Method, Device, Medium, and Program Product for Video Decoding

Abstract

Aspects of the present disclosure include a method, apparatus, medium, and program product for video decoding. The apparatus includes processing circuitry that decodes prediction information for a current block in an encoded video bitstream. The prediction information includes at least one reference picture index used in low-latency inter prediction of the current block. Each of the at least one reference picture index has the same value. The processing circuitry determines a first reference picture in a first reference picture list and a second reference picture in a second reference picture list based on the at least one reference picture index. The current block is encoded using the low-latency inter prediction. The first reference picture list is the same as the second reference picture list. The first reference picture is the same as the second reference picture. The processing circuitry reconstructs the current block based on the first and second reference pictures.

Description

[0001] Incorporation by reference

[0002] This application claims the benefit of priority of U.S. Patent Application No. 17 / 358,797, entitled "Methods and Apparatuses for Video Coding," filed on June 25, 2021, the entire content of which is incorporated herein by reference. Technical Field

[0003] This disclosure describes embodiments generally related to video decoding. Background Art

[0004] The background description provided here is for the purpose of presenting the context of the present disclosure generally. To the extent that the work described in this background section, the work of the presently named inventors, and aspects that may not constitute prior art at the time of the application are neither expressly nor impliedly admitted as prior art to the present disclosure.

[0005] Inter-picture prediction with motion compensation can be used to perform video encoding and decoding. Uncompressed digital video can include a series of pictures, each picture having spatial dimensions such as 1920×1080 luminance samples and associated chrominance samples. The series of pictures can have a fixed or variable frame rate (informally also called the frame rate), e.g., 60 pictures per second or 60 Hz. Uncompressed video has significant bitrate requirements. For example, a 1080p60 4:2:0 video (1920x1080 luminance sample resolution at 60 Hz frame rate) with 8 bits per sample requires a bandwidth of nearly 1.5 Gbit / s. An hour of such video requires more than 600 gigabytes of storage space.

[0006] One goal of video encoding and decoding is to reduce redundancy in the input video signal through compression. Compression helps reduce the above bandwidth or storage space requirements, which can be reduced by two orders of magnitude or more in some cases. Lossless compression, lossy compression, and combinations thereof can be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When lossy compression is used, the reconstructed signal may not be the same as the original signal, but the distortion between the original signal and the reconstructed signal is small enough that the reconstructed signal is useful for the intended application. For video, lossy compression is widely adopted. The amount of distortion that is tolerated depends on the application; for example, users of some consumer streaming applications may tolerate higher distortion than users of television distribution applications. The achievable compression ratio can reflect that higher tolerated / tolerable distortion can result in a higher compression ratio.

[0007] Video encoders and decoders can utilize several broad categories of techniques, including, for example, motion compensation, transformation, quantization, and entropy coding.

[0008] Video codec technology can include techniques known as intra coding. In intra coding, sample values are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, pictures are spatially subdivided into sample blocks. When all sample blocks are coded in the intra mode, the picture can be an intra picture. Intra pictures and their derived pictures (e.g., independent decoder refresh pictures) can be used to reset the decoder state and thus can be used as the first picture in an encoded video bitstream and a video session or as a still image. Samples of an intra block can be transformed, and the transform coefficients can be quantized before entropy coding. Intra prediction can be a technique to minimize sample values in the pre-transform domain. In some cases, the smaller the transformed DC value and the AC coefficients, the fewer bits are required to represent the entropy-coded block for a given quantization step.

[0009] For example, traditional intra coding known from MPEG-2 generation coding techniques does not use intra prediction. However, some newer video compression techniques include techniques that attempt to obtain surrounding sample data and / or metadata, for example, during the encoding and / or decoding of data blocks that are adjacent in space and earlier in the decoding order. Such techniques are hereafter referred to as "intra prediction" techniques. Note that, at least in some cases, the reference data used for intra prediction comes only from the current picture in reconstruction and not from reference pictures.

[0010] There can be many different forms of intra prediction. When more than one such technique can be used in a given video coding technique, the technique used can be coded in an intra prediction mode. In some cases, the mode can have sub-modes and / or parameters that can be coded separately or included in the mode codeword. For a given combination of mode, sub-mode, and / or parameter, which codeword is used affects the coding efficiency gain through intra prediction and thus also affects the entropy coding technique for converting the codeword into a bitstream.

[0011] H.264 introduced specific intra prediction modes, which were improved in H.265 and further improved in more recent coding techniques such as the Joint Exploration Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). Adjacent sample values that already belong to available samples are used to form a prediction block. The sample values of adjacent samples are copied into the prediction block according to a direction. The reference to the direction in use can be coded into the bitstream or can be predicted by itself.

[0012] Referring to FIG. 1A, a subset of 9 prediction directions known from the 33 possible prediction directions of H.265 (corresponding to the 33 angular modes of the 35 intra modes) is depicted in the lower right. The point (101) where the arrows converge represents the sample to be predicted. The arrows indicate the direction from which the predicted sample is taken. For example, arrow (102) indicates that sample (101) is predicted from one or more samples in the upper right at a 45° angle to the horizontal line. Similarly, arrow (103) indicates that sample (101) is predicted from one or more samples in the lower left of sample (101) at a 22.5° angle to the horizontal line.

[0013] Still referring to FIG. 1A, a square block (104) of 4×4 samples (represented by the thick dashed line) is depicted in the upper left. The square block (104) includes 16 samples, each labeled with an “S” along with its position in the Y dimension (e.g., row index) and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample in the Y dimension (counting from the top) and the first sample in the X dimension (counting from the left). Similarly, sample S44 is the fourth sample in both the Y and X dimensions within block (104). Since the block is 4×4 samples in size, S44 is located in the lower right corner. Reference samples following a similar numbering scheme are also shown. The reference samples labeled with an “R”, their Y position (e.g., row index) relative to the block, and their X position (column index) are labeled (104). In H.264 and H.265, the predicted samples are adjacent to the block in the reconstruction; thus, negative values are not required.

[0014] Intra picture prediction can work by copying the reference sample values from adjacent samples in a suitable signal prediction direction. For example, assume that the encoded video bitstream contains a signal for this block indicating a prediction direction consistent with arrow (102) - i.e., a sample predicted from one or more predicted samples in the upper right at a 45° angle to the horizontal. In this case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then sample S44 is predicted from reference sample R08.

[0015] In some cases, the values of multiple reference samples can be combined, e.g., by interpolation, in order to calculate the reference sample; especially when the direction is not divisible by 45°.

[0016] With the development of video coding technology, the number of possible directions has increased. In H.264 (2003), nine different directions could be represented. This increased to 33 in H.265 (2013), while JEM / VVC / BMS could support up to 65 directions at the time of disclosure. Experiments have been conducted to identify the most likely directions, and certain techniques in entropy coding are used to represent those likely directions with a small number of bits, accepting a certain penalty for the less likely directions. Additionally, the direction itself can sometimes be predicted from adjacent directions used in adjacent already decoded blocks.

[0017] Figure 1B shows a schematic diagram (105) depicting 65 intra prediction directions according to JEM to illustrate the increase in the number of prediction directions over time.

[0018] The directions represented by the mapping of intra prediction direction bits in the encoded video bitstream can vary depending on the video coding technology; for example, from a simple direct mapping from the prediction direction to the intra prediction mode, which can cover the range to the codewords, to complex adaptive schemes involving the most likely modes, and similar techniques. However, in all cases, some directions are statistically less likely to occur in video content compared to some other directions. Since the goal of video compression is to reduce redundancy, in better video coding technologies, those less likely directions will be represented by more bits relative to the more likely directions.

[0019] Motion compensation can be a lossy compression technique and can involve techniques where a block of sample data from a previously reconstructed picture or a portion thereof (reference picture) is spatially shifted in the direction indicated by a motion vector (hereinafter referred to as MV) and can then be used to predict a newly reconstructed picture or picture portion. In some cases, the reference picture can be the same as the picture currently being reconstructed. The MV can have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (the reference picture indirectly can be the temporal dimension).

[0020] In some video compression techniques, the MV applicable to a certain area of sample data can be predicted from other MVs. For example, it can be predicted from the MV associated with another area of sample data that is spatially adjacent to the area being reconstructed and is before the MV in the decoding order. Doing so can greatly reduce the amount of data required to encode the MV, thus eliminating redundancy and increasing the compression ratio. MV prediction can work effectively. For example, when encoding an input video signal (referred to as natural video) derived from a camera, there is a statistical possibility that an area larger than the area to which a single MV is applicable moves in a similar direction. Therefore, in some cases, a similar MV derived from the MVs of adjacent areas can be used for prediction. This makes the MV found in a given area similar or identical to the MV predicted from the surrounding MVs, and after entropy coding, this can in turn be represented with fewer bits than when directly encoding the MV. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from the original signal (i.e., sample stream). In other cases, MV prediction itself may be lossy. For example, when calculating the predicted value from several surrounding MVs, rounding errors may occur.

[0021] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H.265, “High Efficiency Video Coding”, December 2016). Among the many MV prediction mechanisms provided by H.265, a technique hereafter referred to as “spatial merge” is described herein.

[0022] Referring to FIG. 1C, the current block (111) includes samples found by the encoder during the motion search process to predict from a previous block of the same size that has been spatially shifted. Instead of directly encoding the MV, the MV associated with any one of five surrounding samples (denoted as A0, A1 and B0, B1, B2 (112 to 116 respectively)) can be used, and the MV is derived from the metadata associated with one or more reference pictures, for example, derived from the nearest (in decoding order) reference picture. In H.265, MV prediction can use a predictor from the same reference picture being used by adjacent blocks. SUMMARY OF THE INVENTION

[0023] Aspects of the present disclosure provide a device for video decoding. A device includes processing circuitry that decodes prediction information for a current block in a current picture that is part of an encoded video bitstream. The prediction information includes at least one reference picture index used in low-latency inter-picture bidirectional prediction for the current block. Each of the at least one reference picture index has the same value; the processing circuitry determines a first picture in a first reference picture list and a second picture in a second reference picture list based on the at least one reference picture index included in the prediction information; encodes the current block using low-latency inter-picture bidirectional prediction, where the first reference picture list is the same as the second reference picture list and the first picture is the same as the second picture; and the processing circuitry reconstructs the current block based on the first picture and the second picture.

[0024] In one embodiment, the at least one reference picture index is a single reference picture index associated with one of the first reference picture list and the second reference picture list, and the processing circuitry determines the single reference picture index as the reference picture index for the other of the first reference picture list and the second reference picture list.

[0025] In one embodiment, the prediction information includes a syntax element indicating that a first reference picture in the first reference picture list is the same as a second reference picture in the second reference picture list, and the syntax element is included in one of a sequence level parameter, a picture level parameter, and a slice level parameter.

[0026] In one embodiment, based on the current block encoded in one of a plurality of merge modes, each bidirectional prediction candidate in the merge candidate list of the current block has the same reference picture index for the first reference picture list and the second reference picture list. The plurality of merge modes include a regular merge mode, an affine merge mode, a merge mode with motion vector difference, advanced motion vector prediction, and a geometric partitioning mode.

[0027] In one embodiment, based on the prediction information indicating that a first reference picture in the first reference picture list is the same as a second reference picture in the second reference picture list, the processing circuitry determines to disable a tool configured to reference a reference picture that is temporally after the current picture.

[0028] In one embodiment, the prediction information includes one of the first reference picture list and the second reference picture list.

[0029] In one embodiment, the at least one reference picture index includes two identical reference picture indexes, and the prediction information includes the first reference picture list, the second reference picture list, and the two identical reference picture indexes.

[0030] Aspects of the present disclosure provide methods for video decoding. In this method, prediction information for a current block in a current picture that is part of an encoded video bitstream is decoded, the prediction information including at least one reference picture index used in low-latency inter-frame bi-directional prediction for the current block; based on the at least one reference picture index included in the prediction information, a first reference picture in a first reference picture list and a second reference picture in a second reference picture list are determined for the current block, and the current block is encoded using low-latency inter-frame bi-directional prediction, where the first reference picture list is the same as the second reference picture list, and the first reference picture is the same as the second reference picture; the current block is reconstructed based on the first reference picture and the second reference picture.

[0031] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by at least one processor, cause the at least one processor to perform any one or combination of the methods for video decoding.

[0032] Aspects of the present disclosure also provide a computer program product including instructions that, when run on a computer, cause the computer to perform any one or combination of the above methods for video decoding. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further features, properties, and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings, in which:

[0034] FIG. 1A is a schematic diagram of an exemplary set of intra-prediction modes;

[0035] FIG. 1B is an illustration of an exemplary intra-prediction direction;

[0036] FIG. 1C is a schematic diagram of a current block and its surrounding spatial merge candidates in an example;

[0037] Figure 2 is a schematic diagram of a simplified block diagram of a communication system according to an embodiment;

[0038] Figure 3 is a schematic diagram of a simplified block diagram of a communication system according to an embodiment;

[0039] Figure 4 is a schematic diagram of a simplified block diagram of a decoder according to an embodiment;

[0040] Figure 5 is a schematic diagram of a simplified block diagram of an encoder according to an embodiment;

[0041] Figure 6 shows a block diagram of an encoder according to another embodiment;

[0042] Figure 7Shows a block diagram of a decoder according to another embodiment;

[0043] Figure 8 Shows an exemplary graphical representation of a random access configuration according to one embodiment;

[0044] Figure 9 Shows an exemplary graphical representation of a low latency configuration according to one embodiment;

[0045] Figure 10 Shows an exemplary flowchart according to one embodiment; and

[0046] Figure 11 Is a schematic diagram of a computer system according to one embodiment. Detailed Description

[0047] I. Video Decoder and Encoder Systems

[0048] Figure 2 Shows a simplified block diagram of a communication system (200) according to an embodiment of the present disclosure. The communication system (200) includes a plurality of terminal devices capable of communicating with each other via, for example, a network (250). For example, the communication system (200) includes a first pair of terminal devices (210) and (220) interconnected via the network (250). In Figure 2 In the example, the first pair of terminal devices (210) and (220) perform unidirectional transmission of data. For example, the terminal device (210) may encode video data (e.g., a video picture stream captured by the terminal device (210)) for transmission via the network (250) to another terminal device (220). The encoded video data may be transmitted in the form of one or more encoded video bitstreams. The terminal device (220) may receive the encoded video data from the network (250), decode the encoded video data to recover the video pictures, and display the video pictures based on the recovered video data. Unidirectional data transmission is common in scenarios such as media service applications.

[0049] In another example, a communication system (200) includes a second pair of terminal devices (230) and (240) that perform two-way transmission of encoded video data, such as for encoded video data generated during a video conference. For two-way transmission of data, in one example, each of the terminal devices (230) and (240) can encode video data (e.g., a video picture stream captured by the terminal device) for transmission via a network (250) to the other of the terminal devices (230) and (240). Each of the terminal devices (230) and (240) can also receive the encoded video data transmitted by the other of the terminal devices (230) and (240), and can decode the encoded video data to recover the video pictures, and can display the video pictures on an accessible display device based on the recovered video data.

[0050] In Figure 2 the example, the terminal devices (210), terminal device (220), terminal device (230), and terminal device (240) may be shown as servers, personal computers, and smart phones, but the principles of the present disclosure are not limited thereto. Embodiments of the present disclosure are applicable to laptop computers, tablet computers, media players, and / or dedicated video conferencing devices. The network (250) represents any number of networks that convey encoded video data between the terminal devices (210), terminal device (220), terminal device (230), and terminal device (240), including, for example, wireline (wired) and / or wireless communication networks. The communication network (250) can exchange data in circuit-switched and / or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For the purposes of the current discussion, the architecture and topology of the network (250) may be unimportant to the operation of the present disclosure, unless explained otherwise below.

[0051] As an example of an application of the disclosed subject matter, Figure 3 illustrates the placement of a video encoder and a video decoder in a streaming environment. The disclosed subject matter is equally applicable to other video-enabled applications, including, for example, video conferencing, digital television, storing compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0052] The streaming system may include: a capture subsystem (313), which may include a video source (301), such as a digital camera; creating, for example, an uncompressed video picture stream (302). In one example, the video picture stream (302) includes samples captured by the digital camera. The video picture stream (302) is depicted as thick lines to emphasize the high amount of data when compared to the encoded video data (304) (or encoded video bitstream), and can be processed by an electronic device (320) including a video encoder (303) coupled to the video source (301). The video encoder (303) may include hardware, software, or a combination thereof to implement or implement various aspects of the disclosed subject matter as described in more detail below. The encoded video data (304) (or encoded video bitstream (304)) is depicted as thin lines to emphasize its lower amount of data when compared to the video picture stream (302), and can be stored on a streaming server (305) for future use. One or more streaming client subsystems (e.g., Figure 3 The client subsystems (306) and (308) in the video processing system may access the streaming server (305) to retrieve copies (307) and (309) of the encoded video data (304). The client subsystem (306) may include, for example, a video decoder (310) in an electronic device (330). The video decoder (310) decodes the copy (307) of the encoded video data and creates an output video picture stream (311) that can be rendered on a display (312) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (304), the copies (307) and (309) of the encoded video data (e.g., an encoded video bitstream) may be encoded according to certain video coding / compression standards. Examples of these standards include ITU-T Recommendation H.265. In one example, the video coding standard under development is informally referred to as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC.

[0053] It should be noted that the electronic devices (320) and (330) may include other components (not shown). For example, the electronic device (320) may include a video decoder (not shown), and the electronic device (330) may also include a video encoder (not shown).

[0054] Figure 4 A block diagram of a video decoder (410) according to an embodiment of the present disclosure is shown. The video decoder (410) may be included in an electronic device (430). The electronic device (430) may include a receiver (431) (e.g., a receiving circuit). The video decoder (410) may be used to replace Figure 3 A video decoder (310) is shown in an example.

[0055] A receiver (431) may receive one or more encoded video bitstreams to be decoded by a video decoder (410); in the same or another embodiment, one encoded video bitstream at a time, where the decoding of each encoded video bitstream is independent of the other encoded video bitstreams. The encoded video bitstreams may be received from a channel (401), which may be a hardware / software link to a storage device storing the encoded video data. The receiver (431) may receive the encoded video data and other data, such as encoded audio data and / or auxiliary data streams, which may be forwarded to their respective consuming entities (not shown). The receiver (431) may separate the encoded video bitstreams from the other data. To counter network jitter, a buffer memory (415) may be coupled between the receiver (431) and an entropy decoder / parser (420) (hereinafter referred to as "parser (420)"). In some applications, the buffer memory (415) is part of the video decoder (410). In other cases, it may be external to the video decoder (410) (not shown). In other cases, there may be a buffer memory (not shown) external to the video decoder (410), e.g., to counter network jitter, and in addition, there may be another buffer memory (415) inside the video decoder (410), e.g., to handle playout timing. When the receiver (431) receives data from a store-and-forward device with sufficient bandwidth and controllability or from an isochronous network, the buffer memory (415) may not be needed or may be small. For use on a best-effort packet network such as the Internet, a buffer memory (415) may be required, which may be relatively large, and may advantageously have an adaptive size, and may be implemented at least partially in an operating system or similar element (not shown) external to the video decoder (410).

[0056] The video decoder (410) may include a parser (420) to reconstruct symbols (421) from the encoded video bitstream. The categories of these symbols include information for managing the operation of the video decoder (410) and potentially information for controlling a rendering device such as a rendering device (412) (e.g., a display screen), which is not part of the electronic device (430) but may be coupled to the electronic device (430), as Figure 4As shown. The control information for the rendering device may be in the form of Supplemental Enhancement Information (SEI message) or a Video Usability Information (VUI) parameter set segment (not shown). The parser (420) may perform parsing / entropy decoding on the received encoded video bitstream. The encoding of the encoded video bitstream may be according to a video coding technology or standard and may follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (420) may extract a set of subgroup parameters for at least one subgroup of pixels in the video decoder from the encoded video bitstream based on at least one parameter corresponding to the set. Subgroups may include Groups of Pictures (GOP), pictures, tiles, slices, macroblocks, Coding Units (CU), blocks, Transform Units (TU), Prediction Units (PU), etc. The parser (420) may also extract information from the encoded video bitstream, such as transform coefficients, quantizer parameter values, MVs, etc.

[0057] The parser (420) may perform an entropy decoding / parsing operation on the video bitstream received from the buffer memory (415) to create symbols (421).

[0058] Depending on the type of the encoded video picture or a part thereof (e.g., inter - frame and intra - frame pictures, inter - frame and intra - frame blocks) and other factors, the reconstruction of the symbols (421) may involve multiple different units. Which units are involved and how they are involved may be controlled by subgroup control information parsed by the parser (420) from the encoded video bitstream. For clarity, this subgroup control information flow between the parser (420) and the multiple units below is not described.

[0059] In addition to the functional blocks already mentioned, the video decoder (410) may be conceptually divided into multiple functional units as described below. In a practical implementation operating under commercial constraints, many of these units interact closely with each other and may be at least partially integrated with each other. However, for the purpose of describing the disclosed subject matter, it is appropriate to conceptually divide into the following functional units.

[0060] The first unit is a scaler / inverse transform unit (451). The scaler / inverse transform unit (451) receives the quantized transform coefficients and control information, including which transform to use, block size, quantization factor, quantization scaling matrix, etc., as symbols (421) from the parser (420). The scaler / inverse transform unit (451) may output blocks including sample values, and these blocks may be input into an aggregator (455).

[0061] In some cases, the output samples of the scaler / inverse transform unit (451) may belong to intra-coded blocks; that is: blocks that do not use prediction information from a previously reconstructed picture, but may use prediction information from a previously reconstructed part of the current picture. Such prediction information may be provided by an intra-picture prediction unit (452). In some cases, the intra-picture prediction unit (452) uses the surrounding already reconstructed information obtained from the current picture buffer (458) to generate a block having the same size and shape as the block being reconstructed. The current picture buffer (458) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. In some cases, the aggregator (455) adds the prediction information already generated by the intra-picture prediction unit (452) to the output sample information provided by the scaler / inverse transform unit (451) based on each sample.

[0062] In other cases, the output samples of the scaler / inverse transform unit (451) may belong to inter-coded and possibly motion-compensated blocks. In such cases, the motion compensation prediction unit (453) may access the reference picture memory (457) to obtain samples for prediction. After motion-compensating the obtained samples according to the symbols (421) related to the block, these samples may be added by the aggregator (455) to the output of the scaler / inverse transform unit (451) (referred to as residual samples or residual signals in this case) to generate output sample information. The address in the reference picture memory (457) from which the motion compensation prediction unit (453) obtains the prediction samples may be controlled by a motion vector (MV), and it is feasible for the motion compensation prediction unit (453) to obtain these addresses in the form of symbols (421), and these symbols may have, for example, X, Y, and reference picture components. When using subsampled accurate MVs, motion compensation may also include interpolation of sample values obtained from the reference picture memory (457), an MV prediction mechanism, etc.

[0063] The output samples of the aggregator (455) can undergo various loop filtering techniques in the loop filter unit (456). Video compression techniques can include loop filtering techniques that are controlled by parameters included in the encoded video bitstream, and the parameters can be used as symbols (421) from the parser (420) in the loop filter unit (456), and can also respond to meta-information obtained during the decoding of the previous (in decoding order) part of the encoded image or encoded video bitstream, and to the sample values of the previous reconstruction and loop filtering.

[0064] The output of the loop filter unit (456) can be a sample stream that can be output to the rendering device (412) and stored in the reference picture memory (457) for future inter-picture prediction.

[0065] Once fully reconstructed, some encoded pictures can be used as reference pictures for future prediction. For example, once the encoded image corresponding to the current picture is fully reconstructed and the encoded picture has been identified as a reference picture (e.g., by the parser (420)), the current picture buffer (458) can become part of the reference picture memory (457), and a new current picture buffer can be reallocated before starting the reconstruction of the next encoded picture.

[0066] The video decoder (410) can perform decoding operations according to predetermined video compression techniques in standards such as ITU-T Rec.H.265. In the sense that the encoded video bitstream conforms to the syntax of the video compression technique or standard and the profiles described in the video compression technique or standard, the encoded video bitstream can conform to the syntax specified by the video compression technique or standard used. Specifically, a profile can select certain tools from all the available tools in the video compression technique or standard as the only available tools under that profile. Conformance to the standard also requires that the complexity of the encoded video bitstream be within the range defined by the level of the video compression technique or standard. In some cases, the level limits the maximum image size, maximum frame rate, maximum reconstruction sampling rate (e.g., measured in megasamples per second), maximum reference picture size, etc. In some cases, the limits set by the level can be further restricted by the Hypothetical Reference Decoder (HRD) specification and the metadata for HRD buffer management signaled in the encoded video bitstream.

[0067] In one embodiment, a receiver (431) may receive additional (redundant) data with the encoded video. The additional data may be included as part of the encoded video bitstream. The video decoder (410) may use the additional data to correctly decode the data and / or more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0068] Figure 5 A block diagram of a video encoder (503) in accordance with an embodiment of the present disclosure is shown. The video encoder (503) is included in an electronic device (520). The electronic device (520) includes a transmitter (540) (e.g., a transmitting circuit). The video encoder (503) may be used in place of Figure 3 the video encoder (303) in the example.

[0069] The video encoder (503) may receive video samples from a video source (501) (which is not Figure 5 part of the electronic device (520) in the example), and the video source may capture video pictures to be encoded by the video encoder (503). In another example, the video source (501) is part of the electronic device (520).

[0070] The video source (501) may provide a source video sequence to be encoded by the video encoder (503) in the form of a digital video sample stream, which may have any suitable bit depth (e.g., 8 bits, 10 bits, 12 bits,...), any color space (e.g., BT.501 Y CrCB, RGB,...), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media service system, the video source (501) may be a storage device storing previously prepared video. In a video conferencing system, the video source (501) may be a camera capturing local image information as a video bitstream. The video data may be provided in the form of a plurality of individual pictures, which, when viewed in sequence, impart motion. These pictures themselves may be organized as a spatial array of pixels, where each pixel may include one or more samples, depending on the sampling structure, color space, etc. being used. Those skilled in the art can readily understand the relationship between pixels and samples. The following description focuses on samples.

[0071] According to one embodiment, a video encoder (503) may encode and compress pictures of a source video sequence into an encoded video bitstream (543) in real time or under any other time constraints required by the application. Implementing an appropriate encoding speed is a function of a controller (550). In some embodiments, the controller (550) controls other functional units as described below and is functionally coupled to other functional units. For clarity, the couplings are not described. Parameters set by the controller (550) may include rate control related parameters (picture skipping, quantizer, λ value of rate-distortion optimization techniques, …), picture size, group of pictures (GOP) layout, maximum MV allowed reference region, etc. The controller (550) may be configured to have other suitable functions related to the video encoder (503) optimized for a particular system design.

[0072] In some embodiments, the video encoder (503) is configured to operate in an encoding loop. As a simplified description, in one example, the encoding loop may include a source encoder (530) (e.g., for creating symbols, e.g., a symbol stream, based on an input picture to be encoded and reference pictures) and a (local) decoder (533) embedded in the video encoder (503). The decoder (533) reconstructs the symbols in a manner similar to that which a (remote) decoder would also create to create sample data (since in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the encoded video bitstream is lossless). The reconstructed sample stream (sample data) is input into a reference picture memory (534). Since the decoding of the symbol stream results in a bit-exact result independent of the decoder location (local or remote), the content in the reference picture memory (534) is also bit-exact between the local encoder and the remote encoder. In other words, when prediction is used during decoding, the prediction part of the encoder “sees” the same sample values as the decoder “sees” as reference picture samples. The basic principle of reference picture synchronization (and the resulting drift if the synchronization cannot be maintained, e.g., due to channel errors) is also used in some related arts.

[0073] The operation of the “local” decoder (533) may be the same as that of a “remote” decoder such as the video decoder (410), which has been described in detail above in conjunction with Figure 4 which. However, briefly referring to Figure 4 , since the symbols are available and the symbol encoding / decoding of the encoded video bitstream by the entropy encoder (545) and the parser (420) can be lossless, the entropy decoding part of the video decoder (410), including the buffer memory (415) and the parser (420), may not be fully implemented in the local decoder (533).

[0074] At this point, it can be observed that, in addition to the parsing / entropy decoding present in the decoder, any decoder technology needs to be present in the corresponding encoder in substantially the same functional form. To this end, the disclosed subject matter focuses on decoder operations. The description of encoder technologies can be simplified because these technologies are the inverse of the decoder technologies described in detail. More detailed descriptions are needed and provided only in certain areas.

[0075] During operation, in some examples, the source encoder (530) may perform motion-compensated predictive coding that predictively encodes an input picture by referring to one or more previously encoded pictures designated as "reference pictures" from a video bitstream. In this way, the encoding engine (532) encodes the difference between a pixel block of the input picture and a pixel block of a reference picture that can be selected as a predictive reference for the input picture.

[0076] The local video decoder (533) may decode the encoded video data of a picture that can be designated as a reference picture based on the symbols created by the source encoder (530). The operation of the encoding engine (532) can be a lossy process advantageously. When the encoded video data can be decoded at a video decoder ( Figure 5 (not shown)), the reconstructed video bitstream can generally be a copy of the source video bitstream with some errors. The local video decoder (533) can replicate the decoding process performed by the video decoder on the reference picture and can cause the reconstructed reference picture to be stored in the reference picture buffer (534). In this way, the video encoder (503) can locally store copies of the reconstructed reference pictures that have the same content as the reconstructed reference pictures that will be obtained by a remote video decoder (in the absence of transmission errors).

[0077] The predictor (535) may perform a prediction search on the encoding engine (532). That is, for a new picture to be encoded, the predictor (535) may search the reference picture memory (534) for sample data (as candidate reference pixel blocks) or certain metadata, such as reference picture motion vectors, block shapes, etc., that can be used as an appropriate prediction reference for the new picture. The predictor (535) may operate on a sample-by-sample block-pixel basis to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (535), the input picture may have a prediction reference extracted from multiple reference pictures stored in the reference picture memory (534).

[0078] The controller (550) may manage the encoding operations of the source encoder (530), including, for example, setting parameters and subgroups of parameters for encoding video data.

[0079] The outputs of all the aforementioned functional units can undergo entropy coding (545) in an entropy encoder. The entropy encoder (545) converts the symbols generated by the various functional units into a coded video bitstream by losslessly compressing the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0080] The transmitter (540) can buffer the coded video bitstream created by the entropy encoder (545) to prepare for transmission via a communication channel (560), which can be a hardware / software link to a storage device that will store the coded video data. The transmitter (540) can combine the coded video data from the video encoder (503) with other data to be transmitted, such as, for example, coded audio data and / or auxiliary data streams (sources not shown).

[0081] The controller (550) can manage the operation of the video encoder (503). During encoding, the controller (550) can assign a specific coded picture type to each coded picture, which can affect the encoding technique applied to the corresponding picture. For example, pictures can generally be assigned to one of the following picture types:

[0082] An intra picture (I picture) can be a picture that is encoded and decoded without using any other picture in the sequence as a prediction source. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh (“IDR”) pictures. Those skilled in the art are aware of those variants of I pictures and their corresponding applications and characteristics.

[0083] A predicted picture (P picture) can be a picture that is encoded and decoded using intra prediction or inter prediction, which uses at most one MV and a reference index to predict the sample values of each block.

[0084] A bi - directionally predicted picture (B picture) can be a picture that is encoded and decoded using intra prediction or inter prediction, which uses at most two MVs and reference indices to predict the sample values of each block. Similarly, a multi - predicted picture can use more than two reference pictures and associated metadata to reconstruct a single block.

[0085] Source pictures can typically be spatially subdivided into multiple sample blocks (e.g., each sample block is 4×4, 8×8, 4×8, or 16×16 sample blocks) and encoded on a block-by-block basis. Blocks are predictively encoded with reference to other (already encoded) blocks, where the other blocks are determined by the coding assignment for the corresponding picture applied to the block. For example, blocks of an I picture can be non-predictively encoded or can be predictively encoded with reference to already encoded blocks of the same picture (spatial prediction or intra-frame prediction). Pixel blocks of a P picture are predictively encoded with reference to a previously encoded reference picture, either via spatial prediction or via temporal prediction. Blocks of a B picture can be predictively encoded with reference to one or two previously encoded reference pictures, either via spatial prediction or via temporal prediction.

[0086] The video encoder (503) can perform encoding operations according to a predetermined video coding technique or standard (e.g., ITU-T Rec. H.265). In its operation, the video encoder (503) can perform various compression operations, including predictive coding operations that exploit the temporal and spatial redundancies in the input video bitstream. Thus, the encoded video data can conform to the syntax specified by the video coding technique or standard being used.

[0087] In one embodiment, the transmitter (540) can transmit additional data along with the encoded video. The source encoder (530) can include data as part of the encoded video bitstream. The additional data can include temporal / spatial / SNR enhancement layers, other forms of redundant data (e.g., redundant pictures and slices), SEI messages, VUI parameter set fragments, etc.

[0088] Multiple source pictures (video pictures) in a time series are captured from the video. Intra-picture prediction (usually abbreviated as intra-frame prediction) exploits the spatial correlation within a given picture, while inter-picture prediction exploits the (temporal or other) correlation between pictures. In one example, a particular picture in the encoding / decoding, called the current picture, is segmented into blocks. When a block in the current picture is similar to a reference block in a reference picture that was previously encoded in the video and is still buffered, the block in the current picture can be encoded by a vector called an MV. In the case of using multiple reference pictures, the MV points to the reference block in the reference picture and can have a third dimension that identifies the reference picture.

[0089] In some embodiments, bidirectional prediction techniques may be used in inter - picture prediction. According to the bidirectional prediction technique, two reference pictures are used, for example, a first reference picture and a second reference picture. Both of these reference pictures are before the current picture in the video in decoding order (but may be in the past and future respectively in display order). A block in the current picture can be encoded by a first MV pointing to a first reference block in the first reference picture and a second MV pointing to a second reference block in the second reference picture. The block can be predicted by a combination of the first reference block and the second reference block.

[0090] In addition, merge mode techniques can be used in inter - picture prediction to improve the encoding efficiency.

[0091] According to some embodiments of the present disclosure, for example, inter - picture prediction and intra - picture prediction are performed in units of blocks. For example, according to the HEVC standard, pictures in a video picture sequence are segmented into Coding Tree Units (CTUs) for compression. CTUs in a picture have the same size, for example, 64×64 pixels, 32×32 pixels, or 16×16 pixels. Generally, a CTU includes three Coding Tree Blocks (CTBs), namely, one luminance CTB and two chrominance CTBs. Each CTU can be recursively quad - tree segmented into one or more Coding Units (CUs). For example, a 64×64 - pixel CTU can be segmented into a 64×64 - pixel CU, or 4 32×32 - pixel CUs, or 16 16×16 - pixel CUs. In one example, each CU is analyzed to determine the prediction type of the CU, for example, an inter - prediction type or an intra - prediction type. According to temporal and / or spatial predictability, the CU is divided into one or more Prediction Units (PUs). Generally, each PU includes one luminance Prediction Block (PB) and two chrominance PBs. In an embodiment, prediction operations in encoding (encoding / decoding) are performed in units of prediction blocks. Taking the luminance prediction block as an example of the prediction block, the prediction block contains a matrix of pixel values (e.g., luminance values), such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0092] Figure 6 A schematic diagram of a video encoder (603) according to another embodiment of the present disclosure is shown. The video encoder (603) is configured to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a video picture sequence and encode the processing block into an encoded image as part of an encoded video bitstream. In one example, the video encoder (603) is used to replace Figure 3 the video encoder (303) in the example.

[0093] In the HEVC example, the video encoder (603) receives a matrix of sample values for a processing block, such as a prediction block of 8×8 samples, etc. The video encoder (603) determines whether to use an intra mode, an inter mode, or a bi-prediction mode such as rate-distortion optimization to optimally encode the processing block. When encoding the processing block in the intra mode, the video encoder (603) may use intra prediction techniques to encode the processing block into an encoded picture; and when encoding the processing block in the inter mode or the bi-prediction mode, the video encoder (603) may use inter prediction or bi-prediction techniques respectively to encode the processing block into an encoded picture. In some video coding techniques, the merge mode may be an inter-picture prediction sub-mode, where the MV is derived from one or more MV predictors without benefiting from encoded motion vector components outside the predictors. In some other video coding techniques, there may be MV components applicable to object blocks. In one example, the video encoder (603) includes other components, such as a mode determination module (not shown) for determining the mode of the processing block.

[0094] In Figure 6 the example of Figure 6 shown, the video encoder (603) includes an inter encoder (630), an intra encoder (622), a residual calculator (623), a switch (626), a residual encoder (624), a general controller (621), and an entropy encoder (625) coupled together as

[0095] The inter encoder (630) is configured to receive samples of a current block (e.g., a processing block), compare the block with one or more reference blocks in a reference picture (e.g., blocks in a previous picture and a subsequent picture), generate inter prediction information (e.g., a description of redundant information according to inter coding techniques, a motion vector, merge mode information), and calculate an inter prediction result (e.g., a prediction block) based on the inter prediction information obtained using any suitable technique. In some examples, the reference picture is a decoded reference picture decoded based on encoded video information.

[0096] The intra encoder (622) is configured to receive samples of a current block (e.g., a processing block), in some cases compare the block with blocks that have already been encoded in the same picture, generate quantized coefficients after transformation, and in some cases also generate intra prediction information (e.g., intra prediction direction information according to one or more intra coding techniques). In one example, the intra encoder (622) also calculates an intra prediction result (e.g., a prediction block) based on intra prediction information and reference blocks in the same picture.

[0097] The general controller (621) is configured to determine general control data and control other components of the video encoder (603) based on the general control data. In one example, the general controller (621) determines the mode of a block and provides a control signal to the switch (626) based on the mode. For example, when the mode is an intra mode, the general controller (621) controls the switch (626) to select the intra mode result for use by the residual calculator (623) and controls the entropy encoder (625) to select the intra prediction information and include the intra prediction information in the bitstream; when the mode is an inter mode, the general controller (621) controls the switch (626) to select the inter prediction result for use by the residual calculator (623) and controls the entropy encoder (625) to select the inter prediction information and include the inter prediction information in the bitstream.

[0098] The residual calculator (623) is configured to calculate the difference (residual data) between a received block and a selected prediction result from the intra encoder (622) or the inter encoder (630). The residual encoder (624) is configured to operate based on the residual data to encode the residual data to generate transform coefficients. In one example, the residual encoder (624) is configured to transform the residual data from the spatial domain to the frequency domain and generate transform coefficients. Then the transform coefficients are quantized to obtain quantized transform coefficients. In various embodiments, the video encoder (603) further includes a residual decoder (628). The residual decoder (628) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data can be appropriately used by the intra encoder (622) and the inter encoder (630). For example, the inter encoder (630) can generate a decoded block based on the decoded residual data and the inter prediction information, and the intra encoder (622) can generate a decoded block based on the decoded residual data and the intra prediction information. The decoded blocks are appropriately processed to generate a decoded picture, and the decoded picture can be cached in a memory circuit (not shown) and, in some examples, used as a reference picture.

[0099] The entropy encoder (625) is configured to format the bitstream to include encoded blocks. The entropy encoder (625) is configured to include various information according to a suitable standard, e.g., the HEVC standard. In one example, the entropy encoder (625) is configured to include general control data, selected prediction information (e.g., intra prediction information or inter prediction information), residual information, and other suitable information in the bitstream. Note that according to the disclosed subject matter, there is no residual information when encoding a block in an inter mode or in a merge submode of a bi - directional prediction mode.

[0100] Figure 7FIG. shows a schematic diagram of a video decoder (710) according to another embodiment of the present disclosure. The video decoder (710) is configured to receive an encoded picture as part of an encoded video bitstream and decode the encoded picture to generate a reconstructed picture. In one example, the video decoder (710) is used to replace Figure 3 the video decoder (310) in the example.

[0101] In Figure 7 the example of, the video decoder (710) includes an entropy decoder (771), an inter-frame decoder (780), a residual decoder (773), a reconstruction module (774), and an intra-frame decoder (772) coupled together as shown in Figure 7 .

[0102] The entropy decoder (771) may be configured to reconstruct certain symbols from the encoded image, and these symbols represent the syntax elements that make up the encoded image. Such symbols may include, for example, the mode for encoding a block (e.g., intra-mode, inter-mode, bi-prediction mode, merge sub-mode, or the latter two modes in another sub-mode), prediction information that can identify certain samples or metadata predicted by the intra-frame decoder (772) or the inter-frame decoder (780) respectively (e.g., intra-prediction information or inter-prediction information), residual information in the form of, for example, quantized transform coefficients, etc. In one example, when the prediction mode is inter or bi-prediction mode, the inter-prediction information is provided to the inter-frame decoder (780); and when the prediction type is intra-prediction type, the intra-prediction information is provided to the intra-frame decoder (772). The residual information may undergo inverse quantization and be provided to the residual decoder (773).

[0103] The inter-frame decoder (780) is configured to receive the inter-frame prediction information and generate an inter-frame prediction result based on the inter-frame prediction information.

[0104] The intra-frame decoder (772) is configured to receive the intra-frame prediction information and generate a prediction result based on the intra-frame prediction information.

[0105] The residual decoder (773) is configured to perform inverse quantization to extract the de-quantized transform coefficients and process the de-quantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residual decoder (773) may also require certain control information (including the quantization parameter (QP)), and this information may be provided by the entropy decoder (771) (the data path is not shown because this may be only a small amount of control information).

[0106] The reconstruction module (774) is configured to combine, in the spatial domain, the residual output by the residual decoder (773) and the prediction result (output by the inter-frame or intra-frame prediction module, as appropriate), to form a reconstruction block, which may be part of a reconstructed picture, which in turn may be part of a reconstructed video. Note that other suitable operations, such as deblocking operations, may be performed to improve the visual quality.

[0107] Note that the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using any suitable technology. In one embodiment, the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (303), (503), and (603) and the video decoders (310), (410), and (710) may be implemented using one or more processors that execute software instructions.

[0108] II. Inter-Frame Prediction in VVC

[0109] For each inter-frame predicted CU, the motion parameters may include a motion vector, a reference picture index, a reference picture list usage index, and additional information required for the new coding features of VVC that will be used for inter-frame prediction sample generation. The motion parameters may be signaled in an explicit or implicit manner. When a CU is encoded in skip mode, the CU may be associated with a PU and does not have significant residual coefficients, coded motion vector deltas, or reference picture indices. In merge mode, the motion parameters of the CU may be obtained from neighboring CUs, including spatial and temporal candidates and additional candidates introduced in VVC. The merge mode may be applied to any inter-frame predicted CU, not just skip mode. An alternative to the merge mode is the explicit transmission of motion parameters, where the motion vectors corresponding to the reference picture indices of each reference picture list, the reference picture list usage flags, and other required information may be explicitly signaled for each CU.

[0110] In addition to the inter - frame coding features of HEVC, many new and improved inter - frame prediction coding tools are introduced in VVC. For example, extended merge prediction, merge mode with MVD (MMVD), symmetric MVD (SMVD) signaling, affine motion compensation prediction, sub - block - based temporal motion vector prediction (SbTMVP), adaptive motion vector resolution (AMVR), motion field storage (e.g., 1 / 16 luminance sample MV storage and 8×8 motion field compression), bi - directional prediction with CU - level weights (BCW), bi - directional optical flow (BDOF), decoder - side motion vector refinement (DMVR), geometric partition mode (GPM), and the combination of inter - frame and intra - frame prediction (CIIP).

[0111] III. Prediction Structures and Reference Picture Lists

[0112] Figure 8 A graphical representation of a random - access configuration according to an embodiment of the present disclosure is shown. For the random - access prediction - structure configuration, a hierarchical B structure can be used for encoding. In Figure 8 , the numbers associated with each picture represent the coding order. Intra - frame pictures can be encoded at certain intervals according to the intra - frame period configuration option or based on other encoder configurations such as scene - change detection. The first intra - frame picture of a video sequence is encoded as an instantaneous - decoding - refresh (IDR) picture, while other intra - frame pictures can be encoded as non - IDR intra - frame pictures ("open GOP"). Pictures located between consecutive intra - frame pictures in the display order can be encoded as B pictures. Inter - frame - predicted pictures (referred to as "general P and B pictures" in Figure 8 and the following description) can be used as the lowest temporal layer, which can perform inter - frame prediction by referring to intra - frame or inter - frame pictures. The second and third temporal layers include reference B pictures, while the highest temporal layer contains only non - reference B pictures. The reference - picture list combination can be used for the management and entropy coding of reference - picture indices.

[0113] Figure 9 A graphical representation of a low - latency configuration according to an embodiment of the present disclosure is shown. The numbers associated with each picture represent the coding order.

[0114] The low - latency configuration including low - latency B and low - latency P can be used for real - time coding applications, such as video conferencing, video chatting, live video streaming, etc.

[0115] For low - latency coding conditions, only the first picture in a video sequence is encoded as an IDR picture. For the low - latency P mode, P slices are used, or for the low - latency B mode, B slices are used, to encode each subsequent picture. For both modes, the P or B slices only refer to pictures before the current picture in the display order. For the low - latency B mode, the two reference lists RefPicList0 and RefPicList1 are the same.

[0116] In the low-latency B mode, B-frames follow intra-frames in temporal order, where each B-frame can have up to two reference picture lists. Each inter-predicted coded block can use either uni-directional prediction or bi-directional prediction. The two reference lists (i.e., reference list L0 and reference list L1) are identical. When bi-directional prediction is used for an encoded block, two different previously encoded pictures can be referred to, one in each reference list.

[0117] In the low-latency P mode, P-frames follow intra-frames in temporal order, where each P-frame can have only one reference picture list. Each inter-predicted coded block uses only one previously encoded picture as the reference picture.

[0118] IV. Same Reference Picture Constraint

[0119] Compared to the low-latency P configuration, the low-latency B mode has the benefit of using bi-directional prediction coding tools (e.g., GPM, BCW, etc.). However, for certain applications with bandwidth constraints, the cost of signaling two reference picture lists and two reference picture indices can be expensive. On the other hand, for certain applications, two different reference pictures can be used in the low-latency B mode. When the network is unstable, this can lead to error recovery problems.

[0120] Aspects of the present disclosure include methods for reference picture signaling in low-latency applications such as video conferencing, video chatting, live video streaming, etc. The present disclosure includes methods for achieving inter-frame bi-directional prediction for low-latency use cases with reduced reference picture signaling cost.

[0121] According to some aspects of the present invention, an optional constraint of using the same reference picture for the two reference lists in inter-frame bi-directional prediction can be added to the low-latency B mode in order to mitigate the error recovery problems caused by two different reference pictures in the low-latency B mode and to reduce the reference index signaling cost.

[0122] In one embodiment, in the low-latency B configuration, a constraint flag can be signaled, for example, at a high-level syntax element, to indicate that the same reference picture is used for both predictions for each inter-frame bi-directionally predicted coded block. When the constraint flag is enabled, only one reference index is signaled. The signaling of this reference index corresponds to one of the two reference lists (e.g., reference list 0), and the reference index corresponding to the other reference list (e.g., reference list 1) can be inferred to be equal to the signaled reference index. For example, when the constraint flag is enabled, the signaling of the reference index for a bi-directional prediction block can signal only the reference index of one reference list.

[0123] In one embodiment, a constraint flag may be signaled at the sequence level (e.g., in the sequence parameter set) and may be referred to as sps_same_ref_pic_for_bi_prediction. In one example, when sps_same_ref_pic_for_bi_prediction is equal to 1, each inter-frame bi-predictive coded block in the sequence can only use the same reference picture for the two reference lists. When signaling the reference index in the bitstream of the bi-predictive coded block, only one reference index is signaled. The signaling of the reference index may correspond to reference list 0 (L0) and may be referred to as ref_idx_0, for example. The reference index corresponding to reference list 1 (L1) may be inferred to be equal to ref_idx_0 and may be referred to as ref_idx_1, for example.

[0124] In one embodiment, for coding tools based on the merge mode, such as, for example, the regular merge mode, the affine merge mode, MMVD, GPM, etc., when each of multiple inter-frame bi-predictive coded blocks uses the same reference picture for the two predictions, for example, when sps_same_ref_pic_for_bi_prediction is equal to 1, pruning may be applied to remove all bi-predictive candidates having different reference index values between L0 and L1 in order to reduce the merge index signaling cost.

[0125] In some embodiments, the constraint flag may be signaled at various levels (e.g., picture level or slice level). In one example, the constraint flag signaled in the picture parameter set may be referred to as pps_same_ref_pic_for_bi_prediction.

[0126] In one embodiment, for a tool, the constraint flag may be signaled before a syntax element (e.g., the on / off flag of the tool) that is configured to reference a future reference picture and a past reference picture. The future reference picture is a picture that is temporally after the current picture in the Picture Order Count (POC) identifier list, and the past reference picture is a picture that is temporally before the current picture in the POC identifier list. In one example, when the constraint flag is on (or true), the syntax element (e.g., the on / off flag of the tool) may be inferred to be false and not signaled. Examples of such tools include DMVR, BDOF, and SMVD.

[0127] According to aspects of the present disclosure, the constraint flag may be signaled at various levels, such as, for example, SPS-level parameters, picture-level parameters, slice-level parameters, etc.

[0128] In one embodiment, each of the multiple inter - frame bi - directional prediction - coded blocks uses the same reference picture for two predictions. For example, when sps_same_ref_pic_for_bi_prediction equals 1, only one of the two reference lists may be signaled. In one example, the other reference list can be inferred to be the same as the signaled reference list.

[0129] In accordance with aspects of the present invention, encoder constraints can be applied to the encoder to ensure that the same reference picture is used for reference list L0 and reference list L1 in inter - frame bi - directional prediction. Under this constraint, the two reference lists L0 and L1 are the same, and the two reference indices ref_index_0 and ref_index_1 are also the same. In one example, both of the two reference indices ref_index_0 and ref_index_1 can be signaled to the decoder. Thereby, the encoding speed can be improved.

[0130] V. Flowchart

[0131] Figure 10 A flowchart is shown that outlines an exemplary process (1000) in accordance with embodiments of the present disclosure. In various embodiments, the process (1000) is executed by a processing circuit, such as the processing circuits in terminal device (210), terminal device (220), terminal device (230), and terminal device (240), the processing circuit that performs the function of video encoder (303), the processing circuit that performs the function of video decoder (310), the processing circuit that performs the function of video decoder (410), the processing circuit that performs the function of intra - prediction module (452), the processing circuit that performs the function of video encoder (503), the processing circuit that performs the function of predictor (535), the processing circuit that performs the function of intra - encoder (622), the processing circuit that performs the function of intra - decoder (772), etc. In some embodiments, the process (1000) is implemented in software instructions, so when the processing circuit executes the software instructions, the processing circuit executes the process (1000).

[0132] The process (1000) generally may start at step (S1010), where the process (1000) decodes prediction information for a current block in a current picture that is part of an encoded video bitstream. The prediction information includes at least one reference picture index used in low - latency inter - frame bi - directional prediction of the current block. Each of the at least one reference picture indices has the same value. Then, the process (1000) proceeds to step (S1020).

[0133] In step (S1020), process (1000) determines a first reference picture in a first reference picture list and a second reference picture in a second reference picture list for the current block based on at least one reference picture index included in the prediction information. The current block is encoded using low-latency inter-picture bidirectional prediction. The first reference picture list is the same as the second reference picture list. The first reference picture is the same as the second reference picture. Then, process (1000) proceeds to step (S1030).

[0134] In step (S1030), process (1000) reconstructs the current block based on the first reference picture and the second reference picture. Then, process (1000) terminates.

[0135] In one embodiment, the at least one reference picture index is a single reference picture index associated with one of the first reference picture list and the second reference picture list, and process (1000) determines the single reference picture index as the reference picture index for the other of the first reference picture list and the second reference picture list.

[0136] In one embodiment, the prediction information includes a syntax element that indicates that the first reference picture in the first reference picture list is the same as the second reference picture in the second reference picture list, and the syntax element is included in one of a sequence level parameter, a picture level parameter, and a slice level parameter.

[0137] In one embodiment, based on the current block encoded in one of multiple merge modes, each bidirectional prediction candidate in the merge candidate list of the current block has the same reference picture index for the first reference picture list and the second reference picture list. The multiple merge modes include a regular merge mode, an affine merge mode, a merge mode with motion vector difference, advanced motion vector prediction, and a geometric partitioning mode.

[0138] In one embodiment, process (1000) determines to disable a tool configured to reference a reference picture that is temporally after the current picture based on prediction information indicating that the first reference picture in the first reference picture list is the same as the second reference picture in the second reference picture list.

[0139] In one embodiment, the prediction information includes one of the first reference picture list and the second reference picture list.

[0140] In one embodiment, the at least one reference picture index includes two identical reference picture indexes, and the prediction information includes the first reference picture list, the second reference picture list, and the two identical reference picture indexes.

[0141] VI. Computer System

[0142] The above - mentioned technology can be implemented as computer software using computer - readable instructions and physically stored in one or more computer - readable media. For example, Figure 11 FIG. shows a computer system (1100) suitable for implementing certain embodiments of the disclosed subject matter.

[0143] The computer software can be encoded using any suitable machine code or computer language, which can undergo assembly, compilation, linking, or similar mechanisms to create code including instructions that can be directly executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc., or executed through interpretation, microcode execution, etc.

[0144] The instructions can be executed on various types of computers or their components, including, for example, personal computers, tablet computers, servers, smartphones, gaming devices, Internet - of - Things devices, etc.

[0145] Figure 11 The components of the computer system (1100) shown are exemplary in nature and are not intended to impose any limitation on the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The configuration of the components should also not be construed as having any dependence on or requirement for any one component or combination of components shown in the exemplary embodiments of the computer system (1100).

[0146] The computer system (1100) may include certain human - machine interface input devices. Such human - machine interface input devices can respond to the input of one or more human users, such as tactile input (e.g., keystrokes, swipes, data - glove movements), audio input (e.g., voice, applause), visual input (e.g., gestures), olfactory input (not shown). The human - machine interface device can also be used to capture certain media not necessarily directly related to a human's conscious input, such as, for example, audio (e.g., voice, music, ambient sound), images (e.g., scanned images, photo images obtained from a still - image camera), video (e.g., two - dimensional video, three - dimensional video including stereoscopic video).

[0147] The input human - machine interface devices can include one or more of the following (each shown only one): keyboard (1101), mouse (1102), trackpad (1103), touchscreen (1110), data glove (not shown), joystick (1105), microphone (1106), scanner (1107), camera (1108).

[0148] The computer system (1100) may also include certain human-machine interface output devices. Such human-machine interface output devices may stimulate the senses of one or more human users, for example, through tactile output, sound, light, and smell / taste. Such human-machine interface output devices may include tactile output devices (e.g., tactile feedback through a touch screen (1110), a data glove (not shown), or a joystick (1105), but there may also be tactile feedback devices that do not serve as input devices), audio output devices (e.g., speakers (1109), headphones (not shown)), visual output devices (e.g., a screen (1110), including a CRT screen, an LCD screen, a plasma screen, an OLED screen, each with or without touch screen input capabilities, each with or without tactile feedback capabilities - some of which are capable of outputting two-dimensional visual output or more than three-dimensional output, through means such as stereoscopic output; virtual reality glasses (not shown), holographic displays, and smoke boxes (not shown)), and printers (not shown). These visual devices (e.g., the screen (1110)) may be connected to the system bus (1148) through a graphics adapter (1150).

[0149] The computer system (1100) may also include human-accessible storage devices and their associated media, for example, including optical media such as a CD / DVD ROM / RW (1120) with a CD / DVD or similar medium (1121), a thumb drive (1122), a removable hard disk drive or a solid-state drive (1123), traditional magnetic media such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD devices such as security dongles (not shown), etc.

[0150] Those skilled in the art should also understand that the term "computer-readable medium" used in connection with the presently disclosed subject matter does not include transmission media, carrier waves, or other transient signals.

[0151] The computer system (1100) may also include an interface (1154) to one or more communication networks (1155). The one or more communication networks (1155) may be, for example, wireless, wired, optical. The one or more communication networks (1155) may also be local area, wide area, metropolitan, vehicular, and industrial, real-time, delay-tolerant, etc. Examples of the one or more communication networks (1155) include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television cable or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicular and industrial networks including CANBus, etc. Certain networks typically require an external network interface adapter connected to certain common data ports or peripheral buses (1149) (e.g., the USB port of the computer system (1100)); others are typically integrated into the core of the computer system (1100) by connecting to the system bus as described below (e.g., the Ethernet interface in a PC computer system or the cellular network interface in a smart phone computer system). Using any of these networks, the computer system (1100) can communicate with other entities. Such communication may be unidirectional, receive-only (e.g., broadcast television), unidirectional, transmit-only (e.g., CANbus to certain CANbus devices), or bidirectional, e.g., to other computer systems using local or wide area digital networks. As described above, certain protocols and protocol stacks may be used on each of these networks and network interfaces.

[0152] The foregoing human-machine interface device, human-accessible storage device, and network interface may be attached to the core (1140) of the computer system (1100).

[0153] The core (1140) may include one or more central processing units (CPUs) (1141), graphics processing units (GPUs) (1142), field programmable gate areas (FPGAs) (1143) in the form of dedicated programmable processing units, hardware accelerators (1144) for certain tasks, graphics adapters (1150), etc. These devices, together with read-only memory (ROM) (1145), random access memory (1146), and internal mass storage such as internal non-user-accessible hard disk drives, SSDs (1147), can be connected via a system bus (1148). In some computer systems, the system bus (1148) can be accessed in the form of one or more physical plugs to allow for the expansion of additional CPUs, GPUs, etc. Peripheral devices can be connected directly or via a peripheral bus (1149) to the system bus (1148) of the core. In one example, a screen (1110) can be connected to the graphics adapter (1150). The architecture of the peripheral bus includes PCI, USB, etc.

[0154] The CPU (1141), GPU (1142), FPGA (1143), and accelerator (1144) can execute certain instructions that, when combined, can constitute the aforementioned computer code. The computer code can be stored in the ROM (1145) or the RAM (1146). Transitional data can also be stored in the RAM (1146), while permanent data can be stored in, for example, the internal mass storage (1147). Fast storage and retrieval of any storage device can be achieved by using a cache memory that can be closely associated with one or more CPUs (1141), GPUs (1142), mass storage (1147), ROM (1145), RAM (1146), etc.

[0155] Computer-readable media can have computer code for performing various computer-implemented operations. The media and the computer code can be of a type specifically designed and constructed for the purposes of this disclosure or can be of the type well-known and available to those skilled in the field of computer software.

[0156] By way of example and not limitation, a computer system (1100) having an architecture, in particular a core (1140), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) that executes software embedded in one or more tangible computer-readable media. Such computer-readable media can be the media associated with the user-accessible mass storage as described above and certain memories of the non-transitory core (1140), e.g., the on-core mass storage (1147) or ROM (1145). The software implementing various embodiments of the present disclosure can be stored in such a device and executed by the core (1140). Depending on specific needs, the computer-readable media can include one or more storage devices or chips. The software can cause the core (1140) and in particular the processors therein (including CPU, GPU, FPGA, etc.) to execute specific processes or specific parts of specific processes described herein, including defining data structures stored in the RAM (1146) and modifying such data structures according to software-defined processes. Additionally or alternatively, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (1144)), which can operate in place of or in conjunction with the software to execute specific processes or specific parts of specific processes described herein. In appropriate cases, references to software can include logic and vice versa. In appropriate cases, references to computer-readable media can include circuitry (e.g., an Integrated Circuit, IC) storing the software to be executed, circuitry containing the logic for execution, or both. The present disclosure encompasses any suitable combination of hardware and software.

[0157] Although the present disclosure has described several exemplary embodiments, there are variations, permutations, and various alternative equivalents that fall within the scope of the present disclosure. Accordingly, it should be understood that those skilled in the art will be able to design many systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are thus within the spirit and scope of the present disclosure.

[0158] Appendix A: Abbreviations

[0159] ALF: Adaptive Loop Filter

[0160] AMVP: Advanced Motion Vector Prediction

[0161] APS: Adaptation Parameter Set

[0162] ASIC: Application-Specific Integrated Circuit

[0163] ATMVP: Alternative / Advanced Temporal Motion Vector Prediction

[0164] AV1: AOMedia Video 1

[0165] AV2: AOMedia Video 2

[0166] BMS: Benchmark Set

[0167] BV: Block Vector

[0168] CANBus: Controller Area Network Bus

[0169] CB: Coding Block

[0170] CC-ALF: Cross-Component Adaptive Loop Filter

[0171] CD: Compact Disc

[0172] CDEF: Constrained Directional Enhancement Filter

[0173] CPR: Current Picture Referencing

[0174] CPU: Central Processing Unit

[0175] CRT: Cathode Ray Tube

[0176] CTB: Coding Tree Block

[0177] CTU: Coding Tree Unit

[0178] CU: Coding Unit

[0179] DPB: Decoder Picture Buffer

[0180] DPCM: Differential Pulse-Code Modulation

[0181] DPS: Decoding Parameter Set

[0182] DVD: Digital Video Disc

[0183] FPGA: Field Programmable Gate Area

[0184] JCCR: Joint CbCr Residual Coding

[0185] JVET: Joint Video Exploration Team

[0186] GOP: Groups of Pictures

[0187] GPU: Graphics Processing Unit

[0188] GSM: Global System for Mobile communications

[0189] HDR: High Dynamic Range

[0190] HEVC: High Efficiency Video Coding

[0191] HRD: Hypothetical Reference Decoder

[0192] IBC: Intra Block Copy

[0193] IC: Integrated Circuit

[0194] ISP: Intra Sub-Partitions

[0195] JEM: Joint Exploration Model

[0196] LAN: Local Area Network

[0197] LCD: Liquid-Crystal Display

[0198] LR: Loop Restoration Filter

[0199] LRU: Loop Restoration Unit

[0200] LTE: Long-Term Evolution

[0201] MPM: Most Probable Mode

[0202] MV: Motion Vector

[0203] OLED: Organic Light-Emitting Diode

[0204] PB: Prediction Blocks

[0205] PCI: Peripheral Component Interconnect

[0206] PDPC: Position Dependent Prediction Combination

[0207] PLD: Programmable Logic Device

[0208] PPS: Picture Parameter Set

[0209] PU: Prediction Unit

[0210] RAM: Random Access Memory

[0211] ROM: Read-Only Memory

[0212] SAO: Sample Adaptive Offset

[0213] SCC: Screen Content Coding

[0214] SDR: Standard Dynamic Range

[0215] SEI: Supplementary Enhancement Information

[0216] SNR: Signal Noise Ratio

[0217] SPS: Sequence Parameter Set

[0218] SSD: Solid-state Drive

[0219] TU: Transform Unit

[0220] USB: Universal Serial Bus

[0221] VPS: Video Parameter Set

[0222] VUI: Video Usability Information

[0223] VVC: Versatile Video Coding

[0224] WAIP: Wide-Angle Intra Prediction

Claims

1. A video decoding method in a decoder, characterized in that, comprising: decoding prediction information of a current block in a current picture that is part of an encoded video bitstream, the prediction information including a reference picture index and syntax elements used in low-latency inter-frame bi-prediction for the current block, the syntax elements including a constraint flag for indicating whether a first reference picture and a second reference picture of the current block are the same, the first reference picture being in a first reference picture list and the second reference picture being in a second reference picture list; when the constraint flag included in the syntax elements is enabled and the current block is encoded based on one of a plurality of merge modes, determining, based on the reference picture index included in the prediction information, the first reference picture of the current block in the first reference picture list and the second reference picture of the current block in the second reference picture list, and removing all bi-prediction candidates of the current block having different reference index values between the first reference picture list and the second reference picture list, wherein the first reference picture list is the same as the second reference picture list, and the first reference picture is the same as the second reference picture, and the current block is encoded using low-latency inter-frame bi-prediction that uses the reference picture index; reconstructing the current block based on the first reference picture and the second reference picture.

2. The method according to claim 1, characterized in that, the reference picture index is a single reference picture index associated with one of the first reference picture list and the second reference picture list, and the determining includes determining the single reference picture index as the reference picture index of the other of the first reference picture list and the second reference picture list.

3. The method according to claim 1, characterized in that, the syntax elements are included in one of sequence-level parameters, picture-level parameters, and slice-level parameters.

4. The method according to claim 1, characterized in that, based on the current block encoded in one of the plurality of merge modes, each bi-prediction candidate in the merge candidate list of the current block has the same reference picture index for the first reference picture list and the second reference picture list, and the plurality of merge modes include a regular merge mode, an affine merge mode, a merge mode with motion vector difference, advanced motion vector prediction, and a geometric segmentation mode.

5. The method according to claim 1, characterized in that, comprising determining to disable a tool configured to reference a reference picture that is temporally after the current picture based on the prediction information indicating that the first reference picture in the first reference picture list is the same as the second reference picture in the second reference picture list.

6. The method according to claim 1, characterized in that, The prediction information includes one of the first reference picture list and the second reference picture list.

7. The method according to claim 1, wherein, the prediction information includes the first reference picture list, the second reference picture list and the one reference picture index.

8. A device for video decoding, wherein, comprising a processor and a memory, the memory is configured to store instructions, the processor is configured to call the instructions stored in the memory to implement the method according to any one of claims 1-7.

9. A non-transitory computer-readable storage medium storing instructions, wherein, when executed by at least one processor, the instructions cause the at least one processor to execute the method according to any one of claims 1-7.

10. A computer program product, wherein, comprising instructions that, when run on a computer, cause the computer to execute the method according to any one of claims 1-7.

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