WO2020112488A1 - Signaling of reference picture lists in video coding - Google Patents

Abstract

A method of encoding a video bitstream implemented by a video encoder is provided. The method includes determining that a reference picture cannot be uniquely identified using picture order count (POC) least significant bits (LSBs) corresponding to other reference pictures, and inserting additional POC LSBs into a slice header of the video bitstream to uniquely identify the reference picture following the determination. The method further includes setting a flag of the video bitstream to a first value (e.g., true or 1) to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture. The method also includes transmitting the video bitstream toward the video decoder.

Description

Signaling of Reference Picture Lists in Video Coding

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 62/773,835, filed November 30, 2018, by Ye-Kui Wang, et ab, and titled“Signaling of Reference Picture Lists in Video Coding,” and U.S. Provisional Patent Application No. 62/774,750, filed December 3, 2018, by Ye-Kui Wang, et ab, and titled“Signaling of Reference Picture Lists in Video Coding,” each of which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] In general, this disclosure describes techniques for signaling efficiency improvements on reference picture management in video coding. More specifically, this disclosure describes techniques for improved signaling for construction of reference picture lists and reference picture marking that is directly based on reference picture lists.

BACKGROUND

[0003] The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in image quality are desirable.

SUMMARY

[0004] A first aspect relates to a method of encoding a video bitstream implemented by a video encoder, the method comprising determining, by the video encoder, that a reference picture cannot be uniquely identified using picture order count (POC) least significant bits (LSBs) corresponding to other reference pictures; inserting, by the video encoder, additional POC LSBs into a slice header of the video bitstream to uniquely identify the reference picture following the determination; setting, by the video encoder, a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture; and transmitting, by the video encoder, the video bitstream toward the video decoder.

[0005] The method provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

[0006] In a first implementation form of the method according to the first aspect as such, the first value is one.

[0007] In a second implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the reference picture is a long term reference picture.

[0008] In a third implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the other reference pictures are from reference picture lists signaled in the slice header.

[0009] In a fourth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the other reference pictures are from a decoded picture buffer (DPB).

[0010] In a fifth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the flag is designated additional_poc_lsb_present.

[0011] In a sixth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the flag is encoded in the slice header. [0012] In a seventh implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the reference picture cannot be uniquely identified when a POC LSB value corresponding to the reference picture is the same as another POC LSB value in a set of previous POC LSB values.

[0013] In an eighth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the set of previous POC LSB values is designated setOfPrevPocVals.

[0014] In a ninth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the set of previous POC values contains a POC LSB value corresponding to a previous picture.

[0015] In a tenth implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the set of previous POC LSB values contains a POC LSB value corresponding to each reference picture in a first reference picture list and a second reference picture list for the previous picture.

[0016] In an eleventh implementation form of the method according to the first aspect as such or any preceding implementation form of the first aspect, the set of previous POC LSB values contains a POC LSB value corresponding to each reference picture following the previous picture in decoding order and each reference picture preceding a current picture in the decoding order.

[0017] A second aspect relates to a method of decoding a video bitstream implemented by a video decoder. The method comprises determining, by the video decoder, that a flag in the coded video bitstream has been set to a first value; determining, by the video decoder, that a slice header of the coded video bitstream contains additional picture order count (POC) least significant bits (LSBs) that uniquely identify a reference picture based on the flag having the first value; parsing, by the video decoder, the slice header to obtain the additional POC LSBs corresponding to the reference picture; utilizing, by the video decoder, the additional POC LSBs to identify the reference picture; and performing, by the video decoder, inter-prediction using the reference picture to generate a reconstructed block.

[0018] The method provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

[0019] In a first implementation form of the method according to the second aspect as such, the first value is one.

[0020] In a second implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the reference picture is a long term reference picture.

[0021] In a third implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the flag is designated additional_poc_lsb_present.

[0022] In a fourth implementation form of the method according to the second aspect as such or any preceding implementation form of the second aspect, the flag is in the slice header.

[0023] A third aspect relates to an encoding device. The encoding device includes a memory containing instructions; a processor coupled to the memory, the processor configured to implement the instructions to cause the encoding device to determine that a reference picture cannot be uniquely identified using picture order count (POC) least significant bits (LSBs) corresponding to other reference pictures; insert additional POC LSBs into a slice header of the video bitstream to uniquely identify the reference picture following the determination; and set a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture; and a transmitter coupled to the processor, the transmitter configured to transmit the video bitstream toward a video decoder.

[0024] The encoding device provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

[0025] In a first implementation form of the encoding device according to the third aspect as such, the first value is one. [0026] In a second implementation form of the encoding device according to the third aspect as such or any preceding implementation form of the third aspect, the reference picture is a long term reference picture.

[0027] In a third implementation form of the encoding device according to the third aspect as such or any preceding implementation form of the third aspect, the other reference pictures are from reference picture lists signaled in the slice header or a decoded picture buffer (DPB).

[0028] In a fourth implementation form of the encoding device according to the third aspect as such or any preceding implementation form of the third aspect, the flag is designated additional_poc_lsb_present.

[0029] In a fifth implementation form of the encoding device according to the third aspect as such or any preceding implementation form of the third aspect, the flag is encoded in the slice header.

[0030] A fourth aspect relates to a decoding device. The decoding device includes a receiver configured to receive a coded video bitstream; a memory coupled to the receiver, the memory storing instructions; and a processor coupled to the memory, the processor configured to execute the instructions to cause the decoding device to: determine that a flag in the coded video bitstream has been set to a first value, determine that a slice header of the coded video bitstream contains additional picture order count (POC) least significant bits (LSBs) that uniquely identify a reference picture based on the flag having the first value; parse the slice header to obtain the additional POC LSBs corresponding to the reference picture; utilize the additional POC LSBs to identify the reference picture; and perform inter-prediction using the reference picture to generate a reconstructed block.

[0031] The decoding device provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed. [0032] In a first implementation form of the decoding device according to the fourth aspect as such, the decoding device further comprises a display configured to display an image generated using the reconstructed block.

[0033] A fifth aspect relates to a coding apparatus. The coding apparatus includes a receiver configured to receive a bitstream to decode; a transmitter coupled to the receiver, the transmitter configured to transmit a decoded image to a display; a memory coupled to at least one of the receiver or the transmitter, the memory configured to store instructions; and a processor coupled to the memory, the processor configured to execute the instmctions stored in the memory to perform the methods described herein.

[0034] The coding apparatus provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

[0035] A sixth aspect relates to a system. The system includes an encoder; and a decoder in communication with the encoder, wherein the encoder or the decoder includes the decoding device, the encoding device, or the coding apparatus disclosed herein.

[0036] The system provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

[0037] A seventh aspect relates to a means for coding. The means for coding includes receiving means configured to receive a bitstream to decode; transmission means coupled to the receiving means, the transmission means configured to transmit a decoded image to a display means; storage means coupled to at least one of the receiving means or the transmission means, the storage means configured to store instructions; and processing means coupled to the storage means, the processing means configured to execute the instructions stored in the storage means to perform the methods disclosed herein.

[0038] The means for coding provides techniques that simplify and make more efficient the coding process. By setting a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference pictures, the coder / decoder (a.k.a.,“codec”) in video coding is improved (e.g., utilizes less bits, demands less bandwidth, is more efficient, etc.) relative to current codecs. As a practical matter, the improved video coding process offers the user a better user experience when videos are sent, received, and/or viewed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0040] FIG. 1 is a block diagram illustrating an example coding system that may utilize bi lateral prediction techniques.

[0041] FIG. 2 is a block diagram illustrating an example video encoder that may implement bi lateral prediction techniques.

[0042] FIG. 3 is a block diagram illustrating an example of a video decoder that may implement bi-lateral prediction techniques.

[0043] FIG. 4 is a schematic diagram illustrating a reference picture set (RPS) having a current picture with entries in all subsets of the RPS.

[0044] FIG. 5 is a schematic diagram of an embodiment of a video bitstream.

[0045] FIG. 6 is an embodiment of a method of encoding a video bitstream.

[0046] FIG. 7 is an embodiment of a method of decoding a coded video bitstream.

[0047] FIG. 8 is a schematic diagram of a video coding device.

[0048] FIG. 9 is a schematic diagram of an embodiment of a means for coding.

DETAILED DESCRIPTION

[0049] The following are various acronyms employed herein: Coded Video Sequence (CVS), Decoded Picture Buffer (DPB), Instantaneous Decoding Refresh (IDR), Intra Random Access Point (IRAP), Least Significant Bit (LSB), Most Significant Bit (MSB), Network Abstraction Layer (NAL), Picture Order Count (POC), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set (SPS), and Working Draft (WD).

[0050] FIG. 1 is a block diagram illustrating an example coding system 10 that may utilize video coding techniques as described herein. As shown in FIG. 1, the coding system 10 includes a source device 12 that provides encoded video data to be decoded at a later time by a destination device 14. In particular, the source device 12 may provide the video data to destination device 14 via a computer- readable medium 16. Source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called“smart” phones, so-called “smart” pads, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device 12 and destination device 14 may be equipped for wireless communication.

[0051] Destination device 14 may receive the encoded video data to be decoded via computer- readable medium 16. Computer-readable medium 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. In one example, computer-readable medium 16 may comprise a communication medium to enable source device 12 to transmit encoded video data directly to destination device 14 in real-time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 12 to destination device 14.

[0052] In some examples, encoded data may be output from output interface 22 to a storage device. Similarly, encoded data may be accessed from the storage device by input interface. The storage device may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, digital video disks (DYD)s, Compact Disc Read-Only Memories (CD-ROMs), flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by source device 12. Destination device 14 may access stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting that encoded video data to the destination device 14. Example file servers include a web server (e.g., for a website), a file transfer protocol (FTP) server, network attached storage (NAS) devices, or a local disk drive. Destination device 14 may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSF), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server. The transmission of encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof.

[0053] The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.

[0054] In the example of FIG. 1, source device 12 includes video source 18, video encoder 20, and output interface 22. Destination device 14 includes input interface 28, video decoder 30, and display device 32. In accordance with this disclosure, video encoder 20 of the source device 12 and/or the video decoder 30 of the destination device 14 may be configured to apply the techniques for video coding. In other examples, a source device and a destination device may include other components or arrangements. For example, source device 12 may receive video data from an external video source, such as an external camera. Fikewise, destination device 14 may interface with an external display device, rather than including an integrated display device.

[0055] The illustrated coding system 10 of FIG. 1 is merely one example. Techniques for video coding may be performed by any digital video encoding and/or decoding device. Although the techniques of this disclosure generally are performed by a video coding device, the techniques may also be performed by a video encoder/decoder, typically referred to as a “CODEC.” Moreover, the techniques of this disclosure may also be performed by a video preprocessor. The video encoder and/or the decoder may be a graphics processing unit (GPU) or a similar device.

[0056] Source device 12 and destination device 14 are merely examples of such coding devices in which source device 12 generates coded video data for transmission to destination device 14. In some examples, source device 12 and destination device 14 may operate in a substantially symmetrical manner such that each of the source and destination devices 12, 14 includes video encoding and decoding components. Hence, coding system 10 may support one way or two-way video transmission between video devices 12, 14, e.g., for video streaming, video playback, video broadcasting, or video telephony.

[0057] Video source 18 of source device 12 may include a video capture device, such as a video camera, a video archive containing previously captured video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source 18 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer- generated video.

[0058] In some cases, when video source 18 is a video camera, source device 12 and destination device 14 may form so-called camera phones or video phones. As mentioned above, however, the techniques described in this disclosure may be applicable to video coding in general, and may be applied to wireless and/or wired applications. In each case, the captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video information may then be output by output interface 22 onto a computer-readable medium 16.

[0059] Computer-readable medium 16 may include transient media, such as a wireless broadcast or wired network transmission, or storage media (that is, non-transitory storage media), such as a hard disk, flash drive, compact disc, digital video disc, Blu-ray disc, or other computer- readable media. In some examples, a network server (not shown) may receive encoded video data from source device 12 and provide the encoded video data to destination device 14, e.g., via network transmission. Similarly, a computing device of a medium production facility, such as a disc stamping facility, may receive encoded video data from source device 12 and produce a disc containing the encoded video data. Therefore, computer-readable medium 16 may be understood to include one or more computer-readable media of various forms, in various examples. [0060] Input interface 28 of destination device 14 receives information from computer- readable medium 16. The information of computer-readable medium 16 may include syntax information defined by video encoder 20, which is also used by video decoder 30, that includes syntax elements that describe characteristics and/or processing of blocks and other coded units, e.g., group of pictures (GOPs). Display device 32 displays the decoded video data to a user, and may comprise any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0061] Video encoder 20 and video decoder 30 may operate according to a video coding standard, such as the High Efficiency Video Coding (HE VC) standard presently under development, and may conform to the HEVC Test Model (HM). Alternatively, video encoder 20 and video decoder 30 may operate according to other proprietary or industry standards, such as the International Telecommunications Union Telecommunication Standardization Sector (ITU-T) H.264 standard, alternatively referred to as Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC), H.265/HEVC, or extensions of such standards. The techniques of this disclosure, however, are not limited to any particular coding standard. Other examples of video coding standards include MPEG-2 and ITU-T H.263. Although not shown in FIG. 1, in some aspects, video encoder 20 and video decoder 30 may each be integrated with an audio encoder and decoder, and may include appropriate multiplexer-demultiplexer (MUX-DEMUX) units, or other hardware and software, to handle encoding of both audio and video in a common data stream or separate data streams. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP).

[0062] Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device. A device including video encoder 20 and/or video decoder 30 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.

[0063] FIG. 2 is a block diagram illustrating an example of video encoder 20 that may implement video coding techniques. Video encoder 20 may perform intra- and inter-coding of video blocks within video slices. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode (I mode) may refer to any of several spatial based coding modes. Inter-modes, such as uni-directional (a.k.a., uni prediction) prediction (P mode) or bi-prediction (a.k.a., bi prediction) (B mode), may refer to any of several temporal-based coding modes.

[0064] As shown in FIG. 2, video encoder 20 receives a current video block within a video frame to be encoded. In the example of FIG. 2, video encoder 20 includes mode select unit 40, reference frame memory 64, summer 50, transform processing unit 52, quantization unit 54, and entropy coding unit 56. Mode select unit 40, in turn, includes motion compensation unit 44, motion estimation unit 42, intra-prediction (a.k.a., intra prediction) unit 46, and partition unit 48. For video block reconstruction, video encoder 20 also includes inverse quantization unit 58, inverse transform unit 60, and summer 62. A deblocking filter (not shown in FIG. 2) may also be included to filter block boundaries to remove blockiness artifacts from reconstructed video. If desired, the deblocking filter would typically filter the output of summer 62. Additional filters (in loop or post loop) may also be used in addition to the deblocking filter. Such filters are not shown for brevity, but if desired, may filter the output of summer 50 (as an in-loop filter).

[0065] During the encoding process, video encoder 20 receives a video frame or slice to be coded. The frame or slice may be divided into multiple video blocks. Motion estimation unit 42 and motion compensation unit 44 perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal prediction. Intra-prediction unit 46 may alternatively perform intra-predictive coding of the received video block relative to one or more neighboring blocks in the same frame or slice as the block to be coded to provide spatial prediction. Video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

[0066] Moreover, partition unit 48 may partition blocks of video data into sub-blocks, based on evaluation of previous partitioning schemes in previous coding passes. For example, partition unit 48 may initially partition a frame or slice into largest coding units (LCUs), and partition each of the LCUs into sub-coding units (sub-CUs) based on rate-distortion analysis (e.g., rate-distortion optimization). Mode select unit 40 may further produce a quad-tree data structure indicative of partitioning of a LCU into sub-CUs. Leaf-node CUs of the quad-tree may include one or more prediction units (PUs) and one or more transform units (TUs).

[0067] The present disclosure uses the term“block” to refer to any of a CU, PU, or TU, in the context of HEYC, or similar data structures in the context of other standards (e.g., macroblocks and sub-blocks thereof in H.264/AYC). A CU includes a coding node, PUs, and TUs associated with the coding node. A size of the CU corresponds to a size of the coding node and is square in shape. The size of the CU may range from 8^c8 pixels up to the size of the treeblock with a maximum of 64x64 pixels or greater. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may describe, for example, partitioning of the CU into one or more PUs. Partitioning modes may differ between whether the CU is skip or direct mode encoded, intra-prediction mode encoded, or inter-prediction (a.k.a., inter prediction) mode encoded. PUs may be partitioned to be non-square in shape. Syntax data associated with a CU may also describe, for example, partitioning of the CU into one or more TUs according to a quad tree. A TU can be square or non-square (e.g., rectangular) in shape.

[0068] Mode select unit 40 may select one of the coding modes, intra- or inter-, e.g., based on error results, and provides the resulting intra- or inter-coded block to summer 50 to generate residual block data and to summer 62 to reconstruct the encoded block for use as a reference frame. Mode select unit 40 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy coding unit 56.

[0069] Motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a PU of a video block within a current video frame or picture relative to a predictive block within a reference frame (or other coded unit) relative to the current block being coded within the current frame (or other coded unit). A predictive block is a block that is found to closely match the block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. In some examples, video encoder 20 may calculate values for sub-integer pixel positions of reference pictures stored in reference frame memory 64. For example, video encoder 20 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.

[0070] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture. The reference picture may be selected from a first reference picture list (List 0) or a second reference picture list (List 1), each of which identify one or more reference pictures stored in reference frame memory 64. Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.

[0071] Motion compensation, performed by motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit 42. Again, motion estimation unit 42 and motion compensation unit 44 may be functionally integrated, in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may locate the predictive block to which the motion vector points in one of the reference picture lists. Summer 50 forms a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values, as discussed below. In general, motion estimation unit 42 performs motion estimation relative to luma components, and motion compensation unit 44 uses motion vectors calculated based on the luma components for both chroma components and luma components. Mode select unit 40 may also generate syntax elements associated with the video blocks and the video slice for use by video decoder 30 in decoding the video blocks of the video slice.

[0072] Intra-prediction unit 46 may intra-predict a current block, as an alternative to the inter prediction performed by motion estimation unit 42 and motion compensation unit 44, as described above. In particular, intra-prediction unit 46 may determine an intra-prediction mode to use to encode a current block. In some examples, intra-prediction unit 46 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and intra-prediction unit 46 (or mode select unit 40, in some examples) may select an appropriate intra-prediction mode to use from the tested modes. [0073] For example, intra-prediction unit 46 may calculate rate-distortion values using a rate- distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (that is, a number of bits) used to produce the encoded block. Intra-prediction unit 46 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra prediction mode exhibits the best rate-distortion value for the block.

[0074] In addition, intra-prediction unit 46 may be configured to code depth blocks of a depth map using a depth modeling mode (DMM). Mode select unit 40 may determine whether an available DMM mode produces better coding results than an intra-prediction mode and the other DMM modes, e.g., using rate-distortion optimization (RDO). Data for a texture image corresponding to a depth map may be stored in reference frame memory 64. Motion estimation unit 42 and motion compensation unit 44 may also be configured to inter-predict depth blocks of a depth map.

[0075] After selecting an intra-prediction mode for a block (e.g., a conventional intra prediction mode or one of the DMM modes), intra-prediction unit 46 may provide information indicative of the selected intra-prediction mode for the block to entropy coding unit 56. Entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. Video encoder 20 may include in the transmitted bitstream configuration data, which may include a plurality of intra-prediction mode index tables and a plurality of modified intra-prediction mode index tables (also referred to as codeword mapping tables), definitions of encoding contexts for various blocks, and indications of a most probable intra-prediction mode, an intra-prediction mode index table, and a modified intra-prediction mode index table to use for each of the contexts.

[0076] Video encoder 20 forms a residual video block by subtracting the prediction data from mode select unit 40 from the original video block being coded. Summer 50 represents the component or components that perform this subtraction operation.

[0077] Transform processing unit 52 applies a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform, to the residual block, producing a video block comprising residual transform coefficient values. Transform processing unit 52 may perform other transforms which are conceptually similar to DCT. Wavelet transforms, integer transforms, sub band transforms or other types of transforms could also be used.

[0078] Transform processing unit 52 applies the transform to the residual block, producing a block of residual transform coefficients. The transform may convert the residual information from a pixel value domain to a transform domain, such as a frequency domain. Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of the matrix including the quantized transform coefficients. Alternatively, entropy encoding unit 56 may perform the scan.

[0079] Following quantization, entropy coding unit 56 entropy codes the quantized transform coefficients. For example, entropy coding unit 56 may perform context adaptive variable length coding (CAYLC), context adaptive binary arithmetic coding (CABAC), syntax-based context- adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy coding technique. In the case of context-based entropy coding, context may be based on neighboring blocks. Following the entropy coding by entropy coding unit 56, the encoded bitstream may be transmitted to another device (e.g., video decoder 30) or archived for later transmission or retrieval.

[0080] Inverse quantization unit 58 and inverse transform unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block. Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the frames of reference frame memory 64. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Summer 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reconstructed video block for storage in reference frame memory 64. The reconstructed video block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block to inter-code a block in a subsequent video frame.

[0081] FIG. 3 is a block diagram illustrating an example of video decoder 30 that may implement video coding techniques. In the example of FIG. 3, video decoder 30 includes an entropy decoding unit 70, motion compensation unit 72, intra-prediction unit 74, inverse quantization unit 76, inverse transformation unit 78, reference frame memory 82, and summer 80. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 20 (FIG. 2). Motion compensation unit 72 may generate prediction data based on motion vectors received from entropy decoding unit 70, while intra-prediction unit 74 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 70.

[0082] During the decoding process, video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video slice and associated syntax elements from video encoder 20. Entropy decoding unit 70 of the video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 70 forwards the motion vectors and other syntax elements to motion compensation unit 72. Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level.

[0083] When the video slice is coded as an intra-coded (I) slice, intra-prediction unit 74 may generate prediction data for a video block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter-coded (e.g., B, P, or GPB) slice, motion compensation unit 72 produces predictive blocks for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 70. The predictive blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in reference frame memory 82.

[0084] Motion compensation unit 72 determines prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit 72 uses some of the received syntax elements to determine a prediction mode (e.g., intra- or inter-prediction) used to code the video blocks of the video slice, an inter-prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter-encoded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information to decode the video blocks in the current video slice.

[0085] Motion compensation unit 72 may also perform interpolation based on interpolation filters. Motion compensation unit 72 may use interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 72 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.

[0086] Data for a texture image corresponding to a depth map may be stored in reference frame memory 82. Motion compensation unit 72 may also be configured to inter-predict depth blocks of a depth map.

[0087] Image and video compression has experienced rapid growth, leading to various coding standards. Such video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Part 2, ITU-T H.262 or ISO/IEC MPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding (AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and High Efficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part 2. AVC includes extensions such as Scalable Video Coding (SVC), Multiview Video Coding (MVC) and Multiview Video Coding plus Depth (MVC+D), and 3D AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC). The latest published specification of HEVC is available at https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.265-201802-1! !PDF- E&type=items.

[0088] There is also a new video coding standard, named Versatile Video Coding (VVC), being developed by the joint video experts team (JVET) of ITU-T and ISO/IEC. The latest Working Draft (WD) of VVC included in JVET-L1001-vl, which is publicly available at http://phenix.int-evry.fr/jvet/doc_end_user/documents/12_Macao/wgl 1/JVET-L 1001 -v4.zip.

[0089] The video coding basics are discussed.

[0090] Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (i.e., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as treeblocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.

[0091] Spatial or temporal prediction results in a predictive block for a block to be coded. Residual data represents pixel differences between the original block to be coded and the predictive block. An inter-coded block is encoded according to a motion vector that points to a block of reference samples forming the predictive block, and the residual data indicating the difference between the coded block and the predictive block. An intra-coded block is encoded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain, resulting in residual transform coefficients, which then may be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned in order to produce a one-dimensional vector of transform coefficients, and entropy coding may be applied to achieve even more compression.

[0092] The reference picture management in video decoding is discussed.

[0093] In a video codec specification, pictures need to be identified for multiple purposes, including for use as a reference picture in inter prediction, for output of pictures from the decoded picture buffer (DPB), for scaling of motion vectors, for weighted prediction, etc. In an embodiment, the DPB is contained in a memory (e.g., reference frame memory 82).

[0094] In AVC and HEVC, pictures can be identified by picture order count (POC).

[0095] In AVC and HEVC, pictures in the DPB can be marked as“used for short-term reference,”“used for long-term reference,” or“unused for reference.” Once a picture has been marked“unused for reference,” the picture can no longer be used for prediction. In addition, when the picture is no longer needed for output the picture can be removed from the DPB.

[0096] In AVC, there are two types of reference pictures, short-term and long-term. A reference picture may be marked as“unused for reference” when the picture becomes no longer needed for prediction reference. The conversion among these three statuses (e.g., short-term, long term, and unused for reference) is controlled by the decoded reference picture marking process. There are two alternative decoded reference picture marking mechanisms, the implicit sliding window process and the explicit memory management control operation (MMCO) process. The sliding window process marks a short-term reference picture as“unused for reference” when the number of reference frames is equal to a given maximum number (max num ref frames in the SPS). The short-term reference pictures are stored in a first-in, first-out manner so that the most recently decoded short-term pictures are kept in the DPB.

[0097] The explicit MMCO process may include multiple MMCO commands. An MMCO command may mark one or more short-term or long-term reference picture as “unused for reference,” mark all the pictures as“unused for reference,” or mark the current reference picture or an existing short-term reference picture as long-term, and assign a long-term picture index to that long-term reference picture.

[0098] In AYC the reference picture marking operations as well as the processes for output and removal of pictures from the DPB are performed after a picture has been decoded.

[0099] HEYC introduces a different approach for reference picture management, referred to as reference picture set (RPS). The most fundamental difference with the RPS concept compared to MMCO/sliding window of AVC is that for each particular slice a complete set of the reference pictures that are used by the current picture or any subsequent picture is provided. Thus, a complete set of all pictures that must be kept in the DPB for use by the current or future picture is signaled. This is different from the AVC scheme where only relative changes to the DPB are signaled. With the RPS concept, no information from earlier pictures in decoding order is needed to maintain the correct status of reference pictures in the DPB.

[00100] The order of picture decoding and DPB operations in HEVC is changed compared to AVC in order to exploit the advantages of RPS and improve error resilience. In AVC picture marking and buffer operations (both output and removal of decoded pictures from the DPB) are generally applied after a current picture has been decoded. In HEVC, the RPS is first decoded from a slice header of the current picture, then picture marking and buffer operations are generally applied before decoding the current picture.

[00101] The signaling of RPS in HEVC is discussed.

[00102] Each slice header in HEVC must include parameters for signaling of the RPS for the picture containing the slices. The only exception is that no RPS is signaled for IDR slices. Instead, the RPS is inferred to be empty. For I slices that do not belong to an IDR picture, an RPS may be provided, even if they belong to an I picture since there may be pictures following the I picture in decoding order which use inter-prediction from pictures that preceded the I picture in decoding order. The number of pictures in an RPS shall not exceed the DPB size limit as specified by the sps_max_dec_pic_buffering syntax element in the SPS.

[00103] Each picture is associated with a POC value that represents the output order. The slice headers contain a fixed-length codeword, pic order cnt lsb, representing the least significant bits of the full POC value, also known as the POC LSB. The length of the codeword is signaled in the SPS and can be between 4 and 16 bits. The RPS concept uses POC to identify reference pictures. Besides its own POC value, each slice header directly contains or inherits from the SPS a coded representation of the POC values (or the LSBs) of each picture in the RPS.

[00104] The RPS for each picture consists of five different lists of reference pictures, also referred to the five RPS subsets: RefPicSetStCurrBefore consists of all short-term reference pictures that are prior to the current picture in both decoding order and output order, and that may be used in inter prediction of the current picture. RefPicSetStCurrAfter consists of all short-term reference pictures that are prior to the current picture in decoding order, that succeed the current picture in output order, and that may be used in inter prediction of the current picture. RefPicSetStFoll consists of all short-term reference pictures that may be used in inter prediction of one or more of the pictures following the current picture in decoding order, and that are not used in inter prediction of the current picture. RefPicSetLtCurr consists of all long-term reference pictures that may be used in inter prediction of the current picture. RefPicSetLtFoll consists of all long term reference pictures that may be used in inter prediction of one or more of the pictures following the current picture in decoding order, and that are not used in inter prediction of the current picture.

[00105] The RPS is signaled using up to three loops iterating over different types of reference pictures; short-term reference pictures with lower POC value than the current picture, short-term reference pictures with higher POC value than the current picture, and long-term reference pictures. In addition, a flag (used_by_curr_pic_X_flag) is sent for each reference picture indicating whether the reference picture is used for reference by the current picture (included in one of the lists RefPicSetStCurrBefore, RefPicSetStCurrAfter or RefPicSetFtCurr) or not (included in one of the lists RefPicSetStFoll or RefPicSetFtFoll). [00106] FIG. 4 illustrates an RPS 400 having a current picture B14 with entries (e.g., a picture) in all subsets 402 of the RPS 400. In the example in FIG. 4, the current picture B14 contains exactly one picture in each of the five subsets 402 (a.k.a., RPS subsets). P8 is the picture in the subset 402 referred to as RefPicSetStCurrBefore because the picture is before in output order and used by B14. PI 2 is the picture in the subset 402 referred to as RefPicSetStCurrAfter because the picture is after in output order and used by B14. PI 3 is the picture in the subset 402 referred to as RefPicSetStFoll because the picture is a short-term reference picture not used by B14 (but must be kept in the DPB since it is used by B15). P4 is the picture in the subset 402 referred to as RefPicSetLtCurr because the picture is a long-term reference picture used by B14. 10 is the picture in the subset 402 referred to as RefPicSetLtFoll since the picture is a long-term reference picture not used by the current picture (but must be kept in the DPB since it is used by B15).

[00107] The short-term part of the RPS 400 may be included directly in the slice header. Alternatively, the slice header may contain only a syntax element which represents an index, referencing to a predefined list of RPSs sent in the active SPS. The short-term part of the RPS 402 can be signaled using either of two different schemes; Inter RPS, as described below, or Intra RPS, as described here. When Intra RPS is used, num_negative_pics and num_positive_pics are signaled representing the length of two different lists of reference pictures. These lists contain the reference pictures with negative POC difference and positive POC difference compared to the current picture, respectively. Each element in these lists is encoded with a variable length code representing the difference in POC value relative to the previous element in the list minus one. For the first picture in each list, the signaling is relative to the POC value of the current picture minus one.

[00108] When encoding the recurring RPSs in the sequence parameter set, it is possible to encode the elements of one RPS (e.g., RPS 400) with reference to another RPS already encoded in the sequence parameter set. This is referred to as Inter RPS. There are no error robustness problems associated with this method as all the RPSs of the sequence parameter set are in the same network abstraction layer (NAL) unit. The Inter RPS syntax exploits the fact that the RPS of the current picture can be predicted from the RPS of a previously decoded picture. This is because all the reference pictures of the current picture must either be reference pictures of the previous picture or the previously decoded picture itself. It is only necessary to indicate which of these pictures should be reference pictures and be used for the prediction of the current picture. Therefore, the syntax comprises the following: an index pointing to the RPS to use as a predictor, a delta POC to be added to the delta POC of the predictor to obtain the delta POC of the current RPS, and a set of indicators to indicate which pictures are reference pictures and whether they are only used for the prediction of future pictures. In an embodiment, delta POC refers to the difference in POC value between a current reference picture and another (e.g., previous) reference picture.

[00109] Encoders that would like to exploit the use of long-term reference pictures must set the SPS syntax element long_term_ref_pics_present_flag to one. Long-term reference pictures can then be signaled in the slice header by fixed-length codewords, poc lsb lt, representing the least significant bits of the full POC value of each long-term picture. Each poc lsb lt is a copy of the pic order cnt lsb codeword that was signaled for a particular long-term picture. It is also possible to signal a set of long-term pictures in the SPS as a list of POC LSB values. The POC LSB for a long-term picture can then be signaled in the slice header as an index to this list.

[00110] The delta_poc_msb_cycle_lt_minusl syntax element can additionally be signaled to enable the calculation of the full POC distance of a long-term reference picture relative to the current picture. It is required that the codeword delta_poc_msb_cycle_lt_minusl is signaled for each long-term reference picture that has the same POC LSB value as any other reference picture in the RPS.

[00111] The reference picture marking in HEYC is discussed.

[00112] Before picture decoding, there will typically be a number of pictures present in the DPB. Some of the pictures may be available for prediction and thus marked as“used for reference.” Other pictures may be unavailable for prediction but waiting for output, thus marked as“unused for reference.” When the slice header has been parsed, a picture marking process is carried out before the slice data is decoded. Pictures that are present in the DPB and marked as “used for reference” but are not included in the RPS are marked“unused for reference.” Pictures that are not present in the DPB but are included in the reference picture set are ignored when the used_by_curr_pic_X_flag is equal to zero. However, when the used_by_curr_pic_X_flag instead is equal to one, this reference picture was intended to be used for prediction in the current picture but is missing. Then an unintentional picture loss is inferred and the decoder should take appropriate actions.

[00113] After decoding the current picture, it is marked“used for short-term reference”.

[00114] The reference picture list construction in HEYC is discussed. [00115] In HEYC, the term inter prediction is used to denote prediction derived from data elements (e.g., sample values or motion vectors) of reference pictures other than the current decoded picture. Like in AYC, a picture can be predicted from multiple reference pictures. The reference pictures that are used for inter prediction are organized in one or more reference picture lists. The reference index identifies which of the reference pictures in the list should be used for creating the prediction signal.

[00116] A single reference picture list, List 0, is used for a P slice and two reference picture lists, List 0 and List 1, are used for B slices. Similar to AVC, the reference picture list construction in HEVC includes reference picture list initialization and reference picture list modification.

[00117] In AVC, the initialization process for List 0 is different for P slice (for which decoding order is used) and B slices (for which output order is used). In HEVC, output order is used in both cases.

[00118] Reference picture list initialization creates default List 0 and List 1 (if the slice is a B slice) based on three RPS subsets: RefPicSetStCurrBefore, RefPicSetStCurr After, and RefPicSetLtCurr. Short-term pictures with earlier (later) output order are firstly inserted into the List 0 (List 1) in ascending order of POC distance to the current picture, then short-term pictures with later (earlier) output order are inserted into the List 0 (List 1) in ascending order of POC distance to the current picture, and finally the long-term pictures are inserted at the end. In terms of RPS, for List 0, the entries in RefPicSetStCurrBefore are inserted in the initial list, followed by the entries in RefPicSetStCurrAfter. Afterwards, the entries in RefPicSetLtCurr, if available, are appended.

[00119] In HEVC, the above process is repeated (reference pictures that have already been added to the reference picture list are added again) when the number of entries in a list is smaller than the target number of active reference pictures (signaled in the picture parameter set or slice header). When the number of entries is larger than the target number the list is truncated.

[00120] After a reference picture list has been initialized, the reference picture may be modified such that the reference pictures for the current picture may be arranged in any order, including the case where one particular reference picture may appear in more than one position in the list, based on the reference picture list modification commands. When the flag that indicates whether the presence of list modifications is set to one, a fixed number (equal to the target number of entries in the reference picture list) of commands are signaled, and each command inserts one entry for a reference picture list. A reference picture is identified in the command by the index to the list of reference pictures for the current picture derived from the RPS signaling. This is different from reference picture list modification in H.264/AYC, wherein a picture is identified either by the picture number (derived from the frame num syntax element) or the long-term reference picture index, and it is possible that fewer commands are needed, e.g., for swapping the first two entries of an initial list or inserting one entry at the beginning of the initial list and shifting the others.

[00121] A reference picture list is not allowed to include any reference picture with Temporalld greater than the current picture. An HEYC bitstream might consist of several temporal sub-layers. Each NAL unit belongs to a specific sub-layer as indicated by the Temporalld (equal to temporal_id_plusl - 1).

[00122] The reference picture management directly based on reference picture lists is discussed.

[00123] JVET document JVET-L0112-v4, publicly available at http://phenix.int- evry.fr/jvet/doc_end_user/documents/12_Macao/wgl 1/JVET-LOl 12-v4.zip includes an approach for reference picture management based on two reference picture lists, reference picture list 0 and reference picture list 1. With that approach, reference picture lists for a picture are directly constructed without using a reference picture list initialization process and a reference picture list modification process. Furthermore, reference picture marking is directly based on the two reference picture lists.

[00124] The reference picture management for long-term reference pictures is discussed.

[00125] In HEVC, signaling of long-term reference pictures was specified by signaling the POC LSB of the long-term reference pictures (LTRPs), which can be signaled in SPS or in each slice header. As the technique only signals POC LSB of the LTRPs, it is possible that the LTRP cannot be differentiated from other reference pictures that are present in the DPB or in the RPS. To solve this issue, delta MSB cycle information may be signaled. Delta MSB cycle for an LTRP specifies the difference of MSB cycle between the LTRP and the current picture.

[00126] In JVET document JVET-L0112-v4, publicly available at http://phenix.int- evry.fr/jvet/doc_end_user/documents/12_Macao/wgl l/JVET-L0112-v4.zip and the present disclosure, another approach of signaling LTRPs is presented. While there are many differences between the signaling of LTRPs in HEYC and in the present disclosure (this also includes techniques described in JVET-L-114-v4), one of the major differences is the mechanism for differentiating LTRPs from other reference pictures when POC LSB is not sufficient. In the present disclosure, instead of signaling the delta MSB cycle between an LTRP and the current picture, additional bits for POC LSB may be signaled for the LTRP.

[00127] The problems of the Routing Protocol for Low-Power and Lossy Networks (RPL)- based reference picture management are discussed.

[00128] Existing approaches for signaling of reference picture management have the following issues.

[00129] In a prior approach, additional POC LSB bits may be signaled in the slice header for LTRPs. The presence of the additional bits is specified by a flag. The value of the flag can be either true or false, depending on what the encoder specified. When an LTRP cannot be differentiated from other reference pictures by only POC LSB, it is mandatory that the additional bits for POC LSB be present, however, the value of the present flag is not constrained to be true for such situation.

[00130] In addition, the signaling approach for LTRPs in HEYC may cost a lot of bits for signaling the delta MSB cycle. As the POC distance between current picture and the LTRP gets further apart, the required bits for the signaling of delta MSB cycle increases.

[00131] In order to solve the above problems, the following inventive aspects are disclosed. Each of them can be applied individually, and some of them can be applied in combination.

[00132] Disclosed herein are video coding techniques that mandate the signaling of additional bits for POC LSB in a slice header when a reference picture (e.g., a LTRP) cannot be uniquely identified using the usual number of POC LSBs from the reference pictures present in the DPB and the reference pictures associated with both reference picture lists signaled in the slice header. This consequently means that the value of an additional_poc_lsb_present_flag associated with the LTRP is equal to 1 when the LTRP cannot be uniquely identified by using the usual number of POC LSBs from the reference pictures present in the DPB and the reference pictures associated with both reference picture lists signaled in the slice header.

[00133] Alternatively, the additional_poc_lsb_present_flag associated with the LTRP is equal to 1 when there is more than one value in a set of setOfPrevPocVals that has the same value as POC LSB of the LTRP. In an embodiment, the setOfPrevPocVals contents are defined as follows: the PicOrderCntVal of prevTidOPic, the PicOrderCntVal of each picture in the RPL (i.e., RefPicList[ 0 ] and RefPicList[ 1 ]) of prevTidOPic, and the PicOrderCntVal of each picture that follows prevTidOPic in decoding order and precedes the current picture in decoding order.

[00134] Instead of signaling delta POC MSB for the LTRPs in reference picture set (RPS), additional POC LSBs are signaled and different pictures within a coded video sequence can use different numbers of additional POC LSBs. In an embodiment, the number of additional POC LSBs for signaling of LTRPs is signaled in the picture parameter set. Alternatively, the number of additional POC LSBs for signaling of LTRPs is signaled in the slice header (a.k.a., tile group header).

[00135] FIG. 5 is a schematic diagram of an embodiment of a video bitstream 500. As used herein the video bitstream 500 may also be referred to as a coded video bitstream, a bitstream, or variations thereof. As shown in FIG. 5, the bitstream 500 comprises a sequence parameter set (SPS) 510, a picture parameter set (PPS) 512, a slice header 514, and image data 520.

[00136] The SPS 510 contains data that is common to all the pictures in a sequence of pictures (SOP). In contrast, the PPS 512 contains data that is common to the entire picture. The slice header 514 contains information about the current slice such as, for example, the slice type, which of the reference pictures will be used, and so on. The SPS 510 and the PPS 512 may be generically referred to as a parameter set. The SPS 510, the PPS 512, and the slice header 514 are types of Network Abstraction Layer (NAL) units. The image data comprises data associated with the images or video being encoded or decoded. The image data 520 may be simply referred to as the payload or data being carried in the bitstream 500.

[00137] In an embodiment, the SPS 510, the PPS 512, the slice header 514, or another portion of the bitstream 500 carries a plurality of reference picture list structures, each of which contains a plurality of reference picture entries. Those skilled in the art will appreciate that the bitstream 500 may contain other parameters and information in practical applications.

[00138] FIG. 6 is an embodiment of a method 600 of encoding a video bitstream (e.g., bitstream 500) implemented by a video encoder (e.g., video encoder 20). The method 600 may be performed when a picture (e.g., from a video) is to be encoded into a video bitstream and then transmitted toward a video decoder (e.g., video decoder 30). The method 600 improves the encoding process (e.g., makes the encoding process more efficient, faster, etc., than conventional encoding processes) because a flag of the video bitstream is set to a first value (e.g., 1, or a true value) to indicate that the slice header contains additional POC LSBs that uniquely identify the reference picture. Therefore, as a practical matter, the performance of a codec is improved, which leads to a better user experience.

[00139] In block 602, the video encoder makes a determination that a reference picture cannot be uniquely identified using picture order count POC LSBs corresponding to other reference pictures. In an embodiment, the reference picture is a long term reference picture. In some circumstances, the other reference pictures are from reference picture lists signaled in the slice header (e.g., slice header 514). In other circumstances, the other reference pictures are from a DPB.

[00140] In an embodiment, the reference picture cannot be uniquely identified when a POC value corresponding to the reference picture is the same as another POC value in a set of previous POC values. In an embodiment, the set of previous POC values is designated setOfPrevPocVals. In an embodiment, the set of previous POC values contains a POC value corresponding to a previous reference picture.

[00141] In an embodiment, the set of previous POC values contains a POC value corresponding to each reference picture in a first reference picture list and a second reference picture list for the previous reference picture. In an embodiment, the set of previous POC values contains a POC value corresponding to each reference picture following the previous reference picture in decoding order and each reference picture preceding the reference picture in the decoding order.

[00142] In block 604, the video encoder inserts additional POC LSBs into the slice header of the video bitstream (e.g., bitstream 500) to uniquely identify the reference picture following the determination. In an embodiment, the additional POC LSBs may be inserted into another portion of the bitstream.

[00143] In block 606, the video encoder sets a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture. In an embodiment, the first value is true. In an embodiment, the first value is numerical such as, for example, 1. In an embodiment, the flag is designated additional_poc_lsb_present.

[00144] In block 608, the video encoder transmits the video bitstream (e.g., bitstream 500) toward a video decoder. The video bitstream may also be referred to as a coded video bitstream or an encoded video bitstream. Once received by the video decoder, the encoded video bitstream may be decoded (e.g., as described below) to generate or produce an image for display to a user on the display or screen of an electronic device (e.g., a smart phone, tablet, laptop, personal computer, etc.).

[00145] FIG. 7 is an embodiment of a method 700 of decoding a coded video bitstream (e.g., bitstream 500) implemented by a video decoder (e.g., video decoder 30). The method 700 may be performed after the decoded bitstream has been directly or indirectly received from a video encoder (e.g., video encoder 20). The method 700 improves the decoding process (e.g., makes the decoding process more efficient, faster, etc., than conventional decoding processes) because a flag of the video bitstream is set to a first value (e.g., 1, or a true value) to indicate that the slice header contains additional POC LSBs that uniquely identify the reference picture. Therefore, as a practical matter, the performance of a codec is improved, which leads to a better user experience.

[00146] In block 702, the video decoder determines that a flag in the coded video bitstream has been set to a first value. In an embodiment, the flag is in the slice header (e.g., the slice header 514). In an embodiment, the first value is true. In an embodiment, the first value is numerical such as, for example, 1. In an embodiment, the flag is designated additional_poc_lsb_present.

[00147] In block 704, the video decoder determines that a slice header of the coded video bitstream contains additional POC LSBs that uniquely identify a reference picture based on the flag having the first value. In an embodiment, the reference picture is a LTRP.

[00148] In block 706, the video decoder parses the slice header to obtain the additional POC LSBs corresponding to the reference picture. In block 708, the video decoder utilizes the additional POC LSBs to identify the reference picture.

[00149] In block 710, the video decoder performs inter-prediction using the reference picture to generate a reconstructed block. In an embodiment, the reconstructed block may be used to generate or produce an image for display to a user on the display or screen of an electronic device (e.g., a smart phone, tablet, laptop, personal computer, etc.).

[00150] A description of the techniques disclosed herein is provided relative to the latest approach in JYET-L0112-v4. Changed parts relative to the approach in JYET-L01 12-v4 are shown in bold, while the texts for the approach in JVET-L01 12-v4 that are not mentioned below apply as they are. In addition, syntax and semantics suitable for implementing the techniques disclosed herein are also provided. [00151] The sequence parameter set RBSP syntax is shown below. The sequence parameter set RBSP syntax in clause 7.3.2.1 of the latest YYC WD is changed as follows (changed parts are in bold):

[00152] The picture parameter set RBSP syntax is shown below. The picture parameter set RBSP syntax in clause 7.3.2.2 of the latest VVC WD is changed as follows (changed parts are in bold):

[00153] The slice header syntax is discussed. The slice header syntax in clause 7.3.3 of the latest YYC WD is changed as follows (changed parts are in bold):

[00154] The reference picture list structure syntax is discussed. Add the reference picture list structure syntax in new clause 7.3.4 to the latest YYC WD as follows:

[00155] The sequence parameter set RBSP semantics are discussed.

[00156] rpl_candidates_present_flag equal to 1 specifies that information about reference picture list candidates is present. rpl_candidates_present_flag equal to 0 specifies that information about reference picture list candidates is not present.

[00157] rpll same as rplO flag equal to 1 specifies that the syntax structures num_ref_pic_lists_in_sps[ 1 ] and ref_pic_list_struct( 1 , rplsldx, ItrpFlag ) are not present and the following applies:

[00158] - The value of num_ref_pic_lists_in_sps[ 1 ] is inferred to be equal to the value of num_ref_pic_lists_in_sps[ 0 ].

[00159] - The value of each of syntax elements in ref_pic_list_struct( 1, rplsldx, ItrpFlag ) is inferred to be equal to the value of corresponding syntax element in ref_pic_list_struct( 0, rplsldx, ItrpFlag ) for rplsldx ranging from 0 to num_ref_pic_lists_in_sps[ 0 ] - 1. [00160] num_ref_pic_lists_in_sps[ i ] specifies the number of the ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structures with listldx equal to i included in the SPS. The value of num_ref_pic_lists_in_sps[ i ] shall be in the range of 0 to 64, inclusive.

[00161] NOTE 2 - For each value of listldx (equal to 0 or 1), a decoder should allocate memory for a total number of num_ref_pic_lists_in_sps[ i ] + 1 ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structures since there may be one ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structure directly signalled in the slice headers of a current picture.

[00162] The picture parameter set RBSP semantics are discussed.

[00163] additional_lt_poc_lsb_len specifies the value of the variable MaxLtPicOrderCntLsb that is used in the decoding process for reference picture lists as follows:

[00164] MaxLtPicOrderCntLsb = 2( log2_max_pic_order_cnt_lsb_minus4 + 4 + addition al lt poc lsb len ) (7-20)

[00165] The value of additional_lt_poc_lsb_len shall be in the range of 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive.

[00166] When not present, the value of additional _lt _poc_lsb_len is inferred to be equal to 0.

[00167] rpll_idx_present_flag equal to 0 specifies that ref_pic_list_sps_flag[ 1 ] and ref_pic_list_idx[ 1 ] are not present in slice headers. rpll_idx_present_flag equal to 1 specifies that ref_pic_list_sps_flag[ 1 ] and ref_pic_list_idx[ 1 ] may be present in slice headers.

[00168] The slice header semantics are discussed.

[00169] ref_pic_list_sps_flag[ i ] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structures with listldx equal to i in the active SPS. ref_pic_list_sps_flag[ i ] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structure with listldx equal to i that is directly included in the slice headers of the current picture. When num_ref_pic_lists_in_sps[ i ] is equal to 0, the value of ref_pic_list_sps_flag[ i ] shall be equal to 0. When rpll_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[ 0 ] is present, the value of ref_pic_list_sps_flag[ 1 ] is inferred to be equal to ref_pic_list_sps_flag[ 0 ]. When not present, the value of rep_pic_list_sps_flag[ i ] is inferred to be equal to 0. [00170] ref_pic_list_idx[ i ] specifies the index, into the list of the ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structures with listldx equal to i included in the active SPS, of the ref_pic_list_struct( listldx, rplsldx, ltrpFlag ) syntax structure with listldx equal to i that is used for derivation of reference picture list i of the current picture. The syntax element ref_pic_list_idx[ i ] is represented by Ceil( Log2( num_ref_pic_lists_in_sps[ i ] ) ) bits. When not present, the value of ref_pic_list_idx[ i ] is inferred to be equal to 0. The value of ref_pic_list_idx[ i ] shall be in the range of 0 to num_ref_pic_lists_in_sps[ i ] - 1, inclusive. When rpll_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[ 0 ] is present, the value of ref_pic_list_idx[ 1 ] is inferred to be equal to ref_pic_list_idx[ 0 ].

[00171] The variable Rplsldx[ i ] is derived as follows:

[00172] Rplsldx[ i ] = ref_pic_list_sps_flag[ i ] ? ref_pic_list_idx[ i ] : num_ref_pic_lists_in_sps[ i ] (7-22)

[00173] additional_poc_lsb_p resen t_flag[ i ] [ j ] equal to 1 specifies that additional_poc_lsb_val[ i ] [ j ] is present. additional_poc_lsb_present_flag[ i ][ j ] equal to 0 specifies that additional_poc_lsb_val[ i ] [ j ] is not present.

[00174] Let prevTidOPic be the previous picture in decoding order that has Temporalld equal to 0 and is not a leading picture (i.e., a picture that follows an IRAP picture in decoding order but precedes the IRAP picture in output order) and not a non-referenced picture. Let setOfPrevPocVals be a set consisting of the following:

[00175] - the PicOrderCntVal of prevTidOPic,

[00176] - the PicOrderCntVal of each picture in the RPL (i.e., RefPicList[ 0 ] and

RefPicList[ 1 ]) of prevTidOPic,

[00177] - the PicOrderCntVal of each picture that follows prevTidOPic in decoding order and precedes the current picture in decoding order.

[00178] When there is more than one value in setOfPrevPocVals for which the value modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[ i ] [ Rplsldx [ i ] ] [ j ], additional_poc_lsb_present_flag[ i ] [ j ] shall be equal to 1.

[00179] additional_poc_lsb_val[ i ] [ j ] specifies the value of FullPocLsbLt[ i ][ j ] as follows: [00180] FullPocLsbLt[ i ] [ Rplsldx[ i ] ] [ j ]

additional_poc_lsb_val[ i ] [ j ] * MaxPicOrderCntLsb + poc_lsb_lt[ i ] [ Rplsldx[ i ] ] [ j ] (7-23)

[00181] The syntax element additional_poc_lsb_val[ i ] [ j ] is represented by additional_lt_poc_lsb_len bits. When not present, the value of additional_poc_lsb_val[ i ] [ j ] is inferred to be equal to 0.

[00182] The reference picture list structure semantics is discussed.

[00183] The ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure may be present in an SPS or in a slice header. Depending on whether the syntax structure is included in a slice header or an SPS, the following applies:

[00184] - If present in a slice header, the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure specifies reference picture list listldx of the current picture (the picture containing the slice).

[00185] - Otherwise (present in an SPS), the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure specifies a candidate for reference picture list listldx, and the term "the current picture" in the semantics specified in the remainder of this clause refers to each picture that 1) has one or more slices containing ref_pic_list_idx[ listldx ] equal to an index into the list of the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structures included in the SPS, and 2) is in a CVS that has the SPS as the active SPS.

[00186] num_strp_entries[ listldx ][ rplsldx ] specifies the number of short-term reference picture (STRP) entries in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure.

[00187] num_ltrp_entries[ listldx ][ rplsldx ] specifies the number of LTRP entries in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure. When not present, the value of num_ltrp_entries[ listldx ][ rplsldx ] is inferred to be equal to 0.

[00188] The variable NumEntriesInList[ listldx ][ rplsldx ] is derived as follows:

NumEntriesInList[ listldx ][ rplsldx ] = num_strp_entries[ listldx ][ rplsldx ] +

num_ltrp_entries[ listldx ][ rplsldx ] (7-27)

[00189] The value of NumEntriesInList[ listldx ][ rplsldx ] shall be in the range of 0 to sps_max_dec_pic_buffering_minusl , inclusive.

[00190] lt_ref_pic_flag[ listldx ][ rplsldx ][ i ] equal to 1 specifies that the i-th entry in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure is an LTRP entry. lt_ref_pic_flag[ listldx ][ rplsldx ][ i ] equal to 0 specifies that the i-th entry in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure is an STRP entry. When not present, the value of lt_ref_pic _flag[ listldx ][ rplsldx ][ i ] is inferred to be equal to 0.

[00191] It is a requirement of bitstream conformance that the sum of lt_ref_pic_flag[ listldx ][ rplsldx ][ i ] for all values of i in the range of 0 to

NumEntriesInList[ listldx ][ rplsldx ] - 1, inclusive, shall be equal to num_ltrp_entries[ listldx ][ rplsldx ].

[00192] delta_poc_st[ listldx ][ rplsldx ][ i ], when the i-th entry is the first STRP entry in ref_pic_list_struct( rplsldx, ItrpFlag ) syntax structure, specifies the absolute difference between the picture order count values of the current picture and the picture referred to by the i-th entry, or, when the i-th entry is an STRP entry but not the first STRP entry in the ref_pic_list_struct( rplsldx, ItrpFlag ) syntax structure, specifies the absolute difference between the picture order count values of the pictures referred to by the i-th entry and by the previous STRP entry in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure.

[00193] The value of delta_poc_st[ listldx ][ rplsldx ][ i ] shall be in the range of -215 to 215 - 1, inclusive.

[00194] strp_entry_sign_flag[ listldx ][ rplsldx ][ i ] equal to 1 specifies that i-th entry in the syntax structure ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) has a value greater than or equal to 0. strp_entry_sign_flag[ listldx ][ rplsldx ] equal to 0 specifies that the i-th entry in the syntax structure ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) has a value less than 0. When not present, the value of strp_entry_sign_flag[ i ][ j ] is inferred to be equal to 1.

[00195] The list DeltaPocSt[ listldx ][ rplsldx ] is derived as follows:

for( i = 0; i < NumEntriesInList[ listldx ][ rplsldx ]; i++ ) {

if( !lt_ref_pic_flag[ i ][ Rplsldx[ i ] ][ j ] ) { (7-28)

DeltaPocSt[ listldx ][ rplsldx ][ i ] = ( strp_entry_sign_flag[ listldx ][ rplsldx ][ i ]) ?

delta_poc_st[ listldx ] [ rplsldx ] [ i ] : 0 - delta_poc_st[ listldx ] [ rplsldx ] [ i ]

}

} [00196] poc_lsb_lt[ listldx ][ rplsldx ][ i ] specifies the value of the picture order count modulo MaxPicOrderCntLsb of the picture referred to by the i-th entry in the ref_pic_list_struct( listldx, rplsldx, ItrpFlag ) syntax structure. The length of the poc_lsb_lt[ listldx ] [ rplsldx ] [ i ] syntax element is log2_max_pic_order_cnt_lsb_minus4 + 4 bits.

[00197] The decoding process is discussed.

[00198] The reference picture lists RefPicList[ 0 ] and RefPicList[ 1 ] are constructed as follows:

for( i = 0; i < 2; i++ )

for( j = 0, pocBase = PicOrderCntVal; j < NumEntriesInList[ i ][ Rplsldx[ i ]; j++) {

if( !lt_ref_pic_flag[ i ][ Rplsldx[ i ][ j ] ) {

RefPicPocList[ i ][ j ] = pocBase - DeltaPocSt[ i ][ Rplsldx[ i ][ j ] if( there is a reference picture picA in the DPB with PicOrderCntVal equal to RefPicPocList[ i ][ j ] )

RefPicList[ i ] [ j ] = picA

else

RefPicList[ i ][ j ] = "no reference picture"

pocBase = RefPicPocList[ i ][ j ] (8-5)

} else {

if( there is a reference picA in the DPB with PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 )

equal to FullPocLsbLt[ i ][ Rplsldx[ i ] ][ j ] ) RefPicList[ i ] [ j ] = picA

else RefPicList[ i ] [ j ] = "no reference picture"

}

}

[00199] A detailed description of the second embodiment of the present disclosure is provided. [00200] This clause documents the embodiment of some of the aspects of the present disclosure summarized above.

[00201] Changed parts relative to the RPS based approach in HEYC are in bold, including removed parts that are shown in italics, while the texts for that approach that are not mentioned below apply as they are.

[00202] The picture parameter set parallel bitstream parser (PBSP) syntax is discussed. The picture parameter set RBSP syntax in clause 7.3.2.3 of the HEYC specification is changed as follows (changed parts are in bold):

[00203] The slice header syntax is discussed.

[00204] The slice header syntax in clause 7.3.6 of the HEVC specification is changed as follows (changed parts are in bold):

[00205] The picture parameter set RBSP semantics are discussed.

[00206] additional_lt_poc_lsb_len specifies the value of the variable MaxLtPicOrderCntLsb that is used in the decoding process for reference picture lists as follows:

MaxLtPicOrderCntLsb 2* ' ⁰

^{a X}_P i ^c_° ril er e n t l s h_m i n u s4 + 4 + additional lt poc lsb len )

[00207] The value of additional_lt_poc_lsb_len shall be in the range of 0 to

32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive.

[00208] When not present, the value of additional_lt_poc_lsb_len is inferred to be equal to 0.

[00209] The slice header semantics are discussed.

[00210] When present, the value of the slice segment header syntax elements slice_pic_parameter_set_id, pic output flag, no_output_of_prior_pics_flag, slice_pic_order_cnt_lsb, short_term_ref_pic_set_sps_flag, short_term_ref_pic_set_idx, num long term sps, num_long_term_pics and slice temporal mvp enabled flag shall be the same in all slice segment headers of a coded picture. When present, the value of the slice segment header syntax elements lt_idx_sps[ i ], poc_lsb_lt[ i ], used_by_curr_pic_lt_flag[ i ], delta _poc_msb _present Jlag[i ] and delta _poc_jnsb_cycleJt[ i yadditional_poc_lsb_present_flag[ i ] and additional_poc_lsb_val[ i ] shall be the same in all slice segment headers of a coded picture for each possible value of i.

[00211] additional_poc_lsb_present_flag[ i ] equal to 1 specifies that additional_poc_lsb_val[ i ] is present. additional_poc_lsb_present_flag[ i ] equal to 0 specifies that additional_poc_lsb_val[ i ] is not present.

[00212] Let prevTidOPic be the previous picture in decoding order that has Temporalld equal to 0 and is not a Random Access Skipped Leading (RASL), Random Access Decodable Leading (RADL) or sub-layer non- reference (SLNR) picture. Let setOfPrevPocVals be a set consisting of the following:

[00213] - the PicOrderCntVal of prevTidOPic,

[00214] - the PicOrderCntVal of each picture in the RPS of prevTidOPic,

[00215] - the PicOrderCntVal of each picture that follows prevTidOPic in decoding order and precedes the current picture in decoding order.

[00216] When there is more than one value in setOfPrevPocVals for which the value modulo MaxPicOrderCntLsb is equal to PocLsbLt[ i ], additional_poc_lsb_present_flag[ i ] shall be equal to 1.

[00217] additional_poc_lsb_val[ i ] specifies the value of FullPocLsbLt[ i ] as follows:

[00218] FullPocLsbLt[ i ] = additional_poc_lsb_val[ i ] * MaxPicOrderCntLsb +

PocLsbLt[ i ] (7-52)

[00219] The syntax element additional_poc_lsb_val[ i ] is represented by additional_lt_poc_lsb_len bits. When not present, the value of additional_poc_lsb_val[ i ] is inferred to be equal to 0.

[00220] delta _poc_msb _present Jlag[i ] equal to 1 specifies that delta _poc_msb_cycle_lt[ i ] is present delta _poc_msb _present Jlag[ i ] equal to 0 specifies that delta _poc_msb_cycle_lt[ i ] is not present.

[00221] Let prevTidOPic be the previous picture in decoding order that has Temporalld equal to 0 and is not a RASL, RADL or SLNR picture. Let setOfPrevPocVals be a set consisting of the following:

[00222] the PicOrderCntVal of prevTidOPic,

[00223] the PicOrderCntVal of each picture in the RPS of prevTidOPic, [00224] - the PicOrderCntVal of each picture that follows prevTidOPic in decoding order and precedes the current picture in decoding order.

[00225] When there is more than one value in setOfPrevPocVals for which the value modulo MaxPicOrderCntLsb is equal to PocLsbLt[ i ], delta _poc_msb _jpresenl Jlag[i ] shall be equal to 1.

[00226] delta _poc_msb_cycle_lt[ i ] is used to determine the value of the most significant bits of the picture order count value of the i-th entry in the long-term RPS of the current picture. When delta _poc_msb_cycle_lt[ i ] is not present, it is inferred to be equal to 0.

The variable DeltaPocMsbCycleLt [ i ] is derived as follows:

[00227] The decoding process is discussed.

[00228] Five lists of picture order count values are constructed to derive the RPS. These five lists are PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr, and PocLtFoll, with NumPocStCurrBefore, NumPocStCurrAfter, NumPocStFoll, NumPocLtCurr, and NumPocLtFoll number of elements, respectively. The five lists and the five variables are derived as follows:

- If the current picture is an IDR picture, PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr, and PocLtFoll are all set to be empty, and NumPocStCurrBefore, NumPocStCurrAfter, NumPocStFoll, NumPocLtCurr, and NumPocLtFoll are all set equal to 0.

- Otherwise, the following applies: for( i = 0, j = 0, k = 0; i < NumNegativePics[ CurrRpsIdx ] ; i++ )

if( UsedByCurrPicS0[ CurrRpsIdx ][ i ] )

PocStCurrBefore[ j++ ] = PicOrderCntVal + DeltaPocS0[ CurrRpsIdx ][ i ] else

PocStFoll[ k++ ] = PicOrderCntVal + DeltaPocS0[ CurrRpsIdx ][ i ] NumPocStCurrBefore = j for( i = 0, j = 0; i < NumPositivePics[ CurrRpsIdx ]; i++ )

if( UsedByCurrPicSl [ CurrRpsIdx ][ i ] )

PocStCurrAfter[ j++ ] = PicOrderCntVal + DeltaPocSl [ CurrRpsIdx ][ i ] else

PocStFoll[ k++ ] = PicOrderCntVal + DeltaPocSl [ CurrRpsIdx ][ i ]

NumPocStCurrAfter = j

NumPocStFoll = k (8-5)

for( i = 0, j = 0, k = 0; i < num_long_term_sps + num_long_term_pics; i++ ) {

pocLt = FullPocLsbLt[ i ]

pocLt = PocLsbLt[ i ]

if( delta _poc_msb _present Jlag[ i ] )

pocLt + = PicOrderCntVal - DeltaPocMsbCycleLt[ i ] * MaxPicOrderCntLsb—

( PicOrderCntVal & ( MaxPicOrderCntLsb - 1 ) )

if( UsedByCurrPicLt[ i ] ) {

PocLtCurr[ j ] = pocLt

CurrDeltaPocMsbPresentFlag[ j+ + ] - della _poc_msb _present Jlag[ i J

CurrAdditionalPocLsbPresentFlag[ j++ ] = additional_poc_lsb_present_flag[ i ]

} else {

PocLtFoll[ k ] = pocLt

FollDeltaPocMsbPresentFlag[ k+ + J = delta _poc_msb _present Jlag[ i ]

FollAdditionalPocLsbPresentFlag[ k++ ] = additional_poc_lsb_present_flag [ i ]

}

}

NumPocLtCurr = j

NumPocLtFoll = k

[00229] where PicOrderCntVal is the picture order count of the current picture as specified in clause 8.3.1.

[00230] NOTE 2 - A value of CurrRpsIdx in the range of 0 to num_short_term_ref_pic_sets - 1 , inclusive, indicates that a candidate short-term RPS from the active SPS for the current layer is being used, where CurrRpsIdx is the index of the candidate short-term RPS into the list of candidate short-term RPSs signalled in the active SPS for the current layer. CurrRpsIdx equal to num_short_term_ref_pic_sets indicates that the short-term RPS of the current picture is directly signalled in the slice header.

[00231] For each i in the range of 0 to NumPocLtCurr - 1, inclusive, when CurrAdditionalPocLsbPresentFlag[ i ] is equal to 1, it is a requirement of bitstream conformance that the following conditions apply:

- There shall be no j in the range of 0 to NumPocStCurrBefore - 1, inclusive, for which PocLtCurr[ i ] is equal to ( PocStCurrBefore[ j ]i|i& ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStCurrAfter - 1 , inclusive, for which PocLtCurr[ i ] is equal to ( PocStCurrAfter[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStFoll - 1, inclusive, for which PocLtCurr[ i ] is equal to ( PocStFoll[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtCurr - 1, inclusive, where j is not equal to i, for which PocLtCurr[ i ] is equal to ( PocLtCurr[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

[00232] For each i in the range of 0 to NumPocLtFoll - 1, inclusive, when FollAdditionalPocLsbPresentFlag[ i ] is equal to 1, it is a requirement of bitstream conformance that the following conditions apply:

- There shall be no j in the range of 0 to NumPocStCurrBefore - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocStCurrBefore[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStCurrAfter - 1 , inclusive, for which PocLtFoll[ i ] is equal to ( PocStCurrAfter[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStFoll - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocStFoll[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtFoll - 1, inclusive, where j is not equal to i, for which PocLtFoll[ i ] is equal to ( PocLtFoll[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtCurr - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocLtCurr[ j ] & ( MaxLtPicOrderCntLsb - 1 ) ). [00233] For each i in the range of 0 to NumPocLtCurr - 1, inclusive, when

CurrAdditionalPocLsbPresentFlag[ i ] is equal to 0, it is a requirement of bitstream conformance that the following conditions apply:

- There shall be no j in the range of 0 to NumPocStCurrBefore - 1, inclusive, for which PocLtCurr[ i ] is equal to ( PocStCurrBefore[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStCurrAfter - 1 , inclusive, for which PocLtCurr[ i ] is equal to ( PocStCurrAfter[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStFoll - 1, inclusive, for which PocLtCurr[ i ] is equal to ( PocStFoll[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtCurr - 1, inclusive, where j is not equal to i, for which PocLtCurr[ i ] is equal to ( PocLtCurr[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

[00234] For each i in the range of 0 to NumPocLtFoll - 1, inclusive, when

FollAdditionalPocLsbPresentFlag[ i ] is equal to 0, it is a requirement of bitstream conformance that the following conditions apply:

- There shall be no j in the range of 0 to NumPocStCurrBefore - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocStCurrBefore[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStCurrAfter - 1 , inclusive, for which PocLtFoll[ i ] is equal to ( PocStCurrAfter[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocStFoll - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocStFoll[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtFoll - 1, inclusive, where j is not equal to i, for which PocLtFoll[ i ] is equal to ( PocLtFoll[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

- There shall be no j in the range of 0 to NumPocLtCurr - 1, inclusive, for which PocLtFoll[ i ] is equal to ( PocLtCurr[ j ] & ( MaxPicOrderCntLsb - 1 ) ).

[00235] The variable NumPicTotalCurr is derived as specified in clause 7.4.7.2. It is a requirement of bitstream conformance that the following applies to the value of NumPicTotalCurr:

- If the current picture is a BLA or CRA picture, the value of NumPicTotalCurr shall be equal to pps_curr_pic_ref_enabled_flag. - Otherwise, when the current picture contains a P or B slice, the value of NumPicTotalCurr shall not be equal to 0.

[00236] 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.

[00237] NOTE 3 - 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.

[00238] The derivation process for the RPS and picture marking are performed according to the following ordered steps:

1. The following applies: for( i = 0; i < NumPocLtCurr; i++ )

if( !CurrAdditionalPocLsbPresentFlag[ i ] )

if( there is a reference picture picX in the DPB with

PicOrderCntVal & ( MaxPicOrderCntLsb - 1 )

equal to PocLtCurr[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetLtCurr[ i ] = picX

else

RefPicSetLtCurr[ i ] = "no reference picture"

else

if( there is a reference picture picX in the DPB with

PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 )

equal to PocLtCurr[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetLtCurr[ i ] = picX

else

RefPicSetLtCurr[ i ] = "no reference picture"

(8-6)

for( i = 0; i < NumPocLtFoll; i++ )

if( !FollAdditionalPocLsbPresentFlag[ i ] )

if( there is a reference picture picX in the DPB with

PicOrderCntVal & ( MaxPicOrderCntLsb - 1 )

equal to PocLtFoll[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetLtFoll[ i ] = picX

else

RefPicSetLtFoll[ i ] = "no reference picture"

else

if( there is a reference picture picX in the DPB with

PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 )

equal to PocLtFoll[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetLtFoll[ i ] = picX

else

RefPicSetLtFoll[ i ] = "no reference picture" All reference pictures that are included in RefPicSetLtCurr or RefPicSetLtFoll and have nuh layer id equal to currPicLayerld are marked as "used for long-term reference". The following applies: for( i = 0; i < NumPocStCurrBefore; i++ )

if( there is a short-term reference picture picX in the DPB

with PicOrderCntVal equal to PocStCurrBefore[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetStCurrBefore[ i ] = picX else

RefPicSetStCurrBefore[ i ] = "no reference picture" for( i = 0; i < NumPocStCurrAfter; i++ )

if( there is a short-term reference picture picX in the DPB

with PicOrderCntVal equal to PocStCurrAfter[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetStCurrAfter[ i ] = picX

else

RefPicSetStCurrAfter[ i ] = "no reference picture" (8-7) for( i = 0; i < NumPocStFoll; i++ )

if( there is a short-term reference picture picX in the DPB

with PicOrderCntVal equal to PocStFoll[ i ] and nuh layer id equal to currPicLayerld )

RefPicSetStFoll[ i ] = picX

else

RefPicSetStFoll[ i ] = "no reference picture"

4. All reference pictures in the DPB that are not included in RefPicSetLtCurr, RefPicSetLtFoll, RefPicSetStCurrBefore, RefPicSetStCurr After, or RefPicSetStFoll and have nuh layer id equal to currPicLayerld are marked as "unused for reference".

[00239] NOTE 4 - There may be one or more entries in the RPS lists that are equal to "no reference picture" because the corresponding pictures are not present in the DPB. Entries in RefPicSetStFoll or RefPicSetLtFoll that are equal to "no reference picture" should be ignored. An unintentional picture loss should be inferred for each entry in RefPicSetStCurrBefore, RefPicSetStCurr After, or RefPicSetLtCurr that is equal to "no reference picture".

[00240] NOTE 5 - A picture cannot be included in more than one of the five RPS lists.

[00241] FIG. 8 is a schematic diagram of a video coding device 800 (e.g., a video encoder 20 or a video decoder 30) according to an embodiment of the disclosure. The video coding device 800 is suitable for implementing the disclosed embodiments as described herein. The video coding device 800 comprises ingress ports 810 and receiver units (Rx) 820 for receiving data; a processor, logic unit, or central processing unit (CPU) 830 to process the data; transmitter units (Tx) 840 and egress ports 850 for transmitting the data; and a memory 860 for storing the data. The video coding device 800 may also comprise optical-to-electrical (OE) components and electrical-to- optical (EO) components coupled to the ingress ports 810, the receiver units 820, the transmitter units 840, and the egress ports 850 for egress or ingress of optical or electrical signals.

[00242] The processor 830 is implemented by hardware and software. The processor 830 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor 830 is in communication with the ingress ports 810, receiver units 820, transmitter units 840, egress ports 850, and memory 860. The processor 830 comprises a coding module 870. The coding module 870 implements the disclosed embodiments described above. For instance, the coding module 870 implements, processes, prepares, or provides the various networking functions. The inclusion of the coding module 870 therefore provides a substantial improvement to the functionality of the video coding device 800 and effects a transformation of the video coding device 800 to a different state. Alternatively, the coding module 870 is implemented as instructions stored in the memory 860 and executed by the processor 830.

[00243] The video coding device 800 may also include input and/or output (I/O) devices 880 for communicating data to and from a user. The I/O devices 880 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I/O devices 880 may also include input devices, such as a keyboard, mouse, trackball, etc., and/or corresponding interfaces for interacting with such output devices.

[00244] The memory 860 comprises one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 860 may be volatile and/or non-volatile and may be read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM).

[00245] FIG. 9 is a schematic diagram of an embodiment of a means for coding 900. In embodiment, the means for coding 900 is implemented in a video coding device 902 (e.g., a video encoder 20 or a video decoder 30). The video coding device 902 includes receiving means 901. The receiving means 901 is configured to receive a picture to encode or to receive a bitstream to decode. The video coding device 902 includes transmission means 907 coupled to the receiving means 901. The transmission means 907 is configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means (e.g., one of the I/O devices 880).

[00246] The video coding device 902 includes a storage means 903. The storage means 903 is coupled to at least one of the receiving means 901 or the transmission means 907. The storage means 903 is configured to store instructions. The video coding device 902 also includes processing means 905. The processing means 905 is coupled to the storage means 903. The processing means 905 is configured to execute the instmctions stored in the storage means 903 to perform the methods disclosed herein.

[00247] It should also be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present disclosure.

[00248] While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

[00249] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

Claims

CLAIMS What is claimed is:

1. A method of encoding a video bitstream implemented by a video encoder, the method comprising:

determining, by the video encoder, that a reference picture cannot be uniquely identified using picture order count (POC) least significant bits (LSBs) corresponding to other reference pictures;

inserting, by the video encoder, additional POC LSBs into a slice header of the video bitstream to uniquely identify the reference picture following the determination;

setting, by the video encoder, a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture; and

transmitting, by the video encoder, the video bitstream toward the video decoder.

2. The method of claim 1 , wherein the first value is one.

3. The method of any of claims 1 to 2, wherein the reference picture is a long term reference picture.

4. The method of any of claims 1 to 3, wherein the other reference pictures are from reference picture lists signaled in the slice header.

5. The method of any of claims 1 to 3, wherein the other reference pictures are from a decoded picture buffer (DPB).

6. The method of any of claims 1 to 5, wherein the flag is designated additional_poc_lsb_present.

7. The method of any of claims 1 to 6, wherein the flag is encoded in the slice header.

8. The method of any of claims 1 to 7, wherein the reference picture cannot be uniquely identified when a POC LSB value corresponding to the reference picture is the same as another POC LSB value in a set of previous POC LSB values.

9. The method of claim 8, wherein the set of previous POC LSB values is designated setOfPrevPocVals.

10. The method of any of claims 8 to 9, wherein the set of previous POC values contains a POC LSB value corresponding to a previous picture.

11. The method of claim 10, wherein the set of previous POC LSB values contains a POC LSB value corresponding to each reference picture in a first reference picture list and a second reference picture list for the previous picture.

12. The method of claim 1 1, wherein the set of previous POC LSB values contains a POC LSB value corresponding to each reference picture following the previous picture in decoding order and each reference picture preceding a current picture in the decoding order.

13. A method of decoding a coded video bitstream implemented by a video decoder, comprising:

determining, by the video decoder, that a flag in the coded video bitstream has been set to a first value;

determining, by the video decoder, that a slice header of the coded video bitstream contains additional picture order count (POC) least significant bits (LSBs) that uniquely identify a reference picture based on the flag having the first value;

parsing, by the video decoder, the slice header to obtain the additional POC LSBs corresponding to the reference picture;

utilizing, by the video decoder, the additional POC LSBs to identify the reference picture; and

performing, by the video decoder, inter-prediction using the reference picture to generate a reconstructed block.

14. The method of claim 13, wherein the first value is one.

15. The method of any of claims 13 to 14, wherein the reference picture is a long term reference picture.

16. The method of any of claims 13 to 15, wherein the flag is designated additional_poc_lsb_present.

17. The method of any of claims 13 to 16, wherein the flag is in the slice header.

18. An encoding device, comprising:

a memory containing instructions;

a processor coupled to the memory, the processor configured to implement the instructions to cause the encoding device to:

determine that a reference picture cannot be uniquely identified using picture order count (POC) least significant bits (LSBs) corresponding to other reference pictures; insert additional POC LSBs into a slice header of the video bitstream to uniquely identify the reference picture following the determination; and

set a flag of the video bitstream to a first value to indicate to a video decoder that the slice header contains the additional POC LSBs that uniquely identify the reference picture; and

a transmitter coupled to the processor, the transmitter configured to transmit the video bitstream toward a video decoder.

19. The encoding device of claim 18, wherein the first value is one.

20. The encoding device of any of claims 18 to 19, wherein the reference picture is a long term reference picture.

21. The encoding device of any of claims 18 to 20, wherein the other reference pictures are from reference picture lists signaled in the slice header or a decoded picture buffer (DPB).

22. The encoding device of any of claims 18 to 21, wherein the flag is designated additional_poc_lsb_present.

23. The encoding device of any of claims 18 to 22, wherein the flag is encoded in the slice header.

24. A decoding device, comprising:

a receiver configured to receive a coded video bitstream;

a memory coupled to the receiver, the memory storing instructions; and

a processor coupled to the memory, the processor configured to execute the instructions to cause the decoding device to:

determine that a flag in the coded video bitstream has been set to a first value, determine that a slice header of the coded video bitstream contains additional picture order count (POC) least significant bits (LSBs) that uniquely identify a reference picture based on the flag having the first value;

parse the slice header to obtain the additional POC LSBs corresponding to the reference picture;

utilize the additional POC LSBs to identify the reference picture; and perform inter-prediction using the reference picture to generate a reconstructed block.

25. The decoding device of claim 24, further comprising a display configured to display an image generated using the reconstructed block.

26. A coding apparatus, comprising:

a receiver configured to receive a bitstream to decode;

a transmitter coupled to the receiver, the transmitter configured to transmit a decoded image to a display; a memory coupled to at least one of the receiver or the transmitter, the memory configured to store instructions; and

a processor coupled to the memory, the processor configured to execute the instructions stored in the memory to perform the method in any of claims 1 to 17.

27. A system, comprising:

an encoder; and

a decoder in communication with the encoder, wherein the encoder or the decoder includes the decoding device, the encoding device, or the coding apparatus of any of claims 18 to 26.

28. A means for coding, comprising:

receiving means configured to receive a bitstream to decode;

transmission means coupled to the receiving means, the transmission means configured to transmit a decoded image to a display means;

storage means coupled to at least one of the receiving means or the transmission means, the storage means configured to store instructions; and

processing means coupled to the storage means, the processing means configured to execute the instructions stored in the storage means to perform the method in any of claims 1 to 17.