Method, apparatus and computer program for decoding a coded video stream

Abstract

To provide an encoding and decoding method capable of changing the resampling and resolution of a reference picture.SOLUTION: The decoding method includes obtaining a sequence parameter set (SPS) network abstraction layer (NAL) unit, a picture parameter set (PPS) NAL unit, a picture header (PH) NAL unit, and a slice NAL unit from a coded video bitstream, and decoding a coded picture based thereon, wherein the SPSNAL unit is available to at least one processor before the PPSNAL unit, and wherein the PPSNAL unit is available to the at least one processor before the PHNAL 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 parameter set referencing and ranges 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 series of pictures, each having spatial dimensions of, for example, 1920 x 1080 luminance (luminance) samples and associated color (chrominance) samples. The series of pictures can have a fixed or variable picture rate (informally known as frame rate), for example, 60 pictures per second, i.e., a 60 Hz picture rate. Uncompressed video has significant bitrate requirements. For example, 1080p60 4:2:0 video (1920 x 1080 luminance sample resolution at a 60 Hz frame rate) 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 can be the reduction of redundancy in the input video signal through compression. Compression can help reduce the aforementioned bandwidth or storage space requirements, sometimes by more than two orders of magnitude. Both lossless and lossy compression, as well as combinations of these, can be used. Lossless compression refers to techniques that allow an exact replica of the original signal to be reconstructed from a compressed version of the original signal. When lossy compression is used, the reconstructed signal may not be identical to the original signal, but the distortion between the original and 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; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television contribution applications. 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, transforms, quantization, and entropy coding, some of which are introduced below.

[0006] Historically, video encoders and decoders have tended to operate with a given picture size that is often defined and kept constant for a coded video sequence (CVS), group of pictures (GOP), or similar multi-picture time frame. For example, in MPEG-2, system designs that vary the horizontal resolution (and therefore the picture size) depending on factors such as scene activity are known, but only for 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; only the reference picture is resampled, potentially to only the portion of the picture canvas used (in the case of downsampling) or only the portion of the scene captured (in the case of upsampling). H.263 Annex Q also allows for 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 prevalent. For example, VP9 allows for reference picture resampling and resolution changes 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, January 9-19, 2019, incorporated herein by reference in its entirety) allow for the resampling of entire reference pictures to different, higher or lower resolutions. That document proposes 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, there is provided a method for decoding a coded video bitstream using at least one processor, 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 for decoding a coded video bitstream is provided, the apparatus including: 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 including: 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. and an output code configured to cause the at least one processor to output the decoded picture based on a sequence parameter set (SPS) included in a NAL unit, 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 stored thereon instructions that, when executed by one or more processors of an apparatus for decoding a coded video bitstream, cause 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 explanation of the drawings]

[0011] Further features, nature and various advantages of the subject matter of the present disclosure 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. [Figure 2] FIG. 1 is a schematic diagram of a simplified block diagram of a communication system according to one embodiment. [Figure 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. [Figure 5B] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment. [Figure 5C] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment. [Figure 5D] 5A-5E are schematic diagrams of options for signaling ARC parameters according to one embodiment. [Figure 5E] 5A-5E are schematic diagrams of options for signaling ARC parameters 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] 1 is an example of a syntax table according to one embodiment. [Figure 9] FIG. 10 is a simplified block diagram schematic 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 multi-layer sub-pictures according to one embodiment. [Figure 11] FIG. 1 is a schematic diagram of displaying a selected sub-picture at an increased resolution according to one embodiment. [Figure 12] FIG. 2 is a block diagram of a process for decoding and displaying a video bitstream containing multi-layer sub-pictures, according to one embodiment. [Figure 13]FIG. 1 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 picture and its corresponding layer and picture prediction structure according to one embodiment. [Figure 15] 1 is an example of layout information of a sub-picture 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 subpicture layout information according to one embodiment. [Figure 16B] 16A-16B are example syntax tables for subpicture layout information according to one embodiment. [Figure 17] 10 is an example syntax table of an SEI message for sub-picture layout information according to one embodiment. [Figure 18] 10 is an example syntax table showing output tier and profile / tier / level information for each output tier set, according to one embodiment. [Figure 19] 10 is an example syntax table showing output layer mode on for each output layer set, according to one embodiment. [Figure 20] 10 is an example syntax table showing the current subpicture of each layer for each output layer set according to one embodiment. [Figure 21] 1 is a flowchart 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 INVENTION

[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 data transmission, a first terminal (110) may locally encode video data 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) configured 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] While the terminals (110-140) may be illustrated in FIG. 1 as servers, personal computers, and smartphones, the principles of the present disclosure are not so limited. Embodiments of the present disclosure find application in laptop computers, tablet computers, media players, and / or dedicated videoconferencing equipment. Network (150) represents any number of networks, including, for example, wired and / or wireless communication networks, that convey encoded video data between the terminals (110-140). 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 network (150) may not be important to the operation of the present disclosure, unless otherwise described below.

[0015] 2 illustrates the placement 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 where video can be used, including, for example, video conferencing, digital TV, and storage of compressed video on digital media including CDs, DVDs, memory sticks, and the like.

[0016] The streaming system can include a capture subsystem (213), which can include a video source (201), such as a digital camera, that produces an uncompressed video sample stream (202). The sample stream (202), depicted as a thick line to emphasize its high data volume compared to an encoded video bitstream, can be processed by an encoder (203) coupled to the camera 201. The encoder (203) can include hardware, software, or a combination thereof to enable or implement aspects of the present disclosure, as described in more detail below. The encoded video bitstream (204), depicted as a thin line to emphasize its low data volume compared to the sample stream, can be stored on a streaming server (205) for later use. One or more streaming clients (206, 208) can 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), which 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] The receiver (310) can receive one or more coded video sequences to be decoded by the decoder (210), and in the same or other embodiments, can 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 can be received from a channel (312), which can be a hardware / software link to a storage device that stores the coded video data. The receiver (310) can also receive the coded video data along with other data, such as coded audio data and / or auxiliary data streams, which can be forwarded to their respective using entities (not shown). The receiver (310) can separate the coded video sequences from other data. To combat network jitter, a buffer memory (315) can be coupled between the receiver (310) and the entropy decoder / parser (320) (hereinafter, "parser"). When the receiver 310 is receiving data from a store-and-forward device with sufficient bandwidth and controllability or from an isosynchronous network, the buffer 315 may not be needed or can be small. For use over a best-effort packet network, such as the Internet, the buffer 315 may be needed and may be 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-encoded video sequence. These symbol categories 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), is not an integral part of the decoder but can be coupled to the decoder as shown in FIG. 3. Control information for one or more rendering devices 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, including variable-length coding, Huffman coding, arithmetic coding with or without context sensitivity, and may follow principles well known to those skilled in the art. The parser (320) can extract a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder from the coded video sequence based on at least one parameter corresponding to the group. A subgroup can 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 can refer to a CU / CTU of a rectangular area within a particular tile column and row of a picture. A brick can refer to a CU / CTU row of a rectangular area within a particular tile. A slice can refer to one or more bricks of a picture that are included in the NAL unit. A subpicture can refer to one or more slices of a rectangular area within a picture. The entropy decoder / parser can 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 clarity.

[0022] Beyond the functional blocks already described, decoder 210 can be conceptually subdivided into a number of functional units, as described below. In a practical implementation operating within commercial constraints, many of these units will 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 division into functional units is appropriate:

[0023] The first unit is a scalar / inverse transform unit (351), which receives quantized transform coefficients as symbol(s) (321) from the parser (320), along with control information including which transform to use, block size, quantization coefficients, quantization scaling matrix, etc. It can output blocks of 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 portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (352). In some cases, the intra-picture prediction unit (352) generates blocks of the same size and shape as the block being reconstructed using surrounding, already reconstructed information fetched from the current (partially reconstructed) picture (358). 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-compensated prediction unit (353) may access a 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 appended by an aggregator (355) to the output of the scalar / inverse transform unit (referred to in this case as residual samples or residual signals) 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 in the form of symbols (321), which may have, for example, 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, and the like.

[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 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 a previous portion of a coded picture or coded video sequence (in decoding order), as well as to previously reconstructed and loop-filtered sample values.

[0027] The output of the loop filter unit (356) can be a sample stream that can be output to a rendering device (212), which can 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 new current picture memory can be reallocated before beginning reconstruction of the next coded picture.

[0029] The video decoder 210 may perform decoding according to a given video compression technique, which may be documented in a standard such as ITU-T Recommendation H.235. The coded video sequence may conform to the syntax specified by the video compression technique or standard used, in the sense of adhering to the syntax of the video compression technique or standard as specified in the video compression technique document or standard, particularly the profile document therein. Compliance also requires that the complexity of the coded video sequence be within the limits set 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 optionally be further constrained through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded 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 one or more encoded video sequences. 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 present disclosure.

[0032] The encoder (203) may receive video samples from a video source (201) (not part of the encoder) that may capture one or more video images to be encoded by the encoder (203).

[0033] The video source (201) may provide the 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 containing pre-prepared video. In a video conferencing system, the video source (201) may be a camera capturing local image information as a video sequence. The video data may be provided as multiple 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 understand 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, whose coupling is 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, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. Those skilled in the art will readily identify other functions of the controller (450) that may be relevant to a video encoder (203) optimized for a particular system design.

[0035] Some video encoders operate in what those skilled in the art will immediately recognize as a "coding loop." As an overly simplistic explanation, the coding loop can consist of a coding portion (430) of the encoder (hereinafter, the "source coder") (responsible for creating symbols based on the input picture to be coded and one or more reference pictures) and a (local) decoder (433) embedded in the encoder (203), which reconstructs the symbols to generate sample data that a (remote) decoder can also create (because in the video compression techniques considered in this 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). Because decoding of the symbol stream yields bit-accurate results 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 portion of the encoder "sees" the exact same sample values ​​as the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchronization (and the resulting drift when synchronization 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 briefly referring also to Figure 4, because symbols are available and the encoding / decoding of 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] It can be noted at this point that any decoder technology, excluding parsing / entropy decoding, present in the decoder must necessarily exist in substantially the same functional form in the corresponding encoder. For this reason, the subject matter of this disclosure focuses on decoder operation. A description of the encoder technology can be omitted, as it is the reverse of the decoder technology that has been thoroughly described. Only in certain areas is a more detailed description required, which 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 a video sequence designated as “reference frames.” Thus, the coding engine (432) codes the differences between pixel blocks of the input frame and pixel blocks of one or more reference frames that can be selected as prediction reference(s) for the input frame.

[0039] The local video decoder (433) may decode the coded video data of frames that may be designated as reference frames based on symbols created by the source coder (430). The operation of the coding engine (432) may advantageously be a lossy process. When the coded video data is 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 error. The local video decoder (433) may replicate the decoding process that may be performed by the video decoder on the reference frames, causing the reconstructed reference frames to be stored in a reference picture cache (434). In this way, the encoder (203) may locally store copies of reconstructed reference frames that have content in common 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 encoding 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 motion vectors or block shapes, that can serve as suitable prediction references for the new picture. The predictor (435) may operate on a pixel block-by-pixel block basis to find suitable prediction references. 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 outputs 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 coded video sequence produced by the entropy coder (445) and prepare it for transmission over a communication channel (460), which may be a hardware or software link to a storage device that stores the coded video data. The transmitter (440) may merge the coded video data from the video coder (430) with other data to be transmitted, such as coded 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 coded picture a particular coded picture type, which may affect the coding 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 one that can be encoded and decoded without using other frames in the 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 and their respective uses and characteristics.

[0046] A predicted 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 coded 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 pictures 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 as determined by the coding assignment applied to their respective pictures. For example, blocks of an I-picture may be coded non-predictively, or they may be predictively coded with reference to already coded blocks of the same picture (spatial prediction or intra-prediction). Pixel blocks of a P-picture may be coded non-predictively or via spatial or temporal prediction with reference to one previously coded reference picture. Blocks of a B-picture 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 predetermined 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 coded video. The video coder (430) may include such data as part of the coded 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, compression-domain aggregation or extraction of multiple semantically independent picture portions 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 the case of a multi-camera surveillance setup) may require separate adaptive resolution settings to address different scene-specific activities at a given time. In other words, an encoder may choose to use different resampling factors for multiple semantically independent pictures that make up the entire 360 ​​scene or surveillance scene at a given time. When combined into a single picture, this requires that reference picture resampling be performed and that adaptive resolution coding signaling be available for the multiple portions of the picture being coded.

[0052] Below we introduce some terms that will be referenced in the remainder of this description.

[0053] A subpicture may refer, in some cases, to a rectangularly configured sample, block, macroblock, coding unit, or similar entity that can be semantically grouped and coded independently at a changed resolution. One or more subpictures can form a picture. One or more coded subpictures can form a coded picture. One or more subpictures can be assembled into a picture, and one or more subpictures can be extracted from a picture. In certain circumstances, one or more coded subpictures can 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 subpictures can 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 within 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 embodiments, 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 complexity it introduces, options for signaling the ARC parameters will be described.

[0056] 5A-5E, several embodiments for signaling ARC parameters are shown. As noted in each of these embodiments, they may have certain advantages and 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 art for signaling ARC parameters. These embodiments are not mutually exclusive and may conceivably be interchanged based on application needs, the standards and technologies involved, or the choice of encoder.

[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 combined or separately, of input picture, output picture, reference picture, coded picture sample, block, macroblock, coding unit (CU), or other suitable unit of granularity. If there are more than one resolution (e.g., one for input picture and 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 the use of flags. See below for more detailed examples.

[0062] - "Warping" coordinates are similar to those used in H.263 Annex P, again at 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 can be devised. For example, the variable-length reversible "Huffman"-style encoding of the warping coordinates of Annex P may be replaced by a suitable-length binary encoding, where the length of the binary codewords may be derived, for example, from the maximum picture size, possibly multiplied by a certain factor to allow "warping" outside the boundaries of the maximum picture size, and offset by a certain value.

[0063] - Up- or downsampling filter parameters. In embodiments, there may be only a single filter for upsampling and / or downsampling. However, in embodiments, it may be desirable to allow more flexibility in 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 appropriate entropy coding techniques), 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 the X and Y dimensions) indicated through a codeword. The codeword may be variable-length coded using Ext-Golomb codes, which are popular 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 the upscaling and downscaling mechanisms available in the video compression technology or standard. 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 selected. 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 embodiments, one or more such tables may be defined in a video coding technology or standard and may be selected, for example, through 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 few codewords that control an up / downsampling filter. 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 to the ARC information are expected. However, the overhead of using H.263-style signaling may be very high, and because picture headers may be transient in nature, scaling factors may not be appropriate across 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 table (506) within sequence parameter set (507) can be justified, according to the author's verbal description, by using SPS as an interoperability negotiation point during capability exchange. Resolution can vary from picture to picture within the limits set by the values ​​in 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-described embodiments. Multiple embodiments may exist simultaneously within the same video coding technology or standard.

[0071] In embodiments such as that shown in FIG. 5C , ARC information (509), e.g., a 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 added 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 allows for picture-wide adaptive resolution changes (as opposed to, e.g., tile group-based adaptive resolution changes), placing the ARC information in the tile group header has certain advantages in terms of error resilience compared to placing 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 within an appropriate parameter set, such as a picture parameter set, a header parameter set, a tile parameter set, or an adaptive parameter set. 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 with the activation of the associated parameter set. For example, if a video coding technology or standard only contemplates picture-based ARC, 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 reside 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, and SPS as used in JVET-M0135-v1 seems unnecessary because picture parameter sets, like sequence parameter sets, can be used for capability negotiation or announcement (and have in certain standards, e.g., RFC3984). However, if the ARC information should also be applicable to, for example, sub-pictures represented by tile groups, a parameter set with activation scope limited to the tile group, such as an adaptive parameter set or a header parameter set, may be a better choice. Also, if the ARC information is of more than negligible magnitude and includes filter control information, such as a large number of filter coefficients, parameters may be a better choice from the perspective of coding efficiency than directly using the header (508), because 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. A 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 end. Such a range may be more appropriate because the possible ARC coefficients may represent decoder capabilities, possibly implemented in hardware, and hardware capabilities are unlikely to change with the CVS (which, at least in some entertainment systems, is a group of pictures, less than one second long). However, including the table in a sequence parameter set is explicitly included in the deployment options described herein, particularly in connection with point 2 below.

[0077] 2. The ARC reference information (513) can 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., quantization matrix information in the PPS, remains the same. Such information can be substantial and needs to be retransmitted to complete the new PPS. Since the ARC reference information (513) can be a single codeword, e.g., an index into a table, and it is the only value that changes, retransmitting all of the quantization matrix information, e.g., can be cumbersome and wasteful. If so, avoiding the circuitous route via the PPS, as proposed in JVET-M0135-v1, can be significantly better in terms of coding efficiency. 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 a sub-picture.

[0078] In the same or another embodiment, signaling of ARC parameters can follow the detailed example outlined in Figures 6A-6B, which show syntax diagrams of expression types using notation loosely following 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 Figure 6A, the tile group header (601) as an exemplary syntax structure for a header applicable to a (possibly rectangular) portion 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 in bold here, 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 numeral 613 refers to both output_pic_width_in_luma_samples and output_pic_height_in_luma_samples, which together can define the resolution of the output picture. Specific limitations on either value may be defined elsewhere in a video coding technology or standard. For example, a level specification may limit the total number of output samples that can 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 the 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 coded value is zero, there is one table entry, and 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 technologies or standards, such as VP9, ​​support spatial scalability by implementing certain forms of reference picture resampling to enable spatial scalability, along with temporal scalability. In particular, certain reference pictures may be upsampled to higher resolutions using ARC-style techniques to form the basis of spatial enhancement layers. These upsampled pictures may then be refined at that higher resolution using conventional prediction mechanisms 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 scalable environments. To enable this, the mapping between coded picture sizes and temporal layers 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 respective picture / slice / tile / NAL unit bitstreams. This time instance can be, for example, the composition time.

[0088] In HEVC and certain other video coding technologies, 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 with the same composition time. In other words, in a scenario where two pictures / slices / tiles carry the same POC value, this may indicate 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 ​​may indicate that the pictures / slices / tiles belong to different AUs and have different composition times.

[0089] In embodiments, 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 times. This, in turn, may enable support for multiple scalable layers without modifying 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 the AU to which a picture / slice / tile belongs from the POC value alone, relative to other pictures / slices / tiles with different POC values, which 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, an SEI message, a parameter set, or an AU delimiter. The AUC value may be used to identify which NAL unit, picture, slice, or tile belongs to a given AU. The AUC value 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 on the numbering space of the AUC values ​​may allow the division operation to be replaced with 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 ​​can 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, can 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, can be associated with an AU with an AUC value equal to 1. Thus, the value of AUC can be estimated by dividing the POC value by the value of poc_cycle_au.

[0093] In embodiments, the value of poc_cycle_au may be derived from information specifying the number of spatial or SNR layers in a coded video sequence, for example, located in a video parameter set (VPS). An example of such a possible relationship is briefly described below. While 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 below the video parameter set, so 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, because the POC value and / or values ​​of syntax elements that indirectly reference the POC may be coded in lower-level syntax structures.

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

[0095] 9 shows a block diagram illustrating an example of the above process. For example, at operation S910, a VPS (or SPS) can be parsed, and at operation S920, it can be determined whether the POC cycle per AU is constant within a coded video sequence. If the POC cycle per AU is constant (YES at operation S920), at operation S930, a value of an access unit count for a particular access unit can be calculated from 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 at operation S920), at operation S940, a value of an access unit count for a particular access unit can be calculated from poc_cycle_au signaled at the picture level and the POC value of the particular access unit. At 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 POC values ​​of the pictures, slices, or tiles may differ. 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 corresponding 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] 7 shows an example of a video sequence structure with combinations of temporal_id, layer_id, POC, and AUC values ​​for adaptive resolution change. In this example, a picture, slice, or tile in the first AU with AUC=0 may have temporal_id=0 and layer_id=0 or 1, and a picture, slice, or tile 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 each 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. Therefore, in this example, the value of POC is increased by 2, and the value of AUC is increased by 1.

[0100] In the above embodiments, 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, a 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 embodiments, the RPS and RPL can be used to indicate an inter-picture or inter-layer prediction structure without any 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 within an access unit. Thus, although each picture within an access unit may have a different POC value, 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 POC within the same AU are considered to be 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 optionally be disabled across pictures if the spatial resolution of the reference picture differs from the spatial resolution of the current picture. When motion vector scaling is enabled, motion vectors are 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 the AUC difference instead of the 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 the AUC difference may be the same as motion vector scaling based on the 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 within the AU can be output for display. The AUC value and layer_id value can be used to identify the output picture.

[0106] In embodiments, a picture may contain 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 contains sub-pictures, the area supported by the sub-pictures may be the same as the area supported by the picture.

[0107] In embodiments, sub-pictures may be coded by a coding method similar to that used for the picture being coded. Sub-pictures may be coded independently or dependently on other sub-pictures or coded pictures. Sub-pictures may or may not have some parsing dependency from other sub-pictures or coded pictures.

[0108] In an embodiment, coded subpictures may be included in one or more layers. The coded subpictures within a layer may have different spatial resolutions. The original subpictures 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 indicates the horizontal and vertical resampling ratio, (W*S w,k ,H*S h,k ), sub-pictures upsampled (or downsampled) from 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 embodiments, a coded subpicture within a layer may have a different visual quality than a coded subpicture of another layer, either within the same subpicture or a different subpicture. For example, subpicture i within layer n may have a quantization parameter Q i,n and subpicture j in layer m is coded with the quantization parameter Q j,m It can be encoded as:

[0111] In embodiments, coded subpictures 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 embodiments, coded subpictures within a layer may be dependently decodable with parsing or decoding dependency from coded subpictures in another layer of the same local region. A subpicture layer that can be dependently decodable by reference to another subpicture layer of the same local region may be a dependent subpicture layer. Coded subpictures within a dependent subpicture layer may reference coded subpictures belonging to the same subpicture, previously coded subpictures in the same subpicture layer, or both.

[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 the 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 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. A background subpicture may be a base subpicture layer, and a 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 include 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 background subpictures. 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 include one or more foreground subpictures, with or without background subpictures. A subpicture in layer a may be further split into multiple subpictures within the same layer. One or more coded subpictures in layer b may reference split subpictures 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 region 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 coded into 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 coded into the coded 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 temporally upsampled (or downsampled) from the original sub-picture sequence, having 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] Figure 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 can include one or more CSPS layers. Background regions that do not belong to any foreground CSPS layer can include the base layer. The base layer can include background and foreground regions, and the enhancement CSPS layer can include foreground regions. The enhancement CSPS layer can have better visual quality than the base layer in the same region. The enhancement CSPS layer can reference 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 subpicture 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 subpicture is stored in a separate track. Each track may or may not have a syntax analysis or decoding dependency from one or more other tracks.

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

[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 substreams corresponding to one subpicture.

[0130] Figure 11 shows an example of a video conference based on the multi-layer subpicture 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 foreground subpictures. 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, which includes one or more user picture-in-picture (PIP) views. 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] 12 shows a block diagram illustrating an example of the above process. For example, at operation S1210, a video bitstream having multiple layers may be decoded. At operation S1220, a background region and one or more foreground subpictures may be identified. At operation S1230, it may be determined whether a particular subpicture region, for example, one of the foreground subpictures, has been selected. If a particular subpicture region has been selected (YES at operation S1230), an augmented subpicture may be decoded and displayed. If a particular subpicture region has not been selected (NO at operation S1230), a 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 subpictures as a base layer. For example, the multiple subpictures may include a back subpicture, a top subpicture, a right subpicture, a left subpicture, a front subpicture, and a bottom subpicture. An enhancement layer for a specific subpicture, e.g., a front subpicture, may be encoded and transmitted to a client. A decoder may be able to decode both the base layer including all subpictures and the enhancement layer for a selected subpicture. If the current viewport is the same as the selected subpicture, the displayed picture may have higher quality using the decoded subpicture with the enhancement layer. Otherwise, the decoded picture with the base layer may be displayed at a 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). 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), and offset information of the top-left corner (x_offset, y_offset). Figure 14 shows an example of a layout of divided sub-pictures, their sub-picture size and position information, and the 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 within the AU. When a reference picture among multiple pictures stored in the DPB is pointed to by using one or more syntax elements within the RPS or RPL structure, the POC value(s) of each sub-picture corresponding to the 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 may be used.

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

[0144] In an embodiment, layout information for sub-region(s) (or sub-picture(s)) may be signaled in a VPS or an SPS. Figure 16A shows an example of syntax elements in a VPS, and Figure 16B shows an example of syntax elements in an SPS. In this example, vps_sub_picturing_dividing_flag is signaled in a VPS. This flag may indicate whether input picture(s) are divided into multiple sub-regions. If the value of vps_sub_picture_dividing_flag is equal to 0, input picture(s) in 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 compositing and display.

[0146] In an embodiment, if the value of vps_sub_picture_dividing_flag is equal to 1, the syntax elements pic_offset_x and pic_offset_y (a) may be signaled in an SPS that corresponds to a specific 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 specific layer. The location of the upper 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 subregion(s) of input picture(s), and dependency information between layer(s) may be signaled in a parameter set or SEI message. Figure 17 shows an example of syntax elements indicating subregion layout information, inter-layer dependencies, and relationships between subregions and one or more layers. In this example, the syntax element num_sub_region indicates the number of (rectangular) subregions in the currently coded video sequence. The syntax element num_layers indicates the number of layers in the currently coded video sequence. The value of num_layers may be equal to or greater than the value of num_sub_region. When a subregion is coded 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 coded 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 of 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 positions of the top left corner of the i-th subregion, respectively. sub_region_width[i] and sub_region_height[i] indicate the width and height of the i-th subregion, respectively.

[0149] In embodiments, one or more syntax elements specifying output layer sets 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. Referring to Figure 18, a syntax element, num_output_layer_sets, may be signaled in a VPS to indicate the number of output layer sets (OLSs) 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 Figure 18, a syntax element num_profile_tile_level may be signaled in the VPS to indicate 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 specific profile tier level information among entries in the profile tier level information, may be signaled in the same number 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, indicating 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 layer that is output is the layer 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 exist for the ith output tier set. Depending on the value of vps_ptl_signal_flag[i], profile tier level information for the ith 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 1 (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 that 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 the 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, 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 a CLVS.

[0168] In an embodiment, all SPS NAL units with a particular value of sps_seq_parameter_set_id in a 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 the 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 PPSs 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, and may be included in at least one AU with a TemporalId equal to the TemporalId of the PPS NAL unit, or 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 the PPS NAL unit in the 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 with 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 the 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 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 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 for 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 the coded slice NAL units that reference the NAL units that reference 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, and may be included in at least one AU with a TemporalId equal to the TemporalId of the PPS NAL unit, or 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 the PPS NAL unit in the 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 with 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 the 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 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 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 for 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 the coded slice NAL units that reference the NAL units that reference 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 before an AU containing a coded slice NAL unit that references the PPS, no VCL NAL units that enable temporal up-layer switching or VCL NAL units that have a nal_unit_type equal to STSA_NUT (which indicates that a 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 reside in the same AU.

[0195] In the same embodiment, the TemporalId value of a VCL NAL unit containing 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 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 flowchart of an example process 2100 for decoding an encoded video bitstream. In some implementations, one or more process blocks of Figure 21 may be performed by decoder 210. In some implementations, one or more process blocks of Figure 21 may be performed by another device or group of devices, such as encoder 203, that is separate from or includes decoder 210.

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

[0200] As further shown in FIG. 21, 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, 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, a PH NAL unit, at least one coded slice NAL unit, and a PPS NAL unit may be included in a single access unit.

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

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

[0211] In an embodiment, the time identifier of a PPS NAL unit may be equal to the time identifier of an 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] The proposed methods may also be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one example, 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] Computer software may be coded using any suitable machine code or computer language that can 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, smartphones, 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 respond 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.), or olfactory input (not shown). The 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.), or 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 touchscreen 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 human user's senses, for example, through tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touchscreen 2210, data gloves, or joystick 2205, although some haptic feedback devices may 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, and organic light-emitting diode (OLED) screens (each with or without touchscreen input capability, each with or without haptic feedback capability, some of which may be capable of outputting two-dimensional visual output, or four or more dimensional output 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 with CD / DVD or similar media 2221, thumb drives 2222, removable hard drives or solid state drives 2223, legacy magnetic media such as tape 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 one or more interfaces to one or more communications networks (2255). The networks may be, for example, wireless, wired, or 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, cellular networks including Global Systems for Mobile Communications (GSM), 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 networks including CANBus, etc. Particular networks typically require an external network interface adapter (2254) attached to a particular general-purpose data port or peripheral bus (2249) (e.g., a Universal Serial Bus (USB) port on computer system 2200), while others are typically integrated into the core of computer system 2200 by attachment to a system bus (e.g., an Ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). As an example, network 2255 may be connected to peripheral bus 2249 using network interface 2254. Using any of these networks, computer system 2200 can communicate with other entities. Such communication may be unidirectional receive only (e.g., broadcast TV), unidirectional transmit only (e.g., CANbus to certain CANbus devices), 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 network and network interface (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 particular 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, and internal mass storage 2247, such as an internal non-user-accessible hard drive, solid-state drive (SSD), 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 specific instructions that, in combination, may constitute the aforementioned computer code. That 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 from any of the memory devices may be enabled through the use of cache memory, which may be associated nearby one or more of the CPU 2241, GPU 2242, mass storage 2247, ROM 2245, RAM 2246, and the like.

[0228] The computer-readable media may 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] By way of example, and not limitation, a computer system having architecture 2200, and particularly core 2240, can provide functionality as a result of processor(s) (including CPUs, GPUs, FPGAs, accelerators, and the like) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be specific storage of core 2240 that is non-transitory in nature, such as core internal mass storage 2247 or ROM 2245, as well as media associated with user-accessible mass storage as introduced above. Software implementing various embodiments of the present disclosure can be stored on such devices and executed by core 2240. Computer-readable media can include one or more memory devices or chips according to particular needs. The software can cause core 2240, and particularly the processors therein (including CPUs, GPUs, FPGAs, and the like), to perform particular processes or portions of particular 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., integrated circuits (ICs)) that store software for execution, circuitry that embodies 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 appreciated 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

[Claim 1] 1. A method for decoding an encoded video bitstream, executed by at least one processor, 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; outputting the decoded picture; and 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 the PH NAL unit and the at least one coded slice NAL unit. method.

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