Method for decoding encoded video stream, apparatus, and computer program

Abstract

To provide a method and apparatus for decoding an encoded video bitstream using at least one processor.SOLUTION: A method includes: obtaining a coded video sequence from an encoded video bitstream; decoding an encoded picture on the basis of PH NAL unit, at least one coded slice NAL unit, PPS NAL unit and SPS NAL unit obtained from the coded video sequence; and outputting the decoded picture. The SPS NAL unit is available to the at least one processor before the PPS NAL unit, and the PPS NAL unit is available to the at least one processor before the PH NAL unit and the at least one coded slice NAL unit.SELECTED DRAWING: Figure 21

Description

[Technical field]

[0001] This application claims priority from U.S. Provisional Patent Application No. 62 / 954,099, filed December 27, 2019, and U.S. Patent Application No. 17 / 063,060, filed October 5, 2020, both of which are incorporated herein by reference in their entireties.

[0002] FIELD OF THE DISCLOSURE The subject matter of this disclosure relates to video encoding and decoding, and more particularly, to referencing and scope of parameter sets in encoded video streams. [Background technology]

[0003] Video encoding and decoding using inter-picture prediction with motion compensation is known. Uncompressed digital video consists of a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance (luminance) samples and associated color (chrominance) samples. The sequence of pictures can have a fixed or variable picture rate (also informally known as frame rate), for example 60 pictures per second, i.e., a picture rate of 60 Hz. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) with 8 bits per sample requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires more than 600 Gbytes of storage space.

[0004] One goal of video encoding and decoding may be the reduction of redundancy in the input video signal through compression. Compression can help reduce the aforementioned bandwidth or storage space requirements, possibly by more than one order of magnitude. Both lossless and lossy compression, as well as combinations of these, may be used. Lossless compression refers to techniques where an exact replica of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. For video, lossy compression is widely used. The amount of acceptable distortion depends on the application, e.g., a user of a particular consumer streaming application may tolerate higher distortion than a user of a television contribution application. The achievable compression ratio reflects this, and higher acceptable / tolerable distortion can result in a higher compression ratio.

[0005] Video encoders and decoders can utilize techniques from several broad categories, including, for example, motion compensation, transform, quantization, and entropy coding, some of which are introduced below.

[0006] Historically, video encoders and decoders have tended to work with a given picture size that is mostly defined and left constant for a coded video sequence (CVS), a group of pictures (GOP), or a similar multi-picture time frame. For example, in MPEG-2, system designs are known that vary the horizontal resolution (and therefore the picture size) depending on factors such as scene activity, but only in I-pictures and therefore typically only for GOPs. Resampling of reference pictures to use different resolutions within a CVS is known, for example, from ITU-T Recommendation H.263 Annex P. However, there the picture size remains the same and only the reference pictures are resampled, possibly to only the part of the picture canvas that is used (in the case of downsampling) or only the part of the scene that is captured (in the case of upsampling). H.263 Annex Q also allows resampling of individual macroblocks by a factor of two (in each dimension) upwards or downwards. Again, the picture size remains the same: the macroblock size is fixed in H.263 and therefore does not need to be signaled.

[0007] In modern video coding, picture size changes in predicted pictures have become more mainstream. For example, VP9 allows resampling and resolution changes of reference pictures for the entire picture. Similarly, certain proposals made for VVC (e.g., Hendry et al., “On adaptive resolution change (ARC) for VVC”, Joint Video Team document JVET-M0135-v1, Jan. 9-19, 2019, incorporated herein by reference in its entirety) allow resampling of the entire reference picture to a different resolution, either higher or lower. In that document, it is proposed that multiple different candidate resolutions be coded in the sequence parameter set and referenced by per-picture syntax elements in the picture parameter set. Summary of the Invention

[0008] In one embodiment, a method for decoding a coded video bitstream using at least one processor is provided, the method comprising: obtaining a coded video sequence from the coded video bitstream; obtaining a picture unit from the coded video sequence; obtaining a picture header (PH) network abstraction layer (NAL) unit included in the picture unit; obtaining at least one coded slice NAL unit included in the picture unit; decoding a coded picture based on the PH NAL unit, the at least one coded slice NAL unit, a picture parameter set (PPS) included in a PPS NAL unit obtained from the coded video sequence, and a sequence parameter set (SPS) included in an SPS NAL unit obtained from the coded video sequence; and outputting the decoded picture, wherein the SPS NAL unit is available to the at least one processor before the PPS NAL unit, and the PPS NAL unit is available to the at least one processor before the PH NAL unit and the at least one coded slice NAL unit.

[0009] In one embodiment, an apparatus is provided for decoding a coded video bitstream, the apparatus comprising: at least one memory configured to store program code; and at least one processor configured to read the program code and operate as instructed by the program code, the program code comprising: a first acquisition code configured to cause the at least one processor to obtain a coded video sequence from the coded video bitstream; a second acquisition code configured to cause the at least one processor to obtain a picture unit from the coded video sequence; a third acquisition code configured to cause the at least one processor to obtain a Picture Header (PH) Network Abstraction Layer (NAL) unit included in the picture unit; a fourth acquisition code configured to cause the at least one processor to obtain at least one coded slice NAL unit included in the picture unit; and a fourth acquisition code configured to cause the at least one processor to obtain the PH NAL unit, the at least one coded slice NAL unit, a Picture Parameter Set (PPS) included in a PPS NAL unit obtained from the coded video sequence, and an SPS NAL unit obtained from the coded video sequence. a decoding code configured to cause a coded picture to be decoded based on a sequence parameter set (SPS) included in a NAL unit; and an output code configured to cause the at least one processor to output the decoded picture, wherein the SPS NAL unit is available to the at least one processor before the PPS NAL unit, and the PPS NAL unit is available to the at least one processor before the PH NAL unit and the at least one coded slice NAL unit.

[0010] In one embodiment, a non-transitory computer-readable medium is provided having instructions stored thereon, the instructions, when executed by one or more processors of an apparatus for decoding a coded video bitstream, causing the one or more processors to obtain a coded video sequence from the coded video bitstream, obtain a picture unit from the coded video sequence, obtain a picture header (PH) network abstraction layer (NAL) unit included in the picture unit, obtain at least one coded slice NAL unit included in the picture unit, decode a coded picture based on the PH NAL unit, the at least one coded slice NAL unit, a picture parameter set (PPS) included in a PPS NAL unit obtained from the coded video sequence, and a sequence parameter set (SPS) included in an SPS NAL unit obtained from the coded video sequence, and output the decoded picture, wherein the SPS NAL unit is available to the one or more processors before the PPS NAL unit, and the PPS NAL unit is available to the one or more processors before the PH NAL unit and the at least one coded slice NAL unit. [Brief description of the drawings]

[0011] Further features, nature and various advantages of the subject matter disclosed herein will become more apparent from the following detailed description and the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Diagram 3] FIG. 2 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment. [Figure 4] FIG. 2 is a schematic diagram of a simplified block diagram of an encoder according to one embodiment. [Figure 5A]5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment, according to one embodiment. [Figure 5B] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment, according to one embodiment. [Figure 5C] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment, according to one embodiment. [Figure 5D] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment, according to one embodiment. [Figure 5E] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment, according to one embodiment. [Figure 6A] 6A-6B are schematic diagrams of example syntax tables according to one embodiment. [Figure 6B] 6A-6B are schematic diagrams of example syntax tables according to one embodiment. [Figure 7] 1 is an example of a prediction structure for scalability with adaptive resolution change, according to one embodiment. [Figure 8] 4 is an example of a syntax table according to one embodiment. [Figure 9] FIG. 2 is a schematic diagram of a simplified block diagram of parsing and decoding POC cycles per access unit and access unit count values ​​according to one embodiment. [Figure 10] FIG. 2 is a schematic diagram of a video bitstream structure including multiple layered sub-pictures according to one embodiment. [Figure 11] FIG. 2 is a schematic diagram of displaying a selected sub-picture at an enhanced resolution according to one embodiment. [Figure 12] FIG. 2 is a block diagram of a process for decoding and displaying a video bitstream that includes multiple layered sub-pictures, according to one embodiment. [Figure 13]FIG. 2 is a schematic diagram of a 360 video display using a sub-picture enhancement layer, according to one embodiment. [Figure 14] 1 is an example of layout information for a subpicture and its corresponding layer and picture prediction structure according to one embodiment. [Figure 15] 1 is an example of sub-picture layout information and its corresponding layer and picture prediction structure using local region spatial scalability modality according to one embodiment. [Figure 16A] 16A-16B are example syntax tables for sub-picture layout information according to one embodiment. [Figure 16B] 16A-16B are example syntax tables for sub-picture layout information according to one embodiment. [Figure 17] 1 is an example syntax table of a SEI message for sub-picture layout information according to one embodiment. [Figure 18] 1 is an example syntax table showing output tier and profile / tier / level information for each output tier set, according to one embodiment. [Figure 19] 11 is an example syntax table showing output layer mode on for each output layer set according to one embodiment. [Figure 20] 1 is an example of a syntax table showing the current subpicture of each layer for each output layer set according to one embodiment. [Figure 21] 1 is a flow diagram of an example process for decoding an encoded video bitstream according to one embodiment. [Figure 22] FIG. 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] FIG. 1 illustrates a simplified block diagram of a communication system (100) according to one embodiment of the present disclosure. The system (100) may include at least two terminals (110-120) interconnected via a network (150). In a one-way transmission of data, a first terminal (110) may encode video data at a local location for transmission to the other terminal (120) via the network (150). The second terminal (120) may receive the other terminal's encoded video data from the network (150), decode the encoded data, and display the reconstructed video data. One-way data transmission may be common in media service provisioning applications and the like.

[0013] 1 illustrates a second pair of terminals (130, 140) arranged to support bidirectional transmission of encoded video, such as may occur during a video conference. In the bidirectional transmission of data, each terminal (130, 140) may encode video data captured at a local location for transmission to the other terminal over the network (150). Each terminal (130, 140) may also receive encoded video data transmitted by the other terminal, decode the encoded data, and display the reconstructed video data on a local display device.

[0014] Although the terminals (110-140) may be illustrated in FIG. 1 as servers, personal computers, and smartphones, the principles of the present disclosure may not be so limited. Embodiments of the present disclosure find application in laptop computers, tablet computers, media players, and / or dedicated videoconferencing equipment. The network (150) represents any number of networks that convey encoded video data between the terminals (110-140), including, for example, wired and / or wireless communication networks. The communication network (150) may exchange data over circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this description, the architecture and topology of the network (150) may not be important to the operation of the present disclosure, unless otherwise described below.

[0015] 2 illustrates the arrangement of video encoders and decoders in a streaming environment as an example of an application of the subject matter of this disclosure, which may be equally applicable to other uses in which video can be used, including, for example, videoconferencing, digital TV, and storage of compressed video on digital media including CDs, DVDs, memory sticks, and the like.

[0016] The streaming system may include a capture subsystem (213), which may include a video source (201), such as a digital camera, that produces an uncompressed video sample stream (202). The sample stream (202) is depicted as a thick line to emphasize its high data volume compared to an encoded video bitstream, and may be processed by an encoder (203) coupled to the camera 201. The encoder (203) may include hardware, software, or a combination thereof to enable or implement aspects of the subject matter of this disclosure, which are described in more detail below. The encoded video bitstream (204) is depicted as a thin line to emphasize its low data volume compared to the sample stream, and may be stored on a streaming server (205) for later use. One or more streaming clients (206, 208) may access the streaming server (205) to retrieve copies (207, 209) of the encoded video bitstream (204). The client (206) may include a video decoder (210) that decodes a copy (207) of the incoming encoded video bitstream and produces an outgoing video sample stream (211) that may be rendered on a display (212) or other rendering device (not shown). In some streaming systems, the video bitstreams (204, 207, 209) may be encoded according to a particular video encoding / compression standard. Examples of such standards include ITU-T Recommendation H.265. A video encoding standard informally known as Versatile Video Coding, or VVC, is under development. The subject matter of this disclosure may be used in the context of VVC.

[0017] FIG. 3 may be a functional block diagram of a video decoder (210) according to one embodiment of this disclosure.

[0018] A receiver (310) may receive one or more coded video sequences to be decoded by the decoder (210), and in the same or other embodiments may receive one coded video sequence at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. The coded video sequences may be received from a channel (312), which may be a hardware / software link to a storage device that stores the coded video data. The receiver (310) may receive the coded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective using entities (not shown). The receiver (310) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (315) may be coupled between the receiver (310) and the entropy decoder / parser (320) (hereinafter the "parser"). When the receiver 310 is receiving data from a store / forward device with sufficient bandwidth and controllability or from an isosynchronous network, the buffer 315 may not be needed or can be made small. For use over a best-effort packet network such as the Internet, the buffer 315 may be needed and can be made relatively large and, advantageously, of an adaptable size.

[0019] The video decoder (210) may include a parser (320) for reconstructing symbols (321) from the entropy coded video sequence. These categories of symbols may include information used to manage the operation of the decoder (210) and possibly information for controlling a rendering device, such as a display (212). A rendering device, such as a display (212), may not be an integral part of the decoder, but may be coupled to the decoder as shown in FIG. 3. The control information for the rendering device(s) may be in the form of a Supplementary Enhancement Information (SEI) message or a Video Usability Information (VUI) parameter set fragment (not shown). The parser (320) may parse / entropy decode the received coded video sequence. The coding of the coded video sequence may be according to a video coding technique or standard and may follow principles well known to those skilled in the art, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (320) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the group. The subgroup may include a group of pictures (GOP), a picture, a subpicture, a tile, a slice, a brick, a macroblock, a coding tree unit (CTU), a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. A tile may point to a CU / CTU of a rectangular area within a particular tile column and row of a picture. A brick may point to a CU / CTU row of a rectangular area within a particular tile. A slice may point to one or more bricks of a picture that are included in the NAL unit. A subpicture may point to one or more slices of a rectangular area within a picture. The entropy decoder / parser may also extract information from the coded video sequence information, such as transform coefficients, quantization parameter values, motion vectors, etc.

[0020] The parser (320) may perform an entropy decoding / parsing process on the video sequence received from the buffer (315) to produce symbols (321).

[0021] The reconstruction of the symbols (321) may involve several different units, depending on the type of coded video picture or portion thereof and other factors (e.g., inter-picture and intra-picture, inter-block and intra-block, etc.). Which units are involved and how can be controlled by subgroup control information parsed from the coded video sequence by the parser (320). The flow of such subgroup control information between the parser (320) and the following units is not shown for the sake of clarity.

[0022] Beyond the functional blocks already described, the decoder 210 can be conceptually subdivided into a number of functional units, as described below. In a practical implementation operating under commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the subject matter of this disclosure, the following conceptual subdivision into functional units is adequate:

[0023] The first unit is a scalar / inverse transform unit (351). The scalar / inverse transform unit (351) receives the quantized transform coefficients as symbol(s) (321) from the parser (320), along with control information including which transform to use, block size, quantization factor, quantization scaling matrix, etc. It can output blocks with sample values ​​that can be input to an aggregator (355).

[0024] In some cases, the output samples of the scaler / inverse transform (351) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed part of the current picture. Such prediction information can be provided by an intra-picture prediction unit (352), which in some cases uses surrounding already reconstructed information fetched from the current (partially reconstructed) picture (358) to generate blocks of the same size and shape as the block being reconstructed. The aggregator (355) optionally adds, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (352) to the output sample information provided by the scaler / inverse transform unit (351).

[0025] In other cases, the output samples of the scalar / inverse transform unit (351) may relate to a block that may be inter-coded and motion-compensated. In such cases, the motion compensation prediction unit (353) may access the reference picture memory (357) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (321) related to the block, these samples may be added by the aggregator (355) to the output of the scalar / inverse transform unit (referred to as residual samples or residual signals in this case) to generate output sample information. The addresses in the reference picture memory from which the motion compensation unit fetches prediction samples may be controlled by motion vectors available to the motion compensation unit, for example in the form of symbols (321) that may have X, Y, and reference picture components. Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory when sub-sample accurate motion vectors are used, motion vector prediction mechanisms, etc.

[0026] The output samples of the aggregator (355) may be subjected to various loop filtering techniques in a loop filter unit (356). Video compression techniques may include in-loop filter techniques, which are controlled by parameters included in the coded video bitstream and made available to the loop filter unit (356) as symbols (321) from the parser (320), but may also be responsive to meta-information obtained during decoding of previous portions of the coded picture or coded video sequence (in decoding order), as well as to previously reconstructed loop filtered sample values.

[0027] The output of the loop filter unit (356) may be a sample stream that can be output to a rendering device (212), which may also be stored in a reference picture memory for use in future inter-picture prediction.

[0028] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future prediction. Once a coded picture is fully reconstructed and identified as a reference picture (e.g., by the parser (320)), the current reference picture (358) can become part of the reference picture buffer (357) and a new current picture memory can be reallocated before beginning reconstruction of the next coded picture.

[0029] The video decoder 210 may perform the decoding process according to a given video compression technique, which may be documented in a standard, such as ITU-T Recommendation H.235. The encoded video sequence may comply with the syntax defined by the video compression technique or standard used, in the sense of adhering to the syntax of the video compression technique or standard as defined in the video compression technique document or standard, in particular in the profile documents therein. Also necessary for compliance is that the complexity of the encoded video sequence is within the limits defined by the level of the video compression technique or standard. In some cases, the level constrains the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may be further constrained in some cases through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the encoded video sequence.

[0030] In one embodiment, the receiver (310) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the encoded video sequence(s). The additional data may be used by the video decoder (210) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or SNR enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0031] FIG. 4 may be a functional block diagram of a video encoder (203) according to one embodiment of the disclosure.

[0032] The encoder (203) may receive video samples from a video source (201) (not part of the encoder) that may capture the video image(s) that are encoded by the encoder (203).

[0033] The video source (201) may provide a source video sequence to be encoded by the encoder (203) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 Y CrCB, RGB, ...), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media service provision system, the video source (201) may be a storage device that stores pre-prepared videos. In a video conferencing system, the video source (201) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures that convey motion when viewed in sequence. The pictures themselves may be organized as a spatial array of pixels, each of which may have one or more samples, depending on the sampling structure, color space, etc. used. Those skilled in the art will readily appreciate the relationship between pixels and samples. The following description focuses on samples.

[0034] According to one embodiment, the encoder (203) may encode and compress pictures of a source video sequence into an encoded video sequence (443) in real-time or under other time constraints required by the application. Enforcing an appropriate encoding rate is one function of the controller (450). The controller controls and is operatively coupled to other functional units, as described below, which couplings are not shown for clarity. Parameters set by the controller may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, ...), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. Those skilled in the art can readily identify other functions of the controller (450) as being relevant for the video encoder (203) to be optimized for a particular system design.

[0035] Some video encoders operate in what those skilled in the art would immediately recognize as a "coding loop." As an oversimplified explanation, the coding loop may consist of a coding part (430) of the encoder (hereafter "source coder") (responsible for creating symbols based on the input picture to be coded and the reference picture(s)) and a (local) decoder (433) embedded in the encoder (203) that reconstructs the symbols to generate sample data that the (remote) decoder may also create (since in the video compression techniques considered in the present disclosure, any compression between the symbols and the coded video bitstream is lossless). The reconstructed sample stream is input to a reference picture memory (434). Since the decoding of the symbol stream results in bit-accurate results that are independent of the decoder location (local or remote), the contents of the reference picture buffer are also bit-accurate between the local and remote encoders. In other words, the predictive part of the encoder "sees" exactly the same sample values ​​as the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, eg, due to channel errors) is well known to those skilled in the art.

[0036] The operation of the "local" decoder (433) may be the same as that of the "remote" decoder (210), which has already been described in detail above in connection with Figure 3. However, and referring briefly to Figure 4 as well, because symbols are available and the encoding / decoding of the symbols into a coded video sequence by the entropy coder (445) and parser (320) may be lossless, the entropy decoding portion of the decoder (210), including the channel (312), receiver (310), buffer (315), and parser (320), may not be fully implemented in the local decoder (433).

[0037] At this point, it can be noted that any decoder technique, except for parsing / entropy decoding, present in the decoder must necessarily exist in the corresponding encoder in substantially the same functional form. For this reason, the subject matter of this disclosure focuses on the decoder operation. The description of the encoder technique can be omitted since it is the reverse of the decoder technique described in detail. Only in certain areas is a more detailed description required and is provided below.

[0038] As part of its operation, the source coder (430) may perform motion-compensated predictive coding, which predictively codes an input frame relative to one or more previously coded frames from the video sequence designated as “reference frames.” Thus, the coding engine (432) codes differences between pixel blocks of the input frame and pixel blocks of the reference frame(s) that may be selected as the prediction reference(s) for the input frame.

[0039] The local video decoder (433) may decode the encoded video data of frames that may be designated as reference frames based on symbols created by the source coder (430). The operation of the encoding engine (432) may advantageously be a lossy process. When the encoded video data may be decoded by a video decoder (not shown in FIG. 4), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (433) may replicate the decoding process that may be performed by a video decoder on the reference frames, causing the reconstructed reference frames to be stored in a reference picture cache (434). Thus, the encoder (203) may locally store copies of reconstructed reference frames that have common content with reconstructed reference frames that will be obtained by a far-end video decoder.

[0040] The predictor (435) may perform a predictive search for the coding engine (432). That is, for a new frame to be encoded, the predictor (435) may search the reference picture memory (434) for sample data (as candidate reference pixel blocks) or specific metadata, such as reference picture video vectors or block shapes, that may serve as suitable prediction references for the new picture. The predictor (435) may operate on a pixel block by pixel block basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (435), the input picture may have prediction references drawn from multiple reference pictures stored in the reference picture memory (434).

[0041] The controller (450) may manage the encoding process of the video coder (430), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0042] The output of all the aforementioned functional units may be subjected to entropy coding in an entropy coder (445), which converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques known to those skilled in the art, such as Huffman coding, variable length coding, arithmetic coding, etc.

[0043] A transmitter (440) may buffer the encoded video sequence produced by the entropy coder (445) and prepare it for transmission over a communication channel (460), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (440) may merge the encoded video data from the video coder (430) with other data to be transmitted, such as encoded audio data and / or auxiliary data streams (sources not shown).

[0044] The controller (450) may manage the operation of the encoder (203). During encoding, the controller (450) may assign each encoded picture a particular encoding picture type, which may affect the encoding technique that may be applied to the respective picture. For example, pictures may often be assigned as one of the following frame types:

[0045] An intra picture (I-picture) may be something that can be encoded and decoded without using other frames in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh pictures. Those skilled in the art are aware of these variants of I-pictures, as well as their respective uses and characteristics.

[0046] A predictive picture (P picture) may be encoded and decoded using intra- or inter-prediction, using at most one motion vector and reference index to predict the sample values ​​of each block.

[0047] Bidirectionally predicted pictures (B-pictures) may be encoded and decoded using intra- or inter-prediction, using at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multi-predictive images may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0048] A source picture is generally spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and may be coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks determined by the coding assignment applied to their respective pictures. For example, blocks of I-pictures may be coded non-predictively or they may be predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of P-pictures may be coded non-predictively or via spatial or temporal prediction with reference to one previously coded reference picture. Blocks of B-pictures may be coded non-predictively or via spatial or temporal prediction with reference to one or two previously coded reference pictures.

[0049] The video coder (203) may perform an encoding process according to a given video encoding technique or standard, such as ITU-T Recommendation H.265. In operation, the video coder (203) may perform various compression processes, including predictive encoding processes that exploit temporal and spatial redundancies in the input video sequence. The encoded video data may therefore conform to a syntax defined by the video encoding technique or standard being used.

[0050] In one embodiment, the transmitter (440) may transmit additional data along with the encoded video. The video coder (430) may include such data as part of the encoded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, Supplemental Enhancement Information (SEI) messages, Video Usability Information (VUI) parameter set fragments, etc.

[0051] Recently, compressed domain aggregation or extraction of multiple semantically independent picture parts into a single video picture has attracted attention. In particular, for example, in the context of 360 coding or certain surveillance applications, multiple semantically independent source pictures (e.g., six cubic surfaces of a cubic projected 360 scene, or individual camera inputs in case of a multi-camera surveillance setup) may require separate adaptive resolution settings to address different activities per scene at a given time. In other words, an encoder may choose to use different resampling factors for multiple different semantically independent pictures that make up the entirety of a 360 scene or surveillance scene at a given time. When combined into a single picture, it requires that resampling of the reference picture is performed and that adaptive resolution coding signaling is available for multiple parts of the picture to be coded.

[0052] The following introduces some terminology that will be referenced in the remainder of this description.

[0053] A sub-picture may refer to a rectangularly organized sample, block, macroblock, coding unit, or similar entity that may be semantically grouped and coded independently at a changed resolution in some cases. One or more sub-pictures may form a picture. One or more coded sub-pictures may form a coded picture. One or more sub-pictures may be assembled into a picture, and one or more sub-pictures may be extracted from a picture. In certain circumstances, one or more coded sub-pictures may be assembled into a coded picture in the compressed domain without transcoding to the sample level, and in the same or other cases, one or more coded sub-pictures may be extracted from a coded picture in the compressed domain.

[0054] Adaptive Resolution Change (ARC) may refer to a mechanism that allows changing the resolution of pictures or sub-pictures in a coded video sequence, for example by reference picture resampling. Hereinafter, ARC parameters refer to the control information needed to perform adaptive resolution change, which may include, for example, filter parameters, scaling factors, output and / or reference picture resolutions, various control flags, etc.

[0055] In an embodiment, encoding and decoding may be performed on a single semantically independent coded video picture. Before describing the implications of encoding / decoding multiple sub-pictures with independent ARC parameters and the additional complexities it introduces, options for signaling the ARC parameters will be described.

[0056] 5A-5E, several embodiments for signaling ARC parameters are shown. As mentioned in each of these embodiments, they may have certain advantages and certain disadvantages in terms of coding efficiency, complexity, and architecture. A video coding standard or technology may select one or more of these embodiments or options known from related technology for signaling ARC parameters. These embodiments are not mutually exclusive and may be interchanged, wherever possible, based on application needs, standards technologies involved, or encoder choices.

[0057] The classes of ARC parameters may include:

[0058] - Separate or combined up / down sampling factors in the X and Y dimensions.

[0059] - An up / down sampling factor with the addition of a time dimension, which indicates a constant speed zoom in / out for a given number of pictures.

[0060] - Either of the above two may involve the encoding of one or more possibly short syntax elements that may point into a table containing the factor(s).

[0061] - Resolution in the X or Y dimension, either in combination or separately, of input picture, output picture, reference picture, sample of coded picture, block, macroblock, coding unit (CU), or other suitable unit of granularity. If there is more than one resolution (e.g. one for input picture, one for reference picture), in certain cases one set of values ​​can be inferred from another set of values. This can be gated, for example by use of a flag. See below for more detailed examples.

[0062] - The "warping" coordinates are similar to those used in H.263 Annex P, again with a suitable granularity as described above. H.263 Annex P specifies one efficient way to encode such warping coordinates, but conceivably other, possibly more efficient ways could be devised. For example, the variable length lossless "Huffman" style encoding of the warping coordinates of Annex P could be replaced by a suitable length binary encoding, where the length of the binary codewords could, for example, be derived from the maximum picture size, possibly multiplied by a certain factor and offset by a certain value to allow "warping" outside the bounds of the maximum picture size.

[0063] - Up- or downsampling filter parameters. In an embodiment, there may be only a single filter for upsampling and / or downsampling. However, in an embodiment, it may be desirable to allow more flexibility in the filter design, which may require signaling of filter parameters. Such parameters may be selected via an index in a list of possible filter designs, the filter may be fully specified (e.g., via a list of filter coefficients, using an appropriate entropy coding technique), or the filter may be selected implicitly through the up / downsampling ratio, which in turn is signaled according to any of the mechanisms described above.

[0064] Hereafter, the description assumes the encoding of a finite set of up / down sampling coefficients (the same coefficients are used in both X and Y dimensions) that are indexed through a codeword. The codeword may be variable length coded, for example using Ext-Golomb codes prevalent for certain syntax elements in video coding specifications such as H.264 and H.265. One suitable mapping of values ​​to up / down sampling coefficients may, for example, follow Table 1: [Table 1]

[0065] Many similar mappings can be devised according to the needs of the application and the capabilities of upscaling and downscaling mechanisms available in video compression techniques or standards. This table may be extended to more values. The values ​​may also be represented by entropy coding mechanisms other than Ext-Golomb codes, for example using binary coding. This may have certain advantages when resampling factors are of interest outside the video processing engine (encoder and decoder first) itself, for example by MANE. Note that in situations where no resolution change is required, a short Ext-Golomb code, which is only one bit in the above table, can be chosen. This may have coding efficiency advantages over using binary codes for the most common cases.

[0066] The number of entries in the table and their semantics may be fully or partially configurable. For example, the basic gist of the table may be conveyed in a "high" parameter set, such as a sequence or decoder parameter set. In an embodiment, one or more such tables may be defined in a video coding technology or standard and may be selected, for example, via a decoder or sequence parameter set.

[0067] Below we explain how the upsampling / downsampling coefficients (ARC information) coded as described above are included in the syntax of a video coding technique or standard. Similar considerations can be applied to one or a small number of codewords that control the up / downsampling filters. See below for a discussion of when a relatively large amount of data is required for a filter or other data structure.

[0068] As shown in Figure 5A, H.263 Annex P includes ARC information (502) in the form of four warping coordinates in the picture header (501), specifically in the H.263 PLUSPTYPE (503) header extension. This may be a reasonable design choice when a) there is a picture header available, and b) frequent changes of the ARC information are expected. However, the overhead when using H.263-style signaling may be very high, and because picture headers may be of a temporary nature, scaling factors may not be appropriate between picture boundaries.

[0069] As shown in Figure 5B, JVCET-M135-v1 includes ARC reference information (505) (index) located in a picture parameter set (504), which in turn indexes a table (506) containing target resolutions located in a sequence parameter set (507). The placement of possible resolutions in the table (506) in the sequence parameter set (507) can be justified by using SPS as an interoperability negotiation point during capability swapping, according to the verbal description given by the author. Resolution can vary from picture to picture, within the limits set by the values ​​in the table (506), by referencing the appropriate picture parameter set (504).

[0070] 5C-5E, the following embodiments may exist for conveying ARC information within a video bitstream. Each of these options has certain advantages over the above-mentioned embodiments. Multiple embodiments may exist simultaneously for the same video coding technology or standard.

[0071] In embodiments such as the embodiment shown in FIG. 5C, the ARC information (509), e.g., resampling (zoom) factor, may be present in a slice header, a GOP header, a tile header, or a tile group header. FIG. 5C illustrates an embodiment in which a tile group header (508) is used. This may be appropriate when the ARC information is small, e.g., a single variable-length ue(v) or a fixed-length codeword of a few bits, as shown above. Having the ARC information directly in the tile group header has the additional advantage that the ARC information may be applicable to, e.g., a sub-picture represented by that tile group, rather than to the entire picture. See also below. Furthermore, even if a video compression technology or standard only envisages picture-wide adaptive resolution change (as opposed to, e.g., tile group-based adaptive resolution change), putting the ARC information in the tile group header has certain advantages in terms of error resilience compared to putting it in an H.263-style picture header.

[0072] In embodiments such as that shown in FIG. 5D, the ARC information (512) itself may reside in an appropriate parameter set, such as a picture parameter set, a header parameter set, a tile parameter set, an adaptive parameter set, etc. FIG. 5D illustrates an embodiment in which an adaptive parameter set (511) is used. The scope of this parameter set may advantageously be no larger than a picture, such as a tile group. The use of ARC information is implicit by the activation of the associated parameter set. For example, if a video coding technology or standard only contemplates picture-based ARC, then a picture parameter set or equivalent may be appropriate.

[0073] In embodiments such as the embodiment shown in Figure 5E, the ARC reference information (513) may be present in a tile group header (514) or similar data structure. This reference information (513) may reference a subset (515) of the ARC information available in a parameter set (516) that has a scope beyond a single picture, such as a sequence parameter set or a decoder parameter set.

[0074] This additional level of indirect implicit activation of the PPS from the tile group header, PPS, SPS as used in JVET-M0135-v1 seems unnecessary since picture parameter sets can be used (and have in certain standards, e.g. RFC3984) for capability negotiation or announcement, similar to sequence parameter sets. However, if the ARC information should also be applicable to e.g. sub-pictures represented by tile groups, a parameter set with activation scope limited to the tile group, e.g. an adaptation parameter set or a header parameter set, may be a better choice. Also, if the ARC information is of more than negligible magnitude and contains filter control information, e.g. a large number of filter coefficients, the parameters may be a better choice in terms of coding efficiency than using the header (508) directly, since their settings can be reused by future pictures or sub-pictures by referencing the same parameter set.

[0075] When using a sequence parameter set, or another higher parameter set with a range spanning multiple pictures, certain of the following considerations may apply.

[0076] 1. The parameter set that stores the ARC information table (516) can be a sequence parameter set in some cases, but advantageously a decoder parameter set in other cases. The decoder parameter set can have a validity range of multiple CVSs, specifically the coded video stream, i.e. all coded video bits from session start to session release. Such a range may be more appropriate, since the possible ARC coefficients may be decoder capabilities, possibly implemented in hardware, and hardware capabilities are not likely to change with the CVS (which is a group of pictures of less than one second duration, at least in some entertainment systems). However, putting the table in a sequence parameter set is clearly included in the deployment options described herein, especially in relation to point 2 below.

[0077] 2. The ARC reference information (513) may advantageously be placed directly in the picture / slice tile / GOP / tile group header, e.g. the tile group header (514), rather than in the picture parameters as in JVCET-M0135-v1. For example, if an encoder wants to change a single value in a picture parameter set, e.g. the ARC reference information, it must create a new PPS and reference the new PPS. Assume that only the ARC reference information changes, and other information, e.g. the quantization matrix information in the PPS, remains the same. Such information may be of significant size and needs to be retransmitted to complete the new PPS. The ARC reference information (513) may be a single codeword, e.g. an index into a table, and since it is the only value that changes, it may be cumbersome and wasteful to retransmit all of the quantization matrix information, e.g. Similarly, placing the ARC reference information within the PPS has the further disadvantage that, because the scope of picture parameter set activation is the picture, the ARC information referenced by the ARC reference information (513) may apply to the entire picture, rather than to sub-pictures.

[0078] In the same or another embodiment, the signaling of ARC parameters may follow the detailed example outlined in Figures 6A-6B, which show syntax diagrams of expression types using a notation that loosely follows C-style programming, e.g., as used in video coding standards since at least 1993. Bold lines indicate syntax elements present in the bitstream, while non-bold lines often indicate control flow or variable setting.

[0079] As shown in Fig. 6A, the tile group header (601) as an example syntax structure of a header applicable to a (possibly rectangular) part of a picture can conditionally contain the variable length Exp-Golomb coding syntax element dec_pic_size_idx (602) (shown in bold). The presence of this syntax element in the tile group header can be gated with the use of a flag value adaptive resolution (603) not shown here in bold, meaning that the flag is present in the bitstream where it occurs in the syntax diagram. Whether adaptive resolution is used for this picture or part of it can be signaled in any high level syntax structure inside or outside the bitstream. In the illustrated example, it is signaled in the sequence parameter set as outlined below.

[0080] Referring to Figure 6B, an excerpt of a sequence parameter set (610) is also shown. The first syntax element shown is the adplicative_pic_resolution_change_flag (611). When true, this flag can indicate the use of adaptive resolution, which in turn may require specific control information. In this example, such control information is conditionally present based on the value of the flag based on an if() statement in the parameter set (612) and the tile group header (601).

[0081] When adaptive resolution is used, in this example, the output resolution is coded in samples (613). Reference 613 refers to both output_pic_width_in_luma_samples and output_pic_height_in_luma_samples, which together may define the resolution of the output picture. Specific limitations on either value may be defined elsewhere in the video coding technology or standard. For example, the level specification may limit the total number of output samples that may be the product of the values ​​of these two syntax elements. Also, a particular video coding technology or standard, or an external technology or standard, such as a system standard, may limit the numbering range (e.g., one or both dimensions must be divisible by a power of two) or the aspect ratio (e.g., width and height must have a relationship such as 4:3 or 16:9). Such limitations may be introduced to facilitate hardware implementation or for other reasons and are well known in the art.

[0082] In certain applications, it may be desirable for the encoder to instruct the decoder to use a given reference picture size rather than implicitly assuming that size as the output picture size. In this example, the syntax element reference_pic_size_present_flag (614) gates the conditional presence of the reference picture dimensions (615) (again, this reference refers to both width and height).

[0083] Finally, a table of possible decoded picture widths and heights is shown. Such a table can be represented, for example, by a table indication (num_dec_pic_size_in_luma_samples_minus1) (616). "minus1" can refer to the interpretation of the value of this syntax element. For example, if the encoded value is zero, there is one table entry, if the value is 5, there are six table entries. For each "line" in the table, the width and height of the decoded picture are included in the syntax (617).

[0084] The presented table entries (617) can be indexed using the syntax element dec_pic_size_idx (602) in the tile group header, allowing for different decoding sizes (effectively, zoom factors) per tile group.

[0085] Certain video coding techniques or standards, e.g., VP9, ​​support spatial scalability by implementing certain forms of reference picture resampling, along with temporal scalability, to enable spatial scalability. In particular, certain reference pictures may be upsampled to a higher resolution using ARC-style techniques to form the basis of spatial enhancement layers. These upsampled pictures may then be refined using conventional prediction mechanisms at that higher resolution to add detail.

[0086] The embodiments described herein can be used in such environments. In certain cases, in the same or another embodiment, a value, such as a Temporal ID field in the NAL unit header, can be used to indicate not only the temporal layer but also the spatial layer. Doing so can have certain advantages for certain system designs, e.g., existing Selected Forwarding Units (SFUs) created and optimized for the temporal layer selected based on the Temporal ID value in the NAL unit header can be used without modification for the scalable environment. To enable this, a mapping between the coded picture size and the temporal layer may need to be indicated by the Temporal ID field in the NAL unit header.

[0087] In some video coding techniques, an access unit (AU) can refer to (one or more) coded pictures, slices, tiles, NAL units, etc. that are captured at a given instance in time and composited into a respective picture / slice / tile / NAL unit bitstream. This time instance can be, for example, the composition time.

[0088] In HEVC and certain other video coding techniques, a picture order count (POC) value may be used to indicate a reference picture selected from multiple reference pictures stored in a decoded picture buffer (DPB). When an access unit (AU) includes one or more pictures, slices, or tiles, each picture, slice, or tile belonging to the same AU may carry the same POC value, from which it can be derived that they are created from content of the same composition time. In other words, in a scenario where two pictures / slices / tiles carry the same POC value, it can be taken as an indication that the two pictures / slices / tiles belong to the same AU and have the same composition time. Conversely, two pictures / tiles / slices with different POC values ​​can indicate that the pictures / slices / tiles belong to different AUs and have different composition times.

[0089] In an embodiment, this strict relationship may be relaxed in that an access unit may contain multiple pictures, slices, or tiles with different POC values. Allowing multiple different POC values ​​within one AU allows the POC values ​​to be used to identify potentially independently decodable pictures / slices / tiles with equal presentation time. This in turn may enable support of multiple scalable layers without modification of reference picture selection signaling, e.g., reference picture set signaling or reference picture list signaling, as described in more detail below.

[0090] However, it is still desirable to be able to identify, from the POC value alone, the AU to which a picture / slice / tile belongs with respect to other pictures / slices / tiles with different POC values. This can be achieved as described below.

[0091] In an embodiment, an access unit count (AUC) may be signaled in a high-level syntax structure, such as a NAL unit header, a slice header, a tile group header, a SEI message, a parameter set, or an AU delimiter. The value of the AUC may be used to identify which NAL units, pictures, slices, or tiles belong to a given AU. The value of the AUC may correspond to distinct synthesis time instances. The AUC value may be equal to a multiple of the POC value. The AUC value may be calculated by dividing the POC value by an integer value. In certain cases, the division operation may impose a certain burden on the decoder implementation. In such cases, a small constraint in the numbering space of the AUC values ​​may allow the division operation to be replaced by a shift operation. For example, the AUC value may be equal to the most significant bit (MSB) value of the POC value range.

[0092] In an embodiment, a value of the POC cycle per AU (poc_cycle_au) may be signaled in a high-level syntax structure, such as a NAL unit header, a slice header, a tile group header, an SEI message, a parameter set, or an AU delimiter. poc_cycle_au may indicate how many consecutive different POC values ​​may be associated with the same AU. For example, if the value of poc_cycle_au is equal to 4, pictures, slices, or tiles with POC values ​​equal to 0-3, inclusive, may be associated with an AU with an AUC value equal to 0, and pictures, slices, or tiles with POC values ​​equal to 4-7, inclusive, may be associated with an AU with an AUC value equal to 1. Thus, the value of AUC may be estimated by dividing the POC value by the value of poc_cycle_au.

[0093] In an embodiment, the value of poc_cycle_au may be derived from information specifying the number of spatial or SNR layers in the coded video sequence, for example located in a video parameter set (VPS). An example of such a possible relationship is briefly described below. Although the above derivation may save a few bits in the VPS and thus improve coding efficiency, in some embodiments, poc_cycle_au may be explicitly coded in an appropriate high-level syntax structure hierarchically under the video parameter set, such that poc_cycle_au can be minimized for a given small portion of the bitstream, such as a picture. This optimization may save more bits than can be saved through the above derivation process, since the POC value, and / or values ​​of syntax elements that indirectly reference the POC, may be coded in a lower level syntax structure.

[0094] In an embodiment, FIG. 8 shows an example of a syntax table for signaling a syntax element of vps_poc_cycle_au in a VPS (or SPS), which indicates the poc_cycle_au used for all pictures / slices in a coded video sequence, and a syntax element of slice_poc_cycle_au, which indicates the poc_cycle_au of the current slice in the slice header. If the POC value increases uniformly per AU, vps_contant_poc_cycle_per_au in the VPS can be set to 1, and vps_poc_cycle_au can be signaled in the VPS. In this case, slice_poc_cycle_au may not be explicitly signaled, and the value of AUC for each AU may be calculated by dividing the value of POC by vps_poc_cycle_au. If the POC value does not increase uniformly per AU, vps_contant_poc_cycle_per_au in the VPS may be set equal to 0. In this case, vps_access_unit_cnt may not be signaled, and slice_access_unit_cnt may be signaled in the slice header of each slice or picture. Each slice or picture may have a different value of slice_access_unit_cnt. The value of AUC for each AU may be calculated by dividing the value of POC by slice_poc_cycle_au.

[0095] FIG. 9 shows a block diagram illustrating an example of the above process. For example, in operation S910, the VPS (or SPS) can be parsed, and in operation S920, it can be determined whether the POC cycle per AU is constant in the coded video sequence. If the POC cycle per AU is constant (YES in operation S920), in operation S930, a value of the access unit count for a particular access unit can be calculated from the poc_cycle_au signaled for the coded video sequence and the POC value of the particular access unit. If the POC cycle per AU is not constant (NO in operation S920), in operation S940, a value of the access unit count for a particular access unit can be calculated from the poc_cycle_au signaled at the picture level and the POC value of the particular access unit. In operation S950, a new VPS (or SPS) can be parsed.

[0096] In an embodiment, pictures, slices, or tiles corresponding to AUs with the same AUC value may be associated with the same decoding or output time instance, even though the values ​​of the POC of the pictures, slices, or tiles may be different. Thus, all or a subset of pictures, slices, or tiles associated with the same AU may be decoded in parallel and output at the same time instance, without cross parsing / decoding dependencies across pictures, slices, or tiles within the same AU.

[0097] In an embodiment, pictures, slices, or tiles that correspond to AUs with the same AUC value may be associated with the same composition / display time instance, even though the POC values ​​of the pictures, slices, or tiles may be different. If the composition time is included in the container format, pictures can be displayed at the same time instance if they have the same composition time, even if they correspond to different AUs.

[0098] In an embodiment, each picture, slice, or tile may have the same temporal identifier (temporal_id) within the same AU. All or a subset of pictures, slices, or tiles corresponding to a time instance may be associated with the same temporal sublayer. In an embodiment, each picture, slice, or tile may have the same or different spatial layer ID (layer_id) within the same AU. All or a subset of pictures, slices, or tiles corresponding to a time instance may be associated with the same or different spatial layers.

[0099] FIG. 7 shows an example of a video sequence structure with combinations of temporal_id, layer_id, POC, and AUC values ​​with adaptive resolution change. In this example, pictures, slices, and tiles in the first AU with AUC=0 may have temporal_id=0 and layer_id=0 or 1, and pictures, slices, and tiles in the second AU with AUC=1 may have temporal_id=1 and layer_id=0 or 1. The value of POC is increased by 1 for every picture, regardless of the values ​​of temporal_id and layer_id. In this example, the value of poc_cycle_au may be equal to 2. In an embodiment, the value of poc_cycle_au may be set equal to the number of (spatial scalability) layers. In this example, the value of POC is therefore increased by 2, and the value of AUC is increased by 1.

[0100] In the above embodiment, all or a subset of inter-picture or inter-layer prediction structures and reference picture indications may be supported by using the existing Reference Picture Set (RPS) signaling or Reference Picture List (RPL) signaling in HEVC. In the RPS or RPL, the selected reference picture may be indicated by signaling a value of POC or a delta value of POC between the current picture and the selected reference picture. In the embodiment, the RPS and RPL may be used to indicate the inter-picture or inter-layer prediction structure without signaling changes, with the following constraints: If the value of the temporal_id of a reference picture is greater than the value of the temporal_id of the current picture, the current picture may not use that reference picture for motion compensation or other prediction. If the value of the layer_id of a reference picture is greater than the value of the layer_id of the current picture, the current picture may not use that reference picture for motion compensation or other prediction.

[0101] In an embodiment, motion vector scaling based on POC difference for temporal motion vector prediction may be disabled across multiple pictures in an access unit. Thus, although each picture may have a different POC value within an access unit, motion vectors are not scaled and are not used for temporal motion vector prediction within the access unit. This is because reference pictures with different POCs within the same AU are considered as reference pictures with the same time instance. Thus, in an embodiment, if the reference picture belongs to the AU associated with the current picture, the motion vector scaling function may return 1.

[0102] In an embodiment, motion vector scaling based on POC difference for temporal motion vector prediction may be optionally disabled across pictures if the spatial resolution of the reference picture is different from the spatial resolution of the current picture. When motion vector scaling is enabled, the motion vector is scaled based on both the POC difference and the spatial resolution ratio between the current picture and the reference picture.

[0103] In an embodiment, motion vectors may be scaled based on AUC difference instead of POC difference for temporal motion vector prediction, especially when poc_cycle_au has non-uniform values ​​(e.g., when vps_contant_poc_cycle_per_au==0). Otherwise (e.g., when vps_contant_poc_cycle_per_au==1), motion vector scaling based on AUC difference may be the same as motion vector scaling based on POC difference.

[0104] In an embodiment, when a motion vector is scaled based on the AUC difference, a reference motion vector in the same AU (having the same AUC value) as the current picture is not scaled based on the AUC difference and is used for motion vector prediction without scaling or with scaling based on the spatial resolution ratio between the current picture and the reference picture.

[0105] In an embodiment, the AUC value can be used to identify AU boundaries and can be used for hypothetical reference decoder (HRD) operations that require input and output timing at AU granularity. In an embodiment, the decoded picture using the highest layer in the AU can be output for display. The AUC value and the layer_id value can be used to identify the output picture.

[0106] In an embodiment, a picture may include one or more sub-pictures. Each sub-picture may cover a local area or the entire area of ​​the picture. The area supported by a sub-picture may or may not overlap with the area supported by another sub-picture. The area covered by one or more sub-pictures may or may not cover the entire area of ​​the picture. When a picture includes a sub-picture, the area supported by the sub-picture may be the same as the area supported by the picture.

[0107] In an embodiment, a sub-picture may be coded by an encoding method similar to that used for the picture being coded. A sub-picture may be coded independently or dependently on another sub-picture or coded picture. A sub-picture may or may not have some parsing dependency from another sub-picture or coded picture.

[0108] In an embodiment, a coded sub-picture may be included in one or more layers. The coded sub-pictures within a layer may have different spatial resolutions. The original sub-pictures may be spatially resampled (e.g., upsampled or downsampled), coded with different spatial resolution parameters, and included in the bitstream corresponding to the layer.

[0109] In an embodiment, a sub-picture having (W,H), where W denotes the width of the sub-picture and H denotes the height of the sub-picture, is coded and included in the coded bitstream corresponding to layer 0, and S w,k , S h,k Let W*S denote the horizontal and vertical resampling ratios. w,k ,H*S h,k ), sub-pictures upsampled (or downsampled) from the sub-pictures with the original spatial resolution may be coded and included in the coded bitstream corresponding to layer k. w,k , S h,kIf the value of S is greater than 1, the resampling may be an upsampling. w,k , S h,k If the value of is less than 1, the resampling may be a downsampling.

[0110] In an embodiment, a coded subpicture within a layer may have a different visual quality than a coded subpicture of another layer, either in the same subpicture or in a different subpicture. For example, subpicture i in layer n may have a quantization parameter Q i,n and subpicture j in layer m is coded with quantization parameter Q j,m It can be encoded as:

[0111] In an embodiment, a coded subpicture within a layer may be independently decodable without parsing or decoding dependencies from coded subpictures in another layer of the same local region. A subpicture layer that may be independently decodable without reference to another subpicture layer of the same local region may be an independent subpicture layer. A coded subpicture within an independent subpicture layer may or may not have decoding or parsing dependencies from previously coded subpictures in the same subpicture layer, but a coded subpicture may not have any dependencies from coded pictures in another subpicture layer.

[0112] In an embodiment, a coded subpicture in a layer may be dependently decodable with parsing or decoding dependency from a coded subpicture in another layer of the same local region. A subpicture layer that can be dependently decodable with reference to another subpicture layer of the same local region may be a dependent subpicture layer. A coded subpicture in a dependent subpicture layer may reference coded subpictures belonging to the same subpicture, previously coded subpictures in the same subpicture layer, or both reference subpictures.

[0113] In an embodiment, a coded subpicture may include one or more independent subpicture layers and one or more dependent subpicture layers. However, at least one independent subpicture layer may be present in a coded subpicture. The value of a layer identifier (layer_id), which may be present in a NAL unit header or other high-level syntax structure of an independent subpicture layer, may be equal to 0. A subpicture layer with a layer_id equal to 0 may be a base subpicture layer.

[0114] In an embodiment, a picture may include one or more foreground subpictures and one background subpicture. The area supported by a background subpicture may be equal to the area of ​​the picture. The area supported by a foreground subpicture may overlap the area supported by a background subpicture. The background subpicture may be a base subpicture layer, and the foreground subpicture may be a non-base (enhancement) subpicture layer. One or more non-base subpicture layers may reference the same base layer for decoding. Each non-base subpicture layer with layer_id equal to a may reference a non-base subpicture layer with layer_id equal to b, where a is greater than b.

[0115] In an embodiment, a picture may contain one or more foreground subpictures, with or without background subpictures. Each subpicture may have its own base subpicture layer and one or more non-base (enhancement) layers. Each base subpicture layer may be referenced by one or more non-base subpicture layers. Each non-base subpicture layer with layer_id equal to a may reference a non-base subpicture layer with layer_id equal to b, where a is greater than b.

[0116] In an embodiment, a picture may include one or more foreground subpictures, with or without a background subpicture. Each coded subpicture in a (base or non-base) subpicture layer may be referenced by one or more non-base layer subpictures that belong to the same subpicture, and by one or more non-base layer subpictures that do not belong to the same subpicture.

[0117] In an embodiment, a picture may contain one or more foreground subpictures, with or without background subpictures. A subpicture in layer a may be further split into multiple subpictures in the same layer. One or more coded subpictures in layer b may reference a split subpicture in layer a.

[0118] In an embodiment, a Coded Video Sequence (CVS) may be a group of coded pictures. A CVS may contain one or more Coded Sub-Picture Sequences (CSPS), which may be a group of coded sub-pictures covering the same local area of ​​a picture. A CSPS may have the same or a different temporal resolution as the Coded Video Sequence.

[0119] In an embodiment, a CSPS may be encoded and included in one or more layers. A CSPS may include one or more CSPS layers. By decoding one or more CSPS layers corresponding to a CSPS, a sequence of sub-pictures corresponding to the same local region can be reconstructed.

[0120] In an embodiment, the number of CSPS layers corresponding to one CSPS may be the same as or different from the number of CSPS layers corresponding to another CSPS.

[0121] In an embodiment, a CSPS layer may have a different temporal resolution (e.g., frame rate) than another CSPS layer, and the original (uncompressed) sub-picture sequence may be temporally resampled (e.g., upsampled or downsampled), coded with different temporal resolution parameters, and included in the bitstream corresponding to the layer.

[0122] In an embodiment, a sub-picture sequence having a frame rate F is encoded and included in the encoded bitstream corresponding to layer 0, and S t,k denotes the time sampling ratio for layer k, F*S t,k A sub-picture sequence that is temporally upsampled (or downsampled) from the original sub-picture sequence, having a sub-picture sequence S t,k If the value of S is greater than 1, the temporal resampling process may be a frame rate up-conversion. t,k If the value of is less than 1, the temporal resampling process may be a frame rate down-conversion.

[0123] In an embodiment, when a subpicture with CSPS layer a is referenced by a subpicture with CSPS layer b for motion compensation or some inter-layer prediction, if the spatial resolution of CSPS layer a is different from the spatial resolution of CSPS layer b, the decoded pixels in CSPS layer a are resampled and used for reference. This resampling process may use upsampling filtering or downsampling filtering.

[0124] FIG. 10 shows an example of a video stream including a background video CSPS with layer_id equal to 0 and multiple foreground CSPS layers. A coded subpicture may include one or more CSPS layers. A background region that does not belong to any foreground CSPS layer may include a base layer. The base layer may include background and foreground regions, and an enhancement CSPS layer may include a foreground region. An enhancement CSPS layer may have better visual quality than the base layer in the same region. An enhancement CSPS layer may refer to the reconstructed pixels and motion vectors of the base layer corresponding to the same region.

[0125] In an embodiment, the video bitstream corresponding to the base layer is included in a track, and the CSPS layer corresponding to each sub-picture is included in a separate track within the video file.

[0126] In an embodiment, the video bitstream corresponding to the base layer is included in a track, and the CSPS layers having the same layer ID are included in separate tracks. In this example, the track corresponding to layer k includes only the CSPS layer corresponding to layer k.

[0127] In an embodiment, each CSPS layer of each sub-picture is stored in a separate track. Each track may or may not have a syntax parsing or decoding dependency from one or more other tracks.

[0128] In an embodiment, assuming 0 < i <= j <= k and k is the top layer of CSPS, each track may include the bitstreams corresponding to the CSPS layers from layer i to layer j of all or a subset of the sub-pictures.

[0129] In an embodiment, a picture includes one or more associated media data including a depth map, an alpha map, 3D geometry data, an occupancy map, etc. Such associated timed media data can each be split into one or more data sub-streams corresponding to one sub-picture.

[0130] FIG. 11 shows an example of a video conference based on the multi-layer sub-picture method. The video stream includes one base layer video bitstream corresponding to a background picture and one or more enhancement layer video bitstreams corresponding to a foreground sub-picture. Each enhancement layer video bitstream may correspond to a CSPS layer. On the display, the picture corresponding to the base layer is displayed by default. This includes one or more user picture-in-pictures (PIPs). When a particular user is selected by client control, the enhancement CSPS layer corresponding to the selected user may be decoded and displayed with increased quality or spatial resolution.

[0131] FIG. 12 shows a block diagram illustrating an example of the above process. For example, in operation S1210, a video bitstream having multiple layers may be decoded. In operation S1220, a background region and one or more foreground sub-pictures may be identified. In operation S1230, it may be determined whether a particular sub-picture region, for example one of the foreground sub-pictures, has been selected. If a particular sub-picture region has been selected (YES in operation S1230), the augmented sub-picture may be decoded and displayed. If a particular sub-picture region has not been selected (NO in operation S1230), the background region may be decoded and displayed.

[0132] In an embodiment, a network middle box (e.g., a router) may select a subset of layers to send to a user depending on its bandwidth. Picture / sub-picture organization may be used for bandwidth adaptation. For example, if a user does not have the bandwidth, the router may strip layers or select some sub-pictures by importance or based on usage setup, which can be done dynamically to adapt to the bandwidth.

[0133] FIG. 13 illustrates an embodiment related to a 360 video use case. When a spherical 360 picture, e.g. picture 1310, is projected onto a planar picture, the projected 360 picture may be divided into multiple sub-pictures as a base layer. For example, the multiple sub-pictures may include a back sub-picture, a top sub-picture, a right sub-picture, a left sub-picture, a front sub-picture, and a bottom sub-picture. An enhancement layer of a specific sub-picture, e.g. a front sub-picture, may be encoded and sent to a client. A decoder may be able to decode both the base layer including all the sub-pictures and the enhancement layer of the selected sub-picture. If the current viewport is the same as the selected sub-picture, the displayed picture may have higher quality with the decoded sub-picture with the enhancement layer. Otherwise, the decoded picture with the base layer may be displayed with lower quality.

[0134] In an embodiment, some layout information for display may be present in the file as supplemental information (e.g., SEI message or metadata, etc.). One or more decoded sub-pictures may be rearranged and displayed according to the signaled layout information. The layout information may be signaled by a streaming server or broadcaster, regenerated by a network entity or cloud server, or determined by a user's customization settings.

[0135] In an embodiment, when an input picture is divided into one or more (rectangular) sub-regions, each sub-region may be coded as an independent layer. Each independent layer corresponding to a local region may have a unique layer_id value. For each independent layer, sub-picture size and position information may be signaled, such as picture size (width, height), top left corner offset information (x_offset, y_offset). Figure 14 shows an example of a layout of divided sub-pictures, their sub-picture size and position information, and corresponding picture prediction structure. This layout information, including sub-picture size(s) and sub-picture position(s), may be signaled in a high-level syntax structure, such as parameter set(s), slice or tile group header, or SEI message.

[0136] In an embodiment, each sub-picture corresponding to an independent layer may have its own POC value in the AU. When a reference picture among multiple pictures stored in the DPB is pointed to by using a syntax element(s) in the RPS or RPL structure, the POC value(s) of each sub-picture corresponding to a layer may be used.

[0137] In an embodiment, the layer_id may not be used to indicate the (inter-layer) prediction structure, but rather the POC(delta) value.

[0138] In an embodiment, a sub-picture having a POC value equal to N corresponding to a layer (or local region) may or may not be used as a reference picture for a sub-picture having a POC value equal to N+K corresponding to the same layer (or the same local region) for motion compensation prediction. In most cases, the value of the number K may be equal to the maximum number of (independent) layers, which may be equal to the number of sub-regions.

[0139] In an embodiment, Figure 15 shows an extended case of Figure 14. When an input picture is divided into multiple (e.g., four) sub-regions, each local region can be coded with one or more layers. In this case, the number of independent layers can be equal to the number of sub-regions, and one or more layers can correspond to a sub-region. Thus, each sub-region can be coded with one or more independent layers and zero or more dependent layers.

[0140] In an embodiment, in Figure 15, the input picture may be divided into four sub-regions. As an example, the top right sub-region may be coded as two layers, layer 1 and layer 4, and the bottom right sub-region may be coded as two layers, layer 3 and layer 5. In this case, layer 4 may refer to layer 1 for motion compensation prediction, and layer 5 may refer to layer 3 for motion compensation.

[0141] In an embodiment, in-loop filtering across layer boundaries (e.g., deblocking filtering, adaptive in-loop filtering, reshaper, bilateral filtering, or any deep learning based filtering) may be (optionally) disabled.

[0142] In an embodiment, motion compensated prediction or intra block copying across layer boundaries may (optionally) be disabled.

[0143] In an embodiment, border padding for motion compensated prediction or in-loop filtering at sub-picture boundaries may be optionally processed. A flag indicating whether border padding is processed or not may be signaled in a high-level syntax structure, such as, for example, a parameter set(s) (VPS, SPS, PPS, or APS), a slice or tile group header, or an SEI message.

[0144] In an embodiment, layout information of the sub-region(s) (or sub-picture(s)) may be signaled in the VPS or SPS. FIG. 16A shows an example of syntax elements in the VPS, and FIG. 16B shows an example of syntax elements in the SPS. In this example, vps_sub_picturing_dividing_flag is signaled in the VPS. This flag may indicate whether the input picture(s) are divided into multiple sub-regions. If the value of vps_sub_picture_dividing_flag is equal to 0, the input picture(s) in the coded video sequence(s) corresponding to the current VPS may not be divided into multiple sub-regions. In this case, the input picture size may be equal to the coded picture size (pic_width_in_luma_samples, pic_height_in_luma_samples) signaled in the SPS. If the value of vps_sub_picture_dividing_flag is equal to 1, the input picture(s) may be divided into multiple sub-regions. In this case, the syntax elements vps_full_pic_width_in_luma_samples and vps_full_pic_height_in_luma_samples are signaled in the VPS. The values ​​of vps_full_pic_width_in_luma_samples and vps_full_pic_height_in_luma_samples may be equal to the width and height of the input picture(s), respectively.

[0145] In an embodiment, the values ​​of vps_full_pic_width_in_luma_samples and vps_full_pic_height_in_luma_samples may not be used for decoding, but may be used for synthesis and display.

[0146] In an embodiment, if the value of vps_sub_picture_dividing_flag is equal to 1, syntax elements pic_offset_x and pic_offset_y may be signaled in the SPS that (a) corresponds to a particular layer(s). In this case, the coded picture size (pic_width_in_luma_samples, pic_height_in_luma_samples) signaled in the SPS may be equal to the width and height of the sub-region corresponding to a particular layer. The location of the top left corner of the sub-region (pic_offset_x, pic_offset_y) may also be signaled in the SPS.

[0147] In an embodiment, the position information (pic_offset_x, pic_offset_y) of the upper left corner of the sub-region may be used for compositing and display without being used for decoding.

[0148] In an embodiment, layout information (size and position) of all or a subset of the subregion(s) of the input picture(s), dependency information between the layers may be signaled in a parameter set or SEI message. FIG. 17 shows an example of syntax elements indicating information of the layout of the subregions, dependencies between layers, and the relationship between the subregions and one or more layers. In this example, the syntax element num_sub_region indicates the number of (rectangular) subregions in the currently encoded video sequence. The syntax element num_layers indicates the number of layers in the currently encoded video sequence. The value of num_layers may be equal to or greater than the value of num_sub_region. When any subregion is encoded as a single layer, the value of num_layers may be equal to the value of num_sub_region. When one or more subregions are encoded as multiple layers, the value of num_layers may be greater than the value of num_sub_region. The syntax element direct_dipendency_flag[i][j] indicates the dependency from the jth layer to the ith layer. num_layers_for_region[i] indicates the number of layers associated with the i-th subregion. sub_region_layer_id[i][j] indicates the layer_id of the j-th layer associated with the i-th subregion. sub_region_offset_x[i] and sub_region_offset_y[i] indicate the horizontal and vertical location, respectively, of the top-left corner of the i-th subregion. sub_region_width[i] and sub_region_height[i] indicate the width and height, respectively, of the i-th subregion.

[0149] In an embodiment, one or more syntax elements specifying an output layer set may be signaled in a high level syntax structure, such as a VPS, DPS, SPS, PPS, APS, or SEI message, to indicate one or more layers to be output with or without profile tier level information. With reference to Figure 18, a syntax element num_output_layer_sets may be signaled in a VPS to indicate the number of output layer sets (OLS) in a coded video sequence that references the VPS. For each output layer set, an output_layer_flag may be signaled as many times as the number of output layers.

[0150] In an embodiment, output_layer_flag[i] equal to 1 specifies that the i-th layer is output. vps_output_layer_flag[i] equal to 0 specifies that the i-th layer is not output.

[0151] In an embodiment, one or more syntax elements specifying profile tier level information for each output layer set may be signaled in a high level syntax structure, such as a VPS, DPS, SPS, PPS, APS, or SEI message. Still referring to FIG. 18, a syntax element num_profile_tile_level may be signaled in the VPS indicating the number of profile tier level information per OLS in a coded video sequence that references the VPS. For each output layer set, a set of syntax elements for profile tier level information or an index pointing to a particular profile tier level information among the entries in the profile tier level information may be signaled as many times as the number of output layers.

[0152] In an embodiment, profile_tier_level_idx[i][j] specifies the index of the profile_tier_level() syntax structure that applies to the jth tier of the ith OLS in the list of profile_tier_level() syntax structures in the VPS.

[0153] In an embodiment, referring to FIG. 19, when the maximum number of layers is greater than 1 (vps_max_layers_minus1>0), the syntax elements num_profile_tile_level and / or num_output_layer_sets may be signaled.

[0154] In an embodiment, referring to FIG. 19, a syntax element vps_output_layers_mode[i] may be present in the VPS to indicate the mode of output layer signaling for the i-th output layer set.

[0155] In an embodiment, vps_output_layers_mode[i] equal to 0 specifies that only the top layer is output in the i-th output layer set. vps_output_layer_mode[i] equal to 1 specifies that all layers are output in the i-th output layer set. vps_output_layer_mode[i] equal to 2 specifies that the layers output are those with vps_output_layer_flag[i][j] equal to 1 in the i-th output layer set. More values ​​may be reserved.

[0156] In an embodiment, output_layer_flag[i][j] may or may not be signaled depending on the value of vps_output_layers_mode[i] for the i-th output layer set.

[0157] In an embodiment, referring to Figure 19, a flag vps_ptl_signal_flag[i] may be present for the i-th output tier set. Depending on the value of vps_ptl_signal_flag[i], profile tier level information for the i-th output tier set may or may not be signaled.

[0158] In an embodiment, referring to FIG. 20, the number of sub-pictures in the current CVS, max_subpics_minus1, may be signaled in a high-level syntax structure, such as a VPS, DPS, SPS, PPS, APS, or SEI message.

[0159] In an embodiment, referring to FIG. 20, if the number of sub-pictures is greater than one (max_subpics_minus1>0), a sub-picture identifier sub_pic_id[i] for the i-th sub-picture may be signaled.

[0160] In an embodiment, one or more syntax elements indicating sub-picture identifiers belonging to each layer of each output layer set may be signaled in the VPS. Referring to Figure 20, sub_pic_id_layer[i][j][k] indicates the kth sub-picture present in the jth layer of the ith output layer set. With this information, the decoder can know which sub-pictures can be decoded and output for each layer of a particular output layer set.

[0161] In an embodiment, a picture header (PH) is a syntax structure that contains syntax elements that apply to all slices of a coded picture. A picture unit (PU) is a collection of NAL units that are related to each other according to a specified classification rule, are consecutive in decoding order, and contain exactly one coded picture. A PU may contain a picture header (PH) and one or more coded slice NAL units or VCL NAL units that contain a coded picture.

[0162] In an embodiment, the SPS (RBSP) is made available to the decoding process before it is referenced, and may be included in at least one AU with TemporalId equal to 0 or provided via external means.

[0163] In an embodiment, the SPS (RBSP) is made available to the decoding process before it is referenced, and may be included in at least one AU with TemporalId equal to 0 in a CVS, which may contain one or more PPSs that reference the SPS, or may be provided via external means.

[0164] In an embodiment, an SPS (RBSP) is made available to the decoding process before it is referenced by one or more PPSs, and may be included in at least one PU with a nuh_layer_id equal to the lowest nuh_layer_id value of a PPS NAL unit that references an SPS NAL unit in a CVS, which may contain one or more PPSs that reference the SPS, or may be provided via external means.

[0165] In an embodiment, an SPS (RBSP) is made available to the decoding process before it is referenced by one or more PPSs, and may be included in at least one PU with TemporalId equal to 0 and nuh_layer_id equal to the lowest nuh_layer_id value of a PPS NAL unit that references the SPS NAL unit, or provided via external means.

[0166] In an embodiment, an SPS (RBSP) is made available to the decoding process before it is referenced by one or more PPSs, and may be included in at least one PU with TemporalId equal to 0 and nuh_layer_id equal to the lowest nuh_layer_id value of a PPS NAL unit that references an SPS NAL unit in a CVS that may contain one or more PPSs that reference the SPS, or may be provided via external means.

[0167] In an embodiment, the pps_seq_parameter_set_id specifies the value of sps_seq_parameter_set_id for the referenced SPS. The value of pps_seq_parameter_set_id may be the same for all PPSs referenced by coded pictures in the CLVS.

[0168] In an embodiment, all SPS NAL units with a particular value of sps_seq_parameter_set_id in the CVS may have the same content.

[0169] In an embodiment, regardless of the nuh_layer_id value, SPS NAL units may share the same value space of sps_seq_parameter_set_id.

[0170] In an embodiment, the nuh_layer_id value of an SPS NAL unit may be equal to the lowest nuh_layer_id value of a PPS NAL unit that references the SPS NAL unit.

[0171] In an embodiment, when an SPS with nuh_layer_id equal to m is referenced by one or more PPS with nuh_layer_id equal to n, the layer with nuh_layer_id equal to m may be the same as the (direct or indirect) reference layer of the layer with nuh_layer_id equal to n or the layer with nuh_layer_id equal to m.

[0172] In an embodiment, the PPS (RBSP) is made available to the decoding process before it is referenced, may be included in at least one AU with TemporalId equal to the TemporalId of the PPS NAL unit, or may be provided via external means.

[0173] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced, and may be included in at least one AU with a TemporalId equal to the TemporalId of a PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS, or may be provided via external means.

[0174] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced by one or more PHs (or coded slice NAL units) and may be included in at least one PU having a nuh_layer_id equal to the lowest nuh_layer_id of a coded slice NAL unit that references a PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS, or may be provided via external means.

[0175] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced by one or more PHs (or coded slice NAL units) and may be included in at least one PU, or provided via external means, that has a TemporalId equal to the TemporalId of the PPS NAL unit and a nuh_layer_id equal to the lowest nuh_layer_id of a coded slice NAL unit that references the PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS.

[0176] In an embodiment, ph_pic_parameter_set_id in the PH specifies the value of pps_pic_parameter_set_id for the reference PPS used. The value of pps_seq_parameter_set_id may be the same for all PPSs referenced by coded pictures in the CLVS.

[0177] In an embodiment, all PPS NAL units with a particular value of pps_pic_parameter_set_id within a PU have the same content.

[0178] In an embodiment, regardless of the nuh_layer_id value, PPS NAL units may share the same value space of pps_pic_parameter_set_id.

[0179] In an embodiment, the nuh_layer_id value of a PPS NAL unit may be equal to the lowest nuh_layer_id value of any coded slice NAL unit that references a NAL unit that references the PPS NAL unit.

[0180] In an embodiment, when a PPS with nuh_layer_id equal to m is referenced by one or more coded slice NAL units with nuh_layer_id equal to n, the layer with nuh_layer_id equal to m may be the same as the (direct or indirect) reference layer of the layer with nuh_layer_id equal to n or the layer with nuh_layer_id equal to m.

[0181] In an embodiment, the PPS (RBSP) is made available to the decoding process before it is referenced, may be included in at least one AU with TemporalId equal to the TemporalId of the PPS NAL unit, or may be provided via external means.

[0182] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced, and may be included in at least one AU with a TemporalId equal to the TemporalId of a PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS, or may be provided via external means.

[0183] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced by one or more PHs (or coded slice NAL units) and may be included in at least one PU having a nuh_layer_id equal to the lowest nuh_layer_id of a coded slice NAL unit that references a PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS, or may be provided via external means.

[0184] In an embodiment, a PPS (RBSP) is made available to the decoding process before it is referenced by one or more PHs (or coded slice NAL units) and may be included in at least one PU, or provided via external means, that has a TemporalId equal to the TemporalId of the PPS NAL unit and a nuh_layer_id equal to the lowest nuh_layer_id of a coded slice NAL unit that references the PPS NAL unit in a CVS that contains one or more PHs (or coded slice NAL units) that reference the PPS.

[0185] In an embodiment, ph_pic_parameter_set_id in the PH specifies the value of pps_pic_parameter_set_id for the reference PPS used. The value of pps_seq_parameter_set_id may be the same for all PPSs referenced by coded pictures in the CLVS.

[0186] In an embodiment, all PPS NAL units with a particular value of pps_pic_parameter_set_id within a PU have the same content.

[0187] In an embodiment, regardless of the nuh_layer_id value, PPS NAL units may share the same value space of pps_pic_parameter_set_id.

[0188] In an embodiment, the nuh_layer_id value of a PPS NAL unit may be equal to the lowest nuh_layer_id value of any coded slice NAL unit that references a NAL unit that references the PPS NAL unit.

[0189] In an embodiment, when a PPS with nuh_layer_id equal to m is referenced by one or more coded slice NAL units with nuh_layer_id equal to n, the layer with nuh_layer_id equal to m may be the same as the (direct or indirect) reference layer of the layer with nuh_layer_id equal to n or the layer with nuh_layer_id equal to m.

[0190] In an embodiment, when the flag no_temporal_sublayer_switching_flag is signaled in a DPS, VPS, or SPS, the TemporalId value of a PPS that references a parameter set that includes the flag equal to 1 may be equal to 0, and the TemporalId value of a PPS that references a parameter set that includes the flag equal to 1 may be equal to or greater than the TemporalId value of the parameter set.

[0191] In an embodiment, each PPS (RBSP) is made available to the decoding process before it is referenced, and may be included in at least one AU with a TemporalId less than or equal to the TemporalId of the coded slice NAL unit (or PH NAL unit) that references it, or may be provided via external means. When a PPS NAL unit is included in an AU prior to the AU containing the coded slice NAL unit that references the PPS, no VCL NAL units that enable temporal up-layer switching or have a nal_unit_type equal to STSA_NUT (which indicates that the picture in the VCL NAL unit may be a stepwise temporal sub-layer access (STSA) picture) may be present after the PPS NAL unit and before the coded slice NAL unit that references the PPS.

[0192] In an embodiment, the PPS NAL unit and the coded slice NAL unit (and its PH NAL unit) that reference the PPS may be included in the same AU.

[0193] In an embodiment, the PPS NAL unit and the STSA NAL unit that reference the PPS may be included in the same AU that precedes the coded slice NAL unit (and its PH NAL unit).

[0194] In an embodiment, the STSA NAL unit, the PPS NAL unit, and the coded slice NAL unit (and its PH NAL unit) that reference the PPS may be in the same AU.

[0195] In the same embodiment, the TemporalId value of a VCL NAL unit that contains a PPS may be equal to the TemporalId value of the preceding STSA NAL unit.

[0196] In the same embodiment, the picture order count (POC) value of the PPS NAL unit may be equal to or greater than the POC value of the STSA NAL unit.

[0197] In the same embodiment, the picture order count (POC) value of a coded slice or a PH NAL unit that references a PPS NAL unit may be equal to or greater than the POC value of the referenced PPS NAL unit.

[0198] Figure 21 is a flow chart of an example of a process 2100 for decoding an encoded video bitstream. In some implementations, one or more process blocks of Figure 21 may be performed by the decoder 210. In some implementations, one or more process blocks of Figure 21 may be performed by another device or group of devices separate from or including the decoder 210, such as, for example, the encoder 203.

[0199] As shown in FIG. 21, process 2100 may include obtaining an encoded video sequence from a coded video bitstream (block 2110).

[0200] As further shown in FIG. 21, the process 2100 may include obtaining a picture unit from the coded video sequence (block 2120).

[0201] As further shown in FIG. 21, the process 2100 may include obtaining a PH NAL unit included in the picture unit (block 2130).

[0202] As further shown in FIG. 21, the process 2100 may include obtaining at least one coded slice NAL unit included in the picture unit (block 2140).

[0203] As further shown in FIG. 21, process 2100 may include decoding the coded picture based on the PH NAL unit, the at least one coded slice NAL unit, a PPS included in a PPS NAL unit obtained from the coded video sequence, and an SPS included in an SPS NAL unit obtained from the coded video sequence, where the SPS NAL unit may be available to at least one processor performing process 2100 before the PPS NAL unit, and the PPS NAL unit may be available to the at least one processor before the PH NAL unit and the at least one coded slice NAL unit (block 2120).

[0204] As further shown in FIG. 21, the process 2100 may include outputting the decoded picture (block 2160).

[0205] In an embodiment, the time indicator of the SPS NAL unit may be equal to zero.

[0206] In an embodiment, the layer identifier of the PPS NAL unit is greater than or equal to the layer identifier of the SPS NAL unit.

[0207] In an embodiment, the layer identifier of at least one coded slice NAL unit may be greater than or equal to the layer identifier of the PPS NAL unit.

[0208] In an embodiment, the PH NAL unit, at least one coded slice NAL unit, and the PPS NAL unit may be included in a single access unit.

[0209] In an embodiment, the coded video sequence may further include a stepwise temporal sub-layer access (STSA) NAL unit corresponding to a STSA picture, where the STSA NAL unit is not located between the PPS NAL unit and the at least one coded slice NAL unit.

[0210] In an embodiment, the PH NAL unit, at least one coded slice NAL unit, the PPS NAL unit, and the STSA NAL unit may be included in a single access unit.

[0211] In an embodiment, the time identifier of the PPS NAL unit may be equal to the time identifier of the STSA NAL unit.

[0212] In an embodiment, the picture order count (POC) of a PPS NAL unit may be greater than or equal to the POC of an STSA NAL unit.

[0213] Although Figure 21 illustrates example blocks of process 2100, in some implementations, process 2100 may include additional, fewer, different, or differently arranged blocks than those illustrated in Figure 21. Additionally or alternatively, two or more of the blocks of process 2100 may be performed in parallel.

[0214] Also, the proposed methods may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium to perform one or more of the proposed methods.

[0215] The techniques described above can be implemented as computer software using computer readable instructions and can be physically stored on one or more computer readable media. For example, Figure 22 illustrates a computer system 2200 suitable for implementing certain embodiments of the disclosed subject matter.

[0216] The computer software may be coded using any suitable machine code or computer language that may be assembled, compiled, linked, or similarly subjected to mechanisms to produce code having instructions that can be executed by a computer central processing unit (CPU), graphics processing unit (GPU), and the like, either directly or via interpretation, microcode execution, and the like.

[0217] The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smart phones, gaming devices, Internet of Things devices, and the like.

[0218] 22 with respect to computer system 2200 are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the present disclosure, nor should the arrangement of components be interpreted as having any dependency or requirement related to any one or combination of components illustrated in this exemplary embodiment of computer system 2200.

[0219] The computer system 2200 may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users, for example, via tactile input (e.g., keystrokes, swipes, moving a data glove, etc.), audio input (e.g., voice, clapping, etc.), visual input (e.g., gestures, etc.), olfactory input (not shown). Human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds, etc.), images (e.g., scanned images, photographic images obtained from a still camera, etc.), video (e.g., two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0220] The input human interface devices may include one or more of a keyboard 2201, a mouse 2202, a trackpad 2203, a touch screen 2210 and associated graphics adapter 2250, a data glove, a joystick 2205, a microphone 2206, a scanner 2207, and a camera 2208 (only one of each is shown).

[0221] The computer system 2200 may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the senses of a human user, for example, through haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen 2210, data gloves, or joystick 2205, although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers 2209, headphones (not shown), etc.), visual output devices (e.g., screens 2210 including cathode ray tube (CRT) screens, liquid crystal display (LCD) screens, plasma screens, organic light emitting diode (OLED) screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may be capable of outputting two-dimensional visual output, or output in four or more dimensions through means such as stereoscopic output), virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown), etc.), and printers (not shown).

[0222] Computer system 2200 may also include human-accessible storage devices and their associated media, such as optical media including, for example, CD / DVD ROM / RW 2220 having CD / DVD or similar media 2221, thumb drives 2222, removable hard drives or solid state drives 2223, legacy magnetic media such as tapes and floppy disks (registered trademark, not shown), specialized ROM / ASIC / PLD based devices (not shown) such as security dongles, and the like.

[0223] Those skilled in the art will also appreciate that the term "computer-readable medium" as used in connection with the subject matter disclosed herein does not include transmission media, carrier waves, or other transitory signals.

[0224] The computer system 2200 may also include an interface(s) to one or more communication networks (2255). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, Global Systems for Mobile Communications (GSM), cellular networks including third generation (3G), fourth generation (4G), fifth generation (5G), Long Term Evolution (LTE) and the like, TV wired or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and industrial including CANBus, etc. Certain networks typically require an external network interface adapter (2254) that attaches to a particular general-purpose data port or peripheral bus (2249) (e.g., a Universal Serial Bus (USB) port of the computer system 2200, etc.), while others are typically integrated into the core of the computer system 2200 by attachment to a system bus as described below (e.g., an Ethernet interface to a PC computer system, or a cellular network interface to a smartphone computer system). As an example, a network 2255 may be connected to the peripheral bus 2249 using a network interface 2254. Using any of these networks, the computer system 2200 may communicate with other entities. Such communications may be unidirectional receive only (e.g., broadcast TV), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used on each of the networks and network interfaces (2254), as described above.

[0225] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to core 2240 of computer system 2200.

[0226] The core 2240 may include one or more central processing units (CPUs) 2241, graphics processing units (GPUs) 2242, specialized programmable processing units in the form of field programmable gate arrays (FPGAs) 2243, hardware accelerators for specific tasks 2244, etc. These devices may be connected via a system bus 2248 along with read only memory (ROM) 2245, random access memory (RAM) 2246, internal mass storage 2247 such as internal non-user accessible hard drives, solid state drives (SSDs), and the like. In some computer systems, the system bus 2248 may be made accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripheral devices may be attached either directly to the core's system bus 2248 or via a peripheral bus 2249. Peripheral bus architectures include peripheral component interconnect (PCI), USB, and the like.

[0227] The CPU 2241, GPU 2242, FPGA 2243, and accelerator 2244 may execute certain instructions that may combine to constitute the aforementioned computer code. The computer code may be stored in ROM 2245 or RAM 2246. Transient data may also be stored in RAM 2246, while permanent data may be stored, for example, in internal mass storage 2247. Rapid storage and retrieval in any of the memory devices may be enabled by the use of cache memories that may be associated proximate to one or more of the CPU 2241, GPU 2242, mass storage 2247, ROM 2245, RAM 2246, and the like.

[0228] The computer-readable media can have computer code thereon for performing various computer-implemented processes. The media and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the kind well known and available to those skilled in the computer software arts.

[0229] As an example, and not by way of limitation, a computer system having architecture 2200, and in particular core 2240, can provide functionality as a result of processor(s) (including CPU, GPU, FPGA, accelerator, and the like) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be media associated with specific storage of core 2240 that is non-transitory in nature, such as mass storage 2247 internal to the core or ROM 2245, and user-accessible mass storage as introduced above. Software implementing various embodiments of the present disclosure can be stored in such devices and executed by core 2240. Computer-readable media can include one or more memory devices or chips according to specific needs. The software can cause core 2240, and in particular processors therein (including CPU, GPU, FPGA, and the like) to perform certain processes or certain parts of certain processes described herein, including defining data structures stored in RAM 2246 and modifying such data structures according to processes defined by the software. Additionally, or alternatively, a computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator 2244) that can operate in place of or in conjunction with software to perform particular processes, or portions of particular processes, described herein. References to software include logic, and vice versa, where appropriate. References to computer-readable media may include circuitry (e.g., an integrated circuit (IC) or the like) that stores software for execution, circuitry embodied with logic for execution, or both, where appropriate. The present disclosure includes any suitable combination of hardware and software.

[0230] While this disclosure describes several exemplary embodiments, there are alterations, permutations, and various equivalent alternatives that fall within the scope of the disclosure. It will thus be understood that those skilled in the art will be able to devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of the disclosure and are therefore within its spirit and scope.

Claims

1. 1. A method for decoding an encoded video bitstream, executed by at least one processor, comprising: obtaining a coded video sequence (CVS) from the coded video bitstream; obtaining an SPS included in a sequence parameter set (SPS) network abstraction layer (NAL) unit of a coded video layer sequence (CLVS) obtained from the CVS, the SPS NAL unit including the SPS being directly referenced by a picture parameter set (PPS) NAL unit, the SPS NAL unit including a layer identifier of the SPS NAL unit, and a value of an SPS parameter_set_id syntax is the same in all SPSs referenced by the CLVS in the CVS; decoding a coded picture based on the PPS NAL unit and the SPS NAL unit; outputting the decoded picture; The method according to claim 1,

2. The method of claim 1 , wherein the time identifier of the SPS NAL unit is equal to zero.

3. the SPS NAL units are available to the at least one processor before the PPS NAL units; and the PPS NAL unit is available to the at least one processor before a picture header (PH) NAL unit included in the coded video bitstream and at least one coded slice NAL unit included in the coded video bitstream. The method of claim 1.

4. The method of claim 3 , wherein a layer identifier of the at least one coded slice NAL unit is greater than or equal to a layer identifier of the PPS NAL unit.

5. The method of claim 3 , wherein the PH NAL unit, the at least one coded slice NAL unit, and the PPS NAL unit are included in a single access unit.

6. The CVS further includes a stepwise temporal sub-layer access (STSA) NAL unit corresponding to an STSA picture; the STSA NAL unit is not located between the PPS NAL unit and the at least one coded slice NAL unit; The method according to claim 3.

7. The method of claim 6 , wherein the PH NAL unit, the at least one coded slice NAL unit, the PPS NAL unit, and the STSA NAL unit are included in a single access unit.

8. The method of claim 6 , wherein a time identifier of the PPS NAL unit is equal to a time identifier of the STSA NAL unit.

9. The method of claim 6 , wherein a picture order count (POC) of the PPS NAL unit is greater than or equal to a POC of the STSA NAL unit.

10. 1. An apparatus for decoding an encoded video bitstream, the apparatus comprising: at least one memory configured to store program code; at least one processor configured to read the program code and to operate as instructed by the program code; having The program code, when executed by the at least one processor, causes the at least one processor to perform the method of any one of claims 1 to 9. Device.

11. A computer program causing a computer to carry out the method according to any one of claims 1 to 9.

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