Image encoding / decoding methods and devices for signaling timing information output to the screen, and computer-readable recording media for storing bit streams.

Abstract

Image encoding / decoding methods and apparatus are provided. The image decoding method performed by the image decoding apparatus according to this disclosure includes the following steps: obtaining a first flag indicating the presence of Network Abstraction Layer (NAL) HRD parameters in the bitstream and a second flag indicating the presence of Video Coding Layer (VCL) HRD parameters in the bitstream; obtaining a third flag indicating whether the time interval between the output times of consecutive frames in the bitstream has a fixed value; deriving the output time of the frames in the bitstream based on at least one of the first, second, and third flags; and processing the frames in the bitstream based on the derived output times, wherein the first flag has a second value indicating that the NAL HRD parameters are not present in the bitstream and the second flag has a second value indicating that the VCL HRD parameters are not present in the bitstream, and the third flag can be restricted to having a first value indicating that the time interval between the output times of consecutive frames in the bitstream has a fixed value.

Description

Technical Field

[0001] This disclosure relates to image encoding / decoding methods and apparatus, and more specifically, to image encoding / decoding methods and apparatus for performing improved signaling for executing screen output timing information, and to a method for transmitting a bit stream generated by the image encoding method / apparatus of this disclosure. Background Technology

[0002] Recently, the demand for high-resolution and high-quality images (such as high-definition (HD) and ultra-high-definition (UHD) images) is increasing across various fields. With the improvement in image data resolution and quality, the amount of information or bits transmitted increases relatively compared to existing image data. This increase in the amount of information or bits transmitted leads to increased transmission and storage costs.

[0003] Therefore, efficient image compression technology is needed to effectively send, store, and reproduce information about high-resolution and high-quality images. Summary of the Invention

[0004] Technical issues

[0005] The purpose of this disclosure is to provide an image encoding / decoding method and apparatus with improved encoding / decoding efficiency.

[0006] Another object of this disclosure is to provide an image encoding / decoding method and apparatus for performing improved signaling for executing screen output timing information.

[0007] Another object of this disclosure is to provide a method for transmitting a bitstream generated by an image encoding method or device according to this disclosure.

[0008] Another object of this disclosure is to provide a recording medium for storing bitstreams generated by an image encoding method or device according to this disclosure.

[0009] Another object of this disclosure is to provide a recording medium that stores a bitstream received, decoded, and used to reconstruct an image by an image decoding apparatus according to this disclosure. For example, a bitstream used to enable the image decoding apparatus according to this disclosure to perform an image decoding method according to this disclosure may be stored in the recording medium.

[0010] The technical problems solved by this disclosure are not limited to those described above, and other technical problems not described herein will become apparent to those skilled in the art based on the following description.

[0011] Technical solution

[0012] An image decoding method performed by an image decoding device according to one aspect of this disclosure may include the following steps: obtaining a first flag indicating whether a specified Network Abstraction Layer (NAL) HRD parameter exists in the bitstream and a second flag indicating whether a specified Video Coding Layer (VCL) HRD parameter exists in the bitstream; obtaining a third flag indicating whether the time interval between the output times of consecutive frames in the bitstream has a fixed value; deriving the output time of the frame in the bitstream based on at least one of the first flag, the second flag, or the third flag; and processing the frame in the bitstream based on the derived output time. Based on the first flag having a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag having a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag may be constrained to have a first value indicating that the time interval between the output times of consecutive frames in the bitstream has a fixed value.

[0013] In the image decoding method disclosed herein, the third flag may be obtained for each time sub-layer in the time sub-layer of the bitstream, and based on the first flag having a second value and the second flag having a second value, the third flag for at least one time sub-layer in the time sub-layer of the bitstream may be constrained to have a first value.

[0014] In the image decoding method disclosed herein, the third flag may be obtained by the maximum number of time sub-layers in the bitstream, and based on the first flag having a second value and the second flag having a second value, at least one of the obtained third flags has a first value.

[0015] In the image decoding method disclosed herein, the first flag and the second flag may be obtained from a general HRD parameter syntax structure in the bitstream, and the third flag is obtained from an HRD parameter syntax structure for the output layer set.

[0016] In the image decoding method disclosed herein, the maximum number of temporal sublayers can be determined differently based on the parameter set used to obtain the HRD parameter syntax structure for the output layer set.

[0017] An image decoding apparatus according to another aspect of this disclosure may include a memory and at least one processor. The at least one processor may perform the following operations: obtaining a first flag indicating the presence of a specified Network Abstraction Layer (NAL) HRD parameter in the bitstream and a second flag indicating the presence of a specified Video Coding Layer (VCL) HRD parameter in the bitstream; obtaining a third flag indicating whether the time interval between the output times of consecutive frames in the bitstream has a fixed value; deriving the output time of the frame in the bitstream based on at least one of the first flag, the second flag, or the third flag; and processing the frame in the bitstream based on the derived output time. Based on the first flag having a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag having a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag may be constrained to have a first value indicating that the time interval between the output times of consecutive frames in the bitstream has a fixed value.

[0018] An image encoding method performed by an image encoding device according to another aspect of this disclosure may include the following steps: determining a first flag indicating the presence of a specified Network Abstraction Layer (NAL) HRD parameter in the bitstream and a second flag indicating the presence of a specified Video Coding Layer (VCL) HRD parameter in the bitstream; determining a third flag indicating whether the time interval between the output times of consecutive frames in the specified bitstream has a fixed value; deriving the output time of the frames in the bitstream based on at least one of the first flag, the second flag, or the third flag; and processing the frames in the bitstream based on the derived output times. Based on the first flag having a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag having a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag may be constrained to have a first value indicating that the time interval between the output times of consecutive frames in the bitstream has a fixed value.

[0019] In the image encoding method disclosed herein, the third flag may be determined for each time sub-layer in the time sub-layer of the bitstream, and based on the first flag having a second value and the second flag having a second value, the third flag for at least one time sub-layer in the time sub-layer of the bitstream may be constrained to have a first value.

[0020] In the image coding method disclosed herein, the third flag may be determined by the maximum number of time sub-layers in the bitstream, and based on the first flag having a second value and the second flag having a second value, at least one of the determined third flags may have a first value.

[0021] In the image encoding method disclosed herein, the first flag and the second flag can be encoded in a general HRD parameter syntax structure in the bitstream, and the third flag can be encoded in an HRD parameter syntax structure for the output layer set.

[0022] In the image coding method disclosed herein, the maximum number of temporal sublayers can be determined differently based on the parameter set to which the HRD parameter syntax structure for the output layer set is encoded.

[0023] Furthermore, according to another aspect of the transmission method of this disclosure, a bit stream generated by an image encoding device or method according to this disclosure can be transmitted.

[0024] Furthermore, according to another aspect of this disclosure, a computer-readable recording medium can store a bitstream generated by an image encoding method or apparatus according to this disclosure.

[0025] Furthermore, according to another aspect of this disclosure, a computer-readable recording medium may store a bitstream for enabling a decoding device to perform an image decoding method according to this disclosure.

[0026] According to another aspect of this disclosure, a non-transitory computer-readable recording medium can store a bitstream generated by an image decoding method and used for reconstructing an image. The bitstream may include a first flag indicating the presence of a Network Abstraction Layer (NAL) HRD parameter, a second flag indicating the presence of a Video Coding Layer (VCL) HRD parameter, and a third flag indicating whether the time interval between the output times of consecutive frames in the bitstream has a fixed value. At least one of the first flag, the second flag, or the third flag can be used to derive the output time of the frames in the bitstream, and the derived output time can be used to process the frames in the bitstream. Based on the first flag having a second value indicating that the NAL HRD parameter is not present in the bitstream and the second flag having a second value indicating that the VCL HRD parameter is not present in the bitstream, the third flag can be constrained to have a first value indicating that the time interval between the output times of consecutive frames in the bitstream has a fixed value.

[0027] The features briefly outlined above are merely exemplary aspects of the detailed description of this disclosure below and do not limit the scope of this disclosure.

[0028] Beneficial effects

[0029] According to this disclosure, an image encoding / decoding method and apparatus with improved encoding / decoding efficiency can be provided.

[0030] According to this disclosure, an image encoding / decoding method and apparatus for performing improved signaling for executing screen output timing information can be provided.

[0031] Furthermore, according to this disclosure, a method for transmitting a bitstream generated by an image encoding method or device according to this disclosure can be provided.

[0032] Furthermore, according to this disclosure, a recording medium may be provided for storing a bitstream generated by an image encoding method or apparatus according to this disclosure.

[0033] Furthermore, according to this disclosure, a recording medium can be provided for storing a bitstream that is received, decoded, and used to reconstruct an image by an image decoding device according to this disclosure.

[0034] Those skilled in the art will understand that the effects achievable through this disclosure are not limited to those specifically described above, and that other advantages of this disclosure will become clearer from the specific embodiments. Attached Figure Description

[0035] Figure 1 This is a view schematically illustrating a video encoding system to which embodiments of this disclosure are applicable.

[0036] Figure 2 This is a schematic view illustrating an image encoding device to which embodiments of the present disclosure are applicable.

[0037] Figure 3 This is a schematic view illustrating an image decoding device to which embodiments of the present disclosure are applicable.

[0038] Figure 4 and Figure 5 This is a view illustrating an example of the screen decoding and encoding process to which embodiments of this disclosure are applicable.

[0039] Figure 6 This is a view illustrating the layer structure of an image for encoding to which embodiments of this disclosure are applicable.

[0040] Figure 7 This is an exemplary view illustrating an HRD structure that is signaled in a VPS.

[0041] Figure 8This is an exemplary view illustrating an HRD structure notified by signals in SPS.

[0042] Figure 9 This is a view that exemplifies the syntax structure of general_hrd_parameters().

[0043] Figure 10 This is a view that exemplifies the syntax structure of ols_hrd_parameters().

[0044] Figure 11 This is a view that exemplifies the sublayer_hrd_parameters() syntax structure.

[0045] Figure 12 This is an exemplary view illustrating the general_hrd_parameters() syntax structure according to an embodiment of this disclosure.

[0046] Figure 13 This is an example of how to illustrate the following: Figure 12 A view of the modified syntax structure of VPS and SPS implementations.

[0047] Figure 14 This is an exemplary view illustrating the general_hrd_parameters() syntax structure according to another embodiment of this disclosure.

[0048] Figure 15 This is an example of how to illustrate the following: Figure 14 A view of the modified syntax structure of VPS and SPS implementations.

[0049] Figure 16 This is an exemplary view illustrating the ols_hrd_parameters() syntax structure according to another embodiment of this disclosure.

[0050] Figure 17 This is an example in Figure 16 The implementation provides a view of the process of deriving DpbOutputElementalInterval[n].

[0051] Figure 18 This is a view illustrating an image encoding method according to this disclosure.

[0052] Figure 19 This is a view illustrating an image decoding method according to the present disclosure.

[0053] Figure 20 This is a view illustrating the content streaming system to which embodiments of this disclosure are applicable. Detailed Implementation

[0054] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings to facilitate implementation by those skilled in the art. However, this disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0055] In describing this disclosure, detailed descriptions of relevant known functions or constructions will be omitted if they unnecessarily obscure the scope of this disclosure. In the accompanying drawings, portions irrelevant to the description of this disclosure are omitted, and similar reference numerals are assigned to similar portions.

[0056] In this disclosure, when a component is "connected," "linked," or "coupled" to another component, it may include not only a direct connection but also an indirect connection with intermediate components. Furthermore, when a component "comprises" or "has" other components, unless otherwise stated, it means that other components may be included, not excluded.

[0057] In this disclosure, the terms first, second, etc., may be used only for the purpose of distinguishing one component from other components and do not limit the order or importance of the components, unless otherwise stated. Accordingly, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0058] In this disclosure, the distinguishing components are intended to clearly describe each feature and do not imply that the components must be separate. That is, multiple components may be integrated and implemented in a single hardware or software unit, or a single component may be distributed and implemented in multiple hardware or software units. Therefore, unless otherwise stated, these implementations, where components are integrated or distributed, are included within the scope of this disclosure.

[0059] In this disclosure, the components described in the various embodiments are not necessarily essential components, and some components may be optional. Therefore, embodiments consisting of a subset of the components described in the embodiments are also included within the scope of this disclosure. In addition, embodiments that include other components besides those described in the various embodiments are also included within the scope of this disclosure.

[0060] This disclosure relates to the encoding and decoding of images. Unless redefined in this disclosure, the terms used herein may have the general meaning commonly used in the art to which this disclosure pertains.

[0061] The methods / implementations disclosed in this disclosure are applicable to methods disclosed in the Universal Video Coding (VVC) standard. Additionally, the methods / implementations disclosed in this disclosure are applicable to methods disclosed in the Basic Video Coding (EVC) standard, the AOMedia Video 1 (AV1) standard, the second-generation Audio Video Coding (AVS2) standard, or next-generation video / image coding standards (e.g., H.267 or H.268).

[0062] This disclosure provides various implementations of video / image encoding, and implementations not described herein can be performed in combination.

[0063] In this disclosure, "video" can mean a set of images over time. A "picture" generally refers to a unit representing an image at a specific time, and a tile is a coding unit that constitutes part of a picture in the encoding process. A tile may include one or more coding tree units (CTUs). A CTU may be divided into one or more CUs.

[0064] A frame can consist of one or more slices / tiles. A tile is a rectangular area within a specific tile row and a specific tile column in a frame, and can consist of multiple CTUs. A tile column can be defined as a rectangular area of ​​a CTU, and can have a height equal to the height of the frame and a width specified by a syntax element signaled from a bitstream portion such as a frame parameter set. A tile row can be defined as a rectangular area of ​​a CTU, and can have a width equal to the width of the frame and a height specified by a syntax element signaled from a bitstream portion such as a frame parameter set.

[0065] Tiled scanning is a specific ordering of CTUs that divide a frame. Here, CTUs are ordered consecutively within a tile using CTU raster scans, while the tiles in a frame are ordered consecutively using the raster scans of the frame's tiles. A slice consists of an integer number of consecutive complete CTU rows or an integer number of complete tiles within a tile of the frame. Slices can be proprietaryly included in a single NAL unit.

[0066] A frame can be divided into two or more sub-frames. A sub-frame can be a rectangular area of ​​one or more slices of the frame.

[0067] A frame can include one or more tile groups. A tile group can include one or more tiles. A tile can represent a rectangular area of ​​CTU rows within a tile in the frame. A tile can include one or more tiles. A tile can represent a rectangular area of ​​CTU rows within a tile. A tile can be divided into multiple tiles, and each tile can include one or more CTU rows belonging to the tile. Tiles that are not divided into multiple tiles can also be considered as tiles.

[0068] A "pixel" or "pixel" can refer to the smallest unit that makes up a picture (or image). Additionally, "sample" can be used as the term corresponding to a pixel. A sample can typically represent a pixel or a pixel value, and can represent only the pixel / pixel value of the luminance component or only the pixel / pixel value of the chrominance component.

[0069] In this disclosure, "unit" can refer to a basic unit of image processing. A unit may include a specific region of an image and at least one of the information associated with that region. A unit may include a luminance block and two chrominance blocks (e.g., Cb and Cr). In some cases, "unit" may be used interchangeably with terms such as "sample array," "block," or "region." In general, an M×N block may include a set (or array) of samples (or transform coefficients) with M columns and N rows.

[0070] In this disclosure, "current block" can mean one of "current coding block," "current coding unit," "coding target block," "decoding target block," or "processing target block." When performing prediction, "current block" can mean "current prediction block" or "prediction target block." When performing transform (inverse transform) / quantization (dequantization), "current block" can mean "current transform block" or "transform target block." When performing filtering, "current block" can mean "filter target block."

[0071] Additionally, in this disclosure, unless explicitly stated as a chroma block, "current block" may mean "the luminance block of the current block". "The chroma block of the current block" can be expressed by including an explicit description of a chroma block such as "chroma block" or "current chroma block".

[0072] In this disclosure, the forward slash " / " or "," should be interpreted as indicating "and / or." For example, the expressions "A / B" and "A, B" can mean "A and / or B." Furthermore, "A / B / C" and "A / B / C" can mean "at least one of A, B, and / or C."

[0073] In this disclosure, the term "or" should be interpreted as indicating "and / or". For example, expressing "A or B" can include 1) only "A", 2) only "B", and / or 3) both "A and B". In other words, in this disclosure, the term "or" should be interpreted as indicating "additionally or alternatively".

[0074] In this disclosure, "at least one of A and B" may mean "only A", "only B" or "both A and B". Furthermore, in this disclosure, "at least one of A or B" or "at least one of A and / or B" may be interpreted as the same as "at least one of A and B".

[0075] Furthermore, in this disclosure, "at least one of A, B, and C" may mean "only A," "only B," "only C," or "any combination of A, B, and C." Additionally, in this disclosure, "at least one of A, B, or C" or "at least one of A, B, and / or C" may be interpreted as the same as "at least one of A, B, and C."

[0076] Furthermore, the parentheses used in this disclosure may mean "for example". Specifically, when describing "prediction (intra-frame prediction)", "intra-frame prediction" may be cited as an example of "prediction". In other words, the "prediction" in this disclosure is not limited to "intra-frame prediction", and "intra-frame prediction" may be cited as an example of "prediction". In addition, even when describing "prediction (i.e., intra-frame prediction)", "intra-frame prediction" may be cited as an example of "prediction".

[0077] In this disclosure, a technical feature described individually in a single figure may be implemented individually or simultaneously.

[0078] Overview of Video Encoding Systems

[0079] Figure 1 This is a view showing a video encoding system according to this disclosure.

[0080] The video encoding system according to the embodiment may include a source device 10 and a receiving device 20. The source device 10 may deliver encoded video and / or image information or data to the receiving device 20 in the form of a file or stream via a digital storage medium or network.

[0081] The source device 10 according to an embodiment may include a video source generator 11, an encoding device 12, and a transmitter 13. The receiving device 20 according to an embodiment may include a receiver 21, a decoding device 22, and a renderer 23. The encoding device 12 may be referred to as a video / image encoding device, and the decoding device 22 may be referred to as a video / image decoding device. The transmitter 13 may be included in the encoding device 12. The receiver 21 may be included in the decoding device 22. The renderer 23 may include a display, and the display may be configured as a separate device or an external component.

[0082] The video source generator 11 can acquire video / images through a process of capturing, compositing, or generating video / images. The video source generator 11 may include a video / image capture device and / or a video / image generation device. The video / image capture device may include, for example, one or more cameras, a video / image archive including previously captured video / images, etc. The video / image generation device may include, for example, a computer, tablet computer, and smartphone, and can generate video / images (electronically). For example, virtual video / images can be generated by a computer, etc. In this case, the video / image capture process can be replaced by a process of generating related data.

[0083] The encoding device 12 can encode the input video / image. For compression and encoding efficiency, the encoding device 12 can perform a series of processes such as prediction, transformation, and quantization. The encoding device 12 can output the encoded data (encoded video / image information) in the form of a bitstream.

[0084] Transmitter 13 can transmit encoded video / image information or data, output in bitstream form, to receiver 21 of receiving device 20 in the form of a file or stream via digital storage medium or network. Digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. Transmitter 13 can include elements for generating media files according to a predetermined file format and may include elements for transmission via broadcast / communication networks. Receiver 21 can extract / receive bitstreams from storage medium or network and transmit the bitstreams to decoding device 22.

[0085] The decoding device 22 can decode video / images by performing a series of processes (such as dequantization, inverse transform, and prediction) corresponding to the operation of the encoding device 12.

[0086] Renderer 23 can render decoded video / images. The rendered video / images can be displayed on a monitor.

[0087] Overview of Image Encoding Devices

[0088] Figure 2 This is a schematic view illustrating an image encoding device to which embodiments of the present disclosure are applicable.

[0089] like Figure 2As shown, the image encoding device 100 may include an image segmenter 110, a subtractor 115, a transformer 120, a quantizer 130, a dequantizer 140, an inverse transformer 150, an adder 155, a filter 160, a memory 170, an inter-frame predictor 180, an intra-frame predictor 185, and an entropy encoder 190. The inter-frame predictor 180 and the intra-frame predictor 185 may be collectively referred to as "predictors". The transformer 120, quantizer 130, dequantizer 140, and inverse transformer 150 may be included in a residual processor. The residual processor may also include a subtractor 115.

[0090] In some implementations, all or at least some of the multiple components configuring the image encoding device 100 may be configured by a single hardware component (e.g., an encoder or a processor). Additionally, the memory 170 may include a decoded screen buffer (DPB) and may be configured by a digital storage medium.

[0091] Image segmenter 110 can segment an input image (or picture or frame) input to image encoding device 100 into one or more processing units. For example, a processing unit may be called an encoding unit (CU). Encoding units can be obtained by recursively segmenting encoding tree units (CTUs) or maximum encoding units (LCUs) according to a quadtree / binary tree / tritree (QT / BT / TT) structure. For example, an encoding unit can be segmented into multiple encoding units of greater depth based on a quadtree structure, a binary tree structure, and / or a ternary tree structure. For the segmentation of encoding units, a quadtree structure can be applied first, and a binary tree structure and / or a ternary tree structure can be applied later. The encoding process according to this disclosure can be performed based on the final encoding unit that is no longer segmented. The maximum encoding unit can be used as the final encoding unit, or a deeper encoding unit obtained by segmenting the maximum encoding unit can be used as the final encoding unit. Here, the encoding process may include prediction, transformation, and reconstruction processes, which will be described later. As another example, the processing unit of the encoding process may be a prediction unit (PU) or a transformation unit (TU). Prediction units and transform units can be partitioned or segmented from the final coding unit. Prediction units can be sample prediction units, and transform units can be units used to derive transform coefficients and / or units used to derive residual signals from transform coefficients.

[0092] The predictor (inter-frame predictor 180 or intra-frame predictor 185) can perform prediction on the block to be processed (the current block) and generate a prediction block that includes prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction based on the current block or CU. The predictor can generate various information related to the prediction of the current block and send the generated information to the entropy encoder 190. The information about the prediction can be encoded in the entropy encoder 190 and output as a bitstream.

[0093] Intra-predictor 185 can predict the current block by referencing samples in the current frame. Depending on the intra-prediction mode and / or intra-prediction technique, the reference samples may be located among the neighbors of the current block or may be placed separately. Intra-prediction modes may include multiple non-directional modes and multiple directional modes. Non-directional modes may include, for example, DC mode and planar mode. Depending on the level of detail in the prediction direction, directional modes may include, for example, 33 or 65 directional prediction modes. However, this is merely an example, and more or fewer directional prediction modes may be used depending on the settings. Intra-predictor 185 can determine the prediction mode to be applied to the current block by using prediction modes applied to neighboring blocks.

[0094] Inter-frame predictor 180 can derive the predicted block of the current block based on a reference block (reference sample array) specified by motion vectors on a reference frame. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. The reference frame including the reference block and the reference frame including the temporally neighboring block may be the same or different. The temporally neighboring block may be referred to as a juxtaposed reference block, a juxtaposed CU (colCU), etc. The reference frame including the temporally neighboring block may be referred to as a juxtaposed frame (colPic). For example, inter-frame predictor 180 can configure a motion information candidate list based on neighboring blocks and generate information indicating which candidate to use to derive the motion vector and / or reference frame index of the current block. Inter-frame prediction can be performed based on various prediction modes. For example, in skip mode and merge mode, the inter-frame predictor 180 can use motion information from neighboring blocks as motion information for the current block. In skip mode, unlike merge mode, residual signals may not be sent. In motion vector prediction (MVP) mode, motion vectors from neighboring blocks can be used as motion vector predictors, and the motion vector of the current block can be signaled by encoding motion vector differences and indicators of the motion vector predictors. The motion vector difference can refer to the difference between the motion vector of the current block and the motion vector predictor.

[0095] The predictor can generate a prediction signal based on various prediction methods and techniques described below. For example, the predictor can apply not only intra-frame prediction or inter-frame prediction, but also both intra-frame prediction and inter-frame prediction simultaneously to predict the current block. A prediction method that simultaneously applies both intra-frame prediction and inter-frame prediction to predict the current block can be called Combined Intra-Inter-Frame Prediction (CIIP). Alternatively, the predictor can perform Intra-Frame Block Copy (IBC) to predict the current block. Intra-Frame Block Copy can be used for content image / video coding in games, for example, Screen Content Coding (SCC). IBC is a method of predicting the current frame using a previously reconstructed reference block in the current frame at a predetermined distance from the current block. When IBC is applied, the position of the reference block in the current frame can be encoded as a vector (block vector) corresponding to the predetermined distance. IBC essentially performs prediction in the current frame, but can be performed similarly to inter-frame prediction because the reference block is derived within the current frame. That is, IBC can use at least one of the inter-frame prediction techniques described in this disclosure.

[0096] The predicted signal generated by the predictor can be used to generate a reconstructed signal or a residual signal. Subtractor 115 generates a residual signal (residual block or residual sample array) by subtracting the predicted signal (predicted block or predicted sample array) output from the predictor from the input image signal (original block or original sample array). The generated residual signal can be sent to transformer 120.

[0097] Transformer 120 can generate transform coefficients by applying transform techniques to the residual signal. For example, the transform techniques may include at least one of Discrete Cosine Transform (DCT), Discrete Sine Transform (DST), Karhunen-Loève Transform (KLT), Graph-Based Transform (GBT), or Conditional Nonlinear Transform (CNT). Here, GBT refers to a transform obtained from a graph when the relationship information between pixels is represented by a graph. CNT refers to a transform obtained based on a prediction signal generated using all previously reconstructed pixels. Furthermore, the transform processing can be applied to square pixel blocks of the same size or to blocks of variable size instead of square.

[0098] Quantizer 130 can quantize the transform coefficients and send them to entropy encoder 190. Entropy encoder 190 can encode the quantized signal (information about the quantized transform coefficients) and output a bitstream. The information about the quantized transform coefficients can be referred to as residual information. Quantizer 130 can rearrange the block-type quantized transform coefficients into a one-dimensional vector form based on the coefficient scan order, and generate information about the quantized transform coefficients based on the one-dimensional vector form of the quantized transform coefficients.

[0099] The entropy encoder 190 can perform various encoding methods, such as exponential Columbus coding, context-adaptive variable-length coding (CAVLC), and context-adaptive binary arithmetic coding (CABAC). The entropy encoder 190 can encode, together or separately, information required for video / image reconstruction other than quantization transform coefficients (e.g., values ​​of syntax elements). The encoded information (e.g., encoded video / image information) can be transmitted or stored in bitstream form at the Network Abstraction Layer (NAL) level. The video / image information may also include information about various parameter sets, such as Adaptive Parameter Set (APS), Picture Parameter Set (PPS), Sequence Parameter Set (SPS), or Video Parameter Set (VPS). Additionally, the video / image information may include general constraint information. The signaled information, transmitted information, and / or syntax elements described in this disclosure can be encoded and included in the bitstream through the above encoding process.

[0100] The bitstream can be transmitted over a network or stored in a digital storage medium. The network may include a broadcast network and / or a communication network, and the digital storage medium may include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitter (not shown) for transmitting the signal output from the entropy encoder 190 and / or a storage unit (not shown) for storing the signal may be included as internal / external components of the image encoding device 100. Alternatively, a transmitter may be provided as a component of the entropy encoder 190.

[0101] The quantization transform coefficients output from quantizer 130 can be used to generate residual signals. For example, the residual signals (residual blocks or residual samples) can be reconstructed by applying dequantization and inverse transform to the quantization transform coefficients through dequantizer 140 and inverse transformer 150.

[0102] Adder 155 adds the reconstructed residual signal to the prediction signal output from inter-frame predictor 180 or intra-frame predictor 185 to generate a reconstructed signal (reconstructed frame, reconstructed block, reconstructed sample array). If the block to be processed has no residual, such as in the case of applying a skip mode, the prediction block can be used as a reconstructed block. Adder 155 can be referred to as a reconstructor or reconstructed block generator. The generated reconstructed signal can be used for intra-frame prediction of the next block to be processed in the current frame, and can be used for inter-frame prediction of the next frame by filtering as described below.

[0103] Filter 160 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, filter 160 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 170, specifically in the DPB of memory 170. Various filtering methods can include, for example, deblocking filtering, sample adaptive shifting, adaptive loop filtering, bilateral filtering, etc. Filter 160 can generate various filtering-related information and send the generated information to entropy encoder 190, as described later in the description of each filtering method. The filtering-related information can be encoded by entropy encoder 190 and output as a bitstream.

[0104] The modified reconstructed frame sent to memory 170 can be used as a reference frame in inter-frame predictor 180. When inter-frame prediction is applied by image encoding device 100, prediction mismatch between image encoding device 100 and image decoding device can be avoided and coding efficiency can be improved.

[0105] The DPB of memory 170 can store modified reconstructed frames for use as reference frames in inter-frame predictor 180. Memory 170 can store motion information of blocks used to derive (or encode) motion information in the current frame and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 180 and used as motion information for spatially or temporally neighboring blocks. Memory 170 can store reconstructed samples of reconstructed blocks in the current frame and can transmit the reconstructed samples to intra-frame predictor 185.

[0106] Overview of image decoding devices

[0107] Figure 3 This is a schematic view illustrating an image decoding device to which embodiments of the present disclosure are applicable.

[0108] like Figure 3 As shown, the image decoding device 200 may include an entropy decoder 210, a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, and an intra-frame predictor 265. The inter-frame predictor 260 and the intra-frame predictor 265 may be collectively referred to as "predictors". The dequantizer 220 and the inverse transformer 230 may be included in a residual processor.

[0109] According to an embodiment, all or at least some of the multiple components configuring the image decoding device 200 may be configured by hardware components (e.g., a decoder or a processor). Additionally, the memory 250 may include a decoded screen buffer (DPB) or may be configured by a digital storage medium.

[0110] The image decoding device 200, having received a bitstream including video / image information, can perform operations related to... Figure 2 The image is reconstructed by processing corresponding to the processing performed by the image encoding device 100. For example, the image decoding device 200 can perform decoding using a processing unit applied in the image encoding device. Therefore, the decoding processing unit can be, for example, an encoding unit. The encoding unit can be obtained by segmenting a coding tree unit or a maximum coding unit. The reconstructed image signal decoded and output by the image decoding device 200 can be reproduced by a reproduction device (not shown).

[0111] Image decoding device 200 can receive data in bitstream form from... Figure 2The signal output by the image encoding device. The received signal can be decoded by the entropy decoder 210. For example, the entropy decoder 210 can parse the bitstream to derive the information (e.g., video / image information) required for image reconstruction (or picture reconstruction). The video / image information may also include information about various parameter sets, such as adaptive parameter sets (APS), picture parameter sets (PPS), sequence parameter sets (SPS), or video parameter sets (VPS). In addition, the video / image information may also include general constraint information. The image decoding device can also decode the picture based on the information about the parameter sets and / or general constraint information. The information and / or syntax elements notified / received by signals described in this disclosure can be decoded and obtained from the bitstream through a decoding process. For example, the entropy decoder 210 decodes the information in the bitstream based on encoding methods such as exponential Golomb coding, CAVLC, or CABAC, and outputs the values ​​of the syntax elements required for image reconstruction and the quantized values ​​of the transform coefficients of the residuals. More specifically, the CABAC entropy decoding method can receive bins corresponding to each syntax element in the bitstream, determine a context model using information about the target syntax element, decoding information of neighboring blocks and the target block, or information about symbols / bins decoded in the previous stage, perform arithmetic decoding on the bins based on the determined context model by predicting the occurrence probability of the bins, and generate symbols corresponding to the value of each syntax element. In this case, the CABAC entropy decoding method can update the context model after determining the context model by using the information of the decoded symbols / bins for the context model of the next symbol / bin. The prediction-related information in the information decoded by the entropy decoder 210 can be provided to the predictors (inter-frame predictor 260 and intra-frame predictor 265), and the residual values ​​of the entropy decoding performed in the entropy decoder 210 (that is, the quantization transform coefficients and related parameter information) can be input to the dequantizer 220. In addition, the filtering information in the information decoded by the entropy decoder 210 can be provided to the filter 240. Furthermore, the receiver (not shown) for receiving signals output from the image encoding device may be further configured as an internal / external element of the image decoding device 200, or the receiver may be a component of the entropy decoder 210.

[0112] Furthermore, the image decoding apparatus according to this disclosure can be referred to as a video / image / screen decoding apparatus. The image decoding apparatus can be divided into an information decoder (video / image / screen information decoder) and a sample decoder (video / image / screen sample decoder). The information decoder may include an entropy decoder 210. The sample decoder may include at least one of a dequantizer 220, an inverse transformer 230, an adder 235, a filter 240, a memory 250, an inter-frame predictor 260, or an intra-frame predictor 265.

[0113] Dequantizer 220 can dequantize the quantized transform coefficients and output transform coefficients. Dequantizer 220 can rearrange the quantized transform coefficients in the form of two-dimensional blocks. In this case, the rearrangement can be performed based on the coefficient scan order performed in the image encoding device. Dequantizer 220 can obtain transform coefficients by performing dequantization on the quantized transform coefficients using quantization parameters (e.g., quantization step size information).

[0114] The inverse transformer 230 can perform inverse transformation on the transformation coefficients to obtain the residual signal (residual block, residual sample array).

[0115] The predictor can perform prediction on the current block and generate a prediction block that includes prediction samples of the current block. The predictor can determine whether to apply intra-frame prediction or inter-frame prediction to the current block based on the prediction information output from the entropy decoder 210, and can determine a specific intra-frame / inter-frame prediction mode (prediction technique).

[0116] Similar to the predictor described in the image coding device 100, the predictor can generate a prediction signal based on various prediction methods (techniques) that will be described later.

[0117] Intra-predictor 265 can predict the current block by referring to samples in the current frame. The description of intra-predictor 185 also applies to intra-predictor 265.

[0118] Inter-frame predictor 260 can deduce the predicted block of the current block based on a reference block (reference sample array) specified by a motion vector on a reference frame. In this case, to reduce the amount of motion information transmitted in inter-frame prediction mode, motion information can be predicted on a block, sub-block, or sample basis based on the correlation between motion information between neighboring blocks and the current block. Motion information may include motion vectors and reference frame indices. Motion information may also include inter-frame prediction direction (L0 prediction, L1 prediction, Bi prediction, etc.) information. In the case of inter-frame prediction, neighboring blocks may include spatially neighboring blocks existing in the current frame and temporally neighboring blocks existing in the reference frame. For example, inter-frame predictor 260 can configure a motion information candidate list based on neighboring blocks and deduce the motion vector and / or reference frame index of the current block based on the received candidate selection information. Inter-frame prediction can be performed based on various prediction modes, and the information about the prediction may include information indicating the inter-frame prediction mode of the current block.

[0119] Adder 235 generates a reconstruction signal (reconstructed frame, reconstruction block, reconstruction sample array) by adding the obtained residual signal to the prediction signal (prediction block, prediction sample array) output from the predictor (including inter-frame predictor 260 and / or intra-frame predictor 265). If the block to be processed has no residual, such as when a skip mode is applied, the prediction block can be used as a reconstruction block. The description of adder 155 also applies to adder 235. Adder 235 may be referred to as a reconstructor or reconstruction block generator. The generated reconstruction signal can be used for intra-frame prediction of the next block to be processed in the current frame, and can be used for inter-frame prediction of the next frame by filtering as described below.

[0120] Filter 240 can improve subjective / objective image quality by applying filtering to the reconstructed signal. For example, filter 240 can generate a modified reconstructed image by applying various filtering methods to the reconstructed image and store the modified reconstructed image in memory 250, specifically in the DPB of memory 250. Various filtering methods may include, for example, deblocking filtering, adaptive sample shifting, adaptive loop filtering, bilateral filtering, etc.

[0121] The (modified) reconstructed frame stored in the DPB of memory 250 can be used as a reference frame in inter-frame predictor 260. Memory 250 can store motion information of blocks used to derive (or decode) motion information in the current frame and / or motion information of already reconstructed blocks in the frame. The stored motion information can be sent to inter-frame predictor 260 to be used as motion information for spatially or temporally neighboring blocks. Memory 250 can store reconstructed samples of reconstructed blocks in the current frame and transmit the reconstructed samples to intra-frame predictor 265.

[0122] In this disclosure, the embodiments described in the filter 160, inter-frame predictor 180 and intra-frame predictor 185 of the image encoding device 100 can be applied equally or correspondingly to the filter 240, inter-frame predictor 260 and intra-frame predictor 265 of the image decoding device 200.

[0123] General image / video encoding process

[0124] In image / video coding, the frames that make up an image / video can be encoded / decoded according to the decoding order. The frame order corresponding to the output order of the decoded frames can be set to be different from the decoding order, and based on this, not only forward prediction but also backward prediction can be performed during inter-frame prediction.

[0125] Figure 4 An example of an illustrative screen decoding process to which embodiments of this disclosure apply is shown. Figure 4In this process, S410 can be executed in the entropy decoder 210 of the decoding device, S420 can be executed in the predictor including the intra-frame predictor 265 and the inter-frame predictor 260, S430 can be executed in the residual processor including the dequantizer 220 and the inverse transformer 230, S440 can be executed in the adder 235, and S450 can be executed in the filter 240. S410 can include the information decoding process described in this disclosure, S420 can include the inter-frame / intra-frame prediction process described in this disclosure, S430 can include the residual processing process described in this disclosure, S440 can include the block / frame reconstruction process described in this disclosure, and S450 can include the in-loop filtering process described in this disclosure.

[0126] refer to Figure 4 The image decoding process can schematically include a process of obtaining image / video information from the bitstream (through decoding) (S410), an image reconstruction process (S420 to S440), and an in-loop filtering process for the reconstructed image (S450). The image reconstruction process can be performed based on prediction samples and residual samples obtained through inter-frame / intra-frame prediction (S420) and residual processing (S430) (dequantization and inverse transform of quantization transform coefficients) as described in this disclosure. For the reconstructed image generated by the image reconstruction process, a modified reconstructed image can be generated through the in-loop filtering process. The modified reconstructed image can be used as the decoded image output, stored in the decoded image buffer or memory 250 of the decoding device, and used as a reference image in the inter-frame prediction process when decoding images later. In some cases, the in-loop filtering process can be omitted. In this case, the reconstructed image can be used as the decoded image output, stored in the decoded image buffer or memory 250 of the decoding device, and used as a reference image in the inter-frame prediction process when decoding images later. The in-loop filtering process (S450) may include a deblocking filtering process, a sample adaptive offset (SAO) process, an adaptive loop filter (ALF) process, and / or a bilateral filter process, some or all of which may be omitted as described above. Furthermore, one or more of the deblocking filtering process, the sample adaptive offset (SAO) process, the adaptive loop filter (ALF) process, and / or the bilateral filter process may be applied sequentially, or all of them may be applied sequentially. For example, the SAO process may be performed after the deblocking filtering process has been applied to the reconstructed frame. Alternatively, for example, the ALF process may be performed after the deblocking filtering process has been applied to the reconstructed frame. This can be performed similarly even in an encoding device.

[0127] Figure 5 An example of an illustrative screen encoding process to which embodiments of this disclosure apply is shown. Figure 5 In the above reference, S510 can be found... Figure 2The coding apparatus described herein includes a predictor comprising an intra-frame predictor 185 or an inter-frame predictor 180. S520 may be executed in a residual processor comprising a transformer 120 and / or a quantizer 130, and S530 may be executed in an entropy encoder 190. S510 may include the inter-frame / intra-frame prediction process described herein, S520 may include the residual processing process described herein, and S530 may include the information encoding process described herein.

[0128] refer to Figure 5 The image encoding process can schematically include not only the process of encoding information used for image reconstruction (e.g., prediction information, residual information, segmentation information, etc.) and outputting that information as a bitstream, but also the process of generating a reconstructed image of the current image and (optionally) applying in-loop filtering to the reconstructed image, as shown in the following example. Figure 2 As described, the encoding device can derive (modified) residual samples from the quantized transform coefficients using dequantizer 140 and inverse transformer 150, and generate a reconstructed frame based on the predicted sample as the output of S510 and the (modified) residual samples. The reconstructed frame generated in this way can be equal to the reconstructed frame generated in the decoding device. The modified reconstructed frame can be generated through an in-loop filtering process for the reconstructed frame, can be stored in the decoded frame buffer or memory 170, and can be used as a reference frame in the inter-frame prediction process when encoding frames later, similar to the case in the decoding device. As mentioned above, in some cases, some or all of the in-loop filtering process can be omitted. When the in-loop filtering process is performed, the (in-loop) filtering-related information (parameters) can be encoded in the entropy encoder 190 and output as a bitstream, and the decoding device can perform the in-loop filtering process based on the filtering-related information using the same method as the encoding device.

[0129] This in-loop filtering process reduces noise generated during image / video encoding (such as block artifacts and ringing artifacts) and improves subjective / objective visual quality. Furthermore, by performing the in-loop filtering process in both the encoding and decoding devices, the encoding and decoding devices can derive the same prediction results, increasing the reliability of image encoding and reducing the amount of data transmitted for image encoding.

[0130] As described above, the image reconstruction process can be performed not only in the decoding device but also in the encoding device. Reconstructed blocks can be generated based on intra-frame prediction / inter-frame prediction on a block-by-block basis, and a reconstructed image including these blocks can be generated. When the current image / slice / patch group is an I-frame / slice / patch group, blocks included in the current image / slice / patch group can be reconstructed based solely on intra-frame prediction. Furthermore, when the current image / slice / patch group is a P-frame / slice / patch group or a B-frame / slice / patch group, blocks included in the current image / slice / patch group can be reconstructed based on either intra-frame prediction or inter-frame prediction. In this case, inter-frame prediction can be applied to some blocks in the current image / slice / patch group, and intra-frame prediction can be applied to the remaining blocks. The color components of the image can include luminance and chrominance components; unless explicitly defined in this disclosure, the methods and implementations of this disclosure can be applied to both luminance and chrominance components.

[0131] Examples of coding layers and structures

[0132] Video / images encoded according to this disclosure can be processed, for example, according to the encoding layers and structures described below.

[0133] Figure 6 This is a view showing the layer structure of an encoded image. Encoded images can be classified into the Video Coding Layer (VCL) for image decoding and its own processing, the lower system for transmitting and storing encoded information, and the Network Abstraction Layer (NAL) that exists between the VCL and the lower system and is responsible for network adaptation functions.

[0134] In VCL, VCL data that includes compressed image data (slice data) can be generated, or additional enhancement information (SEI) messages that include information such as picture parameter set (PPS), sequence parameter set (SPS), or video parameter set (VPS) can be generated for the decoding process of the image.

[0135] In NAL, header information (NAL cell header) can be added to the raw byte sequence payload (RBSP) generated in VCL to generate NAL cells. In this case, RBSP refers to the slice data, parameter set, and SEI message generated in VCL. The NAL cell header may include NAL cell type information specified based on the RBSP data included in the corresponding NAL cell.

[0136] As shown in the figure, NAL units can be classified into VCL NAL units and non-VCL NAL units based on the RBSP generated in the VCL. VCL NAL units can refer to NAL units that include information about the image (slice data), while non-VCL NAL units can refer to NAL units that include information required for decoding the image (parameter set or SEI message).

[0137] VCL NAL units and non-VCL NAL units can be appended with header information and transmitted over a network according to the data standard of the lower system. For example, NAL units can be modified to a predetermined standard data format such as H.266 / VVC file format, RTP (Real-Time Transport Protocol), or TS (Transport Streaming) and transmitted over various networks.

[0138] As described above, in a NAL cell, the NAL cell type can be specified according to the RBSP data structure included in the corresponding NAL cell, and information about the NAL cell type can be stored in the NAL cell header and notified by a signal.

[0139] For example, based on whether the NAL unit includes information about the image (slice data), it can be mainly classified into VCLNAL unit type and non-VCL NAL unit type. VCL NAL unit type can be classified according to the characteristics and type of the image included in the VCL NAL unit, and non-VCL NAL unit type can be classified according to the type of parameter set.

[0140] Below are examples of NAL cell types specified based on the type of parameter set / information included in non-VCL NAL cell types.

[0141] -DCI (Decoding Capability Information) NAL Unit: Includes the type of NAL unit for DCI.

[0142] -VPS (Video Parameter Set) NAL Unit: Includes the type of NAL unit for the VPS.

[0143] -SPS (Sequence Parameter Set) NAL Unit: The type of NAL unit that includes SPS.

[0144] -PPS (Picture Parameter Set) NAL Unit: Includes the types of NAL units for PPS.

[0145] -APS (Adaptive Parameter Set) NAL Unit: The type of NAL unit including APS.

[0146] -PH (Header) NAL Unit: Includes the type of NAL unit for PH.

[0147] The aforementioned NAL unit type can have syntax information specific to the NAL unit type, and this syntax information can be stored in the NAL unit header and signaled. For example, the syntax information can be nal_unit_type, and the NAL unit type can be specified as the nal_unit_type value.

[0148] Furthermore, as mentioned above, a frame can include multiple slices, and a slice can include a slice header and slice data. In this case, a frame header can be further added to multiple slices within a frame (slice header and slice dataset). The frame header (frame header syntax) can include information / parameters that are typically applicable to the frame.

[0149] A slice header (slice header syntax) may include information / parameters typically applicable to a slice. An APS (APS syntax) or PPS (PPS syntax) may include information / parameters typically applicable to one or more slices or frames. An SPS (SPS syntax) may include information / parameters typically applicable to one or more sequences. A VPS (VPS syntax) may include information / parameters typically applicable to multiple layers. A DCI (DCI syntax) may include information / parameters typically applicable to the entire video. A DCI may include information / parameters related to decoding capabilities. In this disclosure, the High-Level Syntax (HLS) may include at least one of the following: APS syntax, PPS syntax, SPS syntax, VPS syntax, DCI syntax, frame header syntax, or slice header syntax. Furthermore, in this disclosure, the Low-Level Syntax (LLS) may include, for example, slice data syntax, CTU syntax, coding unit syntax, transform unit syntax, etc.

[0150] In this disclosure, the image / video information encoded in the encoding device and signaled to the decoding device in the form of a bitstream can include not only intra-frame segmentation related information, intra / inter-frame prediction information, residual information, and intra-loop filtering information, but also information about slice headers, frame headers, APS, PPS, SPS, VPS, and / or DCI. Additionally, the image / video information may also include general constraint information and / or information about NAL unit headers.

[0151] Hypothetical Reference Decoder (HDR) Signaling

[0152] In this disclosure, HRD refers to a hypothetical reference decoder. HRD can be a hypothetical decoder model that specifies constraints on the variability of a NAL unit stream or a byte stream that may be generated during the image encoding process. In this disclosure, CVS can refer to an encoded video sequence.

[0153] The HRD structure can be notified by signals in the VPS (Video Parameter Set) or SPS (Sequence Parameter Set).

[0154] Figure 7 This is an exemplary view illustrating an HRD structure that is signaled in a VPS.

[0155] like Figure 7As shown, a VPS can include various information related to HRD parameters.

[0156] exist Figure 7 In the `vps_general_hrd_params_present_flag` flag, the first value (e.g., 1) specifies that the VPS includes the `general_hrd_parameters()` syntax structure and other HRD parameters. The second value (e.g., 0) specifies that the VPS does not include the `general_hrd_parameters()` syntax structure or other HRD parameters.

[0157] When vps_general_hrd_params_present_flag equals the first value (e.g., 1), the general_hrd_parameters() syntax structure can be signaled in the VPS. The general_hrd_parameters() syntax structure can be a syntax structure used to signal general HRD parameters.

[0158] When vps_max_sublayers_minus1 is greater than 0, the vps_sublayer_cpb_params_present_flag can be notified via a signal. Increasing vps_max_sublayers_minus1 by 1 specifies the maximum number of time-limited sublayers that can exist within the layer specified by the VPS. The value of vps_max_sublayers_minus1 should be in the range of 0 to 6 (inclusive).

[0159] The first value of `vps_sublayer_cpb_params_present_flag` (e.g., 1) specifies that the `iols_hrd_parameters()` syntax structure in the VPS contains HRD parameters for the sublayer representation. In this case, the sublayer can be a sublayer with a TemporalId in the range of 0 to `vps_hrd_max_tid[i]` (inclusive). The second value of `vps_sublayer_cpb_params_present_flag` (e.g., 0) specifies that the `iols_hrd_parameters()` syntax structure in the VPS contains only HRD parameters for the sublayer representation whose TemporalId is equal to `vps_hrd_max_tid[i]`. When `vps_max_sublayers_minus1` is equal to 0, the value of `vps_sublayer_cpb_params_present_flag` is inferred to be equal to 0.

[0160] When vps_sublayer_cpb_params_present_flag equals the second value (e.g., 0), it is inferred that the HRD parameters of the sublayer representation with TemporalId in the range of 0 to vps_hrd_max_tid[i]-1 (inclusive) are the same as the HRD parameters of the sublayer representation with TemporalId equal to vps_hrd_max_tid[i]. In this case, the HRD parameters can include the fixed_pic_rate_general_flag[i] in the ols_hrd_parameters() syntax structure of the sublayer_hrd_parameters(i) syntax structure.

[0161] Increasing `vps_num_ols_hrd_params_minus1` by 1 specifies the number of `ols_hrd_parameters()` syntax structures present in the VPS when `vps_general_hrd_params_present_flag` equals the first value (e.g., 1). The value of `vps_num_ols_hrd_params_minus1` should be in the range of 0 to `NumMultiLayerOlss-1` (inclusive). In this case, `NumMultiLayerOlss` can specify the number of multi-layer OLS, and a multi-layer OLS can mean a set of output layers containing more than one layer.

[0162] `vps_hrd_max_tid[i]` specifies the TemporalId of the highest sublayer representation of the HRD parameters included in the `i`th `ols_hrd_parameters()` syntax structure. The value of `vps_hrd_max_tid[i]` should be in the range of 0 to `vps_max_sublayers_minus1` (inclusive). When it does not exist, the value of `vps_hrd_max_tid[i]` is inferred to be equal to `vps_max_sublayers_minus1`.

[0163] `vps_ols_hrd_idx[i]` specifies the index to the list of `ols_hrd_parameters()` syntax structures in the VPS. `vps_ols_hrd_idx[i]` can specify the `ols_hrd_parameters()` syntax structure applicable to the i-th tier of the OLS. The value of `vps_ols_hrd_idx[i]` should be in the range of 0 to `vps_num_ols_hrd_params_minus1` (inclusive).

[0164] When vps_ols_hrd_idx[i] does not exist, the following is the deduction of vps_ols_hrd_idx[i]:

[0165] - If vps_num_ols_hrd_params_minus1 equals 0, then the value of vps_ols_hrd_idx[[i] is inferred to be equal to 0.

[0166] Otherwise (vps_num_ols_hrd_params_minus1+1 is greater than 1 and equal to NumMultiLayerOlss), the value of vps_ols_hrd_idx[i] is inferred to be equal to i.

[0167] For a single-layer OLS, the applicable ols_hrd_parameters() syntax structure exists in the SPS referenced by the layer in the OLS.

[0168] Each ols_hrd_parameters() syntax structure in a VPS should be referenced by at least one value of vps_ols_hrd_idx[i] for i in the range of 1 to NumMultiLayerOlss-1 (inclusive).

[0169] Figure 8This is an exemplary view illustrating an HRD structure notified by signals in SPS.

[0170] exist Figure 8 In the example shown, a `sps_ptl_dpb_hrd_params_present_flag` equal to the first value (e.g., 1) can specify that the `profile_tier_level()` and `dpb_parameters()` syntax structures exist in SPS. `profile_tier_level()` can be a syntax structure used to send parameters for the profile hierarchy level, and `dpb_parameters()` can be a syntax structure used to send parameters for the DPB (decoded frame buffer). Alternatively, a `sps_ptl_dpb_hrd_params_present_flag` equal to the first value (e.g., 1) can specify that the `general_hrd_parameters()` and `ols_hrd_parameters()` syntax structures exist in SPS. A `sps_ptl_dpb_hrd_params_present_flag` equal to the second value (e.g., 0) can specify that these four syntax structures do not exist in SPS.

[0171] When sps_ptl_dpb_hrd_params_present_flag equals 1, sps_general_hrd_params_present_flag can be notified via a signal.

[0172] A `sps_general_hrd_params_present_flag` equal to the first value (e.g., 1) can specify that SPS includes both the `general_hrd_parameters()` and `ols_hrd_parameters()` syntax structures. A `sps_general_hrd_params_present_flag` equal to the second value (e.g., 0) can specify that SPS does not include either the `general_hrd_parameters()` or `ols_hrd_parameters()` syntax structures.

[0173] like Figure 8As shown, when `sps_max_sublayers_minus1` is greater than 0, `sps_sublayer_cpb_params_present_flag` can be signaled. In this case, adding 1 to `sps_max_sublayers_minus1` specifies the maximum number of temporal sublayers that can exist in each encoded Layer Video Sequence (CLVS) of the reference SPS. `sps_sublayer_cpb_params_present_flag` equal to the first value (e.g., 1) specifies that the `ols_hrd_parameters()` syntax structure in the SPS contains HRD parameters for sublayers whose temporal layer identifier `TemporalId` is equal to 0 to `sps_max_sublayers_minus1`. `sps_sublayer_cpb_params_present_flag` equal to the second value (e.g., 0) specifies that the `ols_hrd_parameters()` syntax structure in the SPS contains HRD parameters for sublayers whose temporal layer identifier `TemporalId` is only for sublayers of `sps_max_sublayers_minus1`. When sps_max_sublayers_minus1 equals 0, the value of sps_sublayer_cpb_params_present_flag can be inferred to be equal to the second value (e.g., 0).

[0174] When sps_sublayer_cpb_params_present_flag is equal to the second value (e.g., 0), it can be inferred that the HRD parameter of the sublayer with the temporal identifier TemporalId is 0 to sps_max_sublayers_minus1-1 is equal to the HRD parameter of the sublayer with the temporal identifier TemporalId being sps_max_sublayers_minus1.

[0175] Figure 9 This is a view that exemplifies the syntax structure of general_hrd_parameters().

[0176] Figure 9 The general_hrd_parameters() syntax structure provides some of the sequence-level HRD parameters for use in HRD operations.

[0177] The requirement for bitstream consistency is that the contents of the general_hrd_parameters() syntax structure should be identical in any VPS or SPS existing in the bitstream.

[0178] When included in a VPS, the `general_hrd_parameters()` syntax applies to all output layers (OLS) specified by the VPS. When included in an SPS, the `general_hrd_parameters()` syntax applies only to the OLS of the lowest layer among the layers that serve as the reference SPS. In this case, the lowest layer can be an independent layer. An independent layer can mean a layer that is encoded / decoded without reference to other layers.

[0179] The following text will focus on Figure 9 The syntax elements shown are those relevant to this disclosure. The meanings and uses of syntax elements not described in this disclosure may be the same as those in the prior art.

[0180] exist Figure 9 In this context, a `general_nal_hrd_params_present_flag` equal to the first value (e.g., 1) indicates the presence of NAL HRD parameters in the `general_hrd_parameters()` syntax structure (related to the Type II bitstream consistency point). A `general_nal_hrd_params_present_flag` equal to the second value (e.g., 0) indicates the absence of NAL HRD parameters in the `general_hrd_parameters()` syntax structure. In the above cases, a Type II bitstream can refer to a bitstream that includes syntax elements (leading_zero_8bits, zero_byte, etc.) that construct a byte stream based on additional non-VCL NAL units and / or a stream of NAL units, as well as VCL NAL units, PH NAL units, and padding data NAL units for all access units (AUs) in the bitstream.

[0181] A `general_vcl_hrd_params_present_flag` equal to the first value (e.g., 1) indicates the presence of VCL HRD parameters in the `general_hrd_parameters()` syntax structure (related to the type I bitstream consistency point). A `general_vcl_hrd_params_present_flag` equal to the second value (e.g., 0) indicates the absence of VCL HRD parameters in the `general_hrd_parameters()` syntax structure. In the above cases, a type I bitstream can refer to a bitstream that includes filter data NAL units, VCL NAL units, and PHNAL units for all access units (AUs) in the bitstream.

[0182] The requirement for bitstream consistency is that both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag, which are included in each general_hrd_parameters() syntax structure, are constrained to not have a second value (e.g., 0).

[0183] Figure 10 This is a view that exemplifies the syntax structure of ols_hrd_parameters().

[0184] When the ols_hrd_parameters() syntax structure is included in a VPS, the VPS specifies the OLS to which the ols_hrd_parameters() syntax structure should be applied. When the ols_hrd_parameters() syntax structure is included in an SPS, the ols_hrd_parameters() syntax structure can be applied to the OLS of only the lowest layer among the layers that serve as the reference SPS. In this case, the lowest layer can be an independent layer.

[0185] The following text will focus on Figure 10 The syntax elements shown are those relevant to this disclosure. The meanings and uses of syntax elements not described in this disclosure may be the same as those in the prior art.

[0186] exist Figure 10 In this context, a fixed_pic_rate_general_flag[i] equal to the first value (e.g., 1) indicates that, when Htid equals i, the time distance between the HRD output times of consecutive frames in output order is constrained as specified below. A fixed_pic_rate_general_flag[i] equal to the second value (e.g., 0) indicates that this constraint may not apply. When fixed_pic_rate_general_flag[i] does not exist, it is inferred to be equal to 0. fixed_pic_rate_general_flag can be information specifying whether a fixed frame rate is typically used.

[0187] In this disclosure, Htid can be an identifier that identifies the highest time sub-layer among the time sub-layers to be decoded in the bitstream.

[0188] A fixed_pic_rate_within_cvs_flag[i] equal to the first value (e.g., 1) indicates that, when Htid equals i, the time distance between the HRD output times of consecutive frames in output order is constrained as specified below. A fixed_pic_rate_within_cvs_flag[i] equal to the second value (e.g., 0) indicates that this constraint may not apply. fixed_pic_rate_within_cvs_flag can be information specifying whether a fixed frame rate is used in CVS.

[0189] When fixed_pic_rate_general_flag[i] is equal to the first value (e.g., 1), it is inferred that the value of fixed_pic_rate_within_cvs_flag[i] is equal to 1.

[0190] The increment of element_duration_in_tc_minus1[i] by 1 (if present) specifies the time interval in clock ticks between the element units of the HRD output time of consecutive frames in output order when Htid equals i. The value of element_duration_in_tc_minus1[i] should be in the range of 0 to 2047 (inclusive).

[0191] When Htid equals i and fixed_pic_rate_general_flag[i] equals the first value (e.g., 1) of the CVS containing frame n, and frame n is the output frame and not the last frame in the output bitstream (in output order), the value of the variable DpbOutputElementalInterval[n] can be specified as shown in Equation 1 below. In this disclosure, DpbOutputElementalInterval[n] can refer to the refresh interval of frame n.

[0192] (Formula 1)DpbOutputElementalInterval[n]=DpbOutputInterval[n] / elementalOutputPeriods

[0193] In Equation 1 above, DpbOutputInterval[n] is the value according to the regular rules, and elementalOutputPeriods is specified as follows:

[0194] - If a PT SEI message exists for frame n, then specify elementalOutputPeriods as equal to the value of pt_display_elemental_periods_minus1+1. A PT SEI message can refer to an SEI message related to frame timing. pt_display_elemental_periods_minus1+1 can specify the number of frame period intervals occupied by the frame decoded by the current access unit (AU) under predetermined conditions.

[0195] - Otherwise, specify elementalOutputPeriods as equal to 1.

[0196] When Htid equals i and fixed_pic_rate_general_flag[i] equals the first value (e.g., 1) for the CVS containing frame n, and frame n is the output frame and not the last frame in the output bitstream (in output order), the value calculated for DpbOutputElementalInterval[n] will be equal to ClockTick*(elemental_duration_in_tc_minus1[i]+1).

[0197] When Htid equals i and fixed_pic_rate_within_cvs_flag[i] equals the first value (e.g., 1) for the CVS containing frame n, and frame n is the output frame and not the last frame in the output CVS (in output order), the value calculated for DpbOutputElementalInterval[n] will be equal to ClockTick*(elemental_duration_in_tc_minus1[i]+1).

[0198] When Htid equals i, low_delay_hrd_flag[i] specifies the HRD operating mode. When it does not exist, the value of low_delay_hrd_flag[i] is inferred to be equal to 0.

[0199] Figure 11 This is a view that exemplifies the sublayer_hrd_parameters() syntax structure.

[0200] When the `sublayer_hrd_parameters()` syntax structure is included in the `i`th `ols_hrd_parameters()` syntax structure in the VPS, the value of `maxSublayersMinus1` is set to equal `vps_hrd_max_tid[i]`. When the `sublayer_hrd_parameters()` syntax structure is included in the `ols_hrd_parameters()` syntax structure in the SPS, the value of `maxSublayersMinus1` is set to equal `sps_max_sublayers_minus1`.

[0201] The following text will focus on Figure 11 The syntax elements shown are those relevant to this disclosure. The meanings and uses of syntax elements not described in this disclosure may be the same as those in the prior art.

[0202] exist Figure 11 In this context, when the CPB is operating at AU level, `bit_rate_value_minus1[i][j]` (along with `bit_rate_scale`) specifies the maximum input bit rate of the j-th CPB where `Htid` equals `i`. `bit_rate_value_minus1[i][j]` should be between 0 and 2. 32 -2 range (inclusive of 0 and 2) 32 -2) Within. For any specific value of j and i that is greater than 0, bit_rate_value_minus1[i][j] should be greater than bit_rate_value_minus1[i][j-1].

[0203] When the CPB is operating at AU level, cpb_size_value_minus1[i][j], together with cpb_size_scale, is used to specify the size of the j-th CPB where Htid equals i. cpb_size_value_minus1[i][j] should be between 0 and 2. 32 -2 range (inclusive of 0 and 2) 32 -2) Within. For any specific value of j and i that is greater than 0, cpb_size_value_minus1[i][j] should be less than or equal to cpb_size_value_minus1[i][j-1].

[0204] When the CPB is operating at the DU level, cpb_size_du_value_minus1[i][j], together with cpb_size_du_scale, is used to specify the size of the i-th CPB where Htid equals i. cpb_size_du_value_minus1[i][j] should be between 0 and 2. 32 -2 range (inclusive of 0 and 2) 32 -2) Within. For any specific value of j and i that is greater than 0, cpb_size_du_value_minus1[i][j] should be less than or equal to cpb_size_du_value_minus1[i][j-1].

[0205] When the CPB is operating at DU level, bit_rate_du_value_minus1[i][j] (along with bit_rate_scale) specifies the maximum input bit rate of the j-th CPB where Htid equals i. bit_rate_du_value_minus1[i][j] should be between 0 and 2. 32 -2 range (inclusive of 0 and 2) 32 -2) Within. For any specific value of j and i that is greater than 0, bit_rate_du_value_minus1[i][j] should be greater than bit_rate_du_value_minus1[i][j-1].

[0206] A cbr_flag[i][j] equal to the second value (e.g., 0) specifies that the hypothetical stream scheduler (HSS) operates in intermittent bit rate mode in order to decode the corresponding bitstream via HRD using the j-th CPB specification. A cbr_flag[i][j] equal to the first value (e.g., 1) specifies that the HSS operates in constant bit rate (CBR) mode.

[0207] When the cbr_flag[i][j] syntax element does not exist, the following inference is made:

[0208] - If general_hrd_params_present_flag is equal to the first value (e.g., 1), then cbr_flag[i][j] is inferred to be equal to cbr_flag[maxSublayersMinus1][j].

[0209] Otherwise (general_hrd_params_present_flag equals the second value (e.g., 0)), the value of cbr_flag[i][j] is inferred to be equal to the second value (e.g., 0).

[0210] The following section will describe issues related to standard HRD parameter signaling.

[0211] As mentioned above, based on the requirements for consistency of the general bitstream, the values ​​of `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` in each `general_hrd_parameters()` syntax structure should not both be equal to the second value (e.g., 0). However, in some use cases, it is useful to have a simple signaling mechanism for the decoder to calculate the timing of the output without having to signal complex HRD parameters. Therefore, it is necessary to provide a mechanism that can improve the general signaling method for HRD parameters.

[0212] According to this disclosure, the following items can be applied to improve conventional signaling methods for HRD parameters. These items can be applied individually or in combination.

[0213] (Item 1) The values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are allowed to both be equal to the second value (e.g., 0).

[0214] (Item 2) When a general HRD parameter structure exists (i.e., vps_general_hrd_params_present_flag equals a first value (e.g., 1) or sps_general_hrd_params_present_flag equals a first value (e.g., 1)), and both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag equal a second value (e.g., 0), information regarding POC-based timing can exist in the general HRD parameter structure (i.e., poc_proportional_to_timing_flag and num_ticks_poc_diff_one_minus1). In Item 2, it can be constrained that when both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag equal the second value (e.g., 0), the value of poc_proportional_to_timing_flag should equal the first value (e.g., 1).

[0215] (Item 3) Alternatively, when a general HRD parameter structure exists (i.e., vps_general_hrd_params_present_flag is equal to a first value (e.g., 1) or sps_general_hrd_params_present_flag is equal to a first value (e.g., 1)) and the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to 0), information about timing based on POC scales is contained in the general HRD parameter (i.e., num_ticks_poc_diff_one_minus1).

[0216] (Item 4) When a general HRD parameter structure exists (i.e., vps_general_hrd_params_present_flag equals the first value (e.g., 1) or sps_general_hrd_params_present_flag equals the first value (e.g., 1)), and the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to the second value (e.g., 0), it can be further specified that the first frame in the CVS (or CLVS) that is not the first frame in the bitstream can be timed proportionally to the output timing of the last output frame before the CVS. That is, it can work as if the last output frame had a POC equal to the first frame in the CVS minus 1.

[0217] (Item 5) Alternatively, a flag may exist to specify whether Item 4 is applied. The flag may be called `initial_poc_proportional_to_timing_flag`. When the flag is equal to 1, Item 4 is applied; otherwise, Item 4 may not be applied.

[0218] (Item 6) When both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are equal to the second value (e.g., 0), there is no further HRD signaling for OLS.

[0219] (Item 7) `num_ticks_poc_diff_one_minus1` can be encoded as `u(v)` instead of `ue(v)`. The length of `num_ticks_poc_diff_one_minus1` (i.e., the number of bits used for signaling) is specified by the new syntax element preceding it that signals the signal. This new syntax element can be called `num_ticks_poc_diff_one_len`. `num_ticks_poc_diff_one_len` can be encoded as `ue(v)`.

[0220] In the above, u(v) can be an unsigned integer using v bits. In this case, the number of bits v can vary in a way that depends on the values ​​of other syntax elements. Alternatively, ue(v) can be an unsigned integer 0-order Exp-Golomb-coded syntax element, where the left bit is first.

[0221] (Item 8) In an alternative to Item 2, `poc_proportional_to_timing_flag` and `num_ticks_poc_diff_one_minus1` exist in the general HRD parameter structure, regardless of the values ​​of `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag`. In this case, the values ​​of the constraints `poc_proportional_to_timing_flag`, `general_nal_hrd_params_present_flag`, and `general_vcl_hrd_params_present_flag` should not all be equal to the second value (e.g., 0). For example, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to 0, the value of the constraint `poc_proportional_to_timing_flag` should be equal to 1.

[0222] (Item 9) In yet another alternative, when the value of poc_proportional_to_timing_flag should be equal to the first value (e.g., 1), the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag should both be equal to the second value (e.g., 0).

[0223] (Item 10) In yet another alternative, OLSHRD signaling may exist when at least one of the following conditions is true.

[0224] (Condition 1) At least general_nal_hrd_params_present_flag or general_vcl_hrd_params_present_flag is equal to the first value (e.g., 1).

[0225] (Condition 2) poc_proportional_to_timing_flag, general_nal_hrd_params_present_flag, and general_vcl_hrd_params_present_flag are all equal to the second value (e.g., 0).

[0226] (Item 11) When both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are equal to the second value (e.g., 0) (i.e., only the minimum HRD signaling exists), the bitstream runs at a fixed frame rate. Item 11 above can be represented as follows.

[0227] - When both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are equal to the second value (e.g., 0), there will be at least one value of fixed_pic_rate_within_cvs_flag[i] that is equal to the first value (e.g., 1). In this case, i can be in the range of 0 to maxSublayersMinus1.

[0228] - Alternatively, when both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are equal to the second value (e.g., 0), at least one value of element_duration_in_tc_minus1[i] will exist.

[0229] (Item 12) When all of poc_proportional_to_timing_flag, general_nal_hrd_params_present_flag, and general_vcl_hrd_params_present_flag are equal to the second value (e.g., 0), the constraint fixed_pic_rate_general_flag[i] or fixed_pic_rate_within_cvs_flag[i] or both should be equal to the first value (e.g., 1).

[0230] Various embodiments of the present invention will be described below. However, the scope of this disclosure is not limited thereto, and may include embodiments combining the various embodiments described below.

[0231] Figure 12 This is an exemplary view illustrating the general_hrd_parameters() syntax structure according to an embodiment of this disclosure.

[0232] Figure 12 It can be shown Figure 9 Modification of the syntax structure of general_hrd_parameters().

[0233] exist Figure 9 and Figure 12 Repeated descriptions will be omitted.

[0234] Figure 12 An implementation method applying at least one of items 1, 2, and 4 through 6 may be shown.

[0235] exist Figure 12 In some implementations, the constraint that general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag should not both be equal to the second value (e.g., 0) may not be applied.

[0236] like Figure 12As shown, some syntax elements can be signaled when `general_nal_hrd_params_present_flag` equals the first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals the first value (e.g., 1). `poc_proportional_to_timing_flag` can be signaled when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal the second value (e.g., 0). Additionally, `num_ticks_poc_diff_one_minus1` can be signaled based on the value of `poc_proportional_to_timing_flag`.

[0237] A `poc_proportional_to_timing_flag` equal to the first value (e.g., 1) indicates that the frame sequence count for each frame in CVS that is not the first frame in CVS in the decoding order is proportional to the output time of the frame relative to the output time of the first frame in CVS. A `poc_proportional_to_timing_flag` equal to the second value (e.g., 0) indicates that the frame sequence count for each frame in CVS that is not the first frame in CVS in the decoding order may or may not be proportional to the output time of the frame relative to the output time of the first frame in CVS. `poc_proportional_to_timing_flag` can be information indicating whether the output time of a frame is proportional to the frame's `POC` value.

[0238] For the first frame in CVS that is not the first frame in the bitstream, its output time can be proportional to the output time of the last output frame preceding CVS. In other words, it can function as if the last output frame had a POC equal to the first frame in CVS minus 1.

[0239] When poc_proportional_to_timing_flag equals the first value (e.g., 1), num_ticks_poc_diff_one_minus1 can be notified by a signal.

[0240] `num_ticks_poc_diff_one_minus1` incremented by 1 specifies the number of clock ticks. The number of clock ticks can correspond to the difference between the frame sequence count value and the value equal to 1. The value of `num_ticks_poc_diff_one_minus1` should be between 0 and 2. 32-2 range (inclusive of 0 and 2) 32 -2) inside.

[0241] In addition, according to Figure 12 The implementation method can change the signaling of HRD parameters in VPS and / or SPS.

[0242] Figure 13 This is an example of how to illustrate the following: Figure 12 A view of the modified syntax structure of VPS and SPS implementations.

[0243] like Figure 13 As shown in the upper grammatical structure, for example, the reference can be changed. Figure 7 The syntax structure of the described VPS is such that the HRD parameters in the VPS are signaled when general_nal_hrd_params_present_flag is equal to the first value (e.g., 1) or general_vcl_hrd_params_present_flag is equal to the first value (e.g., 1).

[0244] Similarly, such as Figure 13 As shown in the lower part of the syntax structure, the reference can be changed. Figure 8 The described syntax structure of the SPS allows the HRD parameters in the SPS to be signaled when general_nal_hrd_params_present_flag equals a first value (e.g., 1) or general_vcl_hrd_params_present_flag equals a first value (e.g., 1).

[0245] according to Figure 12 and / or Figure 13 In some implementations, when `general_nal_hrd_params_present_flag` equals a first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals a first value (e.g., 1), signaling with complex HRD parameters may exist in the prior art. Alternatively, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal a second value (e.g., 0), a simple signaling mechanism for providing timing information can be provided. Figure 12 and / or Figure 13 The implementation method can provide a flexible signaling structure for timing information suitable for various use cases.

[0246] As Figure 12The modification allows for the following: when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to the second value (e.g., 0), `poc_proportional_to_timing_flag` can be notified without signaling, and `num_ticks_poc_diff_one_minus1` can be notified with a signal. Therefore, the number of bits required for a simple signaling mechanism for timing information can be reduced, and the process of parsing `poc_proportional_to_timing_flag` and determining its value can be skipped, thus enabling a faster encoding / decoding process.

[0247] Figure 14 This is an exemplary view illustrating the general_hrd_parameters() syntax structure according to another embodiment of this disclosure.

[0248] Figure 14 It can be shown Figure 9 Modification of the syntax structure of general_hrd_parameters().

[0249] exist Figure 9 and Figure 14 In this document, the description of the overlapping parts will be omitted.

[0250] Figure 14 An implementation method applying item 8 above can be shown.

[0251] exist Figure 14 In some implementations, the constraint that general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag should not both be equal to the second value (e.g., 0) may not be applied.

[0252] like Figure 14 As shown, `poc_proportional_to_timing_flag` can be notified via a signal. Additionally, based on the value of `poc_proportional_to_timing_flag`, `num_ticks_poc_diff_one_minus1` can be notified via a separate signal. The meanings of `poc_proportional_to_timing_flag` and `num_ticks_poc_diff_one_minus1` are described and referenced below. Figure 13 Since the descriptions are the same, repeated descriptions will be omitted.

[0253] Subsequently, signals can be used to notify general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag, and subsequent HRD parameters can be notified using signals based on the values ​​of general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag.

[0254] For example, such as Figure 14 As shown, when `general_nal_hrd_params_present_flag` equals the first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals the first value (e.g., 1), some syntax elements can be notified using a signal. That is, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal the second value (e.g., 0), some syntax elements do not need to be notified using a signal.

[0255] exist Figure 14 In the implementation, the constraint on bitstream consistency is that when both general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are equal to 0, the value of poc_proportional_to_timing_flag should be equal to 1.

[0256] according to Figure 14 In this implementation, when `general_nal_hrd_params_present_flag` equals a first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals a first value (e.g., 1), signaling for complex HRD parameters is possible, as in the prior art. Additionally, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal a second value (e.g., 0), a simple signaling mechanism for timing information can be provided. Figure 14 The implementation method can provide a flexible signaling structure for timing information suitable for various use cases.

[0257] according to Figure 14The implementation method can change the signaling of HRD parameters in VPS and / or SPS.

[0258] Figure 15 This is an example of how to illustrate the following: Figure 14 A view of the modified syntax structure of VPS and SPS implementations.

[0259] For example, such as Figure 15 As shown in the upper grammatical structure, the reference can be changed. Figure 7 The syntax structure of the described VPS allows the HRD parameter in the VPS to be signaled when poc_proportional_to_timing_flag equals the second value (e.g., 0).

[0260] Similarly, such as Figure 15 As shown in the lower part of the syntax structure, the reference can be changed. Figure 8 The syntax structure of the described SPS is such that when poc_proportional_to_timing_flag equals the second value (e.g., 0), the HRD parameter in the SPS is notified by a signal.

[0261] according to Figure 14 and / or Figure 15 In this implementation, when `general_nal_hrd_params_present_flag` equals a first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals a first value (e.g., 1), signaling for complex HRD parameters is possible, as in the prior art. Additionally, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal a second value (e.g., 0), a simple signaling mechanism for timing information can be provided. Figure 14 and / or Figure 15 The implementation method can provide a flexible signaling structure for timing information suitable for various use cases.

[0262] Figure 16 This is an exemplary view illustrating the ols_hrd_parameters() syntax structure according to another embodiment of this disclosure.

[0263] Figure 16 It can be shown Figure 10 Modification of the syntax structure of old_hrd_parameters().

[0264] exist Figure 10 and Figure 16 Repeated descriptions will be omitted.

[0265] Figure 16 An implementation method applying at least one of item 11 or item 12 may be shown.

[0266] like Figure 16 As shown, when `general_nal_hrd_params_present_flag` equals the first value (e.g., 1) or `general_vcl_hrd_params_present_flag` equals the first value (e.g., 1), at least some of the HRD parameters (e.g., `low_delay_hrd_flag`) can be signaled. Therefore, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` equal the second value (e.g., 0), the corresponding parameters do not need to be signaled.

[0267] exist Figure 16 In this implementation, the constraint on bitstream consistency is that when the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to the second value (e.g., 0), the value of fixed_pic_rate_general_flag[i] or fixed_pic_rate_within_cvs_flag[i] will be equal to the first value (e.g., 1). In this case, i can be within the range from the variable firstSubLayer specifying the first sublayer to the variable maxSublayers specifying the maximum sublayer (inclusive).

[0268] exist Figure 16 In this implementation, the requirement for bitstream consistency is that when the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to the second value (e.g., 0), there should be at least one value of fixed_pic_rate_within_cvs_flag[i] equal to the first value (e.g., 1). In this case, i can be in the range of 0 to maxSublayersMinus1.

[0269] exist Figure 16In the implementation, element_duration_in_tc_minus1[i] plus 1 (if present) specifies the clock-beat time distance between element units that specify the HRD output time of consecutive frames in output order when Htid equals i. The value of element_duration_in_tc_minus1[i] should be in the range of 0 to 2047 (inclusive).

[0270] When Htid equals i and fixed_pic_rate_general_flag[i] equals the first value of the CVS containing frame n (e.g., 1), and frame n is the frame that is output and not the last frame in the output bitstream (in output order), it can be as follows: Figure 17 The value of the variable DpbOutputElementalInterval[n] is specified as shown.

[0271] Figure 17 This is an example in Figure 16 The implementation provides a view of the process of deriving DpbOutputElementalInterval[n].

[0272] exist Figure 17 In this context, ClockTick and DpbOutputInterval[n] can be specified as values ​​equal to those according to the regular rules.

[0273] When Htid equals i and fixed_pic_rate_general_flag[i] equals the first value (e.g., 1) of the CVS containing frame n, and frame n is the output frame and not the last frame in the output bitstream (in output order), the value computed for DpbOutputElementalInterval[n] will be equal to ClockTick*(element_duration_in_tc_minus1[i]+1) if one of the following conditions is true for the nextPicInOutputOrder in output order.

[0274] (Condition 3) The screen nextPicInOutputOrder is in the same CVS as screen n.

[0275] (Condition 4) The nextPicInOutputOrder is in a different CVS than the nextPicInOutputOrder and the fixed_pic_rate_general_flag[i] is equal to the first value (e.g., 1) in the CVS containing the nextPicInOutputOrder, the ClockTick value is the same for both CVSs, and the element_duration_in_tc_minus1[i] value is the same for both CVSs.

[0276] As described above, `fixed_pic_rate_general_flag[i]` or `fixed_pic_rate_within_cvs_flag[i]` can specify whether the constraint of the time interval between the HRD output times of consecutive frames in output order is applied when Htid equals i. According to the above constraint, the time interval between the HRD output times of consecutive frames in output order can have a fixed value. That is, the frames in the bitstream (or CVS) can be output at a fixed frame rate. Therefore, `fixed_pic_rate_general_flag[i]` or `fixed_pic_rate_within_cvs_flag[i]` can be information specifying whether the bitstream runs at a fixed frame rate. Alternatively, `fixed_pic_rate_general_flag[i]` or `fixed_pic_rate_within_cvs_flag[i]` can be information specifying whether the time interval between the output times of consecutive frames in output order has a fixed value.

[0277] Figure 18 This is a view illustrating an image encoding method according to this disclosure.

[0278] For example, Figure 18 Image encoding methods can be derived from Figure 2 The image encoding device performs the operation. Alternatively, the image encoding device may include a memory and at least one processor, and the at least one processor can perform the operation. Figure 18 Each step of the image encoding method.

[0279] The image encoding device can determine information about whether a specified HRD parameter exists in the bitstream (S1810). general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag can be the information determined in step S1810.

[0280] The image encoding device can determine the value of `general_nal_hrd_params_present_flag` based on the presence of NAL HRD parameters in the bitstream (e.g., the `general_hrd_parameters()` syntax structure). Specifically, when the NAL HRD parameters are present in the bitstream, the image encoding device can determine `general_nal_hrd_params_present_flag` to a first value (e.g., 1), otherwise it can determine it to a second value (e.g., 0). In this disclosure, `general_nal_hrd_params_present_flag` may be referred to as the "first flag".

[0281] Similarly, the image encoding device can determine the value of `general_vcl_hrd_params_present_flag` based on whether the VCL HRD parameter exists in the bitstream (e.g., the `general_hrd_parameters()` syntax structure). Specifically, when the VCL HRD parameter exists in the bitstream, the image encoding device can determine `general_vcl_hrd_params_present_flag` to a first value (e.g., 1), otherwise it can determine it to a second value (e.g., 0). In this disclosure, `general_vcl_hrd_params_present_flag` may be referred to as the "second flag".

[0282] The image encoding device can determine information regarding whether a specified bitstream is running at a fixed frame rate (S1820). The information determined in step S1820 may be information regarding whether the time interval between the output times of consecutive frames in the specified bitstream has a fixed value. The aforementioned `fixed_pic_rate_within_cvs_flag` may be the information determined in step S1820.

[0283] The image encoding device can determine the value of fixed_pic_rate_within_cvs_flag[i] based on whether the time distance between the HRD output times of consecutive frames in the output order in the bitstream has a fixed value when Htid equals i. Specifically, when Htid equals i, if the time distance between the HRD output times of consecutive frames in the output order in the bitstream has a fixed value, the image encoding device can determine fixed_pic_rate_within_cvs_flag[i] to a first value (e.g., 1), otherwise it can determine it to a second value (e.g., 0). In this disclosure, fixed_pic_rate_within_cvs_flag[i] may be referred to as the "third flag".

[0284] However, the information determined in step S1820 is not limited to fixed_pic_rate_within_cvs_flag[i]. For example, the information determined in step S1820 may be fixed_pic_rate_general_flag[i], or may include both fixed_pic_rate_within_cvs_flag[i] and fixed_pic_rate_general_flag[i].

[0285] According to this disclosure, the constraint on bitstream consistency is that when the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to the second value (e.g., 0), the value of fixed_pic_rate_within_cvs_flag[i] should be equal to the first value (e.g., 1). In this case, i can be in the range of 0 to maxSublayersMinus1 (inclusive).

[0286] According to the constraints, when neither the NAL HRD parameter nor the VCL HRD parameter exists in the bitstream, the signaling for minimum frame timing (fixed frame rate) can be guaranteed by making the time distance between the HRD output times of consecutive frames in the output order in the bitstream have a fixed value for at least one Htid.

[0287] To satisfy bitstream consistency constraints, the image encoding device can determine whether both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to a second value (e.g., 0). Based on this determination, the image encoding device can determine `fixed_pic_rate_within_cvs_flag[i]`. That is, when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to the second value (e.g., 0), the image encoding device can determine that at least one `fixed_pic_rate_within_cvs_flag[i]` has a first value (e.g., 1) for i within the range of 0 to `maxSublayersMinus1`. Therefore, step S1820 can include the step of determining whether both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to the second value (e.g., 0).

[0288] The information determined in step S1810 and step S1820 can be encoded in a bitstream and sent to the image decoding device. As described below, the image decoding device can obtain information (general_nal_hrd_params_present_flag, general_vcl_hrd_params_present_flag, fixed_pic_rate_within_cvs_flag[i], and / or fixed_pic_rate_general_flag[i]) from the bitstream. The output time of the frame in the bitstream can be derived using at least one of the information, and the frame in the bitstream can be processed (output) based on the derived output time.

[0289] For each time sublayer in the bitstream, `fixed_pic_rate_within_cvs_flag[i]` (and / or `fixed_pic_rate_general_flag[i]`) can be signaled. In this case, `i` can be in the range of the variable `firstSubLayer` specifying the first sublayer to the variable `maxSublayers` specifying the largest sublayer. Alternatively, `i` can be in the range from 0 to `maxSublayersMinus1`. That is, for each value of `i`, `fixed_pic_rate_within_cvs_flag[i]` can be signaled, and when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to the second value (e.g., 0), the constraint is that for at least one `i`, `fixed_pic_rate_within_cvs_flag[i]` equals the first value (e.g., 1).

[0290] As described above, general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag can be encoded in a general HRD parameter syntax structure (e.g., the general_hrd_parameters() syntax structure), and fixed_pic_rate_within_cvs_flag[i] (and / or fixed_pic_rate_general_flag[i]) can be encoded in an HRD parameter syntax structure for the output layer set (e.g., the ols_hrd_parameters() syntax structure).

[0291] Above, the variable `maxSublayers`, specifying the maximum sublayer, can be determined based on the parameter set to which the HRD parameter syntax structure for the output layer set is encoded. Specifically, when the HRD parameter syntax structure for the output layer set is encoded in a VPS, the value of `maxSublayers` can be set to equal `vps_hrd_max_tid[i]`. When the HRD parameter syntax structure for the output layer set is encoded in an SPS, the value of `maxSublayers` can be set to equal `sps_max_sublayers_minus1`.

[0292] According to the reference Figure 18The image coding method described in this disclosure can provide an improved signaling mechanism that can signal simple timing information instead of signaling complex HRD timing information.

[0293] Figure 19 This is a view illustrating an image decoding method according to the present disclosure.

[0294] For example, Figure 19 Image decoding methods can be derived from Figure 3 The image decoding device performs the operation. Alternatively, the image decoding device may include a memory and at least one processor, and the at least one processor may perform the operation. Figure 19 Each step of the image decoding method.

[0295] The image decoding device can obtain information about whether a specified HRD parameter exists in the bitstream (S1910). general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag can be the information obtained in step S1910.

[0296] The `general_nal_hrd_params_present_flag` obtained by the image decoding device can specify whether the NAL HRD parameter exists in the bitstream (e.g., the `general_hrd_parameters()` syntax structure). Specifically, `general_nal_hrd_params_present_flag` equal to a first value (e.g., 1) can specify that the NAL HRD parameter exists in the bitstream. Alternatively, `general_nal_hrd_params_present_flag` equal to a second value (e.g., 0) can specify that the NAL HRD parameter does not exist in the bitstream. In this disclosure, `general_nal_hrd_params_present_flag` may be referred to as the "first flag".

[0297] Similarly, the `general_vcl_hrd_params_present_flag` obtained by the image decoding device can specify whether the VCL HRD parameter exists in the bitstream (e.g., the `general_hrd_parameters()` syntax structure). Specifically, `general_vcl_hrd_params_present_flag` equal to a first value (e.g., 1) can specify that the VCL HRD parameter exists in the bitstream. Alternatively, `general_vcl_hrd_params_present_flag` equal to a second value (e.g., 0) can specify that the VCL HRD parameter does not exist in the bitstream. In this disclosure, `general_vcl_hrd_params_present_flag` may be referred to as the "second flag".

[0298] The image decoding device can obtain information on whether a specified bitstream is running at a fixed frame rate (S1920). The information obtained in step S1920 may be information on whether the time interval between the output times of consecutive frames in the specified bitstream has a fixed value. The aforementioned `fixed_pic_rate_within_cvs_flag` may be the information determined in step S1920.

[0299] The `fixed_pic_rate_within_cvs_flag[i]` obtained by the image decoding device can specify whether the time distance between the HRD output times of consecutive frames in the output order in the bitstream has a fixed value when Htid equals i. Specifically, when `fixed_pic_rate_within_cvs_flag[i]` equals a first value (e.g., 1), it can specify that the time distance between the HRD output times of consecutive frames in the output order in the bitstream has a fixed value when Htid equals i. Alternatively, when `fixed_pic_rate_within_cvs_flag[i]` equals a second value (e.g., 0), it can specify that the time distance between the HRD output times of consecutive frames in the output order in the bitstream does not have a fixed value. In this disclosure, `fixed_pic_rate_within_cvs_flag[i]` can be referred to as the "third flag".

[0300] However, the information obtained in step S1920 is not limited to fixed_pic_rate_within_cvs_flag[i]. For example, the information obtained in step S1920 may be fixed_pic_rate_general_flag[i], or may include both fixed_pic_rate_within_cvs_flag[i] and fixed_pic_rate_general_flag[i].

[0301] According to this disclosure, as described above, the requirement for bitstream consistency is that when the values ​​of general_nal_hrd_params_present_flag and general_vcl_hrd_params_present_flag are both equal to the second value (e.g., 0), the value of fixed_pic_rate_within_cvs_flag[i] should be equal to the first value (e.g., 1). In this case, i can be in the range of 0 to maxSublayersMinus1 (inclusive).

[0302] As required, when neither the NAL HRD parameter nor the VCL HRD parameter exists in the bitstream, the signaling for minimum frame timing (fixed frame rate) can be guaranteed by making the time distance between the HRD output times of consecutive frames in the bitstream have a fixed value for at least one Htid.

[0303] The operation of an image encoding device for generating a bitstream that meets the bitstream consistency requirements has been described above. The bitstream received by the image decoding device can meet the bitstream consistency requirements.

[0304] The image decoding device can deduce the output time of the frame in the bitstream based on at least one of the information obtained in step S1910 and / or step S1920 (S1930). Thereafter, the image decoding device can process (output) the frame in the bitstream based on the deduced output time.

[0305] For each time sublayer in the bitstream, `fixed_pic_rate_within_cvs_flag[i]` (and / or `fixed_pic_rate_general_flag[i]`) can be signaled. In this case, `i` can be in the range of the variable `firstSubLayer` specifying the first sublayer to the variable `maxSublayers` specifying the largest sublayer. Alternatively, `i` can be in the range from 0 to `maxSublayersMinus1`. That is, for each value of `i`, `fixed_pic_rate_within_cvs_flag[i]` can be signaled, and when both `general_nal_hrd_params_present_flag` and `general_vcl_hrd_params_present_flag` are equal to the second value (e.g., 0), the constraint is that for at least one `i`, `fixed_pic_rate_within_cvs_flag[i]` equals the first value (e.g., 1).

[0306] As mentioned above, general_nal_hrd_params_present_flag and / or general_vcl_hrd_params_present_flag can be obtained from the general HRD parameter syntax structure (e.g., the general_hrd_parameters() syntax structure), and fixed_pic_rate_within_cvs_flag[i] (and / or fixed_pic_rate_general_flag[i]) can be obtained from the HRD parameter syntax structure for the output layer set (e.g., the ols_hrd_parameters() syntax structure).

[0307] Above, the variable `maxSublayers`, specifying the maximum sublayer, can be determined based on the different parameter sets used to obtain the HRD parameter syntax structure for the output layer set. Specifically, when the HRD parameter syntax structure for the output layer set is obtained from a VPS, the value of `maxSublayers` can be set to equal `vps_hrd_max_tid[i]`. When the HRD parameter syntax structure for the output layer set is obtained from an SPS, the value of `maxSublayers` can be set to equal `sps_max_sublayers_minus1`.

[0308] According to the reference Figure 19 The image decoding method described in this disclosure can provide an improved signaling mechanism capable of receiving simple timing information rather than complex HRD timing information.

[0309] Application and Implementation Methods

[0310] Although the exemplary methods of this disclosure described above are represented as a series of operations for clarity of description, they are not intended to limit the order in which the steps are performed, and these steps may be performed simultaneously or in different orders if necessary. To implement the methods according to this disclosure, the described steps may further include other steps, including steps in addition to some steps, or may include additional steps in addition to some steps.

[0311] In this disclosure, an image encoding device or an image decoding device that performs a predetermined operation (step) can perform an operation (step) that confirms the execution conditions or circumstances of the corresponding operation (step). For example, if it is described that a predetermined operation is performed when predetermined conditions are met, the image encoding device or the image decoding device can perform the predetermined operation after determining whether the predetermined conditions are met.

[0312] The various embodiments of this disclosure are not a list of all possible combinations and are intended to describe representative aspects of this disclosure; the matters described in the various embodiments may be applied independently or in combination of two or more.

[0313] Various embodiments of this disclosure can be implemented in hardware, firmware, software, or a combination thereof. When this disclosure is implemented in hardware, it can be implemented using application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), general-purpose processors, controllers, microcontrollers, microprocessors, etc.

[0314] Furthermore, the image decoding and image encoding devices applying the embodiments of this disclosure can be included in multimedia broadcasting transmitting and receiving devices, mobile communication terminals, home theater video devices, digital cinema video devices, surveillance cameras, video chat devices, real-time communication devices such as video communication, mobile streaming devices, storage media, cameras, video-on-demand (VoD) service providers, OTT (over-the-top video) devices, internet streaming service providers, three-dimensional (3D) video devices, video telephony devices, medical video devices, etc., and can be used to process video signals or data signals. For example, OTT video devices can include game consoles, Blu-ray players, internet access televisions, home theater systems, smartphones, tablet PCs, digital video recorders (DVRs), etc.

[0315] Figure 20 This is a view illustrating a content streaming system to which embodiments of the present disclosure can be applied.

[0316] like Figure 20 As shown, the content streaming system using the embodiments of this disclosure may mainly include an encoding server, a streaming server, a network server, a media storage device, a user device, and a multimedia input device.

[0317] An encoding server compresses content input from multimedia input devices such as smartphones, cameras, and camcorders into digital data to generate a bitstream, which is then sent to a streaming server. As another example, when multimedia input devices such as smartphones, cameras, and camcorders directly generate bitstreams, the encoding server can be omitted.

[0318] The bitstream can be generated by an image encoding method or image encoding device applying the embodiments of this disclosure, and the stream server can temporarily store the bitstream during the sending or receiving of the bitstream.

[0319] A streaming server sends multimedia data to a user's device based on a request from a web server, and the web server acts as a medium for informing the user of the service. When a user requests a service from the web server, the web server can deliver it to the streaming server, and the streaming server can send the multimedia data to the user. In this scenario, the content streaming system may include a separate control server. In this case, the control server is used to control the commands / responses between devices in the content streaming system.

[0320] A streaming server can receive content from media storage devices and / or encoding servers. For example, when receiving content from an encoding server, the content can be received in real time. In this case, to provide a smooth streaming service, the streaming server can store the bitstream for a predetermined period of time.

[0321] Examples of user devices may include mobile phones, smartphones, laptop computers, digital broadcasting terminals, personal digital assistants (PDAs), portable multimedia players (PMPs), navigation devices, slate PCs, tablet PCs, ultrabooks, wearable devices (e.g., smartwatches, smart glasses, head-mounted displays), digital televisions, desktop computers, digital signage, etc.

[0322] In a content streaming system, each server can operate as a distributed server, in which case the data received from each server can be distributed.

[0323] The scope of this disclosure includes software or machine-executable commands (e.g., operating systems, applications, firmware, programs, etc.) for enabling the operation of methods according to various embodiments to be executed on a device or computer, and non-transitory computer-readable media having such software or commands stored thereon and executable on a device or computer.

[0324] Industrial applicability

[0325] The embodiments disclosed herein can be used to encode or decode images.

Claims

1. An image decoding method performed by an image decoding device, the image decoding method comprising the following steps: Obtain a first flag indicating whether the HRD parameter of the specified Network Abstraction Layer (NAL) hypothetical reference decoder exists in the bitstream and a second flag indicating whether the HRD parameter of the specified Video Coding Layer (VCL) exists in the bitstream; A third flag is obtained to determine whether the time distance between the output times of consecutive frames in the specified bitstream has a fixed value; The output time of the frame in the bitstream is derived based on at least one of the first flag, the second flag, or the third flag. as well as The images in the bitstream are processed based on the derived output time. Wherein, based on the fact that the first flag has a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag has a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag is constrained to have a first value indicating that the time distance between the output times of the consecutive frames in the bitstream has a fixed value.

2. The image decoding method according to claim 1, wherein The third flag is obtained for each time sub-layer in the time sub-layer of the bitstream, and Wherein, based on the first flag having the second value and the second flag having the second value, the third flag for at least one time sub-layer in the time sub-layer of the bit stream is constrained to have the first value.

3. The image decoding method according to claim 1, wherein, The third flag is obtained by the maximum number of time sub-layers in the bitstream, and Wherein, based on the first flag having the second value and the second flag having the second value, at least one of the obtained third flags has the first value.

4. The image decoding method according to claim 3, wherein The first and second flags are obtained from the general HRD parameter syntax structure in the bitstream, and the third flag is obtained from the HRD parameter syntax structure for the output layer set.

5. The image decoding method of claim 4, wherein, The maximum number of time sublayers is determined based on the different parameter sets used to obtain the HRD parameter syntax structure for the output layer set.

6. An image encoding method performed by an image encoding device, the image encoding method comprising the following steps: A first flag is used to determine whether the HRD parameter of the specified Network Abstraction Layer (NAL) hypothetical reference decoder exists in the bitstream, and a second flag is used to determine whether the HRD parameter of the specified Video Coding Layer (VCL) exists in the bitstream; as well as A third flag determines whether the time interval between the output times of consecutive frames in the specified bitstream has a fixed value. The output time of the frames in the bitstream is derived based on at least one of the first flag, the second flag, or the third flag. Specifically, the images in the bitstream are processed based on the derived output time. Wherein, based on the fact that the first flag has a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag has a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag is constrained to have a first value indicating that the time distance between the output times of the consecutive frames in the bitstream has a fixed value.

7. The image encoding method according to claim 6, wherein The third flag is determined for each time sub-layer in the time sub-layer of the bitstream, and Wherein, based on the first flag having the second value and the second flag having the second value, the third flag for at least one time sub-layer in the time sub-layer of the bit stream is constrained to have the first value.

8. The image encoding method according to claim 6, wherein, The third flag is determined by the maximum number of time sub-layers in the bitstream, and Wherein, based on the first flag having the second value and the second flag having the second value, at least one of the determined third flags has the first value.

9. The image coding method of claim 8, wherein, The first and second flags are encoded in a general HRD parameter syntax structure in the bitstream, and the third flag is encoded in an HRD parameter syntax structure for the output layer set.

10. The image coding method of claim 9, wherein, The maximum number of time sublayers is determined based on the different parameter sets to which the HRD parameter syntax structure for the output layer set is encoded.

11. A method for transmitting a bit stream, the method comprising the following steps: The bitstream is generated by performing an image encoding method; as well as Transmit the bit stream, The image encoding method includes the following steps: Determine a first flag indicating whether the HRD parameter of the specified Network Abstraction Layer (NAL) hypothetical reference decoder exists in the bitstream and a second flag indicating whether the HRD parameter of the specified Video Coding Layer (VCL) exists in the bitstream; and A third flag determines whether the time interval between the output times of consecutive frames in the specified bitstream has a fixed value. The output time of the frames in the bitstream is derived based on at least one of the first flag, the second flag, or the third flag. Specifically, the images in the bitstream are processed based on the derived output time, and Wherein, based on the fact that the first flag has a second value indicating that the NAL HRD parameter does not exist in the bitstream and the second flag has a second value indicating that the VCL HRD parameter does not exist in the bitstream, the third flag is constrained to have a first value indicating that the time distance between the output times of the consecutive frames in the bitstream has a fixed value.

Images