shall be in the range of <NUM> to sps_max_dec_pic_buffering_minus1. In one example, num_ref_idx_active [ i ] may be based on the following definition. Additionally, in this case when the syntax elements corresponding to the number of active reference pictures are needed to be signaled, they are only signaled when the corresponding reference picture list is not empty. In this case, when not signaled the number of active reference pictures for reference picture list <NUM> and/or reference picture list <NUM> are inferred. This provides bit savings.

In this case the semantics may be as follows:.

In another example, the constraint on NumEntriesInList[ listIdx ][ rplsIdx ] = num_strp_entries[ listIdx ][ rplsIdx ] + num_ltrp_entries[ listIdx ][ rplsIdx ] may be modified as follows:
The value of NumEntriesInList[ listIdx ][ rplsIdx ] shall be in the range of <NUM> to sps_max_dec-pic_buffering_minus <NUM>, inclusive.

Referring to Table <NUM> above, in one example, according to the techniques herein, in one example, the active override syntax may be included in the slice header according to the example illustrated in Table <NUM>.

With respect to Table <NUM>, the following part of the syntax.

Table <NUM> illustrates the relevant syntax for reference picture list structure included for the reference picture management approach described in JVET-L0112.

The value of delta_poc_st[ listIdx ][ rplsIdx ][ i ] shall be in the range of -<NUM><NUM> to <NUM><NUM> - <NUM>, inclusive.

The list DeltaPocSt[ listIdx ][ rplsIdx ] is derived as follows:
<IMG>.

poc_lsb_lt[ listIdx ][ rplsIdx ][ i ] specifies the value of the picture order count modulo MaxLtPicOrderCntLsb of the picture referred to by the i-th entry in the ref_pic_list_struct( listIdx, rplsIdx, ltrpFlag ) syntax structure. The length of the poc_lsb_lt[ listIdx ][ rplsIdx ][ i ] syntax element is Log2( MaxLtPicOrderCntLsb ) bits.

In one example, according to the techniques herein, the relevant syntax for a reference picture list structure may be modified as shown in Table <NUM>, such that the syntax element for number of short term reference picture entries is modified to be signaled with a minus1 coding. This provides bit savings and requires that at least one short term reference picture is signaled.

In this case, the semantics for num_strp_entries_minus1 in Table <NUM> may as follows:
num_strp_entries_minus1[ listIdx ][ rplsIdx ] plus <NUM> specifies the number of STRP entries in the ref pic list_struct( listIdx, rplsIdx, ltrpFlag ) syntax structure.

In this case, the variable NumEntriesInList[ listIdx ][ rplsIdx ] may be derived as follows: <MAT>.

In another example, this constraint may be as follows:.

In this manner, source device <NUM> represents an example of a device configured to signal one or more candidate reference picture lists in a parameter set, and signal an index to one of the candidate reference picture lists in a header associated with a region of a picture.

Referring again to <FIG>, interface <NUM> may include any device configured to receive data generated by data encapsulator <NUM> and transmit and/or store the data to a communications medium. Interface <NUM> may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can send and/or receive information. Further, interface <NUM> may include a computer system interface that may enable a file to be stored on a storage device. For example, interface <NUM> may include a chipset supporting Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect Express (PCIe) bus protocols, proprietary bus protocols, Universal Serial Bus (USB) protocols, I<NUM>C, or any other logical and physical structure that may be used to interconnect peer devices.

Referring again to <FIG>, destination device <NUM> includes interface <NUM>, data decapsulator <NUM>, video decoder <NUM>, and display <NUM>. Interface <NUM> may include any device configured to receive data from a communications medium. Interface <NUM> may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can receive and/or send information. Further, interface <NUM> may include a computer system interface enabling a compliant video bitstream to be retrieved from a storage device. For example, interface <NUM> may include a chipset supporting PCI and PCIe bus protocols, proprietary bus protocols, USB protocols, I<NUM>C, or any other logical and physical structure that may be used to interconnect peer devices. Data decapsulator <NUM> may be configured to receive and parse any of the example syntax structures described herein.

Video decoder <NUM> may include any device configured to receive a bitstream (e.g., a MCTS sub-bitstream extraction) and/or acceptable variations thereof and reproduce video data therefrom. Display <NUM> may include any device configured to display video data. Display <NUM> may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display <NUM> may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in <FIG>, video decoder <NUM> is described as outputting data to display <NUM>, video decoder <NUM> may be configured to output video data to various types of devices and/or sub-components thereof. For example, video decoder <NUM> may be configured to output video data to any communication medium, as described herein.

<FIG> is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure. In one example, video decoder <NUM> may be configured to decode transform data and reconstruct residual data from transform coefficients based on decoded transform data. Video decoder <NUM> may be configured to perform intra prediction decoding and inter prediction decoding and, as such, may be referred to as a hybrid decoder. Video decoder <NUM> may be configured to parse any combination of the syntax elements described above in Tables <NUM>-<NUM>. Video decoder <NUM> may derive reference picture lists based on or according to the processes described above. Video decoder <NUM> may constructing the reference picture lists RefPicList0 and RefPicList1 based on or according to the processes described above. Video decoder may perform video decoding based on the reference picture lists.

In the example illustrated in <FIG>, video decoder <NUM> includes an entropy decoding unit <NUM>, inverse quantization unit and transform coefficient processing unit <NUM>, intra prediction processing unit <NUM>, inter prediction processing unit <NUM>, summer <NUM>, post filter unit <NUM>, and reference buffer <NUM>. Video decoder <NUM> may be configured to decode video data in a manner consistent with a video coding system. It should be noted that although example video decoder <NUM> is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video decoder <NUM> and/or sub-components thereof to a particular hardware or software architecture. Functions of video decoder <NUM> may be realized using any combination of hardware, firmware, and/or software implementations.

As illustrated in <FIG>, entropy decoding unit <NUM> receives an entropy encoded bitstream. Entropy decoding unit <NUM> may be configured to decode syntax elements and quantized coefficients from the bitstream according to a process reciprocal to an entropy encoding process. Entropy decoding unit <NUM> may be configured to perform entropy decoding according any of the entropy coding techniques described above. Entropy decoding unit <NUM> may determine values for syntax elements in an encoded bitstream in a manner consistent with a video coding standard. As illustrated in <FIG>, entropy decoding unit <NUM> may determine a quantization parameter, quantized coefficient values, transform data, and predication data from a bitstream. In the example, illustrated in <FIG>, inverse quantization unit and transform coefficient processing unit <NUM> receives a quantization parameter, quantized coefficient values, transform data, and predication data from entropy decoding unit <NUM> and outputs reconstructed residual data.

Referring again to <FIG>, reconstructed residual data may be provided to summer <NUM> Summer <NUM> may add reconstructed residual data to a predictive video block and generate reconstructed video data. A predictive video block may be determined according to a predictive video technique (i.e., intra prediction and inter frame prediction). Intra prediction processing unit <NUM> may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer <NUM>. Reference buffer <NUM> may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. Inter prediction processing unit <NUM> may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer <NUM>. Inter prediction processing unit <NUM> may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit <NUM> may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block. Post filter unit <NUM> may be configured to perform filtering on reconstructed video data. For example, post filter unit <NUM> may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering, e.g., based on parameters specified in a bitstream. Further, it should be noted that in some examples, post filter unit <NUM> may be configured to perform proprietary discretionary filtering (e.g., visual enhancements, such as, mosquito noise reduction). As illustrated in <FIG>, a reconstructed video block may be output by video decoder <NUM>. In this manner, video decoder <NUM> represents an example of a device configured to parse one or more syntax elements included in a parameter set, the syntax elements indicating one or more candidate reference picture lists, parse an index from a header associated with a region of a picture, the index indicating one of the candidate reference picture lists, and generate video data based on the indicated candidate reference picture list.

In this manner, computer-readable media generally may correspond to (<NUM>) tangible computer-readable storage media which is non-transitory or (<NUM>)a communication medium such as a signal or carrier wave.

Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples are within the claimed subject-matter.

Claim 1:
A method for determining reference picture list information for a reference picture list, the method being carried out by a video decoding device (<NUM>) and comprising:
decoding a reference picture list structure in a sequence parameter set or a slice header;
decoding an override flag in the slice header, in a case that a slice type is a P slice type or a B slice type, wherein the override flag specifies whether number of reference indexes active syntax elements are present;
deriving a reference picture list index for the reference picture list structure according to a value of a reference picture list flag, which specifies the reference picture list;
decoding at least one of the number of reference indexes active syntax elements in the slice header, in a case that (i) a value of the override flag indicates that the number of reference indexes active syntax elements are present and (ii) a number of entries in the reference picture list structure defined by the reference picture list index is greater than <NUM>, wherein the number of reference indexes active syntax elements are used for a derivation of a variable; and
deriving the variable by adding one to a value of at least one of the number of reference indexes active syntax elements, wherein a value of the variable minus one specifies a maximum reference index for the reference picture list, wherein:
the reference picture list structure specifies a list index of a current picture or a candidate for the list index, and
a value of a first syntax element of the number of reference indexes active syntax elements is inferred to be equal to zero, in a case that (i) the slice type of a current slice is the B slice type, (ii) a value of the override flag indicates that the number of reference indexes active syntax elements are present and (iii) the first syntax element is not present.