WO2021062684A1

WO2021062684A1 - Encoder, decoder and corresponding methods for inter prediction

Info

Publication number: WO2021062684A1
Application number: PCT/CN2019/109567
Authority: WO
Inventors: Huanbang CHEN; Haitao Yang; Lian Zhang
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2019-09-30
Filing date: 2019-09-30
Publication date: 2021-04-08

Abstract

An inter prediction method, comprising: determining a target list0 index and a target listl index, wherein a reference picture with the target list0 index and a reference picture with the target listl index are short term reference pictures, the nearest picture to a current picture in list0 and listl respectfully and locate on different sides of the current picture according to a display order; determining whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the listl reference picture index of the current block is the target listl index; and obtaining a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.

Description

AN ENCODER, A DECODER AND CORRESPONDING METHODS FOR INTER PREDICTION

TECHNICAL FIELD

Embodiments of the present application generally relate to the field of picture processing and more particularly to inter prediction.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital TV, video transmission over internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and camcorders of security applications.

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

SUMMARY

Embodiments of the present application provide apparatuses and methods for encoding and decoding according to the independent claims.

In a first aspect of the present application, an inter prediction method comprising: determining a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order; determining whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index; and obtaining a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.

In a feasible implementation, determining whether DMVR mode or BDOF mode is used for decoding the current block in the current picture based on the condition, comprising:

DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.

In a feasible implementation, a size of the reference picture with the target list0 index is the same as a size of the current picture, and a size of the reference picture with the target list1 index is the same as the size of the current picture.

In a feasible implementation, weighting factors for a luma component of the reference picture with the target list0 index are not carried by a bitstream corresponding to the current block, and weighting factors for a luma component of the reference picture with the target list1 index are not carried by the bitstream.

In a feasible implementation, DMVR mode or BDOF mode is used for decoding the current block in the event that at least two conditions are satisfied, and wherein one of the at least two conditions is the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index.

In a second aspect of the present application, an inter prediction apparatus, comprising: determining module, configured to determine a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order; checking module, configured to determine whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index; and calculating module, configured to obtain a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.

In a feasible implementation, the checking module is specifically configured to determine that DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.

In a feasible implementation, weighting factors for a luma component of the reference picture with the target list0 index are not carried by a bitstream corresponding to the current block, and weighting factors for a luma component of the reference picture with the target list0 index are not carried by the bitstream.

In a third aspect of the present application, a decoder, comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to the first aspect of the present application.

In a fourth aspect of the present application, an encoder, comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to the first aspect of the present application.

In a fifth aspect of the present application, a non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method of the first aspect of the present application.

In a sixth aspect of the present application, a computer program product comprising program code for performing the method according to the first aspect of the present application when executed on a computer or a processor.

The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

Particular embodiments are outlined in the attached independent claims, with other embodiments in the dependent claims.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

It is noted that in the present application, some conditions for determining Symmetric MVD mode, DMVR mode and BDOF mode can be unified. Therefore, the logical module for implementing such conditions can be reused. The implementation resource can be saved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in more detail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding system configured to implement embodiments of the invention;

FIG. 1B is a block diagram showing another example of a video coding system configured to implement embodiments of the invention;

FIG. 2 is a block diagram showing an example of a video encoder configured to implement embodiments of the invention;

FIG. 3 is a block diagram showing an example structure of a video decoder configured to implement embodiments of the invention;

FIG. 4 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus;

FIG. 6 is a diagram showing an example of symmetric MVD mode;

FIG. 7 is a diagram showing an example of DMVR mode;

FIG. 8 is a diagram showing an example of BDOF calculating algorithm;

FIG. 9 is a block diagram illustrating an example of a prediction method;

FIG. 10 is a block diagram showing an example of a prediction apparatus configured to implement embodiments of the application;

FIG. 11 is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus;

FIG. 12 is a block diagram showing an example structure of a content supply system 3100 which realizes a content delivery service;

FIG. 13 is a block diagram showing a structure of an example of a terminal device.

In the following identical reference signs refer to identical or at least functionally equivalent features if not explicitly specified otherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps) , even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units) , even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term “picture” the term “frame” or “image” may be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts video encoding and video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission) . Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to “coding” of video pictures (or pictures in general) shall be understood to relate to “encoding” or “decoding” of video pictures or respective video sequences. The combination of the encoding part and the decoding part is also referred to as CODEC (Coding and Decoding) .

In case of lossless video coding, the original video pictures might be reconstructed, i.e. the reconstructed video pictures have the same quality as the original video pictures (assuming no transmission loss or other data loss during storage or transmission) . In case of lossy video coding, further compression, e.g. by quantization, is performed, to reduce the amount of data representing the video pictures, which cannot be completely reconstructed at the decoder, i.e. the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures.

Several video coding standards belong to the group of “lossy hybrid video codecs” (i.e. combine spatial and temporal prediction in the sample domain and 2D transform coding for applying quantization in the transform domain) . Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (video block) level, e.g. by using spatial (intra picture) prediction and/or temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression) , whereas at the decoder the inverse processing compared to the encoder is applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra-and inter predictions) and/or re-constructions for processing, i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a video encoder 20 and a video decoder 30 are described based on Figs. 1 to 3.

Fig. 1A is a schematic block diagram illustrating an example coding system 10, e.g. a video coding system 10 (or short coding system 10) that may utilize techniques of this present application. Video encoder 20 (or short encoder 20) and video decoder 30 (or short decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12 configured to provide encoded picture data 21 e.g. to a destination device 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e. optionally, comprise a picture source 16, a pre-processor (or pre-processing unit) 18, e.g. a picture pre-processor 18, and a communication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture) . The picture source may be any kind of memory or storage storing any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed by the pre-processing unit 18, the picture or picture data 17 may also be referred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 and to perform pre-processing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. Pre-processing performed by the pre-processor 18 may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr) , color correction, or de-noising. It might be understood that the pre-processing unit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picture data 19 and provide encoded picture data 21 (further details will be described below, e.g., based on Fig. 2) . Communication interface 22 of the source device 12 may be configured to receive the encoded picture data 21 and to transmit the encoded picture data 21 (or any further processed version thereof) over communication channel 13 to another device, e.g. the destination device 14 or any other device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder 30) , and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, a post-processor 32 (or post-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 is configured receive the encoded picture data 21 (or any further processed version thereof) , e.g. directly from the source device 12 or from any other source, e.g. a storage device, e.g. an encoded picture data storage device, and provide the encoded picture data 21 to the decoder 30.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded picture data 21 or encoded data 13 via a direct communication link between the source device 12 and the destination device 14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof.

The communication interface 22 may be, e.g., configured to package the encoded picture data 21 into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a communication link or communication network.

The communication interface 28, forming the counterpart of the communication interface 22, may be, e.g., configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel 13 in Fig. 1A pointing from the source device 12 to the destination device 14, or bi-directional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 and provide decoded picture data 31 or a decoded picture 31 (further details will be described below, e.g., based on Fig. 3 or Fig. 5) .

The post-processor 32 of destination device 14 is configured to post-process the decoded picture data 31 (also called reconstructed picture data) , e.g. the decoded picture 31, to obtain post-processed picture data 33, e.g. a post-processed picture 33. The post-processing performed by the post-processing unit 32 may comprise, e.g. color format conversion (e.g. from YCbCr to RGB) , color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured to receive the post-processed picture data 33 for displaying the picture, e.g. to a user or viewer. The display device 34 may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD) , organic light emitting diodes (OLED) displays, plasma displays, projectors , micro LED displays, liquid crystal on silicon (LCoS) , digital light processor (DLP) or any kind of other display.

Although Fig. 1A depicts the source device 12 and the destination device 14 as separate devices, embodiments of devices may also comprise both or both functionalities, the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device 12 and/or destination device 14 as shown in Fig. 1A may vary depending on the actual device and application.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a video decoder 30) or both encoder 20 and decoder 30 may be implemented via processing circuitry as shown in Fig. 1B, such as one or more microprocessors, digital signal processors (DSPs) , application-specific integrated circuits (ASICs) , field-programmable gate arrays (FPGAs) , discrete logic, hardware, video coding dedicated or any combinations thereof. The encoder 20 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to encoder 20of FIG. 2 and/or any other encoder system or subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to embody the various modules as discussed with respect to decoder 30 of FIG. 3 and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. As shown in Fig. 5, if the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Either of video encoder 20 and video decoder 30 may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in Fig. 1B.

Source device 12 and destination device 14 may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers) , broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in Fig. 1A is merely an example and the techniques of the present application may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

For convenience of description, embodiments of the invention are described herein, for example, by reference to High-Efficiency Video Coding (HEVC) or to the reference software of Versatile Video coding (VVC) , the next generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG) . One of ordinary skill in the art will understand that embodiments of the invention are not limited to HEVC or VVC.

Encoder and Encoding Method

Fig. 2 shows a schematic block diagram of an example video encoder 20 that is configured to implement the techniques of the present application. In the example of Fig. 2, the video encoder 20 comprises an input 201 (or input interface 201) , a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, and inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270 and an output 272 (or output interface 272) . The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254 and a partitioning unit 262. Inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown) . A video encoder 20 as shown in Fig. 2 may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, whereas the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, wherein the backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see video decoder 30 in Fig. 3) . The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244 and the intra-prediction unit 254 are also referred to forming the “built-in decoder” of video encoder 20.

Pictures &Picture Partitioning (Pictures &Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, a picture 17 (or picture data 17) , e.g. picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture 19 (or pre-processed picture data 19) . For sake of simplicity the following description refers to the picture 17. The picture 17 may also be referred to as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture) .

A (digital) picture is or might be regarded as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as pixel (short form of picture element) or a pel. The number of samples in horizontal and vertical direction (or axis) of the array or picture define the size and/or resolution of the picture. For representation of color, typically three color components are employed, i.e. the picture may be represented or include three sample arrays. In RBG format or color space a picture comprises a corresponding red, green and blue sample array. However, in video coding each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which comprises a luminance component indicated by Y (sometimes also L is used instead) and two chrominance components indicated by Cb and Cr. The luminance (or short luma) component Y represents the brightness or grey level intensity (e.g. like in a grey-scale picture) , while the two chrominance (or short chroma) components Cb and Cr represent the chromaticity or color information components. Accordingly, a picture in YCbCr format comprises a luminance sample array of luminance sample values (Y) , and two chrominance sample arrays of chrominance values (Cb and Cr) . Pictures in RGB format may be converted or transformed into YCbCr format and vice versa, the process is also known as color transformation or conversion. If a picture is monochrome, the picture may comprise only a luminance sample array. Accordingly, a picture may be, for example, an array of luma samples in monochrome format or an array of luma samples and two corresponding arrays of chroma samples in 4: 2: 0, 4: 2: 2, and 4: 4: 4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioning unit (not depicted in Fig. 2) configured to partition the picture 17 into a plurality of (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macro blocks (H. 264/AVC) or coding tree blocks (CTB) or coding tree units (CTU) (H. 265/HEVC and VVC) . The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receive directly a block 203 of the picture 17, e.g. one, several or all blocks forming the picture 17. The picture block 203 may also be referred to as current picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or might be regarded as a two-dimensional array or matrix of samples with intensity values (sample values) , although of smaller dimension than the picture 17. In other words, the block 203 may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture 17, or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture 17) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block 203 define the size of block 203. Accordingly, a block may, for example, an MxN (M-column by N-row) array of samples, or an MxN array of transform coefficients.

Embodiments of the video encoder 20 as shown in Fig. 2 may be configured to encode the picture 17 block by block, e.g. the encoding and prediction is performed per block 203.

Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using slices (also referred to as video slices) , wherein a picture may be partitioned into or encoded using one or more slices (typically non-overlapping) , and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H. 265/HEVC and VVC) or bricks (VVC) ) .

Embodiments of the video encoder 20 as shown in Fig. 2 may be further configured to partition and/or encode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles) , wherein a picture may be partitioned into or encoded using one or more slices/tile groups (typically non-overlapping) , and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs) , e.g. complete or fractional blocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the picture block 203 and a prediction block 265 (further details about the prediction block 265 are provided later) , e.g. by subtracting sample values of the prediction block 265 from sample values of the picture block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST) , on the sample values of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H. 265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit 212 (and the corresponding inverse transform, e.g. by inverse transform processing unit 312 at video decoder 30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 206, at an encoder 20 may be specified accordingly.

Embodiments of the video encoder 20 (respectively transform processing unit 206) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g. directly or encoded or compressed via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transform coefficients 207 to obtain quantized coefficients 209, e.g. by applying scalar quantization or vector quantization. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m-bit Transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP) . For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP) . The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit 210, may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208) may be configured to output quantization parameters (QP) , e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., the video decoder 30 may receive and apply the quantization parameters for decoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, e.g. by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 211 may also be referred to as dequantized residual coefficients 211 and correspond -although typically not identical to the transform coefficients due to the loss by quantization -to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured to add the transform block 213 (i.e. reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, e.g. by adding –sample by sample -the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220) , is configured to filter the reconstructed block 215 to obtain a filtered block 221, or in general, to filter reconstructed samples to obtain filtered sample values. The loop filter unit is, e.g., configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 220 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF) , a noise suppression filter (NSF) , or any combination thereof. In an example, the loop filter unit 220 may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit 220 is shown in FIG. 2 as being an in loop filter, in other configurations, the loop filter unit 220 may be implemented as a post loop filter. The filtered block 221 may also be referred to as filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220) may be configured to output loop filter parameters (such as SAO filter parameters or ALF filter parameters or LMCS parameters) , e.g. directly or encoded via the entropy encoding unit 270, so that, e.g., a decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) , including synchronous DRAM (SDRAM) , magnetoresistive RAM (MRAM) , resistive RAM (RRAM) , or other types of memory devices. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded picture buffer 230 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks 221, of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples) , for example for inter prediction. The decoded picture buffer (DPB) 230 may be also configured to store one or more unfiltered reconstructed blocks 215, or in general unfiltered reconstructed samples, e.g. if the reconstructed block 215 is not filtered by loop filter unit 220, or any other further processed version of the reconstructed blocks or samples.

Mode Selection (Partitioning &Prediction)

The mode selection unit 260 comprises partitioning unit 262, inter-prediction unit 244 and intra-prediction unit 254, and is configured to receive or obtain original picture data, e.g. an original block 203 (current block 203 of the current picture 17) , and reconstructed picture data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from decoded picture buffer 230 or other buffers (e.g. line buffer, not shown) .. The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra or inter prediction mode) and generate a corresponding prediction block 265, which is used for the calculation of the residual block 205 and for the reconstruction of the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit 260) , which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage) , or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage) , or which considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO) , i.e. select the prediction mode which provides a minimum rate distortion. Terms like “best” , “minimum” , “optimum” etc. in this context do not necessarily refer to an overall “best” , “minimum” , “optimum” , etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a “sub-optimum selection” but reducing complexity and processing time.

In other words, the partitioning unit 262 may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs) , and the CTU 203 may be further partitioned into smaller block partitions or sub-blocks (which form again blocks) , e.g. iteratively using quad-tree-partitioning (QT) , binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g., the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block 203 and the prediction modes are applied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) and prediction processing (by inter-prediction unit 244 and intra-prediction unit 254) performed by an example video encoder 20 will be explained in more detail.

Partitioning

The partitioning unit 262 may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs) , and the partitioning unit 262 may partition (or split) a coding tree unit (CTU) 203 into smaller partitions, e.g. smaller blocks of square or rectangular size. For a picture that has three sample arrays, a CTU consists of an N×N block of luma samples together with two corresponding blocks of chroma samples. The maximum allowed size of the luma block in a CTU is specified to be 128×128 in the developing versatile video coding (VVC) , but it might be specified to be value rather than 128x128 in the future, for example, 256x256. The CTUs of a picture may be clustered/grouped as slices/tile groups, tiles or bricks. A tile covers a rectangular region of a picture, and a tile might be divided into one or more bricks. A brick consists of a number of CTU rows within a tile. A tile that is not partitioned into multiple bricks might be referred to as a brick. However, a brick is a true subset of a tile and is not referred to as a tile. There are two modes of tile groups are supported in VVC, namely the raster-scan slice/tile group mode and the rectangular slice mode. In the raster-scan tile group mode, a slice/tile group contains a sequence of tiles in tile raster scan of a picture. In the rectangular slice mode, a slice contains a number of bricks of a picture that collectively form a rectangular region of the picture. The bricks within a rectangular slice are in the order of brick raster scan of the slice. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to tree-partitioning or hierarchical tree-partitioning, wherein a root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0) , may be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level 1, depth 1) , wherein these blocks may be again partitioned into two or more blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2, depth 2) , etc. until the partitioning is terminated, e.g. because a termination criterion is fulfilled, e.g. a maximum tree depth or minimum block size is reached. Blocks which are not further partitioned are also referred to as leaf-blocks or leaf nodes of the tree. A tree using partitioning into two partitions is referred to as binary-tree (BT) , a tree using partitioning into three partitions is referred to as ternary-tree (TT) , and a tree using partitioning into four partitions is referred to as quad-tree (QT) .

For example, a coding tree unit (CTU) may be or comprise a CTB of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly, a coding tree block (CTB) may be an NxN block of samples for some value of N such that the division of a component into CTBs is a partitioning. A coding unit (CU) may be or comprise a coding block of luma samples, two corresponding coding blocks of chroma samples of a picture that has three sample arrays, or a coding block of samples of a monochrome picture or a picture that is coded using three separate colour planes and syntax structures used to code the samples. Correspondingly a coding block (CB) may be an MxN block of samples for some values of M and N such that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may be split into CUs by using a quad-tree structure denoted as coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the leaf CU level. Each leaf CU might be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a leaf CU might be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU.

In embodiments, e.g., according to the latest video coding standard currently in development, which is referred to as Versatile Video Coding (VVC) , a combined Quad-tree nested multi-type tree using binary and ternary splits segmentation structure, for example used to partition a coding tree unit. In the coding tree structure within a coding tree unit, a CU can have either a square or rectangular shape. For example, the coding tree unit (CTU) is first partitioned by a quaternary tree. Then the quaternary tree leaf nodes might be further partitioned by a multi-type tree structure. There are four splitting types in multi-type tree structure, vertical binary splitting (SPLIT_BT_VER) , horizontal binary splitting (SPLIT_BT_HOR) , vertical ternary splitting (SPLIT_TT_VER) , and horizontal ternary splitting (SPLIT_TT_HOR) . The multi-type tree leaf nodes are called coding units (CUs) , and unless the CU is too large for the maximum transform length, this segmentation is used for prediction and transform processing without any further partitioning. This means that, in most cases, the CU, PU and TU have the same block size in the quadtree with nested multi-type tree coding block structure. The exception occurs when maximum supported transform length is smaller than the width or height of the colour component of the CU. VVC develops a unique signaling mechanism of the partition splitting information in quadtree with nested multi-type tree coding tree structure. In the signaling mechanism, a coding tree unit (CTU) is treated as the root of a quaternary tree and is first partitioned by a quaternary tree structure. Each quaternary tree leaf node (when sufficiently large to allow it) is then further partitioned by a multi-type tree structure. In the multi-type tree structure, a first flag (mtt_split_cu_flag) is signaled to indicate whether the node is further partitioned; when a node is further partitioned, a second flag (mtt_split_cu_vertical_flag) is signaled to indicate the splitting direction, and then a third flag (mtt_split_cu_binary_flag) is signaled to indicate whether the split is a binary split or a ternary split. Based on the values of mtt_split_cu_vertical_flag and mtt_split_cu_binary_flag, the multi-type tree slitting mode (MttSplitMode) of a CU might be derived by a decoder based on a predefined rule or a table. It should be noted, for a certain design, for example, 64×64 Luma block and 32×32 Chroma pipelining design in VVC hardware decoders, TT split is forbidden when either width or height of a luma coding block is larger than 64, as shown in Fig. 6. TT split is also forbidden when either width or height of a chroma coding block is larger than 32. The pipelining design will divide a picture into Virtual pipeline data units (VPDUs) which are defined as non-overlapping units in a picture. In hardware decoders, successive VPDUs are processed by multiple pipeline stages simultaneously. The VPDU size is roughly proportional to the buffer size in most pipeline stages, so it is important to keep the VPDU size small. In most hardware decoders, the VPDU size might be set to maximum transform block (TB) size. However, in VVC, ternary tree (TT) and binary tree (BT) partition may lead to the increasing of VPDUs sizes.

In addition, it should be noted that, when a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block is forced to be split until the all samples of every coded CU are located inside the picture boundaries.

As an example, the Intra Sub-Partitions (ISP) tool may divide luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size. In one example, the mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

As described above, the video encoder 20 is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in HEVC, or may comprise 67 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined for VVC. As an example, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks, e.g. as defined in VVC. As another example, to avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks. And, the results of intra prediction of planar mode may be further modified by a position dependent intra prediction combination (PDPC) method.

The intra-prediction unit 254 is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block 265 according to an intra-prediction mode of the set of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit 260) is further configured to output intra-prediction parameters (or in general information indicative of the selected intra prediction mode for the block) to the entropy encoding unit 270 in form of syntax elements 266 for inclusion into the encoded picture data 21, so that, e.g., the video decoder 30 may receive and use the prediction parameters for decoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP 230) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel, quarter-pel and/or 1/16 pel interpolation, or not.

Additional to the above prediction modes, skip mode, direct mode and/or other inter prediction mode may be applied.

For example, Extended merge prediction, the merge candidate list of such mode is constructed by including the following five types of candidates in order: Spatial MVP from spatial neighbor CUs, Temporal MVP from collocated CUs, History-based MVP from an FIFO table, Pairwise average MVP and Zero MVs. And a bilateral-matching based decoder side motion vector refinement (DMVR) may be applied to increase the accuracy of the MVs of the merge mode. Merge mode with MVD (MMVD) , which comes from merge mode with motion vector differences. A MMVD flag is signaled right after sending a skip flag and merge flag to specify whether MMVD mode is used for a CU. And a CU-level adaptive motion vector resolution (AMVR) scheme may be applied. AMVR allows MVD of the CU to be coded in different precision. Dependent on the prediction mode for the current CU, the MVDs of the current CU might be adaptively selected. When a CU is coded in merge mode, the combined inter/intra prediction (CIIP) mode may be applied to the current CU. Weighted averaging of the inter and intra prediction signals is performed to obtain the CIIP prediction. Affine motion compensated prediction, the affine motion field of the block is described by motion information of two control point (4-parameter) or three control point motion vectors (6-parameter) . Subblock-based temporal motion vector prediction (SbTMVP) , which is similar to the temporal motion vector prediction (TMVP) in HEVC, but predicts the motion vectors of the sub-CUs within the current CU. Bi-directional optical flow (BDOF) , previously referred to as BIO, is a simpler version that requires much less computation, especially in terms of number of multiplications and the size of the multiplier. Triangle partition mode, in such a mode, a CU is split evenly into two triangle-shaped partitions, using either the diagonal split or the anti-diagonal split. Besides, the bi-prediction mode is extended beyond simple averaging to allow weighted averaging of the two prediction signals.

The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in Fig. 2) . The motion estimation unit may be configured to receive or obtain the picture block 203 (current picture block 203 of the current picture 17) and a decoded picture 231, or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures 231, for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures 231, or in other words, the current picture and the previously decoded pictures 231 may be part of or form a sequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit. This offset is also called motion vector (MV) .

The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 265. Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists.

The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder 30 in decoding the picture blocks of the video slice. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, an entropy encoding algorithm or scheme (e. g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CAVLC) , an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC) , syntax-based context-adaptive binary arithmetic coding (SBAC) , probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients 209, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data 21 which might be output via the output 272, e.g. in the form of an encoded bitstream 21, so that, e.g., the video decoder 30 may receive and use the parameters for decoding, . The encoded bitstream 21 may be transmitted to video decoder 30, or stored in a memory for later transmission or retrieval by video decoder 30.

Other structural variations of the video encoder 20 might be used to encode the video stream. For example, a non-transform based encoder 20 can quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

Fig. 3 shows an example of a video decoder 30 that is configured to implement the techniques of this present application. The video decoder 30 is configured to receive encoded picture data 21 (e.g. encoded bitstream 21) , e.g. encoded by encoder 20, to obtain a decoded picture 331. The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice (and/or tile groups or tiles) and associated syntax elements.

In the example of Fig. 3, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g. a summer 314) , a loop filter 320, a decoded picture buffer (DBP) 330, a mode application unit 360, an inter prediction unit 344 and an intra prediction unit 354. Inter prediction unit 344 may be or include a motion compensation unit. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 344 and the intra prediction unit 354 are also referred to as forming the “built-in decoder” of video encoder 20. Accordingly, the inverse quantization unit 310 may be identical in function to the inverse quantization unit 110, the inverse transform processing unit 312 may be identical in function to the inverse transform processing unit 212, the reconstruction unit 314 may be identical in function to reconstruction unit 214, the loop filter 320 may be identical in function to the loop filter 220, and the decoded picture buffer 330 may be identical in function to the decoded picture buffer 230. Therefore, the explanations provided for the respective units and functions of the video 20 encoder apply correspondingly to the respective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21 (or in general encoded picture data 21) and perform, for example, entropy decoding to the encoded picture data 21 to obtain, e.g., quantized coefficients 309 and/or decoded coding parameters (not shown in Fig. 3) , e.g. any or all of inter prediction parameters (e.g. reference picture index and motion vector) , intra prediction parameter (e.g. intra prediction mode or index) , transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. Entropy decoding unit 304 maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit 270 of the encoder 20. Entropy decoding unit 304 may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode application unit 360 and other parameters to other units of the decoder 30. Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receive quantization parameters (QP) (or in general information related to the inverse quantization) and quantized coefficients from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients 309 to obtain dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include use of a quantization parameter determined by video encoder 20 for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receive dequantized coefficients 311, also referred to as transform coefficients 311, and to apply a transform to the dequantized coefficients 311 in order to obtain reconstructed residual blocks 213 in the sample domain. The reconstructed residual blocks 213 may also be referred to as transform blocks 313. The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may be further configured to receive transform parameters or corresponding information from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) to determine the transform to be applied to the dequantized coefficients 311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configured to add the reconstructed residual block 313, to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit 320 may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF) , a noise suppression filter (NSF) , or any combination thereof. In an example, the loop filter unit 220 may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit 320 is shown in FIG. 3 as being an in loop filter, in other configurations, the loop filter unit 320 may be implemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decoded picture buffer 330, which stores the decoded pictures 331 as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. via output 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular to the motion compensation unit) and the intra prediction unit 354 may be identical to the inter prediction unit 254 in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data 21 (e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) . Mode application unit 360 may be configured to perform the prediction (intra or inter prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block 365.

When the video slice is coded as an intra coded (I) slice, intra prediction unit 354 of mode application unit 360 is configured to generate prediction block 365 for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g. motion compensation unit) of mode application unit 360 is configured to produce prediction blocks 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB 330. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices) , e.g. a video may be coded using I, P or B tile groups and /or tiles.

Mode application unit 360 is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors or related information and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the mode application unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice) , construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices) , e.g. a video may be coded using I, P or B tile groups and/or tiles.

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using slices (also referred to as video slices) , wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping) , and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H. 265/HEVC and VVC) or bricks (VVC) ) .

Embodiments of the video decoder 30 as shown in Fig. 3 may be configured to partition and/or decode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles) , wherein a picture may be partitioned into or decoded using one or more slices/tile groups (typically non-overlapping) , and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs) , e.g. complete or fractional blocks.

Other variations of the video decoder 30 might be used to decode the encoded picture data 21. For example, the decoder 30 can produce the output video stream without the loop filtering unit 320. For example, a non-transform based decoder 30 can inverse-quantize the residual signal directly without the inverse-transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 can have the inverse-quantization unit 310 and the inverse-transform processing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, a processing result of a current step may be further processed and then output to the next step. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering.

It should be noted that further operations may be applied to the derived motion vectors of current block (including but not limit to control point motion vectors of affine mode, sub-block motion vectors in affine, planar, ATMVP modes, temporal motion vectors, and so on) . For example, the value of motion vector is constrained to a predefined range according to its representing bit. If the representing bit of motion vector is bitDepth, then the range is -2^ (bitDepth-1) ～ 2^ (bitDepth-1) -1, where “^” means exponentiation. For example, if bitDepth is set equal to 16, the range is -32768 ～ 32767; if bitDepth is set equal to 18, the range is -131072～131071. For example, the value of the derived motion vector (e.g. the MVs of four 4x4 sub-blocks within one 8x8 block) is constrained such that the max difference between integer parts of the four 4x4 sub-block MVs is no more than N pixels, such as no more than 1 pixel. Here provides two methods for constraining the motion vector according to the bitDepth.

FIG. 4 is a schematic diagram of a video coding device 400 according to an embodiment of the disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device 400 may be a decoder such as video decoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports 410) and receiver units (Rx) 420 for receiving data; a processor, logic unit, or central processing unit (CPU) 430 to process the data; transmitter units (Tx) 440 and egress ports 450 (or output ports 450) for transmitting the data; and a memory 460 for storing the data. The video coding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 410, the receiver units 420, the transmitter units 440, and the egress ports 450 for egress or ingress of optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor) , FPGAs, ASICs, and DSPs. The processor 430 is in communication with the ingress ports 410, receiver units 420, transmitter units 440, egress ports 450, and memory 460. The processor 430 comprises a coding module 470. The coding module 470 implements the disclosed embodiments described above. For instance, the coding module 470 implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module 470 therefore provides a substantial improvement to the functionality of the video coding device 400 and effects a transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 460 may be, for example, volatile and/or non-volatile and may be a read-only memory (ROM) , random access memory (RAM) , ternary content-addressable memory (TCAM) , and/or static random-access memory (SRAM) .

Fig. 5 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 12 and the destination device 14 from Fig. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 might be a central processing unit. Alternatively, the processor 502 might be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations might be practiced with a single processor as shown, e.g., the processor 502, advantages in speed and efficiency might be achieved using more than one processor.

A memory 504 in the apparatus 500 might be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device might be used as the memory 504. The memory 504 can include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 can further include an operating system 508 and application programs 510, the application programs 510 including at least one program that permits the processor 502 to perform the methods described here. For example, the application programs 510 can include applications 1 through N, which further include a video coding application that performs the methods described here. The apparatus 500 can also include one or more output devices, such as a display 518. The display 518 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 518 might be coupled to the processor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500 might be composed of multiple buses. Further, the secondary storage 514 might be directly coupled to the other components of the apparatus 500 or might be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations.

Some techniques which might be implemented with the current solution of this application are introduced as following. It is noted that the description of the techniques refers to the document JVET-O2002-v2, which can be downloaded from the website http: //phenix. int-evry. fr/jvet/. The specific implementation might have different variants based on the techniques introduced by JVET-O2002-v2, which is not limited by the present application.

Symmetric MVD coding

Besides the normal unidirectional prediction and bi-directional prediction mode MVD signalling, symmetric MVD mode for bi-predictional MVD signalling is applied. In the symmetric MVD mode, motion information including reference picture indices of both list0 and list1 and MVD of list1 are not signaled but derived.

The decoding process of the symmetric MVD mode is as follows:

1. At slice level, variables BiDirPredFlag, RefIdxSymL0 and RefIdxSymL1 are derived as follows:

– If mvd_l1_zero_flag is 1, BiDirPredFlag is set equal to 0.

– Otherwise, if the nearst reference picture in list0 and the nearst reference picture in list1 form a forward and backward pair of reference pictures or a backward and forward pair of reference pictures, as shown in Fig. 6, BiDirPredFlag is set to 1, and both list0 and list1 reference pictures are short-term reference pictures. Otherwise BiDirPredFlag is set to 0.

2.A t CU level, a symmetrical mode flag indicating whether symmetrical mode is used or not is explicitly signaled if the CU is bi-prediction coded and BiDirPredFlag is equal to 1.

The enabling condition of the symmetrical mode flag can be considered as:

When the symmetrical mode flag is true, only mvp_l0_flag, mvp_l1_flag and MVD0 are explicitly signaled. The reference indices for list0 and list1 are set equal to the pair of reference pictures, respectively. MVD1 is set equal to (–MVD0) . The final motion vectors are shown in below formula.

In the encoder, symmetric MVD motion estimation starts with initial MV evaluation. A set of initial MV candidates comprising of the MV obtained from uni-prediction search, the MV obtained from bi-prediction search and the MVs from the AMVP list. The one with the lowest rate-distortion cost is chosen to be the initial MV for the symmetric MVD motion search.

The decoding process for symmetric motion vector difference reference indices is descibed by a section of pseudo code as follows. And it is noted that the definition of the item using in the pseudo code might be refered to the document JVET-O2001-v14, which can be downloaded from the website http: //phenix. int-evry. fr/jvet/.

Example 1:

Output of this process are RefIdxSymL0 and RefIdxSymL1 specifying the list 0 and list 1 reference picture indices for symmetric motion vector differences, i.e., when sym_mvd_flag is equal to 1 for a coding unit.

The variable RefIdxSymLX with X being 0 and 1 is derived as follows:

– The variable currPic specifies the current picture.

– RefIdxSymL0 is set equal to -1.

– For each index i with i = 0.. NumRefIdxActive [0] -1, the following applies:

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) > 0,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) <DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.

– RefIdxSymL1 is set equal to -1.

– For each index i with i = 0.. NumRefIdxActive [1] -1, the following applies:

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) < 0,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) >

DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1.

– When RefIdxSymL0 is equal to -1 or RefIdxSymL1 is equal to -1, the following applies:

– RefIdxSymL0 is set equal to -1 and RefIdxSymL1 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) < 0,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) >

DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) > 0,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) <

Decoder side motion vector refinement (DMVR)

In bi-prediction operation, a refined MV is searched around the initial MVs in the reference picture list L0 and reference picture list L1. The BM method calculates the distortion between the two candidate blocks in the reference picture list L0 and list L1. As illustrated in Fig. 7, the SAD between the red blocks based on each MV candidate around the initial MV is calculated. The MV candidate with the lowest SAD becomes the refined MV and used to generate the bi-predicted signal.

The DMVR can be applied for the CUs which are coded with following modes and features:

● CU level merge mode with bi-prediction MV

● One reference picture is in the past and another reference picture is in the future with respect to the current picture

● The distances (i.e. POC difference) from both reference pictures to the current picture are same

● CU has more than 64 luma samples

● Both CU height and CU width are larger than or equal to 8 luma samples

● BCW weight index indicates equal weight

● WP is not enabled for the current block

● CIIP mode is not used for the current block

The refined MV derived by DMVR process is used to generate the inter prediction samples and also used in temporal motion vector prediction for future pictures coding. While the original MV is used in deblocking process and also used in spatial motion vector prediction for future CU coding.

In DMVR, the search points are surrounding the initial MV and the MV offset obey the MV difference mirroring rule. In other words, any points that are checked by DMVR, denoted by candidate MV pair (MV0, MV1) obey the following two equations:

MV0′=MV0+MV_offset

MV1′=MV1-MV_offset

Where MV_offset represents the refinement offset between the initial MV and the refined MV in one of the reference pictures. The refinement search range is two integer luma samples from the initial MV. The searching includes the integer sample offset search stage and fractional sample refinement stage.

25 points full search is applied for integer sample offset searching. The SAD of the initial MV pair is first calculated. If the SAD of the initial MV pair is smaller than a threshold, the integer sample stage of DMVR is terminated. Otherwise SADs of the remaining 24 points are calculated and checked in raster scanning order. The point with the smallest SAD is selected as the output of integer sample offset searching stage. To reduce the penalty of the uncertainty of DMVR refinement, it is proposed to favor the original MV during the DMVR process. The SAD between the reference blocks referred by the initial MV candidates is decreased by 1/4 of the SAD value.

The integer sample search is followed by fractional sample refinement. To save the calculation complexity, the fractional sample refinement is derived by using parametric error surface equation, instead of additional search with SAD comparison. The fractional sample refinement is conditionally invoked based on the output of the integer sample search stage. When the integer sample search stage is terminated with center having the smallest SAD in either the first iteration or the second iteration search, the fractional sample refinement is further applied.

In parametric error surface based sub-pixel offsets estimation, the center position cost and the costs at four neighboring positions from the center are used to fit a 2-D parabolic error surface equation of the following form

E (x, y) =A(x-x _min) ²+B(y-y _min) ²+C

where (x _min, y _min) corresponds to the fractional position with the least cost and C corresponds to the minimum cost value. By solving the above equations by using the cost value of the five search points, the (x _min, y _min) is computed as:

x _min= (E (-1, 0) -E(1, 0) ) / (2 (E(-1, 0) +E (1, 0) -2E (0, 0) ) )

y _min= (E (0, -1) -E (0, 1) ) / (2 ( (E (0, -1) + (0, 1) -2E (0, 0) ) )

The value of x _min and y _min are automatically constrained to be between –8 and 8 since all cost values are positive and the smallest value is E (0, 0) . This corresponds to half peal offset with 1/16th-pel MV accuracy in VTM6. The computed fractional (x _min, y _min) are added to the integer distance refinement MV to get the sub-pixel accurate refinement delta MV.

The resolution of the MVs is 1/16 luma samples. The samples at the fractional position are interpolated using an 8-tap interpolation filter. In DMVR, the search points are surrounding the initial fractional-pel MV with integer sample offset, therefore the samples of those fractional position needs to be interpolated for DMVR search process. To reduce the calculation complexity, the bi-linear interpolation filter is used to generate the fractional samples for the searching process in DMVR. Another important effect is that by using bi-linear filter is that with 2-sample search range, the DMVR does not access more reference samples compared to the normal motion compensation process. After the refined MV is attained with DMVR search process, the normal 8-tap interpolation filter is applied to generate the final prediction. In order to not access more reference samples to normal MC process, the samples, which is not needed for the interpolation process based on the original MV but is needed for the interpolation process based on the refined MV, will be padded from those available samples.

The Decoder side motion vector refinement process is descibed by a section of pseudo code as follows.

Example 2:

Inputs to this process are:

– a luma location (xSb, ySb) specifying the top-left sample of the current coding subblock relative to the top-left luma sample of the current picture,

– a variable sbWidth specifying the width of the current coding subblock in luma samples,

– a variable sbHeight specifying the height of the current coding subblock in luma samples,

– the luma motion vectors in 1/16 fractional-sample accuracy mvL0 and mvL1,

– the selected luma reference picture sample arrays refPicL0 _L and refPicL1 _L.

Outputs of this process are:

– delta luma motion vectors dMvL0 and dMvL1,

– a variable dmvrSAD specifying the mimimum sum of absolute differences.

The variable subPelFlag is set equal to 0, the variable srRange is set equal to 2 and the integer sample offset (intOffX, intOffY) is set equal to (0, 0) .

Both components of the delta luma motion vectors dMvL0 and dMvL1 are set equal to zero and modified as follows:

– For each X being 0 or 1, the (sbWidth + 2 *srRange) x (sbHeight + 2 *srRange) array predSamplesLX _L of prediction luma sample values is derived by invoking the fractional sample bilinear interpolation process specified in sub-section 1 with the luma location (xSb, ySb) , the prediction block width set equal to (sbWidth + 2 *srRange) , the prediction block height set equal to (sbHeight + 2 *srRange) , the reference picture sample array refPicLX _L, the motion vector mvLX and the refinement search range srRange as inputs.

– The variable minSad is derived by invoking the sum of absolute differences calculation process specified in sub-section 3 with the width sbW and height sbH of the current coding subblock set equal to sbWidth and sbHeight, the prediction sample arrays pL0 and pL1 set equal to predSamplesL0 _L and predSamplesL1 _L, and the offset (dX, dY) set equal to (0, 0) as inputs, and minSad as output.

– The variable dmvrSAD is set equal to minSad.

– When minSad is greater than or equal to sbHeight *sbWidth, the following applies:

– The 2-D array sadArray [dX + 2] [dY + 2] with dX = -2.. 2 and dY = -2.. 2 is derived by invoking the sum of absolute differences calculation process specified in sub-section 3 with the width sbW and height sbH of the current coding subblock set equal to sbWidth and sbHeight, the prediction sample arrays pL0 and pL1 set equal to predSamplesL0 _L and predSamplesL1 _L, and the offset (dX, dY) as inputs, and sadArray [dX + 2] [d Y + 2] as output.

– The integer sample offset (intOffX, intOffY) is modified by invoking the array entry selection process specified in sub-section 4 with the 2-D array sadArray [dX + 2] [dY + 2] with dX = -2.. 2 and dY = -2.. 2, the best integer sample offset (intOffX, intOffY) , and minSad as input, the modified best integer sample offset (intOffX, intOffY) and dmvrSad as outputs.

– When intOffX is not equal to -2 or 2, and intOffY is not equal to -2 or 2, subPelFlag is set equal to 1.

– The delta luma motion vector dMvL0 is modified as follows:

dMvL0 [0] += 16 *intOffX

dMvL0 [1] += 16 *intOffY

– When subPelFlag is equal to 1, the parametric motion vector refinement process specified in sub-section 5 is invoked with the 3x3 2-D array sadArray [dX + 2] [dY + 2] with dX = intOffX -1, intOffX, intOffX + 1 and dY = intOffY -1, intOffY, intOffY + 1, and the delta motion vector dMvL0 as inputs and the modified dMvL0 as output.

– The delta motion vector dMvL1 is derived as follows:

dMvL1 [0] = -dMvL0 [0]

dMvL1 [1] = -dMvL0 [1]

Sub-section 1 Fractional sample bilinear interpolation process

Inputs to this process are:

– a luma location (xSb, ySb) specifying the top-left sample of the current subblock relative to the top-left luma sample of the current picture,

– a variable pbWidth specifying the width of the current prediction block in luma samples,

– a variable pbHeight specifying the height of the current prediction block in luma samples,

– a luma motion vector mvLX given in 1/16-luma-sample units,

– the selected reference picture sample array refPicLX _L,

– the refinement search range srRange.

Output of this process is:

– a (pbWidth) x (pbHeight) array predSamplesLX _L of luma prediction sample values.

Let (xInt _L, yInt _L) be a luma location given in full-sample units and (xFrac _L, yFrac _L) be an offset given in 1/16-sample units. These variables are used only in this section for specifying fractional-sample locations inside the reference sample array refPicLX _L.

For each luma sample location (x _L = 0.. pbWidth -1, y _L = 0.. pbHeight -1) inside the luma prediction sample array predSamplesLX _L, the corresponding luma prediction sample value predSamplesLX _L [x _L] [y _L] is derived as follows:

– The variables xInt _L, yInt _L, xFrac _L and yFrac _L are derived as follows:

xInt _L = xSb + (mvLX [0] >> 4) + x _L -srRange

yInt _L = ySb + (mvLX [1] >> 4) + y _L -srRange

xFrac _L = mvLX [0] &15

yFrac _L = mvLX [1] &15

– The luma prediction sample value predSamplesLX _L [x _L] [y _L] is derived by invoking the luma sample bilinear interpolation process specified in sub-section 2 with (xInt _L, yInt _L) , (xFrac _L, yFrac _L) and refPicLX _L as inputs.

Sub-section 2 Luma sample bilinear interpolation process

Inputs to this process are:

– a luma location in full-sample units (xInt _L, yInt _L) ,

– a luma location in fractional-sample units (xFrac _L, yFrac _L) ,

– the luma reference sample array refPicLX _L.

Output of this process is a predicted luma sample value predSampleLX _L

The variables shift1, shift2, shift3, shift4, offset1, offset2 and offset3 are derived as follows:

shift1 = BitDepth _Y -6

offset1 = 1 << (shift1 -1)

shift2 = 4

offset2 = 1 << (shift2 -1)

shift3 = 10 -BitDepth _Y

shift4 = BitDepth _Y -10

offset4 = 1 << (shift4 -1)

The variable picW is set equal to pic_width_in_luma_samples and the variable picH is set equal to pic_height_in_luma_samples.

The luma interpolation filter coefficients fb _L [p] for each 1/16 fractional sample position p equal to xFrac _L or yFrac _L are specified in following table.

The luma locations in full-sample units (xInt _i, yInt _i) are derived as follows for i = 0.. 1:

– If subpic_treated_as_pic_flag [SubPicIdx] is equal to 1, the following applies:

xInt _i = Clip3 (SubPicLeftBoundaryPos, SubPicRightBoundaryPos, xInt _L + i)

yInt _i = Clip3 (SubPicTopBoundaryPos, SubPicBotBoundaryPos, yInt _L + i)

– Otherwise (subpic_treated_as_pic_flag [SubPicIdx] is equal to 0) , the following applies:

xInt _i = Clip3 (0, picW -1, sps_ref_wraparound_enabled_flag ?

ClipH ( (sps_ref_wraparound_offset_minus1 + 1) *MinCbSizeY, picW, (xInt _L + i) ) : xInt _L + i)

yInt _i = Clip3 (0, picH -1, yInt _L + i)

The predicted luma sample value predSampleLX _L is derived as follows:

– If both xFrac _Land yFrac _L are equal to 0, the value of predSampleLX _L is derived as follows:

predSampleLX _L = BitDepth _Y <= 10 ? (refPicLX _L [xInt ₀] [yInt ₀] << shift3) : ( (refPicLX _L [xInt ₀] [yInt ₀] + offset4) >> shift4)

– Otherwise, if xFrac _L is not equal to 0 and yFrac _L is equal to 0, the value of predSampleLX _L is derived as follows:

– Otherwise, if xFrac _L is equal to 0 and yFrac _L is not equal to 0, the value of predSampleLX _L is derived as follows:

– Otherwise, if xFrac _L is not equal to 0 and yFrac _L is not equal to 0, the value of predSampleLX _L is derived as follows:

– The sample array temp [n] with n = 0.. 1, is derived as follows:

– The predicted luma sample value predSampleLX _L is derived as follows:

Specification of the luma bilinear interpolation filter coefficients f _L [p] for each 1/16 fractional sample position p.

Sub-section 3 Sum of absolute differences calculation process

Inputs to this process are:

– two variables nSbW and nSbH specifying the width and the height of the current subblock,

– two (nSbW + 4) x (nSbH + 4) arrays pL0 and pL1 containing the predicted samples for L0 and L1 respectively,

– an integer sample offset (dX, dY) in L0.

Output of this process is:

– the variable sad specifying the sum of absolute differences at the integer sample at the offset (dX, dY) in L0.

The variable sad is derived as follows:

When both dX and dY are equal to 0, the value of sad is modified as follows:

sad = sad - (sad >> 2)

Sub-section 4 Array entry selection process

Inputs to this process are:

– a 2-D array of sum of absolute differences values sadArray [dX + 2] [d Y + 2] with dX = -2.. 2 and dY = -2.. 2,

– an integer sample offset (intOffX, intOffY) ,

– a variable minSad.

Outputs of this process are:

– the modified integer sample (intOffX, intOffY) ,

– a variable dmvrSAD.

The following steps are applied to modify the integer sample offset (intOffX, intOffY) :

The variable dmvrSAD is set equal to minSad.

Sub-section 5 Parametric motion vector refinement process

Inputs to this process are:

– a 3x3 2-D array sadArray [dX + 1] [dY + 1] with dX = -1.. 1 and dY = -1.. 1,

– a delta luma motion vector dMvL0.

Output of this process is the modified delta luma motion vector dMvL0.

The variable dMvX is derived by invoking the derivation process for delta motion vector component offset specified in sub-section 1 with the SAD values sadMinus, sadCenter and sadPlus set equal to sadArray [0] [1] , sadArray [1] [1] , and sadArray [2] [1] as inputs, and dMvX set equal to the output dMVc.

The variable dMvY is derived by invoking the derivation process for delta motion vector component offset specified in sub-section 1 with the SAD values sadMinus, sadCenter and sadPlus set equal to sadArray [1] [0] , sadArray [1] [1] , and sadArray [1] [2] as inputs, and dMvY set equal to the output dMVc.

The delta luma motion vector dMvL0 is modified as follows:

dMvL0 [0] += dMvX

dMvL0 [1] += dMvY

Sub-section 5 Derivation process for delta motion vector component offset

Inputs to this process are 3 SAD values sadMinus, sadCenter, and sadPlus.

Output of this process is the delta motion vector component correction offset dMvC.

The offset dMVc is derived using the following pseudo code:

Bi-directional optical flow (BDOF)

BDOF is used to refine the bi-prediction signal of a CU at the 4×4 subblock level. BDOF is applied to a CU if it satisfies all the following conditions:

● The CU is coded using “true” bi-prediction mode, i.e., one of the two reference pictures is prior to the current picture in display order and the other is after the current picture in display order

● The CU is not coded using affine mode or the ATMVP merge mode

● CU has more than 64 luma samples

● Both CU height and CU width are larger than or equal to 8 luma samples

● BCW weight index indicates equal weight

● WP is not enabled for the current CU

● CIIP mode is not used for the current CU

BDOF is only applied to the luma component. As its name indicates, the BDOF mode is based on the optical flow concept, which assumes that the motion of an object is smooth. For each 4×4 subblock, a motion refinement (v _x, v _y) is calculated by minimizing the difference between the L0 and L1 prediction samples. The motion refinement is then used to adjust the bi-predicted sample values in the 4x4 subblock. The following steps are applied in the BDOF process.

First, the horizontal and vertical gradients,

and

k=0, 1, of the two prediction signals are computed by directly calculating the difference between two neighboring samples, i.e.,

where I ^(k) (i, j) are the sample value at coordinate (i, j) of the prediction signal in list k, k=0, 1, and shift1 is calculated based on the luma bit depth, bitDepth, as shift1 = max (6, bitDepth-6) .

Then, the auto-and cross-correlation of the gradients, S ₁, S ₂, S ₃, S ₅ and S ₆, are calculated as

S ₁=∑ _(i, j) _∈ΩAbs (ψ _x (i, j) ) , S ₃=∑ _(i, j) _∈Ωθ (i, j) ·Sign (ψ _x (i, j) )

S ₅=∑ _(i, j) _∈ΩAbs (ψ _y (i, j) ) , S ₆=∑ _(i, j) _∈Ωθ (i, j) ·Sign (ψ _y (i, j) )

where

θ (i, j) = I ⁽¹⁾ (i, j) >>n _b) - (I ⁽⁰⁾ (i, j) >>n _b)

where Ω is a 6×6 window around the 4×4 subblock, and the values of n _a and n _b are set equal to min(1, bitDepth-11) and min (4, bitDepth-8) , respectively.

The motion refinement (v _x, v _y) is then derived using the cross-and auto-correlation terms using the following:

where

is the floor function, and

Based on the motion refinement and the gradients, the following adjustment is calculated for each sample in the 4×4 subblock:

Finally, the BDOF samples of the CU are calculated by adjusting the bi-prediction samples as follows:

pred _BDOF (x, y) = I ⁽⁰⁾ (x, y) + ⁽¹⁾ (x, y) + (x, y) +o _offset) >>shift

These values are selected such that the multipliers in the BDOF process do not exceed 15-bit, and the maximum bit-width of the intermediate parameters in the BDOF process is kept within 32-bit.

In order to derive the gradient values, some prediction samples I ^(k) (i, j) in list k (k=0, 1) outside of the current CU boundaries need to be generated. As depicted in Fig. 8, the BDOF uses one extended row/column around the CU’s boundaries. In order to control the computational complexity of generating the out-of-boundary prediction samples, prediction samples in the extended area (white positions) are generated by taking the reference samples at the nearby integer positions (using floor () operation on the coordinates) directly without interpolation, and the normal 8-tap motion compensation interpolation filter is used to generate prediction samples within the CU (gray positions) . These extended sample values are used in gradient calculation only. For the remaining steps in the BDOF process, if any sample and gradient values outside of the CU boundaries are needed, they are padded (i.e. repeated) from their nearest neighbors.

The Bi-directional optical flow prediction process is descibed by a section of pseudo code as follows.

Example 3:

Inputs to this process are:

– two variables nCbW and nCbH specifying the width and the height of the current coding block,

– two (nCbW + 2) x (nCbH + 2) luma prediction sample arrays predSamplesL0 and predSamplesL1,

– the prediction list utilization flags predFlagL0 and predFlagL1,

– the reference indices refIdxL0 and refIdxL1,

– the bi-directional optical flow utilization flags bdofUtilizationFlag [xIdx] [yIdx] with xIdx = 0.. (nCbW >> 2) -1, yIdx = 0.. (nCbH >> 2) -1.

Output of this process is the (nCbW) x (nCbH) array pbSamples of luma prediction sample values.

Variables bitDepth, shift1, shift2, shift3, shift4, offset4, and mvRefineThres are derived as follows:

– The variable bitDepth is set equal to BitDepth _Y.

– The variable shift1 is set to equal to Max (6, bitDepth -6) .

– The variable shift2 is set to equal to Max (4, bitDepth -8) .

– The variable shift3 is set to equal to Max (1, bitDepth -11) .

– The variable shift4 is set equal to Max (3, 15 -bitDepth) and the variable offset4 is set equal to 1 << (shift4 -1) .

– The variable mvRefineThres is set equal to 1 << Max (5, bitDepth -7) .

For xIdx = 0.. (nCbW >> 2) -1 and yIdx = 0.. (nCbH >> 2) -1, the following applies:

– The variable xSb is set equal to (xIdx << 2) + 1 and ySb is set equal to (yIdx << 2) + 1.

– If bdofUtilizationFlag [xIdx] [yIdx] is equal to FALSE, for x = xSb -1.. xSb + 2, y = ySb -1.. ySb + 2, the prediction sample values of the current subblock are derived as follows:

pbSamples [x] [y] = Clip3 (0, (2 ^bitDepth) -1, (predSamplesL0 [x + 1] [y + 1] + offset4 + predSamplesL1 [x + 1] [y + 1] ) >> shift4)

– Otherwise (bdofUtilizationFlag [xIdx] [yIdx] is equal to TRUE) , the prediction sample values of the current subblock are derived as follows:

– For x =xSb -1.. xSb + 4, y = ySb -1.. ySb + 4, the following ordered steps apply:

1. The locations (h _x, v _y) for each of the corresponding sample locations (x, y) inside the prediction sample arrays are derived as follows:

h _x = Clip3 (1, nCbW, x)

v _y = Clip3 (1, nCbH, y)

2. The variables gradientHL0 [x] [y] , gradientVL0 [x] [y] , gradientHL1 [x] [y] and gradientVL1 [x] [y] are derived as follows:

gradientHL0 [x] [y] = (predSamplesL0 [h _x + 1] [v _y] >> shift1) - (predSampleL0 [h _x -1] [v _y] ) >> shift1)

gradientVL0 [x] [y] = (predSampleL0 [h _x] [v _y + 1] >> shift1) - (predSampleL0 [h _x] [v _y -1] ) >> shift1)

gradientHL1 [x] [y] = (predSamplesL1 [h _x + 1] [v _y] >> shift1) - (predSampleL1 [h _x -1] [v _y] ) >> shift1)

gradientVL1 [x] [y] = (predSampleL1 [h _x] [v _y + 1] >> shift1) - (predSampleL1 [h _x] [v _y -1] ) >> shift1)

3. The variables diff [x] [y] , tempH [x] [y] and tempV [x] [y] are derived as follows:

diff [x] [y] = (predSamplesL0 [h _x] [v _y] >> shift2) - (predSamplesL1 [h _x] [v _y] >> shift2)

tempH [x] [y] = (gradientHL0 [x] [y] + gradientHL1 [x] [y] ) >> shift3

tempV [x] [y] = (gradientVL0 [x] [y] + gradientVL1 [x] [y] ) >> shift3

– The variables sGx2, sGy2, sGxGy, sGxdI and sGydI are derived as follows:

sGx2 = Σ _iΣ _j Abs (tempH [xSb + i] [ySb + j] ) with i, j = -1.. 4

sGy2 = Σ _iΣ _j Abs (tempV [xSb + i] [ySb + j] ) with i, j = -1.. 4

sGxGy = Σ _iΣ _j (Sign (tempV [xSb + i] [ySb + j] ) *tempH [xSb + i] [ySb + j] ) with i, j = -1.. 4

sGxGy _m = sGxGy >> 12

sGxGy _s = sGxGy & ( (1 << 12) -1)

sGxdI = Σ _iΣ _j (-Sign (tempH [xSb + i] [ySb + j] ) *diff [xSb + i] [ySb + j] ) with i, j = -1.. 4

sGydI = Σ _iΣ _j (-Sign (tempV [xSb + i] [ySb + j] ) *diff [xSb + i] [ySb + j] ) with i, j = -1.. 4

– The horizontal and vertical motion offset of the current subblock are derived as:

v _x = sGx2 > 0 ? Clip3 (-mvRefineThres, mvRefineThres, - (sGxdI << 3) >> Floor (Log2 (sGx2) ) ) : 0

v _y = sGy2 > 0 ? Clip3 (-mvRefineThres, mvRefineThres, ( (sGydI << 3) -

( (v _x *sGxGy _m) << 12 + v _x *sGxGy _s) >> 1) >> Floor (Log2 (sGy2) ) ) :

0

– For x =xSb -1.. xSb + 2, y = ySb -1.. ySb + 2, the prediction sample values of the current sub-block are derived as follows:

bdofOffset = (v _x * (gradientHL0 [x + 1] [y + 1] -gradientHL1 [x + 1] [y + 1] ) ) >> 1 + (v _y * (gradientVL0 [x + 1] [y + 1] -gradientVL1 [x + 1] [y + 1] ) ) >> 1

pbSamples [x] [y] = Clip3 (0, (2 ^bitDepth) -1, (predSamplesL0 [x + 1] [y + 1] + offset4 + predSamplesL1 [x + 1] [y + 1] + bdofOffset) >> shift4)

As described in Example 1, in the prior art, RefIdxSymL0 and RefIdxSymL1 are derived only for Symmetric MVD coding.

RefIdxSymL0 is set to an index i, when all of the following conditions are true:

(1) The picture with index i in the list 0 is a short term reference picture;

(2) The display order (POC) of the picture with index i is smaller than that of the current picture;

(3) The picture with index i is a nearest picture comparing to any other reference picture i’ satisfies the above two conditions, or RefIdxSymL0 is -1.

RefIdxSymL1 is set to an index j, when all of the following conditions are true:

(1) The picture with index j in the list 1 is a short term reference picture;

(2) The display order (POC) of the picture with index j is larger than that of the current picture;

(3) The picture with index j is a nearest picture comparing to any other reference picture j’ satisfies the above two conditions, or RefIdxSymL1 is -1.

When any of RefIdxSymL0 and RefIdxSymL1 is -1 after the above procedure:

RefIdxSymL0 and RefIdxSymL1 are set to -1.

(4) The picture with index i in the list 0 is a short term reference picture;

(5) The display order (POC) of the picture with index i is larger than that of the current picture;

(6) The picture with index i is a farthest picture comparing to any other reference picture i’ satisfies the above two conditions, or RefIdxSymL0 is -1.

(4) The picture with index j in the list 1 is a short term reference picture;

(5) The display order (POC) of the picture with index j is smaller than that of the current picture;

(6) The picture with index j is a farthest picture comparing to any other reference picture j’ satisfies the above two conditions, or RefIdxSymL1 is -1.

In a first embodiment of the present application, RefIdxSymL0 and RefIdxSymL1 are also derived by the DMVR mode and BDOF mode. The enabling of DMVR mode or BDOF mode depends on the values of RefIdxSymL0 and RefIdxSymL1. For example, DMVR or BDOF mode is considered as a forbidden mode in the event that the reference picture index in list 0 of the current block is different from RefIdxSymL0 or the reference picture index in list 1 of the current block is different from RefIdxSymL1.

In a specific example:

– Example 4:

– When all of the following conditions are true, dmvrFlag is set equal to TRUE (which means DMVR mode is used for decoding the current block) :

– sps_dmvr_enabled_flag is equal to 1 and slice_disable_bdof_dmvr_flag is equal to 0

– general_merge_flag [xCb] [yCb] is equal to 1

– both predFlagL0 [0] [0] and predFlagL1 [0] [0] are equal to 1

– mmvd_merge_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– BcwIdx [xCb] [yCb] is equal to 0

– Both luma_weight_l0_flag [refIdxL0] and luma_weight_l1_flag [refIdxL1] are equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight*cbWidth is greater than or equal to 128

– For X being each of 0 and 1, the pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture refPicLX associated with the refIdxLX are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively.

In another specific example:

– Example 5:

– If all of the following conditions are true, bdofFlag is set equal to TRUE. (which means BDOF mode is used for decoding the current block) :

– sps_bdof_enabled_flag is equal to 1 and slice_disable_bdof_dmvr_flag is equal to 0

– predFlagL0 [xSbIdx] [ySbIdx] and predFlagL1 [xSbIdx] [ySbIdx] are both equal to 1

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– MotionModelIdc [xCb] [yCb] is equal to 0

– merge_subblock_flag [xCb] [yCb] is equal to 0

– sym_mvd_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– BcwIdx [xCb] [yCb] is equal to 0

– luma_weight_l0_flag [refIdxL0] and luma_weight_l1_flag [refIdxL1] are both equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight *cbWidth is greater than or equal to 128

– For X being each of 0 and 1, the pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture refPicLX associated with the refIdxLX are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively

– cIdx is equal to 0.

It is noted that except for the condition “RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1” , other any condition in the above examples can be removed or replaced, or other condition can be added into the above condition sets, which is not limited in the present application.

According to the above examples, for DMVR mode, the condition in the prior art “DiffPicOrderCnt (currPic, RefPicList [0] [refIdxL0] ) is equal to DiffPicOrderCnt (RefPicList [1] [refIdxL1] , currPic) ” , which means the current picture is located between the list 0 reference picture and the list 1 reference picture according to the display order and the distance between the current picture and the list 0 reference picture is the same as the distance between the current picture and the list 1 reference picture, is replaced by the condition “RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1” . For BDOF mode, the condition in the prior art “DiffPicOrderCnt (currPic, RefPicList [0] [refIdxL0] ) *DiffPicOrderCnt (currPic, RefPicList [1] [refIdxL1] ) is less than 0” , which means the current picture is located between the list 0 reference picture and the list 1 reference picture according to the display order, is replaced by the condition “RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1” . Therefore, the same logical implementation can be reused for DMVR mode and BDOF mode, implementation resource can be saved.

In a second embodiment of the present application, RefIdxSymL0 and RefIdxSymL1 are also derived by the DMVR mode and BDOF mode. And the condition “RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1” is also used for determining DMVR mode or BDOF mode for the current block as the examples in the first embodiment.

But it is noted that the definition of RefIdxSymL0 and RefIdxSymL1 might be changed according to the different specific examples.

In a feasible implementation, RefIdxSymL0 is i means the size of the reference picture with index i in list 0 has the same size of the current picture. More specifically,

Example 6:

The variable RefIdxSymLX with X being 0 and 1 is derived as follows:

– The variable currPic specifies the current picture.

– RefIdxSymL0 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) > 0,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) <DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1,

– The pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture list 0 associated with the reference index i are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively.

– RefIdxSymL1 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) < 0,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) >DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1,

– The pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture list 1 associated with the reference index i are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively.

– RefIdxSymL0 is set equal to -1 and RefIdxSymL1 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) < 0,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) >DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1,

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) > 0,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) <DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1,

Accordingly, for DMVR or BDOF mode, the similar condition in the prior art to determining DMVR or BDOF mode “For X being each of 0 and 1, the pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture refPicLX associated with the refIdxLX are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively” is removed.

In a specific example:

– Example 7:

– general_merge_flag [xCb] [yCb] is equal to 1

– both predFlagL0 [0] [0] and predFlagL1 [0] [0] are equal to 1

– mmvd_merge_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– BcwIdx [xCb] [yCb] is equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight*cbWidth is greater than or equal to 128

In another specific example:

– Example 8:

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– MotionModelIdc [xCb] [yCb] is equal to 0

– merge_subblock_flag [xCb] [yCb] is equal to 0

– sym_mvd_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– BcwIdx [xCb] [yCb] is equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight *cbWidth is greater than or equal to 128

– cIdx is equal to 0.

In a third embodiment of the present application, RefIdxSymL0 and RefIdxSymL1 are also derived by the DMVR mode and BDOF mode. And the condition “RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1” is also used for determining DMVR mode or BDOF mode for the current block as the examples in the second embodiment.

In a feasible implementation, RefIdxSymL0 is i means the weighting factors for the luma component of list 0 prediction are not carried by the bitstream corresponding to the current block. More specifically,

Example 9:

The variable RefIdxSymLX with X being 0 and 1 is derived as follows:

– The variable currPic specifies the current picture.

– RefIdxSymL0 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) > 0,

– The pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture list 0 associated with the reference index i are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively,

– The luma_weight_l0_flag [i] is equal to 0.

– RefIdxSymL1 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) < 0,

– The pic_width_in_luma_samples and pic_height_in_luma_samples of the reference picture list 1 associated with the reference index i are equal to the pic_width_in_luma_samples and pic_height_in_luma_samples of the current picture, respectively,

– The luma_weight_l1_flag [i] is equal to 0.

– RefIdxSymL0 is set equal to -1 and RefIdxSymL1 is set equal to -1.

– When all of the following conditions are true, RefIdxSymL0 is set to i:

– RefPicList [0] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [0] [i] ) < 0,

– The luma_weight_l0_flag [i] is equal to 0.

– When all of the following conditions are true, RefIdxSymL1 is set to i:

– RefPicList [1] [i] is a short-term-reference picture,

– DiffPicOrderCnt (currPic, RefPicList [1] [i] ) > 0,

– The luma_weight_l1_flag [i] is equal to 0.

Accordingly, for DMVR or BDOF mode, the similar condition in the prior art to determining DMVR or BDOF mode “both luma_weight_l0_flag [refIdxL0] and luma_weight_l1_flag [refIdxL1] are equal to 0” is removed.

In a specific example:

– Example 10:

– general_merge_flag [xCb] [yCb] is equal to 1

– both predFlagL0 [0] [0] and predFlagL1 [0] [0] are equal to 1

– mmvd_merge_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– BcwIdx [xCb] [yCb] is equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight*cbWidth is greater than or equal to 128

In another specific example:

– Example 11:

– RefIdxL0 is equal to RefIdxSymL0 and RefIdxL1 is equal to RefIdxSymL1

– MotionModelIdc [xCb] [yCb] is equal to 0

– merge_subblock_flag [xCb] [yCb] is equal to 0

– sym_mvd_flag [xCb] [yCb] is equal to 0

– ciip_flag [xCb] [yCb] is equal to 0

– BcwIdx [xCb] [yCb] is equal to 0

– cbWidth is greater than or equal to 8

– cbHeight is greater than or equal to 8

– cbHeight *cbWidth is greater than or equal to 128

– cIdx is equal to 0.

Fig. 9 shows an inter prediction method of the present application.

S901, determining the values of RefIdxSymL0 and RefIdxSymL1 for a current block. determining a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order.

In a feasible implementation, the conditions to determine the values of RefIdxSymL0 and RefIdxSymL1 might further comprise: a size of the reference picture with the target list0 index is the same as a size of the current picture, and a size of the reference picture with the target list1 index is the same as the size of the current picture.

In a feasible implementation, the conditions to determine the values of RefIdxSymL0 and RefIdxSymL1 might further comprise: weighting factors for a luma component of the reference picture with the target list0 index are not carried by a bitstream corresponding to the current block, and weighting factors for a luma component of the reference picture with the target list1 index are not carried by the bitstream.

The specific implementation can be referred to Example 3, 6 or 9.

S902, determining whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is RefIdxSymL0 and the list1 reference picture index of the current block is RefIdxSymL1.

In a feasible implementation, DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.

The specific implementation can be referred to Example 4, 5, 7, 8, 10 and 11. And it is understandable that Example 4 and 5 correspond to Example 3, Example 7 and 8 correspond to Example 6, and Example 10 and 11 correspond to Example 9.

S903, obtaining the prediction value of the current block based on the determined DMVR or BDOF mode.

And if the conditions for determining DMVR or BDOF mode are not satisfied, the prediction value of the current block will be obtained by other prediction mode.

Fig. 10 shows an inter prediction apparatus 1000 of the present application.

The inter prediction apparatus 1000, comprising: determining module 1001, configured to determine a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order; checking module 1002, configured to determine whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index; and calculating module 1003, configured to obtain a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.

In a feasible implementation, the checking module 1002 is specifically configured to determine that DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.

Fig. 11 shows another inter prediction apparatus 1100 of the present application, the apparatus 1100 might be a decoder or an encoder. The apparatus 1100 comprising: one or more processors 1101; and a non-transitory computer-readable storage medium 1102 coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method in Fig. 9.

In another embodiment, a computer program product comprising program code for performing the method in Fig. 9 when executed on a computer or a processor.

In another embodiment, a non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method in Fig. 9.

Following is an explanation of the applications of the encoding method as well as the decoding method as shown in the above-mentioned embodiments, and a system using them. FIG. 12 is a block diagram showing a content supply system 3100 for realizing content distribution service. This content supply system 3100 includes capture device 3102, terminal device 3106, and optionally includes display 3126. The capture device 3102 communicates with the terminal device 3106 over communication link 3104. The communication link may include the communication channel 13 described above. The communication link 3104 includes but not limited to WIFI, Ethernet, Cable, wireless (3G/4G/5G) , USB, or any kind of combination thereof, or the like.

The capture device 3102 generates data, and may encode the data by the encoding method as shown in the above embodiments. Alternatively, the capture device 3102 may distribute the data to a streaming server (not shown in the Figures) , and the server encodes the data and transmits the encoded data to the terminal device 3106. The capture device 3102 includes but not limited to camera, smart phone or Pad, computer or laptop, video conference system, PDA, vehicle mounted device, or a combination of any of them, or the like. For example, the capture device 3102 may include the source device 12 as described above. When the data includes video, the video encoder 20 included in the capture device 3102 may actually perform video encoding processing. When the data includes audio (i.e., voice) , an audio encoder included in the capture device 3102 may actually perform audio encoding processing. For some practical scenarios, the capture device 3102 distributes the encoded video and audio data by multiplexing them together. For other practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. Capture device 3102 distributes the encoded audio data and the encoded video data to the terminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives and reproduces the encoded data. The terminal device 3106 could be a device with data receiving and recovering capability, such as smart phone or Pad 3108, computer or laptop 3110, network video recorder (NVR) /digital video recorder (DVR) 3112, TV 3114, set top box (STB) 3116, video conference system 3118, video surveillance system 3120, personal digital assistant (PDA) 3122, vehicle mounted device 3124, or a combination of any of them, or the like capable of decoding the above-mentioned encoded data. For example, the terminal device 3106 may include the destination device 14 as described above. When the encoded data includes video, the video decoder 30 included in the terminal device is prioritized to perform video decoding. When the encoded data includes audio, an audio decoder included in the terminal device is prioritized to perform audio decoding processing.

For a terminal device with its display, for example, smart phone or Pad 3108, computer or laptop 3110, network video recorder (NVR) /digital video recorder (DVR) 3112, TV 3114, personal digital assistant (PDA) 3122, or vehicle mounted device 3124, the terminal device can feed the decoded data to its display. For a terminal device equipped with no display, for example, STB 3116, video conference system 3118, or video surveillance system 3120, an external display 3126 is contacted therein to receive and show the decoded data.

When each device in this system performs encoding or decoding, the picture encoding device or the picture decoding device, as shown in the above-mentioned embodiments, might be used.

FIG. 13 is a diagram showing a structure of an example of the terminal device 3106. After the terminal device 3106 receives stream from the capture device 3102, the protocol proceeding unit 3202 analyzes the transmission protocol of the stream. The protocol includes but not limited to Real Time Streaming Protocol (RTSP) , Hyper Text Transfer Protocol (HTTP) , HTTP Live streaming protocol (HLS) , MPEG-DASH, Real-time Transport protocol (RTP) , Real Time Messaging Protocol (RTMP) , or any kind of combination thereof, or the like. After the protocol proceeding unit 3202 processes the stream, stream file is generated. The file is outputted to a demultiplexing unit 3204. The demultiplexing unit 3204 can separate the multiplexed data into the encoded audio data and the encoded video data. As described above, for some practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. In this situation, the encoded data is transmitted to video decoder 3206 and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES) , audio ES, and optionally subtitle are generated. The video decoder 3206, which includes the video decoder 30 as explained in the above mentioned embodiments, decodes the video ES by the decoding method as shown in the above-mentioned embodiments to generate video frame, and feeds this data to the synchronous unit 3212. The audio decoder 3208, decodes the audio ES to generate audio frame, and feeds this data to the synchronous unit 3212. Alternatively, the video frame may store in a buffer (not shown in FIG. 13) before feeding it to the synchronous unit 3212. Similarly, the audio frame may store in a buffer (not shown in FIG. 13) before feeding it to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audio frame, and supplies the video/audio to a video/audio display 3214. For example, the synchronous unit 3212 synchronizes the presentation of the video and audio information. Information may code in the syntax using time stamps concerning the presentation of coded audio and visual data and time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodes the subtitle, and synchronizes it with the video frame and the audio frame, and supplies the video/audio/subtitle to a video/audio/subtitle display 3216.

The present invention is not limited to the above-mentioned system, and either the picture encoding device or the picture decoding device in the above-mentioned embodiments might be incorporated into other system, for example, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to those used in the C programming language. However, the results of integer division and arithmetic shift operations are defined more precisely, and additional operations are defined, such as exponentiation and real-valued division. Numbering and counting conventions generally begin from 0, e.g., "the first" is equivalent to the 0-th, "the second" is equivalent to the 1-th, etc.

Arithmetic operators

The following arithmetic operators are defined as follows:

+ Addition

- Subtraction (as a two-argument operator) or negation (as a unary prefix operator)

* Multiplication, including matrix multiplication

Logical operators

The following logical operators are defined as follows:

x &&y Boolean logical "and" of x and y

x | | y Boolean logical "or" of x and y

! Boolean logical "not"

x ? y : z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z.

Relational operators

The following relational operators are defined as follows:

> Greater than

>= Greater than or equal to

< Less than

<= Less than or equal to

= = Equal to

!= Not equal to

When a relational operator is applied to a syntax element or variable that has been assigned the value "na" (not applicable) , the value "na" is treated as a distinct value for the syntax element or variable. The value "na" is considered not to be equal to any other value.

Bit-wise operators

The following bit-wise operators are defined as follows:

& Bit-wise "and" . When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

| Bit-wise "or" . When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

^ Bit-wise "exclusive or" . When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.

x >> y Arithmetic right shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y.Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation.

x << y Arithmetic left shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y.Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.

Assignment operators

The following arithmetic operators are defined as follows:

= Assignment operator

+ + Increment, i.e., x+ + is equivalent to x = x + 1; when used in an array index, evaluates to the value of the variable prior to the increment operation.

-- Decrement, i.e., x--is equivalent to x = x -1; when used in an array index, evaluates to the value of the variable prior to the decrement operation.

+= Increment by amount specified, i.e., x += 3 is equivalent to x = x + 3, and x += (-3) is equivalent to x = x + (-3) .

-= Decrement by amount specified, i.e., x -= 3 is equivalent to x = x -3, and x -= (-3) is equivalent to x = x - (-3) .

Range notation

The following notation is used to specify a range of values:

x = y.. z x takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y.

Mathematical functions

The following mathematical functions are defined:

Asin (x) the trigonometric inverse sine function, operating on an argument x that is in the range of -1.0 to 1.0, inclusive, with an output value in the range of -π÷2 to π÷2, inclusive, in units of radians

Atan (x) the trigonometric inverse tangent function, operating on an argument x, with an output value in the range of -π÷2 to π÷2, inclusive, in units of radians

Ceil (x) the smallest integer greater than or equal to x.

Clip1 _Y (x) = Clip3 (0, (1 << BitDepth _Y) -1, x)

Clip1 _C (x) = Clip3 (0, (1 << BitDepth _C) -1, x)

Cos (x) the trigonometric cosine function operating on an argument x in units of radians.

Floor (x) the largest integer less than or equal to x.

Ln (x) the natural logarithm of x (the base-e logarithm, where e is the natural logarithm base constant 2.718 281 828...) .

Log2 (x) the base-2 logarithm of x.

Log10 (x) the base-10 logarithm of x.

Round (x) = Sign (x) *Floor (Abs (x) + 0.5)

Sin (x) the trigonometric sine function operating on an argument x in units of radians

Swap (x, y) = (y, x)

Tan (x) the trigonometric tangent function operating on an argument x in units of radians

Order of operation precedence

When an order of precedence in an expression is not indicated explicitly by use of parentheses, the following rules apply:

– Operations of a higher precedence are evaluated before any operation of a lower precedence.

– Operations of the same precedence are evaluated sequentially from left to right.

The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language, the order of precedence used in this Specification is the same as used in the C programming language.

Table: Operation precedence from highest (at top of table) to lowest (at bottom of table)

Text description of logical operations

In the text, a statement of logical operations as would be described mathematically in the following form:

if (condition 0)

statement 0

else if (condition 1)

statement 1

...

else /*informative remark on remaining condition */

statement n

may be described in the following manner:

... as follows /... the following applies:

– If condition 0, statement 0

– Otherwise, if condition 1, statement 1

– ...

– Otherwise (informative remark on remaining condition) , statement n

Each "If ... Otherwise, if ... Otherwise, ... " statement in the text is introduced with "... as follows" or "... the following applies" immediately followed by "If ... " . The last condition of the "If ... Otherwise, if ... Otherwise, ... " is always an "Otherwise, ... " . Interleaved "If ... Otherwise, if ... Otherwise, ... " statements might be identified by matching "... as follows" or "... the following applies" with the ending "Otherwise, ... " .

if (condition 0a &&condition 0b)

statement 0

else if (condition 1a | | condition 1b)

statement 1

...

else

statement n

may be described in the following manner:

... as follows /... the following applies:

– If all of the following conditions are true, statement 0:

– condition 0a

– condition 0b

– Otherwise, if one or more of the following conditions are true, statement 1:

– condition 1a

– condition 1b

– ...

– Otherwise, statement n

if (condition 0)

statement 0

if (condition 1)

statement 1

may be described in the following manner:

When condition 0, statement 0

When condition 1, statement 1

Embodiments, e.g. of the encoder 20 and the decoder 30, and functions described herein, e.g. with reference to the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over communication media as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that might be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limiting, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that might be used to store desired program code in the form of instructions or data structures and that might be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs) , general purpose microprocessors, application specific integrated circuits (ASICs) , field programmable logic arrays (FPGAs) , or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor, ” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set) . Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Claims

An inter prediction method, comprising:

determining a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order;

determining whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index; and

obtaining a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.
The method of claim 1, wherein determining whether DMVR mode or BDOF mode is used for decoding the current block in the current picture based on the condition, comprising:

DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.
The method of claim 1 or 2, wherein a size of the reference picture with the target list0 index is the same as a size of the current picture, and a size of the reference picture with the target list1 index is the same as the size of the current picture.
The method of any one of claims 1-3, wherein weighting factors for a luma component of the reference picture with the target list0 index are not carried by a bitstream corresponding to the current block, and weighting factors for a luma component of the reference picture with the target list1 index are not carried by the bitstream.
The method of any one of claims 1-4, wherein DMVR mode or BDOF mode is used for decoding the current block in the event that at least two conditions are satisfied, and wherein one of the at least two conditions is the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index.
An inter prediction apparatus, comprising:

determining module, configured to determine a target list0 index and a target list1 index, wherein a reference picture with the target list0 index and a reference picture with the target list1 index are short term reference pictures, the nearest picture to a current picture in list0 and list1 respectfully and locate on different sides of the current picture according to a display order;

checking module, configured to determine whether DMVR mode or BDOF mode is used for decoding a current block in the current picture based on a condition that whether the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index; and

calculating module, configured to obtain a prediction value of the current block based on DMVR mode or BDOF mode in the event that DMVR mode or BDOF mode is determined to be used for decoding the current block.
The apparatus of claim 6, wherein the checking module is specifically configured to determine that DMVR mode or BDOF mode is not used for decoding the current block in the event that the list0 reference picture index of the current block is not the target list0 index and/or the list1 reference picture index of the current block is not the target list1 index.
The apparatus of claim 5 or 6, wherein a size of the reference picture with the target list0 index is the same as a size of the current picture, and a size of the reference picture with the target list1 index is the same as the size of the current picture.
The apparatus of any one of claims 5-8, wherein weighting factors for a luma component of the reference picture with the target list0 index are not carried by a bitstream corresponding to the current block, and weighting factors for a luma component of the reference picture with the target list0 index are not carried by the bitstream.
The apparatus of any one of claims 5-9, wherein DMVR mode or BDOF mode is used for decoding the current block in the event that at least two conditions are satisfied, and wherein one of the at least two conditions is the list0 reference picture index of the current block is the target list0 index and the list1 reference picture index of the current block is the target list1 index.
A computer program product comprising program code for performing the method according to any one of the claims 1 to 5when executed on a computer or a processor.
A decoder, comprising:

one or more processors; and

a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to any one of the claims 1 to 5.
An encoder, comprising:

one or more processors; and

a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to any one of the claims 1 to 5.
A non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method of any one of the claims 1 to 5.