Video coding method and device using motion vector difference

Abstract

To provide video coding method and device.SOLUTION: In a video coding method according to an embodiment, a prediction procedure can be performed for video / video coding, and includes MMVD (Merge Mode Motion Vector Differences) and SMVD (Symmetric Motion Vector Differences) using inter prediction. The inter prediction is performed on the basis of a current picture reference picture, and the type of reference picture (for example, a long-term reference picture, a short-term reference picture, etc.) may be considered for inter prediction. Therefore, the performance and the coding efficiency in the prediction procedure can be increased.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] This document relates to a video coding method and apparatus using motion vector difference.

Background Art

[0002] In recent years, the demand for high-resolution and high-quality images / videos such as 4K or 8K and above UHD (Ultra High Definition) images / videos has been increasing in various fields. As the image / video data becomes higher in resolution and quality, the amount of information or bits transmitted relatively increases compared to the existing image / video data. Therefore, when transmitting image data using a medium such as an existing wired or wireless broadband line, or storing image / video data using an existing storage medium, the transmission cost and storage cost increase.

[0003] Also, in recent years, the interest and demand for immersive media such as VR (Virtual Reality), AR (Artificial Reality) contents, and holograms have been increasing, and the broadcasting of images / videos having image characteristics different from real images, such as game images, has been increasing.

[0004] Accordingly, in order to effectively compress, transmit, store, and reproduce the information of high-resolution and high-quality images / videos having various characteristics as described above, a highly efficient image / video compression technology is required.

[0005] In particular, inter prediction in video / video coding can utilize motion vector difference. In relation to the above procedure, there is a discussion on deriving motion vector difference based on a reference picture type (for example, a short-term or long-term reference picture).

Summary of the Invention

Means for Solving the Problems

[0006] According to one embodiment of this document, a method and an apparatus for improving video coding efficiency are provided.

[0007] According to one embodiment of this document, a method and an apparatus for performing efficient inter prediction in a video coding system are provided.

[0008] According to one embodiment of this document, a method and an apparatus for signaling information related to motion vector difference in inter prediction are provided.

[0009] According to one embodiment of this document, when dual prediction is applied to a current block, a method and an apparatus for signaling information related to L0 motion vector difference and L1 motion vector difference are provided.

[0010] According to an embodiment of this document, a method and an apparatus for signaling an SMVD flag are provided.

[0011] According to one embodiment of this document, a specific reference picture type is used for deriving symmetric motion vector difference.

[0012] According to one embodiment of this document, a procedure for deriving an SMVD reference index is performed using a short-term reference picture (a picture marked as being used for short-term reference).

[0013] According to one embodiment of this document, a video decoding method executed by a decoding apparatus is provided.

[0014] According to one embodiment of this document, a decoding apparatus for performing video decoding is provided.

[0015] According to one embodiment of this document, a video encoding method executed by an encoding apparatus is provided.

[0016] According to one embodiment of this document, an encoding device that performs video / video encoding is provided.

[0017] According to one embodiment of this document, a computer-readable digital storage medium storing encoded video / video information generated by a video / video encoding method disclosed in at least one of the embodiments of this document is provided.

[0018] According to one embodiment of this document, a computer-readable digital storage medium storing encoded information or encoded video / video information for executing a video / video decoding method disclosed in at least one of the embodiments of this document by a decoding device is provided.

Advantages of the Invention

[0019] According to this document, the overall video / video compression efficiency can be increased.

[0020] According to this document, information regarding motion vector differences can be efficiently signaled.

[0021] According to this document, when dual prediction is applied to the current block, the L1 motion vector difference can be efficiently derived.

[0022] According to this document, the information used for deriving the L1 motion vector difference is signaled based on the type of reference picture, and thus the complexity of the coding system can be reduced.

[0023] According to the embodiment of this document, efficient inter prediction can be performed by using a specific reference picture type for deriving the reference picture index for SMVD.

[0024] The effects that can be obtained through a specific example of this document are not limited to the effects listed above. For example, there may be various technical effects that can be understood or induced by a person having ordinary skill in the related art from this document. Accordingly, the specific effects of this document can include various effects that can be understood or induced from the technical features of this document, rather than being limited to those explicitly described in this document. Brief Description of the Drawings

[0025]

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Mode for Carrying Out the Invention

[0026] The disclosure of this document can be modified in various ways and can have various embodiments, but specific embodiments are illustrated in the drawings and will be described in detail. However, this is not intended to limit the present disclosure to specific embodiments. The terms used in this document are merely used to describe specific embodiments and are not intended to limit the technical idea of the embodiments in this document. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this document, terms such as "including" or "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the document, and should be understood not to preclude in advance the presence or addition of one or more different features, numbers, steps, operations, components, parts, or combinations thereof.

[0027] On the one hand, each component in the drawings described in this document is shown independently for the convenience of explaining different characteristic functions, and it does not mean that each component is implemented by separate hardware or separate software. For example, among the components, two or more components may be combined to form one component, and one component may be divided into multiple components. Examples in which each component is integrated and / or separated are also included in the disclosure scope of this document.

[0028] Hereinafter, with reference to the accompanying drawings, examples of this document will be described. Hereinafter, the same reference numerals may be used for the same components on the drawings, and duplicate descriptions for the same components may be omitted.

[0029] FIG. 1 schematically shows an example of a video / image coding system to which the examples of this document can be applied.

[0030] As shown in FIG. 1, the video / image coding system can include a first device (source device) and a second device (receiver device). The source device can transmit encoded video / image information or data to the receiver device via a digital storage medium or a network in a file or streaming form.

[0031] The source device can include a video source, an encoding device, and a transmission unit. The receiver device can include a reception unit, a decoding device, and a renderer. The encoding device can be called a video / image encoding device, and the decoding device can be called a video / image decoding device. A transmitter can be provided in the encoding device. A receiver can be provided in the decoding device. The renderer can include a display unit, and the display unit can also be composed of a separate device or an external component.

[0032] The video source can obtain video / video through processes such as video / video capture, synthesis, or generation (processing). The video source can include a video / video capture device and / or a video / video generation device. The video / video capture device can include, for example, one or more cameras, a video / video archive containing previously captured video / video, and the like. The video / video generation device can include, for example, a computer, a tablet, or a smartphone, etc., and can generate (electronically) video / video. For example, virtual video / video can be generated via a computer or the like, and in this case, the video / video capture process can be replaced by the process of generating related data.

[0033] The encoding device can encode the input video / video. The encoding device can perform a series of procedures such as prediction, transformation, quantization, etc. for compression and coding efficiency. The encoded data (encoded video / video information) can be output in the form of a bitstream.

[0034] The transmission unit can transmit the encoded video / video information or data output in the form of a bitstream to the receiving unit of the receiving device via a digital storage medium or a network in the form of a file or a stream. The digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. The transmission unit can include elements for generating a media file via a predetermined file format and can include elements for transmission via a broadcast / communication network. The receiving unit can receive / extract the above bitstream and transmit it to the decoding device.

[0035] The decoding device can decode the video / video by performing a series of procedures such as inverse quantization, inverse transformation, prediction, etc. corresponding to the operation of the encoding device.

[0036] The renderer can render the decoded video / video image. The rendered video / video image can be displayed (presented) via the display unit.

[0037] This document relates to video / video image coding. For example, the methods / embodiments disclosed in this document can be applied to the methods disclosed in the VVC (Versatile Video Coding) standard. Also, the methods / embodiments disclosed in this document can be applied to the methods disclosed in the EVC (Essential Video Coding) standard, the AV1 (AOMedia Video 1) standard, the AVS2 (2nd generation of Audio Video Coding Standard), or next-generation video / video image coding standards (e.g., 267 or H.268, etc.).

[0038] This document presents various embodiments related to video / video image coding, and unless otherwise mentioned, the above embodiments may be combined with each other.

[0039] In this document, a video can mean a collection of a series of images over time. A picture generally means a unit indicating one image at a specific time (period), and a slice / tile is a unit that constitutes a part of a picture in coding. A slice / tile can include one or more CTUs (Coding Tree Units). One picture can be composed of one or more slices / tiles. A tile is a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. The tile column is a rectangular region of CTUs having a height equal to the height of the picture and a width that can be specified by syntax elements in the picture parameter set. The tile row is a rectangular region of CTUs having a width specified by syntax elements in the picture parameter set and a height that can be the same as the height of the picture.A tile scan may indicate a specific sequential ordering of CTUs partitioning a picture, where the CTUs may be ordered consecutively in a CTU raster scan within a tile, and tiles within a picture may be ordered consecutively in a raster scan of the tiles of the picture. A slice may include an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile of a picture that may be exclusively contained in a single NAL unit.

[0040] On the other hand, one picture can be divided into two or more sub-pictures. A sub-picture can be a rectangular region of one or more slices within a picture.

[0041] A pixel or pel can mean the smallest unit that makes up one picture (or video). Also, as a term corresponding to a pixel, "sample" can be used. A sample can generally indicate a pixel or a pixel value, can indicate only the pixel / pixel value of the luma component, or can also indicate only the pixel / pixel value of the chroma component.

[0042] A unit can indicate the basic unit of video processing. A unit can include at least one of a specific area of a picture and information related to that area. One unit can include one luma block and two chroma (e.g., cb, cr) blocks. A unit can, in some cases, be used interchangeably with terms such as "block" or "area". In general, an M×N block can include a set (or array) of samples (or sample array) or transform coefficients consisting of M columns and N rows.

[0043] In this document, "A or B" can mean "only A", "only B", or "both A and B". In other words, in this document, "A or B" can be interpreted as "A and / or B". For example, in this document, "A, B or C" can mean "only A", "only B", "only C", or "any combination of A, B and C".

[0044] The slashes ( / ) and commas used in this document can mean "and / or". For example, "A / B" can mean "A and / or B". Thus, "A / B" can mean "only A", "only B", or "both A and B". For example, "A, B, C" can mean "A, B or C".

[0045] In this document, "at least one of A and B" may mean "only A", "only B", or "both A and B". Also, in this document, expressions such as "at least one of A or B" and "at least one of A and / or B" may be interpreted in the same way as "at least one of A and B".

[0046] Also, in this document, "at least one of A, B and C" may mean "only A", "only B", "only C", or "any combination of A, B and C". Also, "at least one of A, B or C" and "at least one of A, B and / or C" may mean "at least one of A, B and C".

[0047] Also, the parentheses used in this document may mean "for example". Specifically, when it is displayed as "prediction (intra prediction)", "intra prediction" may be proposed as an example of "prediction". In other words, "prediction" in this document is not limited to "intra prediction", and "intra prediction" may be proposed as an example of "prediction". Also, when it is displayed as "prediction (that is, intra prediction)", "intra prediction" may be proposed as an example of "prediction".

[0048] The technical features separately described within one drawing in this document may be embodied separately or simultaneously.

[0049] Figure 2 is a diagram schematically explaining the configuration of a video / video encoding device to which the embodiments of this document can be applied. Hereinafter, the encoding device can include a video encoding device and / or a video encoding device.

[0050] As shown in FIG. 2, the encoding device 200 can be configured to include an image partitioner 210, a predictor 220, a residual processor 230, an entropy encoder 240, an adder 250, a filter 260, and a memory 270. The predictor 220 can include an inter-prediction unit 221 and an intra-prediction unit 222. The residual processor 230 can include a transformer 232, a quantizer 233, a dequantizer 234, and an inverse transformer 235. The residual processor 230 can further include a subtractor (231). The adder 250 can be called a reconstructor or a reconstructed block generator. The above-described video splitter 210, predictor 220, residual processor 230, entropy encoder 240, adder 250, and filtering unit 260 can be configured by one or more hardware components (for example, an encoder chipset or a processor) according to the embodiment. Further, the memory 270 can include a DPB (Decoded Picture Buffer) and can also be configured by a digital storage medium. The above hardware components can further include the memory 270 as an internal / external component.

[0051] The video segmentation unit 210 can divide the input video (or picture, frame) input to the encoding device 200 into one or more processing units. As an example, the processing unit can be called a coding unit (CU). In this case, the coding unit can be recursively divided from a coding tree unit (CTU) or a largest coding unit (LCU) by a QTBTTT (Quad-Tree Binary-Tree Ternary-Tree) structure. For example, one coding unit can be divided into multiple coding units with a deeper depth based on a quad-tree structure, a binary-tree structure, and / or a ternary-tree structure. In this case, for example, the quad-tree structure can be applied first, and then the binary-tree structure and / or the ternary-tree structure can be applied. Alternatively, the binary-tree structure can also be applied first. The coding procedure according to the present disclosure can be performed based on the final coding unit that cannot be further divided. In this case, based on the coding efficiency according to the video characteristics, etc., the largest coding unit can be used as the final coding unit, or, if necessary, the coding unit can be recursively divided into coding units with a deeper depth so that the coding unit with an optimal size can be used as the final coding unit. Here, the coding procedure can include procedures such as prediction, conversion, and restoration, which will be described later. As another example, the processing unit can further include a prediction unit (PU: Prediction Unit) or a transform unit (TU: Transform Unit). In this case, the prediction unit and the transform unit can each be divided or partitioned from the final coding unit described above.The prediction unit can be a unit of sample prediction, and the conversion unit can be a unit for deriving a conversion coefficient and / or a unit for deriving a residual signal from the conversion coefficient.

[0052] The term "unit" can, in some cases, be used interchangeably with terms such as "block" or "area". In general, an M×N block can represent a set of samples or transform coefficients consisting of M columns and N rows. A sample can generally represent a pixel or a pixel value, and can represent only the pixel / pixel value of the luma component, or only the pixel / pixel value of the chroma component. A sample can be used as a term corresponding to a pixel or a pel in one picture (or video).

[0053] The encoding device 200 can subtract a prediction signal (predicted block, predicted sample array) output from the inter prediction unit 221 or the intra prediction unit 222 from an input video signal (original block, original sample array) to generate a residual signal (residual signal, residual block, residual sample array), and the generated residual signal is transmitted to the conversion unit 232. In this case, as shown in the figure, the unit that subtracts the prediction signal (predicted block, predicted sample array) from the input video signal (original block, original sample array) within the encoder 200 can be called the subtraction unit 231. The prediction unit can perform prediction on a block to be processed (hereinafter referred to as the current block) and generate a predicted block including predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied in units of the current block or CU. The prediction unit can generate various pieces of information related to prediction, such as prediction mode information, and transmit them to the entropy encoding unit 240 as described later in the description of each prediction mode. The information related to prediction can be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0054] The intra prediction unit 222 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located in the neighborhood of the current block according to the prediction mode, or can also be located remotely. In intra prediction, the prediction mode can include a plurality of non-directional modes and a plurality of directional modes. The non-directional modes can include, for example, the DC mode and the planar mode. The directional modes can include, for example, 33 directional prediction modes or 65 directional prediction modes depending on the degree of fineness of the prediction direction. However, this is only an example, and more or fewer directional prediction modes can be used depending on the setting. The intra prediction unit 222 can also determine the prediction mode to be applied to the current block by using the prediction mode applied to the neighboring blocks.

[0055] The inter prediction unit 221 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on the reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The motion information can include a motion vector and a reference picture index. The motion information can further include inter prediction direction (L0 prediction, L1 prediction, BI prediction, etc.) information. In the case of inter prediction, the neighboring blocks can include spatial neighboring blocks existing in the current picture and temporal neighboring blocks existing in the reference picture. The reference picture including the reference block and the reference picture including the temporal neighboring block can be the same or different. The temporal neighboring blocks can be called by names such as collocated reference blocks, collocated CUs (col CUs), etc., and the reference picture including the temporal neighboring blocks can also be called a collocated picture (colPic). For example, the inter prediction unit 221 can construct a motion information candidate list based on the neighboring blocks, and generate information indicating which candidate is used to derive the motion vector and / or reference picture index of the current block. Inter prediction can be performed based on various prediction modes. For example, in the case of the skip mode and the merge mode, the inter prediction unit 221 can use the motion information of the neighboring blocks as the motion information of the current block. In the case of the skip mode, unlike the merge mode, the residual signal may not be transmitted.In the case of the Motion Vector Prediction (MVP) mode, the motion vector of a neighboring block is used as a motion vector predictor, and the motion vector difference is signaled to indicate the motion vector of the current block.

[0056] The prediction unit 220 can generate a prediction signal based on various prediction methods described later. For example, the prediction unit can apply not only intra prediction or inter prediction for the prediction of one block, but also apply intra prediction and inter prediction simultaneously. This can be called Combined Inter and Intra Prediction (CIIP). Also, the prediction unit can be based on the Intra Block Copy (IBC) prediction mode for the prediction of a block, or can be based on the palette mode. The above IBC prediction mode or palette mode can be used for content video / movie coding such as games, for example, like SCC (Screen Content Coding). IBC basically performs prediction within the current picture, but can be performed in the same way as inter prediction in terms of deriving a reference block within the current picture. That is, IBC can use at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, the sample values within the picture can be signaled based on the information regarding the palette table and the palette index.

[0057] The prediction signal generated via the above prediction unit (including the inter prediction unit 221 and / or the intra prediction unit 222) can be used to generate a restored signal or can be used to generate a residual signal. The conversion unit 232 can apply a conversion technique to the residual signal to generate transform coefficients. For example, the conversion technique can include at least one of DCT (Discrete Cosine Transform), DST (Discrete Sine Transform), GBT (Graph-Based Transform), and CNT (Conditionally Non-linear Transform). Here, GBT means a transform obtained from a graph when representing the relationship information between pixels by a graph. CNT means a transform obtained based on generating a prediction signal using all previously reconstructed pixels. Further, the conversion process may be applied to a pixel block having the same size of a square or may be applied to a block of a variable size that is not a square.

[0058] The quantization unit 233 quantizes the transform coefficients and transmits them to the entropy encoding unit 240. The entropy encoding unit 240 can encode the quantized signal (information regarding the quantized transform coefficients) and output it as a bitstream. The information regarding the quantized transform coefficients can be called residual information. The quantization unit 233 can reorder the block-form quantized transform coefficients in a one-dimensional vector form based on the coefficient scan order, and can also generate the information regarding the quantized transform coefficients based on the quantized transform coefficients in the one-dimensional vector form. The entropy encoding unit 240 can perform various encoding methods such as, for example, exponential Golomb, CAVLC (Context-Adaptive Variable Length Coding), CABAC (Context-Adaptive Binary Arithmetic Coding). In addition to the quantized transform coefficients, the entropy encoding unit 240 can also encode, together or separately, information necessary for video / image restoration (such as the values of syntax elements). The encoded information (such as the encoded video / video information) can be transmitted or stored in units of NAL (Network Abstraction Layer) units in bitstream form. The video / video information can further include information regarding various parameter sets such as an Adaptation Parameter Set (APS), a Picture Parameter Set (PPS), a Sequence Parameter Set (SPS), or a Video Parameter Set (VPS). Also, the video / video information can further include general constraint information. In this document, the information and / or syntax elements transmitted / signaled from the encoding device to the decoding device can be included in the video / video information. The video / video information can be encoded through the above-described encoding procedure and included in the above bitstream.The above bitstream can be transmitted via a network or stored in a digital storage medium. Here, the network can include a broadcast network and / or a communication network, etc., and the digital storage medium can include various storage media such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, etc. A transmitting unit (not shown) for transmitting and / or a storage unit (not shown) for storing the signal output from the entropy encoding unit 240 can be configured as internal / external elements of the encoding device 200, or the transmitting unit can also be included in the entropy encoding unit 240.

[0059] The quantized transform coefficients output from the quantization unit 233 can be used to generate a prediction signal. For example, by applying inverse quantization and inverse transformation to the quantized transform coefficients via the inverse quantization unit 234 and the inverse transformation unit 235, a residual signal (residual block or residual sample) can be restored. The addition unit 155 can generate a reconstructed signal (reconstructed picture, reconstructed block, reconstructed sample array) by adding the restored residual signal to the prediction signal output from the inter prediction unit 221 or the intra prediction unit 222. When there is no residual for the block to be processed, as in the case where the skip mode is applied, the predicted block can be used as the reconstructed block. The addition unit 250 can be called a restoration unit or a reconstructed block generation unit. The generated reconstructed signal can be used for intra prediction of the next block to be processed within the current picture, and as will be described later, can also be used for inter prediction of the next picture after passing through filtering.

[0060] On the other hand, LMCS (Luma Mapping With Chroma Scaling) can also be applied in the picture encoding and / or restoration process.

[0061] The filtering unit 260 can apply filtering to the restored signal to improve subjective / objective image quality. For example, the filtering unit 260 can apply various filtering methods to the restored picture to generate a modified restored picture, and store the modified restored picture in the memory 270, specifically, in the DPB of the memory 270. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc. The filtering unit 260 can generate various information related to filtering and transmit it to the entropy encoding unit 240, as will be described later in the description of each filtering method. The information related to filtering can be encoded by the entropy encoding unit 240 and output in the form of a bitstream.

[0062] The modified restored picture transmitted to the memory 270 can be used as a reference picture in the inter prediction unit 221. When inter prediction is applied through this, the encoding device can avoid prediction mismatches between the encoding device 100 and the decoding device, and can also improve the encoding efficiency.

[0063] The DPB of the memory 270 can store the modified restored picture for use as a reference picture in the inter prediction unit 221. The memory 270 can store the motion information of the blocks where the motion information within the current picture has been derived (or encoded) and / or the motion information of the blocks within the already restored picture. The stored motion information can be transmitted to the inter prediction unit 221 for utilization as the motion information of spatial neighboring blocks or temporal neighboring blocks. The memory 270 can store the restored samples of the restored blocks within the current picture and transmit them to the intra prediction unit 222.

[0064] FIG. 3 is a diagram schematically illustrating the configuration of a video / video decoding apparatus to which an embodiment of this document can be applied. Hereinafter, the decoding apparatus can include a video decoding apparatus and / or a video decoding apparatus.

[0065] As shown in FIG. 3, the decoding apparatus 300 can be configured to include an entropy decoder 310, a residual processor 320, a predictor 330, an adder 340, a filtering unit 350, and a memory 360. The predictor 330 can include an intra predictor 331 and an inter predictor 332. The residual processor 320 can include a dequantizer 321 and an inverse transformer 321. The above-described entropy decoder 310, residual processor 320, predictor 330, adder 340, and filtering unit 350 can be configured by one hardware component (e.g., a decoder chipset or a processor) according to an embodiment. Further, the memory 360 can include a DPB (Decoded Picture Buffer) and can also be configured by a digital storage medium. The above hardware component can further include the memory 360 as an internal / external component.

[0066] When a bitstream including video / video information is input, the decoding device 300 can restore the video corresponding to the process in which the video / video information was processed by the encoding device of FIG. 3. For example, the decoding device 300 can derive units / blocks based on the block division related information obtained from the above bitstream. The decoding device 300 can perform decoding using the processing unit applied in the encoding device. Therefore, the processing unit for decoding can be, for example, a coding unit, and the coding unit can be divided from a coding tree unit or a maximum coding unit according to a quadtree structure, a binary tree structure, and / or a ternary tree structure. One or more transform units can be derived from the coding unit. Then, the restored video signal decoded and output via the decoding device 300 can be played back via a playback device.

[0067] The decoding device 300 can receive the signal output from the encoding device in FIG. 3 in the form of a bitstream, and the received signal can be decoded via the entropy decoding unit 310. For example, the entropy decoding unit 310 can parse the above bitstream to derive information (e.g., video / video information) necessary for video restoration (or picture restoration). The above video / video information can further include information regarding various parameter sets such as an adaptation parameter set (APS), a picture parameter set (PPS), a sequence parameter set (SPS), or a video parameter set (VPS). Further, the above video / video information can further include general constraint information. The decoding device can further decode a picture based on the information regarding the above parameter set and / or the above general constraint information. The signaling / received information and / or syntax elements described later in this document can be decoded via the above decoding procedure and obtained from the above bitstream. For example, the entropy decoding unit 310 can decode the information in the bitstream based on a coding method such as exponential Golomb coding, CAVLC, or CABAC, and output the value of the syntax element necessary for video restoration and the quantized value of the transform coefficient regarding the residual. More specifically, the CABAC entropy decoding method receives the bin corresponding to each syntax element in the bitstream, determines a context model using the syntax element information to be decoded and the decoding information of the adjacent and decoding target blocks or the information of the symbol / bin decoded in the previous step, predicts the occurrence probability of the bin by the determined context model, performs arithmetic decoding of the bin, and can generate a symbol corresponding to the value of each syntax element.At this time, the CABAC entropy decoding method can update the context model by using the information of the decoded symbol / bin for the next symbol / bin context model after determining the context model. Among the information decoded by the entropy decoding unit 310, the information related to prediction is provided to the prediction unit (inter prediction unit 332 and intra prediction unit 331), and the residual value obtained by performing entropy decoding by the entropy decoding unit 310, that is, the quantized transform coefficient and related parameter information, can be input to the residual processing unit 320. The residual processing unit 320 can derive a residual signal (residual block, residual sample, residual sample array). Also, among the information decoded by the entropy decoding unit 310, the information related to filtering can be provided to the filtering unit 350. On the other hand, a receiving unit (not shown) that receives the signal output from the encoding device can be further configured as an internal / external element of the decoding device 300, or the receiving unit can also be a component of the entropy decoding unit 310. On the other hand, the decoding device according to this document can be called a video / video / picture decoding device, and the above decoding device can also be classified into an information decoder (video / video / picture information decoder) and a sample decoder (video / video / picture sample decoder). The above information decoder can include the above entropy decoding unit 310, and the above sample decoder can include at least one of the above inverse quantization unit 321, inverse transform unit 322, addition unit 340, filtering unit 350, memory 360, inter prediction unit 332, and intra prediction unit 331.

[0068] In the inverse quantization unit 321, the quantized transform coefficients can be inverse quantized to output transform coefficients. The inverse quantization unit 321 can reorder the quantized transform coefficients in a two-dimensional block form. In this case, the above reordering can be performed based on the coefficient scan order performed by the encoding device. The inverse quantization unit 321 can perform inverse quantization on the quantized transform coefficients using quantization parameters (for example, quantization step size information) to obtain transform coefficients.

[0069] In the inverse transform unit 322, the transform coefficients are inverse transformed to obtain a residual signal (residual block, residual sample array).

[0070] The prediction unit can perform prediction on the current block and generate a predicted block including predicted samples for the current block. The prediction unit can determine whether intra prediction or inter prediction is applied to the current block based on the information regarding the prediction output from the entropy decoding unit 310, and can determine a specific intra / inter prediction mode.

[0071] The prediction unit 330 can generate a prediction signal based on various prediction methods described below. For example, for the prediction of one block, the prediction unit can apply not only intra prediction or inter prediction, but also can apply intra prediction and inter prediction simultaneously. This can be called Combined Inter and Intra Prediction (CIIP). Also, the prediction unit can be based on the Intra Block Copy (IBC) prediction mode or the palette mode for the prediction of a block. The above IBC prediction mode or palette mode can be used for content video / moving picture coding such as games, for example, like SCC (Screen Content Coding). IBC basically performs prediction within the current picture, but can be performed in the same way as inter prediction in terms of deriving a reference block within the current picture. That is, IBC can utilize at least one of the inter prediction techniques described in this document. The palette mode can be regarded as an example of intra coding or intra prediction. When the palette mode is applied, information regarding the palette table and palette index can be included in and signaled in the above video / video information.

[0072] The intra prediction unit 331 can predict the current block by referring to samples within the current picture. The samples to be referred to can be located around (neighbor) the current block or can be located far away depending on the prediction mode. In intra prediction, the prediction mode can include a plurality of non-directional modes and a plurality of directional modes. The intra prediction unit 331 can also determine the prediction mode to be applied to the current block using the prediction mode applied to the surrounding blocks.

[0073] The inter prediction unit 332 can derive a predicted block for the current block based on a reference block (reference sample array) specified by a motion vector on a reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information can be predicted in units of blocks, sub-blocks, or samples based on the correlation of motion information between neighboring blocks and the current block. The above motion information can include a motion vector and a reference picture index. The above motion information can further include inter prediction direction (L0 prediction, L1 prediction, BI prediction, etc.) information. In the case of inter prediction, the neighboring blocks can include spatial neighboring blocks existing within the current picture and temporal neighboring blocks existing in the reference picture. For example, the inter prediction unit 332 can construct a motion information candidate list based on neighboring blocks, and derive the motion vector and / or reference picture index of the current block based on the received candidate selection information. Inter prediction can be performed based on various prediction modes, and the information regarding the prediction can include information indicating the mode of inter prediction for the current block.

[0074] The addition unit 340 can generate a restored signal (restored picture, restored block, restored sample array) by adding the obtained residual signal to the prediction signal (predicted block, predicted sample array) output from the prediction unit (including the inter prediction unit 332 and / or the intra prediction unit 331). When there is no residual for the processing target block, as in the case where the skip mode is applied, the predicted block can be used as the restored block.

[0075] The addition unit 340 can be referred to as a restoration unit or a restoration block generation unit. The generated restoration signal can be used for intra prediction of the next processing target block within the current picture, and as will be described later, can be output after filtering, or can also be used for inter prediction of the next picture.

[0076] On the other hand, LMCS (Luma Mapping with Chroma Scaling) can also be applied during the picture decoding process.

[0077] The filtering unit 350 can apply filtering to the restoration signal to improve subjective / objective image quality. For example, the filtering unit 350 can apply various filtering methods to the restored picture to generate a modified restored picture, and can transmit the modified restored picture to the memory 360, specifically, to the DPB of the memory 360. The various filtering methods can include, for example, deblocking filtering, sample adaptive offset, adaptive loop filter, bilateral filter, etc.

[0078] The (modified) restored picture stored in the DPB of the memory 360 can be used as a reference picture in the inter prediction unit 332. The memory 360 can store the motion information of the blocks for which the motion information in the current picture has been derived (or decoded) and / or the motion information of the blocks in the already restored picture. The stored motion information can be transmitted to the inter prediction unit 260 for utilization as the motion information of spatial neighboring blocks or temporal neighboring blocks. The memory 360 can store the restored samples of the restored blocks in the current picture and can transmit them to the intra prediction unit 331.

[0079] In this specification, the embodiments described in the filtering unit 260, the inter prediction unit 221, and the intra prediction unit 222 of the encoding device 200 can be applied to the filtering unit 350, the inter prediction unit 332, and the intra prediction unit 331 of the decoding device 300 in the same or corresponding manner, respectively.

[0080] As described above, when performing video coding, prediction is performed to improve the compression efficiency. Through this, a predicted block including prediction samples for the current block, which is the block to be coded, can be generated. Here, the predicted block includes prediction samples in the spatial domain (domain) (or pixel domain). The predicted block is derived in the same way in the encoding device and the decoding device, and the encoding device can improve the video coding efficiency by signaling information (residual information) regarding the residual between the original block and the predicted block, rather than the original sample values of the original block, to the decoding device. The decoding device can derive a residual block including residual samples based on the residual information, and combine the residual block and the predicted block to generate a restored block including restored samples, and can generate a restored picture including the restored block.

[0081] The residual information can be generated through transformation and quantization procedures. For example, an encoding device can derive a residual block between the original block and the predicted block, execute a transformation procedure on the residual samples (residual sample array) included in the residual block to derive transformation coefficients, and execute a quantization procedure on the transformation coefficients to derive quantized transformation coefficients, so as to signal (via a bitstream) the relevant residual information to a decoding device. Here, the residual information can include information such as the value information, position information, transformation technique, transformation kernel, quantization parameter, etc. of the quantized transformation coefficients. The decoding device can execute an inverse quantization / inverse transformation procedure based on the residual information to derive residual samples (or a residual block). The decoding device can generate a restored picture based on the predicted block and the residual block. Also, the encoding device can inverse quantize / inverse transform the quantized transformation coefficients for reference in the inter prediction of subsequent pictures to derive a residual block, and generate a restored picture based on this.

[0082] In this document, at least one of quantization / inverse quantization and / or transformation / inverse transformation can be omitted. When the quantization / inverse quantization is omitted, the quantized transformation coefficients can be referred to as transformation coefficients. When the transformation / inverse transformation is omitted, the transformation coefficients can also be referred to as coefficients or residual coefficients, or, for the sake of consistency of expression, can still be referred to as transformation coefficients.

[0083] In this document, the quantized transform coefficients and the transform coefficients can each be referred to as transform coefficients and scaled transform coefficients, respectively. In this case, the residual information can include information regarding the transform coefficient(s), and the information regarding the transform coefficient(s) can be signaled via a residual coding syntax. The transform coefficients can be derived based on the residual information (or the information regarding the transform coefficient(s)), and the scaled transform coefficients can be derived via an inverse transform (scaling) for the transform coefficients. The residual samples can be derived based on an inverse transform (transformation) for the scaled transform coefficients. This can be applied / expressed similarly in other parts of this document.

[0084] Intra prediction can indicate a prediction that generates prediction samples for a current block based on reference samples within a picture (hereinafter referred to as the current picture) to which the current block belongs. When intra prediction is applied to the current block, the neighboring reference samples used for intra prediction of the current block can be derived. The neighboring reference samples of the current block can include a total of 2×nH samples adjacent to the left boundary of the current block of size nW×nH and adjacent to the bottom-left, samples adjacent to the top boundary of the current block and a total of 2×nW samples adjacent to the top-right, and one sample adjacent to the top-left of the current block. Alternatively, the neighboring reference samples of the current block can also include a plurality of columns of upper neighboring samples and a plurality of rows of left neighboring samples. Also, the neighboring reference samples of the current block can include a total of nH samples adjacent to the right boundary of the current block of size nW×nH, a total of nW samples adjacent to the bottom boundary of the current block, and one sample adjacent to the bottom-right of the current block.

[0085] However, some of the neighboring reference samples of the current block may not have been decoded yet or may not be available. In this case, the decoder can substitute unavailable samples with available samples to form the neighboring reference samples used for prediction. Alternatively, the decoder can form the neighboring reference samples used for prediction through interpolation of available samples.

[0086] When the neighboring reference samples are derived, (i) the predicted samples can be derived based on the average or interpolation of the neighboring reference samples of the current block, and (ii) the predicted samples can also be derived based on the reference samples that exist in a specific (predicted) direction with respect to the predicted samples among the neighboring reference samples of the current block. In the case of (i), it is called a non-directional mode or a non-angular mode, and in the case of (ii), it can be called a directional mode or an angular mode.

[0087] Also, based on the predicted samples of the current block among the neighboring reference samples, the predicted samples can be generated through interpolation between a first neighboring sample located in the prediction direction of the intra prediction mode of the current block and a second neighboring sample located in the opposite direction of the prediction direction. In the case described above, it can be called Linear Interpolation Intra Prediction (LIP). Also, chroma predicted samples can be generated based on luma samples using a linear model. In this case, it can be called the LM mode.

[0088] Also, a temporary prediction sample of the current block is derived based on the filtered peripheral reference samples, and a weighted sum of the existing peripheral reference samples, i.e., at least one reference sample derived by the intra prediction mode among the non-filtered peripheral reference samples and the temporary prediction sample, is calculated to derive the prediction sample of the current block. In the case described above, it can be called PDPC (Position Dependent Intra Prediction).

[0089] Also, the reference sample line with the highest prediction accuracy among the peripheral multi-reference sample lines of the current block is selected, and a prediction sample is derived using the reference sample located in the prediction direction on the corresponding line. At this time, intra prediction coding can be performed by indicating (signaling) the used reference sample line to the decoding device. In the case described above, it can be called multi-reference line intra prediction or MRL-based intra prediction.

[0090] Also, the current block is divided into vertical or horizontal sub-partitions, and intra prediction is performed based on the same intra prediction mode. Peripheral reference samples can be derived and used in units of the sub-partitions. That is, in this case, the intra prediction mode for the current block is also applied to the sub-partitions, and by deriving and using peripheral reference samples in units of the sub-partitions, the intra prediction performance can be enhanced in some cases. Such a prediction method can be called intra prediction based on ISP (Intra Sub-Partitions).

[0091] The intra prediction method described above can be called an intra prediction type, distinguished from the intra prediction mode. The above intra prediction type can be called by various terms such as an intra prediction technique or an additional intra prediction mode. For example, the above intra prediction type (or an additional intra prediction mode, etc.) can include at least one of the LIP, PDPC, MRL, and ISP described above. A general intra prediction method excluding specific intra prediction types such as the above LIP, PDPC, MRL, and ISP can be called a normal intra prediction type. The normal intra prediction type can be generally applied when the above specific intra prediction types are not applicable, and prediction can be performed based on the intra prediction mode described above. On the other hand, if necessary, post-processing filtering on the derived prediction sample can also be performed.

[0092] Specifically, the intra prediction procedure can include an intra prediction mode / type determination step, a peripheral reference sample derivation step, and an intra prediction mode / type-based prediction sample derivation step. Also, if necessary, a post-processing filtering step on the derived prediction sample can be performed.

[0093] When intra prediction is applied, the intra prediction mode applied to the current block can be determined using the intra prediction modes of neighboring blocks. For example, the decoding device can select one of the MPM (Most Probable Mode) candidates in the MPM list derived based on the intra prediction modes of the neighboring blocks (e.g., left and / or upper neighboring blocks) of the current block and additional candidate modes based on the received MPM index, or can select one of the remaining intra prediction modes not included in the above MPM candidates (and the planar mode) based on the remaining intra prediction mode information. The above MPM list can be configured with or without including the planar mode as a candidate. For example, when the above MPM list includes the planar mode as a candidate, the above MPM list can have 6 candidates, and when the above MPM list does not include the planar mode as a candidate, the above MPM list can have 5 candidates. When the above MPM list does not include the planar mode as a candidate, a not planar flag (e.g., intra_luma_not_planar_flag) indicating that the intra prediction mode of the current block is not the planar mode can be signaled. For example, the MPM flag can be signaled first, and the MPM index and the not planar flag can be signaled when the value of the MPM flag is 1. Also, the above MPM index can be signaled when the value of the not planar flag is 1. Here, the reason for configuring the above MPM list not to include the planar mode as a candidate is not that the planar mode is not an MPM, but rather to signal the flag (not planar flag) first to confirm whether it is the planar mode in advance because the planar mode is always considered as an MPM.

[0094] For example, whether the intra prediction mode applied to the current block is within the MPM candidates (and the planar mode) or within the remaining modes can be indicated based on an MPM flag (e.g., intra_luma_mpm_flag). A value of 1 for the MPM flag can indicate that the intra prediction mode for the current block is within the MPM candidates (and the planar mode), and a value of 0 for the MPM flag can indicate that the intra prediction mode for the current block is not within the MPM candidates (and the planar mode). A value of 0 for the above non-planar flag (e.g., intra_luma_not_planar_flag) can indicate that the intra prediction mode for the current block is the planar mode, and a value of 1 for the non-planar flag can indicate that the intra prediction mode for the current block is not the planar mode. The above MPM index can be signaled in the form of the mpm_idx or intra_luma_mpm_idx syntax element, and the above remaining intra prediction mode information can be signaled in the form of the rem_intra_luma_pred_mode or intra_luma_mpm_remainder syntax element. For example, the above remaining intra prediction mode information can index one of the remaining intra prediction modes not included in the MPM candidates (and the planar mode) among all the intra prediction modes in the order of prediction mode numbers. The above intra prediction mode is the intra prediction mode for the luma component (samples). Hereinafter, the intra prediction mode information can include at least one of the above MPM flag (e.g., intra_luma_mpm_flag), the above non-planar flag (e.g., intra_luma_not_planar_flag), the above MPM index (e.g., mpm_idx or intra_luma_mpm_idx), and the above remaining intra prediction mode information (rem_intra_luma_pred_mode or intra_luma_mpm_remainder). In this document, the MPM list can be referred to by various terms such as the MPM candidate list, candModeList, etc.When MIP is applied to the current block, separate mpm flags for MIP (e.g., intra_mip_mpm_flag), mpm indices (e.g., intra_mip_mpm_idx), and the remaining intra prediction mode information (e.g., intra_mip_mpm_remainder) can be signaled, and the above not planar flag is not signaled.

[0095] That is, generally in the case of block partitioning for video, the current block to be coded and neighboring blocks tend to have similar video characteristics. Therefore, the current block and neighboring blocks are likely to have the same or similar intra prediction modes. Thus, the encoder can utilize the intra prediction mode of neighboring blocks to encode the intra prediction mode of the current block.

[0096] For example, the encoder / decoder can construct an MPM (Most Probable Modes) list for the current block. The above MPM list can also be referred to as an MPM candidate list. Here, MPM can be meant as a mode used to improve coding efficiency considering the similarity between the current block and neighboring blocks during intra prediction mode coding. As described above, the MPM list can be constructed to include the planar mode or can be constructed to exclude the planar mode. For example, when the MPM list includes the planar mode, the number of candidates in the MPM list is 6. And when the MPM list does not include the planar mode, the number of candidates in the MPM list is 5.

[0097] The encoder / decoder can construct an MPM list including 5 or 6 MPMs.

[0098] To construct the MPM list, three types of modes can be considered: Default intra modes, Neighbour intra modes, and Derived intra modes.

[0099] For the above Neighbour intra modes, two neighbour blocks, namely, the left neighbour block and the upper neighbour block can be considered.

[0100] As described above, when the MPM list is configured not to include the planar mode, the planar mode is excluded from the above list, and the number of the above MPM list candidates can be set to 5.

[0101] Also, among the intra prediction modes, the non-directional mode (or non-angle mode) can include the average-based DC mode or the interpolation-based planar mode of the neighboring reference samples of the current block.

[0102] When inter prediction is applied, the prediction unit of the encoding device / decoding device can perform inter prediction on a block-by-block basis to derive predicted samples. Inter prediction can indicate a prediction derived in a way that depends on data elements (e.g., sample values or motion information) of pictures other than the current picture. When inter prediction is applied to the current block, a predicted block (predicted sample array) for the current block can be derived based on a reference block (reference sample array) specified by a motion vector on a reference picture pointed to by the index of the reference picture. At this time, in order to reduce the amount of motion information transmitted in the inter prediction mode, the motion information of the current block can be predicted in units of blocks, sub-blocks, or samples based on the correlation of the motion information between the neighboring blocks and the current block. The above motion information can include a motion vector and an index of a reference picture. The above motion information can further include information on the inter prediction type (L0 prediction, L1 prediction, BI prediction, etc.). When inter prediction is applied, the neighboring blocks can include spatial neighboring blocks existing within the current picture and temporal neighboring blocks existing in the reference picture. The reference picture including the above reference block and the reference picture including the above temporal neighboring block may be the same or different. The above temporal neighboring block may be called by names such as a collocated reference block or a collocated CU (colCU), and the reference picture including the above temporal neighboring block may also be called a collocated picture (colPic). For example, a candidate list of motion information can be configured based on the neighboring blocks of the current block, and a flag or index information indicating which candidate is selected (used) can be signaled in order to derive the motion vector and / or the index of the reference picture of the current block.Inter prediction is performed based on various prediction modes. For example, in the case of skip mode and merge mode, the motion information of the current block may be the same as that of the selected neighboring block. In the case of skip mode, unlike merge mode, a residual signal may not be transmitted. In the case of motion vector prediction (MVP) mode, the motion vector of the selected neighboring block is used as a motion vector predictor, and the motion vector difference can be signaled. In this case, the motion vector of the current block can be derived using the sum of the motion vector predictor and the motion vector difference.

[0103] The above motion information can include L0 motion information and / or L1 motion information according to the inter prediction type (such as L0 prediction, L1 prediction, BI prediction, etc.). The motion vector in the L0 direction can be called the L0 motion vector or MVL0, and the motion vector in the L1 direction can be called the L1 motion vector or MVL1. The prediction based on the L0 motion vector can be called L0 prediction, the prediction based on the L1 motion vector can be called L1 prediction, and the prediction based on both the above L0 motion vector and the above L1 motion vector can be called bi (Bi) prediction. Here, the L0 motion vector can indicate a motion vector related to the reference picture list L0 (L0), and the L1 motion vector can indicate a motion vector related to the reference picture list L1 (L1). The reference picture list L0 can include reference pictures that are earlier than the current picture in the output order, and the reference picture list L1 can include pictures that are later than the current picture in the output order. The above previous pictures can be called forward (reference) pictures, and the above later pictures can be called backward (reference) pictures. The reference picture list L0 can further include pictures that are later than the current picture in the output order as reference pictures. In this case, the above previous pictures are indexed first within the reference picture list L0, and the above later pictures can be indexed thereafter. The reference picture list L1 can further include pictures that are earlier than the current picture in the output order as reference pictures. In this case, the above later pictures are indexed first within the reference picture list 1, and the above previous pictures can be indexed thereafter. Here, the output order can correspond to the POC (Picture Order Count) order (order).

[0104] The video / video encoding procedure based on inter prediction generally includes, for example, the following.

[0105] FIG. 4 shows an example of an inter prediction-based video / video encoding method.

[0106] The encoding device performs inter prediction on the current block (S400). The encoding device derives the inter prediction mode and motion information of the current block and generates prediction samples for the block. Here, the procedures of inter prediction mode determination, motion information derivation, and prediction sample generation may be performed simultaneously, or one procedure may be performed prior to the other procedures. For example, the inter prediction unit of the encoding device includes a prediction mode determination unit, a motion information derivation unit, and a prediction sample derivation unit. The prediction mode determination unit determines the prediction mode for the current block, the motion information derivation unit derives the motion information of the current block, and the prediction sample derivation unit derives the prediction samples of the current block. For example, the inter prediction unit of the encoding device searches for a block similar to the current block within a certain area (search area) of the reference picture by motion estimation, and derives a reference block whose difference from the current block is the smallest or below a certain criterion. Based on this, a reference picture index indicating the reference picture where the reference block is located can be derived, and a motion vector can be derived based on the positional difference between the reference block and the current block. The encoding device determines the mode to be applied to the current block among various prediction modes. The encoding device can compare the RD costs for the various prediction modes and determine the optimal prediction mode for the current block.

[0107] For example, when the skip mode or the merge mode is applied to the current block, the encoding device constructs a merge candidate list described later, and can derive a reference block whose difference from the current block is the smallest or below a certain criterion among the reference blocks pointed to by the merge candidates included in the merge candidate list. In this case, the merge candidate related to the derived reference block is selected, and merge index information indicating the selected merge candidate is generated and signaled to the decoding device. The motion information of the current block can be derived using the motion information of the selected merge candidate.

[0108] As another example, when the (A)MVP mode is applied to the current block, the encoding device configures an (A)MVP candidate list described later, and can use the motion vector of the selected mvp (motion vector predictor) candidate among the mvp candidates included in the (A)MVP candidate list as the mvp of the current block. In this case, for example, the motion vector pointing to the reference block derived by the above-mentioned motion estimation can be used as the motion vector of the current block, and among the mvp candidates, the mvp candidate having the motion vector with the smallest difference from the motion vector of the current block can be the selected mvp candidate. An MVD (Motion Vector Difference), which is the difference obtained by subtracting the mvp from the motion vector of the current block, can be derived. In that case, information regarding the MVD can be signaled to the decoding device. Further, when the (A)MVP mode is applied, the value of the reference picture index is composed of reference picture index information and is separately signaled to the decoding device.

[0109] The encoding device derives a residual sample based on the prediction sample (S410). The encoding device can derive the residual sample by comparing the original sample of the current block with the prediction sample.

[0110] The encoding device encodes video information including prediction information and residual information (S420). The encoding device outputs the encoded video information in the form of a bitstream. The prediction information is information related to the prediction procedure, and includes prediction mode information (e.g., skip flag, merge flag, or mode index, etc.) and information related to motion information. The information related to the motion information includes candidate selection information (e.g., merge index, mvp flag, or mvp index) which is information for deriving a motion vector. Also, the information related to the motion information includes information related to the aforementioned MVD and / or reference picture index information. Also, the information related to the motion information includes information indicating whether L0 prediction, L1 prediction, or bi-prediction is applied. The residual information is information related to the residual samples. The residual information includes information related to the quantized transform coefficients for the residual samples.

[0111] The output bitstream may be stored in a (digital) storage medium and transmitted to the decoding device, or may be transmitted to the decoding device via a network.

[0112] On the other hand, as described above, the encoding device generates a reconstructed picture (including reconstructed samples and reconstructed blocks) based on the reference samples and the residual samples. This is to derive from the encoding device the same prediction result as that performed at the decoding device, thereby improving the coding efficiency. Therefore, the encoding device can store the reconstructed picture (or reconstructed samples, reconstructed blocks) in the memory and utilize it as a reference picture for inter prediction. As described above, loop filtering procedures and the like can be further applied to the reconstructed picture.

[0113] The video / video decoding procedure based on inter prediction generally includes, for example, the following.

[0114] FIG. 5 shows an example of an inter-prediction-based video / video decoding method.

[0115] As shown in FIG. 5, the decoding device performs operations corresponding to the operations performed by the encoding device. The decoding device can perform prediction on the current block based on the received prediction information and derive a prediction sample.

[0116] Specifically, the decoding device determines a prediction mode for the current block based on the received prediction information (S500). The decoding device can determine which inter-prediction mode is applied to the current block based on the prediction mode information in the prediction information.

[0117] For example, based on the merge flag, it can be determined whether the merge mode is applied to the current block, or whether the (A)MVP mode is determined. Alternatively, any one of various inter-prediction mode candidates can be selected based on the mode index. The inter-prediction mode candidates include a skip mode, a merge mode, and / or the (A)MVP mode, or various inter-prediction modes to be described later.

[0118] The decoding device derives motion information of the current block based on the determined inter-prediction mode (S510). For example, when the skip mode or the merge mode is applied to the current block, the decoding device constructs a merge candidate list to be described later and selects any one merge candidate included in the merge candidate list. The selection is performed based on the aforementioned selection information (merge index). The motion information of the selected merge candidate can be used to derive the motion information of the current block. The motion information of the selected merge candidate can be used as the motion information of the current block.

[0119] As another example, when the (A)MVP mode is applied to the current block, the decoding device constructs the (A)MVP candidate list described below, and the motion vector of the selected mvp (motion vector predictor) candidate among the mvp candidates included in the (A)MVP candidate list can be used as the mvp of the current block. The selection is made based on the selection information (mvp flag or mvp index) described above. In this case, the MVD of the current block can be derived based on the information regarding the MVD, and the motion vector of the current block can be derived based on the mvp of the current block and the MVD. Also, the reference picture index of the current block can be derived based on the reference picture index information. In the reference picture list related to the current block, the picture pointed to by the reference picture index can be derived as the reference picture to be referred to for the inter prediction of the current block.

[0120] On the other hand, as described below, the motion information of the current block can be derived without constructing a candidate list. In this case, the motion information of the current block can be derived according to the procedure disclosed in the prediction mode described below. In this case, the candidate list construction as described above may be omitted.

[0121] The decoding device generates a prediction sample for the current block based on the motion information of the current block (S520). In this case, the reference picture can be derived based on the reference picture index of the current block, and the prediction sample of the current block can be derived using the sample of the reference block pointed to by the motion vector of the current block on the reference picture. In this case, as described below, in some cases, a prediction sample filtering procedure may be further performed on all or part of the prediction samples of the current block.

[0122] For example, the inter prediction unit of the decoding device includes a prediction mode determination unit, a motion information derivation unit, and a prediction sample derivation unit. Based on the prediction mode information received by the prediction mode determination unit, it determines the prediction mode for the current block, derives the motion information (such as motion vectors and / or reference picture indices) of the current block based on the information related to the motion information received by the motion information derivation unit, and can derive the prediction sample of the current block from the prediction sample derivation unit.

[0123] The decoding device generates a residual sample for the current block based on the received residual information (S530). The decoding device generates a restored sample for the current block based on the prediction sample and the residual sample, and generates a restored picture based on this (S540). As described above, subsequent loop filtering procedures and the like can be further applied to the restored picture.

[0124] FIG. 6 exemplarily shows the inter prediction procedure.

[0125] Referring to FIG. 6, as described above, the inter prediction procedure includes an inter prediction mode determination step, a motion information derivation step according to the determined prediction mode, and a prediction execution (prediction sample generation) step based on the derived motion information. The inter prediction procedure is performed in the encoding device and the decoding device as described above. In this document, the coding device includes the encoding device and / or the decoding device.

[0126] As shown in FIG. 6, the coding device determines an inter prediction mode for the current block (S600). Various inter prediction modes can be used for predicting the current block in the picture. For example, various modes such as a merge mode, a skip mode, an MVP (Motion Vector Prediction) mode, an Affine mode, a sub-block merge mode, an MMVD (merge with MVD) mode, etc. can be used. A DMVR (Decoder Side Motion Vector Refinement) mode, an AMVR (Adaptive Motion Vector Resolution) mode, Bi-prediction with CU-level Weight (BCW), Bi-Directional Optical Flow (BDOF), etc. can be used additionally or alternatively as accompanying modes. The Affine mode may be called an affine motion prediction mode. The MVP mode may be called an "AMVP (Advanced Motion Vector Prediction) mode". In this document, some modes and / or motion information candidates derived by some modes may be included as one of the motion information related candidates of other modes. For example, an HMVP candidate may be added as a merge candidate of the above merge / skip mode, or may be added as an mvp candidate of the above MVP mode. When the above HMVP candidate is used as a motion information candidate of the above merge mode or skip mode, the above HMVP candidate may be called an HMVP merge candidate.

[0127] Prediction mode information indicating an inter prediction mode of a current block can be signaled from an encoding device to a decoding device. The prediction mode information can be included in a bitstream and received by the decoding device. The prediction mode information includes index information indicating one of a number of candidate modes. Alternatively, the inter prediction mode can also be indicated via hierarchical signaling of flag information. In this case, the prediction mode information includes one or more flags. For example, a skip flag is signaled to indicate whether the skip mode is applied, and when the skip mode is not applied, a merge flag is signaled to indicate whether the merge mode is applied. When the merge mode is not applied, it can also be indicated that the MVP mode is applied, or additional flags for further classification can be signaled. The affine mode may be signaled as an independent mode, or may be signaled as a mode subordinate to the merge mode or the MVP mode, etc. For example, the affine mode includes an affine merge mode and an affine MVP mode.

[0128] On the one hand, information indicating whether the aforementioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current coding unit) can be signaled. The above information may be referred to as motion prediction direction information, inter prediction direction information, or inter prediction indication information, and can be configured / encoded / signaled, for example, in the form of an inter_pred_idc syntax element. That is, the inter_pred_idc syntax element can indicate whether the aforementioned list0 (L0) prediction, list1 (L1) prediction, or bi-prediction is used in the current block (current coding unit). In this document, for the convenience of explanation, the inter prediction type (L0 prediction, L1 prediction, or BI prediction) indicated by the inter_pred_idc syntax element may be shown as the motion prediction direction. L0 prediction may be represented as pred_L0, L1 prediction may be represented as pred_L1, and bi-prediction may be represented as pred_BI. For example, the following prediction types can be indicated by the value of the inter_pred_idc syntax element.

[0129]

Table 1

[0130] As described above, one picture includes one or more slices. A slice can have one of the slice types including an I (Intra) slice, a P (Predictive) slice, and a B (Bi-Predictive) slice. The above slice type is indicated based on the slice type information. For blocks within an I slice, only intra prediction is used without using inter prediction for prediction. Of course, in this case, it is also possible to code and signal the original sample value without prediction. For blocks within a P slice, either intra prediction or inter prediction is used, and when inter prediction is used, only uni (single) prediction can be used. On the other hand, for blocks within a B slice, either intra prediction or inter prediction is used, and when inter prediction is used, up to maximum bi (bi-directional) prediction can be used.

[0131] L0 and L1 include reference pictures encoded / decoded before the current picture. For example, L0 includes reference pictures before and / or after the current picture in POC order, and L1 includes reference pictures after and / or before the current picture in POC order. In this case, a relatively lower reference picture index is assigned to L0 with respect to the reference picture before the current picture in POC order, and a relatively lower reference picture index is assigned to L1 with respect to the reference picture after the current picture in POC order. In the case of a B slice, bi-prediction is applied, and in this case, either uni-directional bi-prediction or bi-directional bi-prediction may be applied. Bi-directional bi-prediction is also called true bi-prediction.

[0132] The following table shows the syntax for a coding unit according to an embodiment of this document.

[0133]

Table 2-1

Table 2-2

[0134] Referring to Table 2 above, general_merge_flag indicates that general merge is available. When the value of general_merge_flag is 1, regular merge mode, mmvd mode, and merge subblock mode (subblock merge mode) are available. For example, when the value of general_merge_flag is 1, merge data syntax can be parsed from video / image information (or bitstream) encoded with merge data syntax, and merge data syntax is configured / coded to include information as shown in the following table.

[0135] [[]]END]] [Table 3]

[0136] The coding device derives motion information for the current block (S610). The derivation of the motion information can be based on the inter prediction mode.

[0137] The coding device can perform inter prediction using the motion information of the current block. The encoding device can derive optimal motion information for the current block through a motion estimation procedure. For example, the encoding device can search for highly correlated similar reference blocks within a determined search range in the reference picture in units of fractional pixels using the original block in the original picture for the current block, thereby deriving motion information. The similarity of the blocks can be derived based on the difference in phase-based sample values. For example, the similarity of the blocks can be calculated based on the SAD (Sum Of Absolute Differences) between the current block (or a template of the current block) and the reference block (or a template of the reference block). In this case, the motion information can be derived based on the reference block with the smallest SAD within the search space (search area). The derived motion information is signaled to the decoding device in various ways based on the inter prediction mode.

[0138] The coding device performs inter prediction based on the motion information for the current block (S620). The coding device can derive prediction sample(s) for the current block based on the motion information. The current block including the prediction sample may be called a predicted block.

[0139] When the merge mode is applied, instead of directly transmitting the motion information of the current prediction block, the motion information of the current prediction block is derived using the motion information of the surrounding prediction blocks. Therefore, by transmitting flag information indicating the use of the merge mode and a merge index indicating which surrounding prediction block is used, the motion information of the current prediction block can be indicated. The merge mode may be called the regular merge mode.

[0140] The encoder must search for a merge candidate block that is used to derive the motion information of the current prediction block in order to perform the merge mode. For example, up to 5 merge candidate blocks can be used, but the embodiments of this document are not limited to this. And the maximum number of the merge candidate blocks is transmitted in the slice header or the tile group header. After finding the merge candidate block, the encoder can generate a merge candidate list and select the merge candidate block with the minimum cost among them as the final merge candidate block.

[0141] For example, 5 merge candidate blocks can be used in the merge candidate list. For example, 4 spatial merge candidates and 1 temporal merge candidate can be used. Hereinafter, the spatial merge candidate or the spatial MVP candidate described later may be referred to as SMVP, and the temporal merge candidate or the temporal MVP candidate described later may be referred to as TMVP.

[0142] Hereinafter, a method of constructing a merge candidate list according to this document will be described.

[0143] The coding device (encoder / decoder) inserts the spatial merge candidates derived by searching the spatial neighboring blocks of the current block into the merge candidate list. For example, the spatial neighboring blocks include the lower left corner neighboring block, the left neighboring block, the upper right corner neighboring block, the upper neighboring block, and the upper left corner neighboring block of the current block. However, this is an example, and in addition to the aforementioned spatial neighboring blocks, additional neighboring blocks such as the right neighboring block, the lower neighboring block, and the lower right corner neighboring block can also be used as the spatial neighboring blocks. The coding device can search the spatial neighboring blocks based on the priority to detect available blocks and derive the motion information of the detected blocks as the spatial merge candidates.

[0144] The coding device inserts the temporal merge candidates derived by searching the temporal neighboring blocks of the current block into the merge candidate list. The temporal neighboring blocks may be located on a reference picture that is a picture different from the current picture in which the current block is located. The reference picture on which the temporal neighboring blocks are located may be referred to as a collocated picture or a col picture. The temporal neighboring blocks can be searched in the order of the peripheral blocks of the lower right corner and the lower right center block of the co-located block with respect to the current block on the col picture. On the other hand, when motion data compression is applied, specific motion information is stored as representative motion information for each fixed storage unit in the col picture. In this case, it is not necessary to store the motion information for all blocks within the fixed storage unit, and thus the compression effect of motion data can be obtained. In this case, the fixed storage unit may be predetermined, for example, in units of 16×16 samples or 8×8 samples, or size information regarding the fixed storage unit may be signaled from the encoder to the decoder. When the motion data compression is applied, the motion information of the temporal neighboring blocks can be replaced with the representative motion information of the fixed storage unit in which the temporal neighboring blocks are located. That is, in this case, from the perspective of implementation, instead of the prediction block located at the coordinates of the temporal neighboring blocks, based on the coordinates (upper left sample position (position)) of the temporal neighboring blocks, after arithmetic right shift by a certain value, the temporal merge candidates are derived based on the motion information of the prediction block covering the position after arithmetic left shift. For example, when the fixed storage unit is a 2n×2n sample unit, if the coordinates of the temporal neighboring blocks are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>n)<<n),(yTnb>n)<<n)) is used for the temporal merge candidates.Specifically, for example, when the above-mentioned fixed memory unit is a 16×16 sample unit, if the coordinates of the above-mentioned temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>4)<<4), (yTnb>4)<<4)) is used for the above-mentioned temporal merge candidate. Alternatively, for example, when the above-mentioned fixed memory unit is an 8×8 sample unit, if the coordinates of the above-mentioned temporal neighboring block are (xTnb, yTnb), the motion information of the prediction block located at the corrected position ((xTnb>3)<<3), (yTnb>3)<<3)) is used for the above-mentioned temporal merge candidate.

[0145] The coding device can check whether the number of current merge candidates is smaller than the number of maximum merge candidates. The number of the above-mentioned maximum merge candidates can be predefined or signaled from the encoder to the decoder. For example, the encoder generates information regarding the number of the above-mentioned maximum merge candidates, encodes it, and transmits it to the above-mentioned decoder in the form of a bit stream. When the number of the above-mentioned maximum merge candidates is satisfied, the subsequent candidate addition process may not be performed.

[0146] As a result of the above-mentioned check, if the number of the current merge candidates is smaller than the number of the above-mentioned maximum merge candidates, the coding device inserts an additional merge candidate into the above-mentioned merge candidate list.

[0147] As a result of the above-mentioned check, if the number of the current merge candidates is not smaller than the number of the above-mentioned maximum merge candidates, the coding device terminates the configuration of the above-mentioned merge candidate list. In this case, the encoder can select the optimal merge candidate among the merge candidates that constitute the above-mentioned merge candidate list based on the RD (Rate-Distortion) cost, and can signal selection information (for example, merge index) indicating the above-mentioned selected merge candidate to the decoder. The decoder selects the above-mentioned optimal merge candidate based on the above-mentioned merge candidate list and the above-mentioned selection information.

[0148] The motion information of the selected merge candidate can be used as the motion information of the current block, and as described above, a prediction sample of the current block can be derived based on the motion information of the current block. The encoder can derive a residual sample of the current block based on the prediction sample and signal residual information regarding the residual sample to the decoder. As described above, the decoder can generate a restored sample based on the residual sample derived based on the residual information and the prediction sample, and generate a restored picture based on this.

[0149] When the skip mode is applied, the motion information of the current block can be derived in the same way as when the above-described merge mode is applied. However, when the skip mode is applied, the residual signal for the corresponding block is omitted, and thus the prediction sample can be immediately used as the restored sample.

[0150] When the MVP mode is applied, a motion vector predictor (mvp) candidate list is generated using the motion vectors of the restored spatial neighboring blocks and / or the motion vectors corresponding to the temporal neighboring blocks (or Col blocks). That is, the motion vectors of the restored spatial neighboring blocks and / or the motion vectors corresponding to the temporal neighboring blocks can be used as motion vector predictor candidates. When dual prediction is applied, an mvp candidate list for L0 motion information derivation and an mvp candidate list for L1 motion information derivation can be individually generated and utilized. The aforementioned prediction information (or information related to prediction) includes selection information (e.g., an MVP flag or an MVP index) indicating the selected optimal motion vector predictor candidate among the motion vector predictor candidates included in the above list. Here, the prediction unit can select the motion vector predictor of the current block from among the motion vector predictor candidates included in the motion vector candidate list by using the above selection information. The prediction unit of the encoding device can obtain the motion vector difference (MVD) between the motion vector of the current block and the motion vector predictor, and encode this and output it in the form of a bitstream. That is, the MVD is obtained as the value obtained by subtracting the above motion vector predictor from the motion vector of the current block. Here, the prediction unit of the decoding device can obtain the motion vector difference included in the above prediction-related information, and derive the motion vector of the current block by adding the above motion vector difference and the above motion vector predictor. The prediction unit of the decoding device can obtain or derive from the above prediction-related information a reference picture index indicating a reference picture, etc.

[0151] Hereinafter, a method for constructing a motion vector predictor candidate list according to this document will be described.

[0152] One embodiment first searches for spatial candidate blocks for motion vector prediction and inserts them into the prediction candidate list. Thereafter, in one embodiment, it is determined whether the number of spatial candidate blocks is less than 2. For example, in one embodiment, if the number of spatial candidate blocks is less than 2, temporal candidate blocks are searched for and additionally inserted into the prediction candidate list, and if the temporal candidate blocks are unavailable, a zero motion vector is used. That is, a zero motion vector can be additionally inserted into the prediction candidate list. Thereafter, in one embodiment, the configuration of the preliminary candidate list is terminated. Alternatively, in one embodiment, if the number of spatial candidate blocks is not less than 2, the configuration of the preliminary candidate list is terminated. Here, the preliminary candidate list indicates the MVP candidate list.

[0153] On the other hand, when the MVP mode is applied, the reference picture index is explicitly signaled. In this case, it can be signaled separately for the reference picture index (refidxL0) for L0 prediction and the reference picture index (refidxL1) for L1 prediction. For example, when the MVP mode is applied and bi-prediction is applied, both the information regarding refidxL0 and the information regarding refidxL1 can be signaled.

[0154] When the MVP mode is applied, as described above, the information regarding the MVD derived from the encoding device is signaled to the decoding device. The information regarding the MVD can include, for example, information indicating the x and y components of the MVD absolute value and the sign. In this case, whether the MVD absolute value is greater than 0 and whether it is greater than 1, and the information indicating the rest of the MVD can be signaled step by step. For example, the information indicating whether the MVD absolute value is greater than 1 can be signaled only when the value of the flag information indicating whether the MVD absolute value is greater than 0 is 1.

[0155] For example, the information regarding the MVD is configured in a syntax as shown in the following table, encoded in the encoding device, and signaled to the decoding device.

[0156]

Table 4

[0157] For example, in Table 4, the abs_mvd_greater0_flag syntax element indicates information regarding whether the difference (MVD) is greater than 0, and the abs_mvd_greater1_flag syntax element indicates information regarding whether the difference (MVD) is greater than 1. Also, the abs_mvd_minus2 syntax element indicates information regarding the value obtained by performing -2 on the difference (MVD), and the mvd_sign_flag syntax element indicates information regarding the sign of the difference (MVD). Also, in Table 4, [0] of each syntax element indicates information regarding L0, and [1] indicates information regarding L1.

[0158] For example, MVD[compIdx] is derived based on abs_mvd_greater0_flag[compIdx] * (abs_mvd_minus2[compIdx] + 2) * (1 - 2 * mvd_sign_flag[compIdx]). Here, compIdx (or cpIdx) indicates the index of each component and can have a value of 0 or 1. compIdx 0 indicates the x component, and compIdx 1 indicates the y component. However, this is an example, and it is also possible to represent values for each component using other coordinate systems instead of the x, y coordinate system.

[0159] On the other hand, the MVD for L0 prediction (MVD L0) and the MVD for L1 prediction (MVD L1) may be separately signaled, and the information regarding the above MVD may include information regarding MVD L0 and / or information regarding MVD L1. For example, when the MVP mode is applied to the current block and BI prediction is applied, both the information regarding MVD L0 and the information regarding MVD L1 are signaled.

[0160] FIG. 7 is a diagram for explaining SMVD (Symmetric Motion Vector Differences).

[0161] When BI prediction is applied, SMVD (Symmetric MVD) may be used in consideration of coding efficiency. In this case, some of the signaling of the motion information may be omitted. For example, when SMVD is applied to the current block, information regarding refidxL0, information regarding refidxL1, and information regarding MVD L1 can be derived internally without being signaled from the encoding device to the decoding device. For example, when the MVP mode and BI prediction are applied to the current block, flag information (e.g., SMVD flag information or sym_mvd_flag syntax element) indicating whether SMVD can be applied is signaled, and when the value of the above flag information is 1, the decoding device determines that SMVD is applied to the above current block.

[0162] When the SMVD mode is applied (i.e., when the value of the SMVD flag information is 1), information regarding mvp_l0_flag, mvp_l1_flag, and MVD L0 (Motion Vector Difference L0) is explicitly signaled, and signaling of information regarding refidxL0, refidx1, and MVD L1 (Motion Vector Difference L1) as described above is omitted and can be derived internally. For example, refidxL0 can be derived as an index that points to the previous reference picture closest to the current picture in terms of the POC procedure within the reference picture list 0 (which may be called list0 or L0). refidxL1 can be derived as an index that points to the subsequent reference picture closest to the current picture in terms of the POC procedure within the reference picture list 1 (which may be called list1 or L1). Alternatively, for example, both refidxL0 and refidxL1 can be derived as 0 respectively. Alternatively, for example, the above refidxL0 and refidxL1 can be derived as the minimum indices having the same POC difference in relation to the current picture respectively. Specifically, for example, when "[POC of the current picture] - [POC of the first reference picture indicated by refidxL0]" is called the first POC difference and "[POC of the current picture] - [POC of the second reference picture indicated by refidxL1]" is called the second POC difference, the value of refidxL0 that points to the first reference picture is derived as refidxL0 of the current block and the value of refidxL1 that points to the second reference picture is derived as refidxL1 of the current block only when the first POC difference and the second POC difference are the same. Also, for example, when there are multiple sets where the first POC difference and the second POC difference are the same, refidxL0 and refidxL1 of the set with the smallest difference among them can be derived as refidxL0 and refidxL1 of the current block.

[0163] As shown in FIG. 7, reference picture list 0, reference picture list 1, and MVD L0, MVD L1 are shown. Here, MVD L1 is symmetric to MVD L0.

[0164] MVD L1 can be derived as minus (-) MVD L0. For example, the final (improved or corrected) motion information (motion vector: MV) for the current block is derived based on the following formula.

[0165] <Equation 1>

Number

[0166] In Equation 1, mvx0 and mvy0 represent the x and y components of the motion vector for L0 motion information or L0 prediction, and mvx1 and mvy1 represent the x and y components of the motion vector for L1 motion information or L1 prediction. Also, mvpx0 and mvpy0 represent the x and y components of the motion vector predictor for L0 prediction, and mvpx1 and mvpy1 represent the x and y components of the motion vector predictor for L1 prediction. Also, mvdx0 and mvdy0 represent the x and y components of the motion vector difference for L0 prediction.

[0167] On the other hand, the MMVD mode is a method of applying MVD (Motion Vector Difference) to the merge mode, and the motion information directly used for generating the prediction sample of the current block (i.e., the current CU) can be implicitly derived. For example, an MMVD flag (e.g., mmvd_flag) indicating whether to use MMVD for the current block (i.e., the current CU) is signaled, and MMVD can be performed based on this MMVD flag. When MMVD is applied to the current block (e.g., when mmvd_flag is 1), additional information regarding MMVD can be signaled.

[0168] Here, the additional information regarding MMVD includes a merge candidate flag (e.g., mmvd_cand_flag) indicating whether the first candidate or the second candidate in the merge candidate list is used together with the MVD, a distance index (e.g., mmvd_distance_idx) for indicating the magnitude of motion, and a direction index (mmvd_direction_idx) for indicating the direction of motion.

[0169] In the MMVD mode, two candidates (i.e., the first candidate or the second candidate) located at the first and second entries among the candidates in the merge candidate list can be used, and either one of the two candidates (i.e., the first candidate or the second candidate) can be used as the base MV. For example, a merge candidate flag (e.g., mmvd_cand_flag) can be signaled to indicate either one of the two candidates (i.e., the first candidate or the second candidate) in the merge candidate list.

[0170] Also, the distance index (e.g., mmvd_distance_idx) indicates motion magnitude information and can indicate a predetermined offset from the starting point. The offset may be added to the horizontal or vertical component of the starting motion vector. The relationship between the distance index and the predetermined offset can be shown as in the following table.

[0171] [Table 5]

[0172] Referring to Table 5 above, the distance of the MVD (e.g., MmvdDistance) is determined by the value of the distance index (e.g., mmvd_distance_idx), and the distance of the MVD (e.g., MmvdDistance) can be derived using integer sample precision or fractional sample precision based on the value of tile_group_fpel_mmvd_enabled_flag. For example, when tile_group_fpel_mmvd_enabled_flag is 1, it indicates that the distance of the MVD is derived using integer sample precision in the current tile group (or picture header), and when tile_group_fpel_mmvd_enabled_flag is 0, it indicates that the distance of the MVD is derived using fractional sample precision in the tile group (or picture header). In Table 1, the information (flags) for the tile group can be replaced with the information for the picture header. For example, tile_group_fpel_mmvd_enabled_flag can be replaced with ph_fpel_mmvd_enabled_flag (or ph_mmvd_fullpel_only_flag).

[0173] Also, the direction index (e.g., mmvd_direction_idx) indicates the direction of the MVD with respect to the starting point and indicates 4 directions as shown in Table 5 below. Here, the direction of the MVD can indicate the sign of the MVD. The relationship between the direction index and the MVD sign is shown as follows in the table.

[0174]

Table 6

[0175] Referring to Table 6 above, the sign of the MVD (e.g., MmvdSign) is determined by the value of the direction index (e.g., mmvd_direction_idx), and the sign of the MVD (e.g., MmvdSign) is derived for the L0 reference picture and the L1 reference picture.

[0176] Based on the distance index (e.g., mmvd_distance_idx) and the direction index (e.g., mmvd_direction_idx) as described above, the offset of the MVD can be calculated as in the following formula.

[0177] <Equation 2>

Number

[0178] <Equation 3>

Number

[0179] In Equation 2 and Equation 3, the MMVD distance (MmvdDistance[x0][y0]) and the MMVD signs (MmvdSign[x0][y0][0], MmvdSign[x0][y0][1]) are derived based on Table 5 and / or Table 6. In summary, in the MMVD mode, among the merge candidate flags (e.g., mmvd_cand_flag) of the merge candidates in the merge candidate list derived based on the peripheral blocks, the merge candidate indicated by the merge candidate flag is selected, and the selected merge candidate can be used as the base candidate (e.g., MVP). Then, the motion information (i.e., the motion vector) of the current block can be derived by adding the MVD derived using the distance index (e.g., mmvd_distance_idx) and the direction index (e.g., mmvd_direction_idx) based on the base candidate.

[0180] Based on the motion information derived by the prediction mode, a predicted block for the current block can be derived. The predicted block includes the prediction samples (prediction sample array) of the current block. When the motion vector of the current block refers to fractional sample units, an interpolation procedure can be performed, whereby the prediction samples of the current block can be derived based on the reference samples of fractional sample units in the reference picture. When dual prediction is applied, the prediction samples derived based on L0 prediction (i.e., prediction using the reference picture in reference picture list L0 and MVL0) and the prediction samples derived based on L1 prediction (i.e., prediction using the reference picture in reference picture list L1 and MVL1) can be used as the prediction samples of the current block by weighted sum or weighted average (according to the phase). When dual prediction is applied, if the reference picture used for L0 prediction and the reference picture used for L1 prediction are located in different temporal directions with respect to the current picture (i.e., when it corresponds to bidirectional prediction while being dual prediction), this may be called true dual prediction.

[0181] As described above, restoration samples and a restored picture can be generated based on the derived prediction samples, and then procedures such as in-loop filtering can be executed.

[0182] As described above, according to this document, when dual prediction is applied to the current block, a predicted sample can be derived based on a weighted average. Conventionally, the dual prediction signal (i.e., the dual prediction sample) was derived by a simple average of the L0 prediction signal (L0 prediction sample) and the L1 prediction signal (L1 prediction sample). That is, the dual prediction sample was derived as the average of the L0 prediction sample based on the L0 reference picture and MVL0 and the L1 prediction sample based on the L1 reference picture and MVL1. However, according to this document, when dual prediction is applied, the dual prediction signal (dual prediction sample) can be derived by a weighted average of the L0 prediction signal and the L1 prediction signal as follows.

[0183] In the embodiments related to the aforementioned MMVD, a method considering the long-term reference picture in the MVD derivation process of MMVD can be proposed, thereby enabling the maintenance and increase of compression efficiency in various applications. Also, the method proposed in the embodiments of this document can be similarly applied to the symmetric MVD technology SMVD used in the inter mode (MVP mode) in addition to the MMVD technology used in MERGE.

[0184] FIG. 8 is a diagram for explaining a method of deriving a motion vector in inter prediction.

[0185] In one embodiment of this document, in the process of motion vector scaling (MV scaling) of a temporal motion candidate (temporal merge candidate, or temporal mvp candidate), an MV derivation method considering the long-term reference picture is used. The temporal motion candidate can correspond to mvCol (mvLXCol). The temporal motion candidate may be referred to as "TMVP".

[0186] The following table explains the definition of the long-term reference picture.

[0187] [Table 7]

[0188] Referring to Table 7 above, when LongTermRefPic (aPic, aPb, refIdx, LX) is 1 (true), the corresponding reference picture is marked as being used for long - term reference. For example, a reference picture that is not marked as being used for long - term reference can be a reference picture that is marked as being used for short - term reference. In other examples, a reference picture that is not marked as being used for long - term reference and is not marked as not being used can be a reference picture that is marked as being used for short - term reference. Hereinafter, a reference picture marked as being used for long - term reference may be referred to as a long - term reference picture, and a reference picture marked as being used for short - term reference may be referred to as a short - term reference picture.

[0189] The following table explains the derivation of TMVP (mvLXCol).

[0190] [Table 8]

[0191] Referring to FIG. 8 and Table 8, when the reference picture type pointed to by the current picture (e.g., indicating whether it is a long - term reference picture (LTRP) or a short - term reference picture (STRP)) is not the same as the type of the collocated reference picture pointed to by the collocated picture, the temporal motion vector (mvLXCol) is not used. That is, when all are long - term reference pictures or all are short - term reference pictures, colMV is derived; when there are other types, colMV is not derived. Also, when all are long - term reference pictures and the POC difference between the current picture and the reference picture of the current picture is the same as the POC difference between the collocated picture and the reference picture of the collocated picture, the collocated motion vector can be used as it is without scaling. When it is a short - term reference picture and the POC differences are different, the motion vector of the scaled collocated block is used.

[0192] In the embodiments of this document, the MMVD used in the MERGE / SKIP mode signals the base motion vector index, distance index, and direction index for one coding block as information for deriving MVD information. When performing uni - directional prediction, MVD is derived from the motion information; when performing bi - directional prediction, symmetric MVD information is generated using mirroring and scaling methods.

[0193] When performing bi - directional prediction, the MVD information for L0 or L1 is scaled to generate the MVD for L1 or L0, but when referring to a long - term reference picture, changes in the MVD derivation process are required.

[0194] Figures 9 to 13 show the MVD derivation method of MMVD according to the embodiments of this document. The method shown in Figures 9 to 13 may be for blocks to which bidirectional prediction is applied.

[0195] In one embodiment according to Figure 9, when the distance to the L0 reference picture and the distance to the L1 reference picture are the same, the derived MmvdOffset can be used directly as the MVD. When the POC differences (the POC difference between the L0 reference picture and the current picture and the POC difference between the L1 reference picture and the current picture) are different, the MVD can be derived by scaling or simple mirroring (i.e., -1*MmvdOffset) according to the POC difference and whether it is a long-term or short-term reference picture.

[0196] As an example, the method of deriving a symmetric MVD using MMVD for blocks to which bidirectional prediction is applied does not conform to blocks using long-term reference pictures. In particular, when the reference picture types in each direction are different, it is difficult to expect performance improvement when using MMVD. Therefore, in the following figures and embodiments, examples are introduced in which MMVD is not applied when the reference picture types of L0 and L1 are different.

[0197] In one embodiment according to Figure 10, different MVD derivation methods are applied depending on whether the reference picture referred to by the current picture (or the current slice, current block) is a LTRP (Long-Term Reference Picture) or a STRP (Short-Term Reference Picture). In one example, when the method of the embodiment according to Figure 10 is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0198]

Table 9-1

Table 9-2

[0199] In one embodiment according to FIG. 11, different MVD derivation methods are applied depending on whether the reference picture referred to by the current picture (or current slice, current block) is an LTRP (Long-Term Reference Picture) or an STRP (Short-Term Reference Picture). In one example, when the method of the embodiment according to FIG. 11 is applied, a part of the standard document according to this embodiment is described as in the following table.

[0200]

Table 10-1

Table 10-2

[0201] In summary, when the reference picture types in each direction are different, the MVD derivation process of MMVD that does not derive MVD is described.

[0202] In one embodiment according to FIG. 12, MVD is not derived in all cases where a long-term reference picture is referred to. That is, when at least one of the L0 and L1 reference pictures is a long-term reference picture, MVD is set to 0, and MVD can be derived only when there is a short-term reference picture.

[0203] In one example, based on the highest priority condition (RefPicL0!=LTRP && RefPicL1!=STRP), when the current picture (or current slice, current block) refers to only short-term reference pictures, MVD for MMVD can be derived. In one example, when the method of the embodiment according to FIG. 12 is applied, a part of the standard document according to this embodiment is described as in the following table.

[0204]

Table 11-1

Table 11-2

[0205] In one embodiment according to FIG. 13, when the reference picture types in each direction are different, if there is a short-term reference picture, an MVD is derived, and if there is a long-term reference picture, the MVD is derived to be 0.

[0206] In one example, when the reference picture types in each direction are different, when referring to a reference picture close to the current picture (short-term reference picture), MmvdOffset is applied, and when referring to a reference picture far from the current picture (long-term reference picture), the MVD has a value of 0. Here, a picture close to the current picture can be regarded as having a short-term reference picture, but if the close picture is a long-term reference picture, mmvdOffset can be applied to the motion vector of the list pointing to the short-term reference picture.

[0207]

Table 12

[0208] For example, according to the four paragraphs included in the above Table 12, the content of the bottom block of the flowchart (sequence diagram) included in the above FIG. 13 can be sequentially replaced.

[0209] In one example, when the method of the embodiment according to FIG. 13 is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0210]

Table 13-1

Table 13-2

[0211] The following table shows a comparison between the examples included in this document.

[0212] [Table 14]

[0213] Referring to Table 14, a comparison is shown between the methods of applying offsets considering the reference picture type for the MVD derivation of MMVD described in the examples according to FIGS. 9 to 13. In Table 14, Example A relates to an existing MMVD, Example B shows the examples according to FIGS. 9 to 11, Example C shows the example according to FIG. 12, and Example D shows the example according to FIG. 13.

[0214] That is, in the examples according to FIGS. 9, 10, and 11, a method of deriving an MVD only when the reference picture types in both directions are the same is described. In the example according to FIG. 12, a method of deriving an MVD only when both are short-term reference pictures in both directions is described. In the case of the example according to FIG. 12, if it is a long-term reference picture for unidirectional prediction, the MVD is set to 0. Also, in the example according to FIG. 13, a method of deriving an MVD in only one direction when the reference picture types in both directions are different is described. Such differences between the examples show various features of the technology described in this document, and it can be understood by those with ordinary knowledge in the technical field to which this document belongs that the effects that the examples according to this document attempt to achieve can be realized based on the above features.

[0215] In the embodiments according to this document, when the reference picture type is a long-term reference picture, there is a separate process. When including a long-term reference picture, since scaling or mirroring based on POC difference (POCDiff) has no impact on performance improvement, an MmvdOffset value is assigned to the MVD in the direction with short-term reference pictures, and a value of 0 is assigned to the MVD in the direction with long-term reference pictures. In one example, when this embodiment is applied, a part of the standard document according to this embodiment is described as follows in the following table.

[0216]

Table 15-1

Table 15-2

[0217] In other examples, a part of Table 15 above can be replaced with the following table. Referring to Table 16, the Offset is applied based on the reference picture type instead of POCDiff.

[0218]

Table 16

[0219] In still other examples, a part of Table 15 above can be replaced with the following table. Referring to Table 17, MmvdOffset can always be set to L0 and -MmvdOffset to L1 without considering the reference picture type.

[0220]

Table 17

[0221] According to one embodiment of this document, similar to the MMVD used in the aforementioned MERGE mode, the SMVD in the inter mode can be performed. When performing bidirectional prediction, whether symmetric MVD derivation is possible is signaled from the encoding device to the decoding device. When the related flag (e.g., sym_mvd_flag) is true (or its value is 1), the second-direction MVD (e.g., MVD L1) is derived by mirroring the first-direction MVD (e.g., MVD L0). In this case, scaling for the first-direction MVD may not be performed.

[0222] The following table shows the syntax regarding the coding unit according to one embodiment of this document.

[0223]

Table 18

[0224]

Table 19

[0225] Referring to Table 18 and Table 19 above, when inter_pred_idc == PRED_BI and the reference pictures of L0 and L1 are available (e.g., RefIdxSymL0 > -1 && RefIdxSymL1 > -1), sym_mvd_flag is signaled.

[0226] The following table shows the decoding procedure for the MMVD reference index by way of an example.

[0227]

Table 20

[0228] Referring to Table 20, the derivation procedure of the availability of the reference pictures of L0 and L1 is described. That is, if there is a reference picture in the forward direction among the L0 reference pictures, the reference picture index closest to the current picture is set to RefIdxSymL0, and the corresponding value is set to the reference index of L0. Also, if there is a reference picture in the backward direction among the L1 reference pictures, the reference picture index closest to the current picture is set to RefIdxSymL1, and the corresponding value is set to the reference index of L1.

[0229] The following Table 21 shows the decoding procedure for the MMVD reference index according to another example.

[0230]

Table 21

[0231] Referring to Table 21, as in the embodiments described with FIGS. 9, 10, and 11, when the L0 or L1 reference picture types are different, that is, when long-term reference pictures and short-term reference pictures are used, after deriving the reference index for SMVD to prevent SMVD, if the reference picture types of L0 and L1 are different, do not use SMVD (see the bottom paragraph of Table 20).

[0232] In one embodiment of this document, similar to the MMVD used in the merge mode, in the inter mode, SMVD can be applied. As in the embodiment described with FIG. 12, when long-term reference pictures are used, in order to prevent SMVD, the long-term reference pictures can be excluded in the process of deriving the reference index for SMVD as shown in the following table.

[0233]

Table 22

[0234] The following table according to another example of this embodiment shows an example of processing such that the SMVD is not applied when using a long-term reference picture after the derivation of the reference picture index for SMVD.

[0235]

Table 23

[0236] In one embodiment of this document, when the reference picture type of the current picture is different from the reference picture type of the collocated picture in the derivation process of colMV of TMVP, the motion vector MV is set to 0. However, since it is different from the derivation methods in the cases of MMVD and SMVD, it is made to be unified.

[0237] Even when the reference picture type of the current picture is a long-term reference picture and the reference picture type of the collocated picture is a long-term reference picture, the motion vector directly uses the collocated motion vector value. However, in MMVD and SMVD, in this case, MV is set to 0. Here, TMVP also sets MV to 0 without additional derivation.

[0238] Also, even if the reference picture types are different, since there may be a long-term reference picture close to the current picture, instead of setting MV to 0 in consideration of this, colMV can be used as MV without scaling.

[0239] The following drawings are created to illustrate a specific example of this specification. Since the names of the specific apparatuses and the names of the specific signal message fields described in the drawings are presented exemplarily, the technical features of this specification are not limited to the specific names used in the following drawings.

[0240] Figures 14 and 15 schematically show an example of a video / video encoding method and related components according to one or more embodiments of this document. The method disclosed in FIG. 14 is performed by the encoding device disclosed in FIG. 2. Specifically, for example, S1400 to S1450 in FIG. 14 are performed by the prediction unit 220 of the encoding device, and S1460 is performed by the residual processing unit 230 of the encoding device. S1470 is performed by the entropy encoding unit 240 of the encoding device. The method disclosed in FIG. 14 includes the embodiments described above in this document.

[0241] Referring to FIG. 14, the encoding device derives an inter prediction mode for the current block in the current picture (S1400). Here, the inter prediction mode includes the aforementioned merge mode, AMVP mode (mode using motion vector predictor candidates), MMVD, and SMVD.

[0242] The encoding device derives a reference picture for the inter prediction mode. The encoding device constructs a reference picture list for deriving the reference picture. In one example, the reference picture list includes reference picture list 0 (or, L0, reference picture list L0) or reference picture list 1 (or, L1, reference picture list L1). For example, the encoding device can construct a reference picture list for each slice included in the current picture.

[0243] The encoding device constructs an MVP candidate list for the current block based on the peripheral blocks of the current block (S1410). In one example, the peripheral blocks are included in the current picture including the current block. In other examples, the peripheral blocks are included in a previous (reference) picture or a next (subsequent) (reference) picture of the current picture. Here, the POC of the previous picture may be smaller than the POC of the current picture, and the POC of the subsequent picture may be larger than the POC of the current picture. According to one example, the POC difference between the current picture and the previous (reference) picture of the current picture is greater than 0. In other examples, the POC difference between the current picture and the next (reference) picture of the current picture is less than 0. However, this is merely exemplary.

[0244] The encoding device derives an MVP for the current block based on the MVP candidate list (S1420). The encoding device derives the optimal motion vector predictor candidate among the motion vector predictor candidates included in the MVP candidate list. The encoding device can generate selection information (e.g., an MVP flag or an MVP index) indicating the optimal motion vector predictor candidate.

[0245] The encoding device generates prediction-related information including the inter prediction mode (S1430). In one example, the prediction-related information includes information regarding MVD (Motion Vector Difference) for the current block. Further, the information regarding the prediction includes information regarding MMVD, information regarding SMVD, and the like.

[0246] The encoding device derives motion information for the prediction of the current block based on the inter prediction mode (S1440). For example, the motion information includes a reference index for SMVD. The reference index for SMVD indicates a reference picture for applying SMVD. The reference index for SMVD includes a reference index L0 (RefIdxSumL0) and a reference index L1 (RefIdxSumL1).

[0247] The encoding device generates a prediction sample based on the above motion information (S1450). The encoding device generates the prediction sample based on the motion vector and the reference picture index included in the above motion information. For example, the prediction sample is generated based on the block (or sample) indicated by the motion vector among the blocks (or samples) in the reference picture pointed to by the reference picture index.

[0248] The encoding device derives residual information based on the above prediction sample (S1460). Specifically, the encoding device can derive a residual sample based on the above prediction sample and the original sample. The encoding device can derive residual information based on the above residual sample. For the derivation of the above residual information, the above-mentioned conversion and quantization processes are performed.

[0249] The encoding device encodes video / video information including the above prediction-related information and the above residual information (S1470). The encoded video / video information can be output in the form of a bitstream. The above bitstream can be transmitted to the decoding device via a network or a (digital) storage medium.

[0250] The above video / video information includes various information according to the embodiments of this document. For example, the above video / video information includes the information disclosed in any one of Tables 1 to 23 described above.

[0251] In one embodiment, the above motion information includes a motion vector and a reference picture index. The above motion vector is derived based on the information regarding the above MVD and the above MVP. The above reference picture index is derived based on the short-term reference picture among the reference pictures included in the reference picture list.

[0252] In one embodiment, a motion vector for the current block is derived based on the sum between the MVD and the MVP.

[0253] In one embodiment, the prediction-related information includes information regarding the SMVD. For example, when the reference picture index is derived based on the POC difference between the short-term reference picture and the current picture including the current block, the value of the information regarding the SMVD can be 1.

[0254] In one embodiment, an MVD L0 for L0 prediction can be derived. For example, when an MVD L1 for L1 prediction is derived from the MVD L0 and the motion information is derived based on the MVD L0 and the MVD L1, the value of the information regarding the SMVD can be 1.

[0255] In one embodiment, the magnitude of the MVD L1 can be the same as the magnitude of the MVD L0. The sign of the MVD L1 can be opposite to the sign of the MVD L0.

[0256] In one embodiment, the reference picture index points to the short-term reference picture.

[0257] In one embodiment, the reference picture list 0 includes the short-term reference picture. The reference picture index can be derived based on the POC difference between each of the reference pictures included in the reference picture list 0 and the current block including the current block.

[0258] In one embodiment, the reference picture index is derived based on a comparison between the POC differences.

[0259] Figures 16 and 17 schematically show an example of a video / video decoding method and related components according to an embodiment of this document. The method disclosed in Figure 16 is performed by the decoding device disclosed in Figure 3. Specifically, for example, S1600 in Figure 16 is performed by the entropy decoding unit 310 of the decoding device, and S1610 to S1650 are performed by the prediction unit 330 of the decoding device. The method disclosed in Figure 16 includes the embodiments described above in this document.

[0260] As shown in Figure 16, the decoding device receives / acquires video / video information (S1600). The decoding device can receive / acquire the above video / video information via a bitstream. The above video / video information includes prediction-related information (including prediction mode information) and residual information. The above prediction-related information includes information related to mMVD, information related to SMVD, etc. Also, the above video / video information includes various information according to the embodiments of this document. For example, the above video / video information includes the information described together with Figures 1 to 15 and / or the information disclosed in at least one of the aforementioned Tables 1 to 23.

[0261] The decoding device derives an inter prediction mode for the current block based on the above prediction-related information (S1610). Here, the inter prediction mode includes the aforementioned merge mode, AMVP mode (mode using motion vector predictor candidates), MMVD, and SMVD.

[0262] The decoding device constructs an MVP candidate list for the current block based on the peripheral blocks of the current block (S1620). In one example, the peripheral blocks are included in the current picture including the current block. In other examples, the peripheral blocks are included in a previous (reference) picture or a next (subsequent) (reference) picture from the current picture. Here, the POC of the previous picture may be smaller than the POC of the current picture, and the POC of the subsequent picture may be larger than the POC of the current picture. According to one example, the POC difference between the current picture and the previous (reference) picture of the current picture is greater than 0. In other examples, the POC difference between the current picture and the next (reference) picture of the current picture is less than 0. However, this is merely exemplary.

[0263] The decoding device derives an MVP for the current block based on the MVP candidate list (S1630). The decoding device can derive the optimal motion vector predictor candidate among the motion vector predictor candidates included in the MVP candidate list. The encoding device can generate selection information (e.g., an MVP flag or an MVP index) indicating the optimal motion vector predictor candidate.

[0264] The decoding device derives motion information for the current block based on the information regarding the MVD and the MVP (S1640). For example, the motion information includes a reference index for SMVD. The reference index for SMVD indicates a reference picture for applying SMVD. The reference index for SMVD includes a reference index L0 (RefIdxSumL0) and a reference index L1 (RefIdxSumL1).

[0265] The decoding device generates a prediction sample based on the above motion information (S1650). The decoding device can generate the prediction sample based on the motion vector and the reference picture index included in the motion information. For example, the prediction sample can be generated based on the block (or sample) indicated by the motion vector among the blocks (or samples) in the reference picture pointed to by the reference picture index.

[0266] The decoding device can generate a residual sample based on the above residual information. Specifically, the decoding device can derive the quantized transform coefficients based on the above residual information. The quantized transform coefficients can have a one-dimensional vector form based on the coefficient scan order. The decoding device can derive the transform coefficients based on the inverse quantization procedure for the above quantized transform coefficients. The decoding device can derive the residual sample based on the inverse transform procedure for the above transform coefficients.

[0267] The decoding device generates a restored sample of the current picture based on the above prediction sample and the above residual sample. The decoding device can further perform a filtering procedure to generate a (modified) restored sample.

[0268] In one embodiment, the motion information includes a motion vector and a reference picture index. The motion vector is derived based on the information regarding the MVD and the above MVP. The reference picture index is derived based on the short-term reference picture among the reference pictures included in the reference picture list.

[0269] In one embodiment, the MVD can be derived based on the information regarding the MVD. The motion vector for the current block is derived based on the sum between the above MVD (MVP) and the above MVP.

[0270] In one embodiment, the prediction-related information includes information about the SMVD. For example, when the value of the information about the SMVD is 1, the reference picture index is derived based on the POC difference between the short-term reference picture and the current picture including the current block.

[0271] In one embodiment, MVD L0 for L0 prediction is derived based on the information about the MVD. For example, when the value of the information about the SMVD is 1, MVD L1 for L1 prediction is derived from MVD L0, and the motion information is derived based on the MVD L0 and the MVD L1.

[0272] In one embodiment, the magnitude of the MVD L1 may be the same as the magnitude of the MVD L0. The sign of the MVD L1 may be opposite to the sign of the MVD L0.

[0273] In one embodiment, the reference picture index may point to the short-term reference picture.

[0274] In one embodiment, the reference picture list 0 includes the short-term reference picture. The reference picture index is derived based on the POC difference between each of the reference pictures included in the reference picture list 0 and the current block including the current block.

[0275] In one embodiment, the reference picture index is derived based on a comparison between the POC differences.

[0276] In one embodiment, the reference picture index (e.g., ref_idx_l1[x0][y0]) is derived based on the information about the SMVD without being directly signaled.

[0277] In the foregoing embodiments, the method is described based on a flowchart as a series of steps or blocks, but the corresponding embodiments are not limited to the order of the steps. A certain step may occur in a different step and a different order than described above, or simultaneously. Also, those skilled in the art can understand that the steps shown in the flowchart are not exclusive, and different steps may be included, or one or more steps of the flowchart may be deleted without affecting the scope of the embodiments of this document.

[0278] The method according to the embodiments of this document described above can be embodied in the form of software, and the encoding device and / or decoding device according to this document can be included in a device that performs video processing, such as a TV, a computer, a smartphone, a set-top box, a display device, etc.

[0279] In this document, when an embodiment is embodied in software, the method described above can be embodied by modules (processes, functions, etc.) that perform the above-described functions. The modules can be stored in a memory and executed by a processor. The memory may be inside or outside the processor and may be connected to the processor by various well-known means. The processor can include an ASIC (Application-Specific Integrated Circuit), other chip sets, logic circuits, and / or data processing devices. The memory can include a ROM (Read-Only Memory), a RAM (Random Access Memory), a flash memory, a memory card, a storage medium, and / or other storage devices. That is, the embodiments described in this document can be embodied and performed on a processor, a microprocessor, a controller, or a chip. For example, the functional units shown in each drawing can be embodied and performed on a computer, a processor, a microprocessor, a controller, or a chip. In this case, information for embodiment (for example, information on instructions) or an algorithm can be stored in a digital storage medium.

[0280] In addition, the decoding device and encoding device to which the embodiments of this document are applied can be included in a multimedia broadcast transceiver, a mobile communication terminal, a home cinema video device, a digital cinema video device, a surveillance camera, a video conferencing device, a real-time communication device such as video communication, a mobile streaming device, a storage medium, a camcorder, a video-on-demand (VoD) service providing device, an OTT video (Over the Top video) device, an Internet streaming service providing device, a three-dimensional (3D) video device, a VR (Virtual Reality) device, an AR (Augmented Reality) device, a videophone video device, a transportation means terminal (e.g., a vehicle (including an autonomous driving vehicle) terminal, an airplane terminal, a ship terminal, etc.) and a medical video device, etc., and can be used to process video signals or data signals. For example, as an OTT video (Over The Top video) device, it can include a game console, a Blu-ray player, an Internet access TV, a home theater system, a smartphone, a tablet PC, a DVR (Digital Video Recorder), etc.

[0281] In addition, the processing method to which the embodiments of this document are applied can be produced in the form of a program executed by a computer and can be stored in a recording medium readable by a computer. Multimedia data having a data structure according to the embodiments of this document can also be stored in a recording medium readable by a computer. The above-mentioned recording medium readable by a computer includes all types of storage devices and distributed storage devices in which data readable by a computer is stored. The above-mentioned recording medium readable by a computer can include, for example, Blu-ray Disc (BD), Universal Serial (Universal Serial) Bus (USB), ROM, PROM, EPROM, EEPROM, RAM, CD-ROM, magnetic tape, floppy disk, and optical data storage devices. Further, the above-mentioned recording medium readable by a computer includes a medium embodied in the form of a carrier wave (for example, transmission via the Internet). Also, a bitstream generated by an encoding method can be stored in a recording medium readable by a computer or can be transmitted via a wired or wireless communication network.

[0282] In addition, the embodiments of this document can be embodied in a computer program product by program code, and the above program code can be executed by a computer according to the embodiments of this document. The above program code can be stored on a carrier readable by a computer.

[0283] FIG. 18 shows an example of a content streaming system to which the embodiments disclosed in this document can be applied.

[0284] Referring to FIG. 18, the content streaming system to which the embodiments of this document are applied can generally include an encoding server, a streaming server, a web server, a media storage, a user device, and a multimedia input device.

[0285] The encoding server compresses the content input from multimedia input devices such as smartphones, cameras, and camcorders into digital data to generate a bitstream, and serves to transmit this to the streaming server. As another example, when a multimedia input device such as a smartphone, camera, or camcorder directly generates a bitstream, the encoding server may be omitted.

[0286] The bitstream can be generated by an encoding method or a bitstream generation method to which the embodiments of this document are applied, and the streaming server can temporarily store the bitstream in the process of transmitting or receiving the bitstream.

[0287] The streaming server transmits multimedia data to a user device based on a user request via a web server, and the web server serves as a medium to inform the user of what services are available. If the user requests a desired service from the web server, the web server transmits this to the streaming server, and the streaming server transmits multimedia data to the user. At this time, the content streaming system can include another control server, and in this case, the control server serves to control commands / responses between each device in the content streaming system.

[0288] The streaming server can receive content from a media storage device (repository) and / or an encoding server. For example, when receiving content from the encoding server, the content can be received in real time. In this case, in order to provide a smooth streaming service, the streaming server can store the bitstream for a certain period of time.

[0289] In the above examples of user devices, there may be mobile phones, smart phones, laptop computers, digital broadcast terminals, PDAs (Personal Digital Assistants), PMPs (Portable Multimedia Players), navigations, slate PCs, tablet PCs, ULTRABOOKs (registered trademark), wearable devices (for example, smartwatches (watch-type terminals), smart glasses (glass-type terminals), HMDs (Head Mounted Displays)), digital TVs, desktop computers, digital signatures (signid), etc.

[0290] Each server in the above content streaming system can be operated as a distributed server, and in this case, the data received by each server can be distributedly processed.

[0291] The claims described in this specification can be combined in various ways. For example, the technical features of the method claims in this specification can be combined and implemented as a device, and the technical features of the device claims in this specification can be combined and implemented as a method. Also, the technical features of the method claims in this specification and the technical features of the device claims can be combined and implemented as a device, and the technical features of the method claims in this specification and the technical features of the device claims can be combined and implemented as a method.

Claims

1. A video decoding method performed by a decoding apparatus, comprising: obtaining video information including prediction-related information, information regarding an MVP (motion vector predictor) index, and information regarding an MVD (Motion Vector Difference) via a bitstream, wherein the prediction-related information includes information regarding SMVD (symmetric motion vector differences); deriving an inter prediction mode for a current block based on the prediction-related information; deriving a reference picture index for L0 and a reference picture index for L1 based on the information regarding the SMVD; constructing an MVP candidate list including an MVP candidate list for L0 and an MVP candidate list for L1 based on peripheral blocks of the current block; deriving an MVP for the current block including an MVP for L0 and an MVP for L1 from an MVP candidate indicated by an MVP index in the MVP candidate list; deriving a motion vector for L0 by summing an MVD for L0 and the MVP for L0, and deriving a motion vector for L1 by summing an MVD for L1 and the MVP for L1; generating a prediction sample for the current block based on motion information for L0 including the reference picture index for L0 and the motion vector for L0, and motion information for L1 including the reference picture index for L1 and the motion vector for L1; wherein the MVD for L0 is derived from the information regarding the MVD; the MVD for L1 is derived from the MVD for L0; a reference picture list including a reference picture list L0 and a reference picture list L1 is derived for the current block; when the value of the information regarding the SMVD is 1, a reference picture index of a first reference picture in the reference picture list L0 is the first reference picture is a short-term reference picture; The difference in POC (picture order count) between the current picture including the current block and the first reference picture is greater than 0, By confirming that the POC difference between the current picture and the first reference picture is smaller than the POC differences between the current picture and other reference pictures in the reference picture list L0, it is derived as the reference picture index for L0, The reference picture index of the second reference picture in the reference picture list L1 is The second reference picture is the short-term reference picture, The POC difference between the current picture and the second reference picture is smaller than 0, By confirming that the POC difference between the current picture and the second reference picture is greater than the POC differences between the current picture and other reference pictures in the reference picture list L1, it is derived as the reference picture index for L1, a video decoding method.

2. A video encoding method performed by an encoding device, A step of deriving an inter prediction mode for a current block, A step of deriving a reference picture index for L0 and a reference picture index for L1 based on SMVD (symmetric motion vector differences), A step of constructing an MVP (motion vector predictor) candidate list including an MVP candidate list for L0 and an MVP candidate list for L1 based on the peripheral blocks of the current block, A step of deriving an MVP for the current block including an MVP for L0 and an MVP for L1 based on the MVP candidate list, A step of generating information regarding the MVP index related to the MVP for the current block included in the MVP candidate list, A step of deriving motion information for L0 including a motion vector for L0 and the reference picture index for L0, and deriving motion information for L1 including a motion vector for L1 and the reference picture index for L1, Deriving an MVD (Motion Vector Difference) for L0 based on the MVP for L0 and the motion vector for L0; Generating prediction-related information related to the inter prediction mode and generating information regarding the MVD based on the MVD for L0; Generating a prediction sample for the current block based on the motion information for L0 and the motion information for L1; Generating residual information based on the prediction sample; Encoding video information including the information regarding the MVP index, the prediction-related information, the information regarding the MVD, and the residual information; The prediction-related information includes information regarding the SMVD; Deriving a reference picture list including reference picture list L0 and reference picture list L1 for the current block; When the value of the information regarding the SMVD is 1; The reference picture index of the first reference picture in reference picture list L0; The first reference picture is a short-term reference picture; The difference in POC (picture order count) between the current picture including the current block and the first reference picture is greater than 0; By confirming that the POC difference between the current picture and the first reference picture is smaller than the POC difference between the current picture and other reference pictures in reference picture list L0, it is derived as the reference picture index for L0; The reference picture index of the second reference picture in reference picture list L1; The second reference picture is the short-term reference picture; The POC difference between the current picture and the second reference picture is smaller than 0; By confirming that the POC difference between the current picture and the second reference picture is greater than the POC difference between the current picture and other reference pictures in reference picture list L1, it is derived as the reference picture index for L1, a video encoding method.

3. A method for transmitting data related to video, comprising: Generating a bitstream related to the video by performing the video encoding method according to claim 2; A transmission method including the step of transmitting the data including the bit stream.

Images