CN111988617A - Video decoding method and apparatus, computer device, and storage medium - Google Patents

Abstract

Aspects of the present disclosure provide a video decoding method and apparatus. The method comprises the following steps: decoding, in a first encoding pass, a first syntax element at an encoding position within a transform block of a current block, the first encoding pass scanning the encoding position within the transform block; in a second encoding pass, decoding a second syntax element at an encoding position within the transform block, the second encoding pass following the first encoding pass and scanning the encoding position within the transform block; determining a residual in the transform block based on at least the decoded first syntax element and the decoded second syntax element at the encoding position in the transform block; and reconstructing samples of the current block based on the residuals in the transformed block.

Description

Video decoding method and apparatus, computer device, and storage medium

Cross-referencing

The present disclosure claims priority from united states provisional application No. 62/851,496, "TU-LEVEL coeffient CODING," filed on 22/5/2019 and united states formal application No. 16/865,072, filed on 1/5/2020, the entire contents of which are incorporated herein by reference.

Technical Field

The present disclosure relates to the field of video encoding and decoding technology. In particular, the present disclosure provides a video decoding method and apparatus, and a computer device and a storage medium.

Background

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present application.

Inter picture prediction with motion compensation can be used for video encoding and decoding. Uncompressed digital video may comprise a sequence of pictures, each picture having a spatial dimension of, for example, 1920 x 1080 luma samples and associated chroma samples. The series of pictures may have a fixed or variable picture rate (informally also referred to as frame rate), for example 60 pictures per second or 60 Hz. Uncompressed video has significant bit rate requirements. For example, 1080p 604: 2:0 video (1920 × 1080 luminance sample resolution at 60Hz frame rate) with 8 bits per sample requires close to 1.5Gbit/s bandwidth. One hour of such video requires over 600 gigabytes of storage space.

One purpose of video encoding and decoding may be to reduce redundancy in the input video signal by compression. Compression can help reduce the bandwidth or storage requirements described above, by two orders of magnitude or more in some cases. Lossless compression and lossy compression, as well as combinations of the two, may be employed. Lossless compression refers to a technique by which an exact copy of an original signal can be reconstructed from a compressed original signal. When lossy compression is used, the reconstructed signal may not be identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. Lossy compression is widely used in video. The amount of distortion that can be tolerated depends on the application; for example, users of certain consumer streaming applications may tolerate higher distortion than users of television distribution applications. The achievable compression ratio may reflect that higher allowable/tolerable distortion can result in higher compression ratios.

Video encoders and decoders can utilize techniques in several broad categories including, for example, motion compensation, transform, quantization, and entropy coding.

Video codec techniques may include a technique referred to as intra-coding. In intra coding, sample values are represented without reference to samples or other data from a previously reconstructed reference picture. In some video codecs, a picture is spatially subdivided into blocks of samples. When all sample blocks are encoded in intra mode, the picture may be an intra coded picture. Intra coded pictures and derivatives thereof, such as 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 video session, or as still images. The samples of the intra-coded block may be transformed and the transform coefficients may be quantized prior to entropy coding. Intra prediction may be a technique that minimizes sample values in the pre-transform domain. In some cases, the smaller the DC value after transformation, and the smaller the AC coefficient, the fewer bits are needed to represent the block after entropy encoding for a given quantization step.

Conventional intra-frame coding, such as known from, for example, MPEG-2 generation coding techniques, does not use intra-frame prediction. However, some newer video compression techniques include techniques that attempt to proceed from surrounding sample data and/or metadata acquired during encoding/decoding, e.g., data blocks that are spatially adjacent and preceding in decoding order. Such techniques are hereinafter referred to as "intra-prediction" techniques. Note that in at least some cases, intra prediction only uses reference data from reconstructed current pictures and not reference data from reference pictures.

Intra prediction can take many different forms. When more than one such technique is available in a given video coding technique, the technique in use may be coded in intra-prediction mode. In some cases, modes may have sub-modes and/or parameters, and those can be encoded separately or included in the mode codeword. Which codeword is used for a given mode/sub-mode/parameter combination may have an impact on the coding efficiency gain through intra prediction, and thus entropy coding techniques can be used to convert the codeword into a code stream.

The mode of intra prediction is introduced by h.264, refined in h.265, and further refined in newer coding techniques such as joint development model (JEM), universal video coding (VVC), and reference set (BMS). The predictor block may be formed using neighboring sample values belonging to already available samples. Sample values of neighboring samples are copied into the predictor block according to the direction. The reference to the direction in use may be encoded in the codestream or may itself be predicted.

The context-coded bins contribute different coding gains to different syntax elements compared to bypass coding. For example, the context-coded bin contributes more coding gain to sig _ coeff _ flag than abs _ level _ gtX _ flag. However, since the total budget for context-coded bins is specified for the current TU, but the encoding pass is performed at the CG level, some of the sig _ coeff _ flags in the CG later encoded in the current TU may not have a chance to be context-coded, since all syntax elements in the previous CG consume all of the budget for context-coded bins, which may affect encoding efficiency.

Disclosure of Invention

The embodiment of the application provides a video decoding method, which comprises the following steps:

in a first encoding pass, decoding a first syntax element at an encoding position within a transform block of a current block, the first encoding pass scanning the encoding position within the transform block;

decoding, in a second coding pass, a second syntax element at the coding position within the transform block, the second coding pass following the first coding pass and scanning the coding position within the transform block;

determining a residual in the transform block based at least on the decoded first syntax element and the decoded second syntax element at the coding position in the transform block; and

reconstructing samples of the current block based on the residual in the transform block.

An embodiment of the present application provides a video decoding apparatus, including:

a first decoding module for decoding a first syntax element at an encoding position within a transform block of a current block in a first encoding pass that scans the encoding position within the transform block;

a second decoding module for decoding, in a second coding pass, second syntax elements at the coding positions within the transform blocks, the second coding pass following the first coding pass and scanning the coding positions within the transform blocks;

a determination module to determine a residual in the transform block based at least on the decoded first syntax element and the decoded second syntax element at the coding position in the transform block; and

a reconstruction module to reconstruct samples of the current block based on the residual in the transformed block.

The embodiment of the present application provides a computer device, which includes one or more processors and one or more memories, where at least one instruction is stored in the one or more memories, and the at least one instruction is loaded and executed by the one or more processors to implement the method according to any embodiment of the present application.

The embodiments of the present application provide a non-transitory computer-readable medium, on which instructions are stored, and when the instructions are executed by a computer, the computer is caused to execute the method of any of the embodiments of the present application.

The embodiment of the application provides an entropy coding technology of transformation coefficients, residual coding of TSM and residual coding of BDPCM mode. The entropy coding technique can prioritize syntax elements with higher context coding gain for context coding at TU level and use the context coding budget in an optimal manner, thereby improving coding efficiency.

Drawings

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:

fig. 1 is a schematic diagram of a simplified block diagram of a communication system 100 according to an embodiment;

fig. 2 is a schematic diagram of a simplified block diagram of a communication system 200 according to another embodiment;

FIG. 3 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment;

FIG. 4 is a schematic diagram of a simplified block diagram of an encoder according to an embodiment;

FIG. 5 shows a block diagram of an encoder according to another embodiment;

FIG. 6 shows a block diagram of a decoder according to another embodiment;

FIG. 7 shows an example of a transform block;

fig. 8A-8B illustrate tables of residual coding syntax for transform skip mode used in some examples;

FIG. 9 illustrates an example of scan order in an encoding pass according to some embodiments of the present disclosure;

FIG. 10 shows a flowchart outlining an example of a process according to some embodiments of the present disclosure;

fig. 11 is a schematic diagram of a computer system, according to an embodiment.

Detailed Description

Fig. 1 is a simplified block diagram of a communication system (100) according to an embodiment disclosed herein. The communication system (100) comprises a plurality of terminal devices which may communicate with each other via, for example, a network (150). For example, a communication system (100) includes a first terminal device (110) and a second terminal device (120) interconnected by a network (150). In the embodiment of fig. 1, the first terminal device (110) and the second terminal device (120) perform unidirectional data transmission. For example, a first end device (110) may encode video data, such as a stream of video pictures captured by the end device (110), for transmission over a network (150) to a second end device (120). The encoded video data is transmitted in the form of one or more encoded video streams. The second terminal device (120) may receive the encoded video data from the network (150), decode the encoded video data to recover the video data, and display a video picture according to the recovered video data. Unidirectional data transmission is common in applications such as media services.

In another embodiment, a communication system (100) includes a third end device (130) and a fourth end device (140) that perform bidirectional transmission of encoded video data, which may occur, for example, during a video conference. For bi-directional data transmission, each of the third end device (130) and the fourth end device (140) may encode video data (e.g., a stream of video pictures captured by the end device) for transmission over the network (150) to the other of the third end device (130) and the fourth end device (140). Each of the third terminal device (130) and the fourth terminal device (140) may also receive encoded video data transmitted by the other of the third terminal device (130) and the fourth terminal device (140), and may decode the encoded video data to recover the video data, and may display video pictures on an accessible display device according to the recovered video data.

In the embodiment of fig. 1, the first terminal device (110), the second terminal device (120), the third terminal device (130), and the fourth terminal device (140) may be a server, a personal computer, and a smart phone, but the principles disclosed herein may not be limited thereto. Embodiments disclosed herein are applicable to laptop computers, tablet computers, media players, and/or dedicated video conferencing equipment. Network (150) represents any number of networks that communicate encoded video data between first terminal device (110), second terminal device (120), third terminal device (130), and fourth terminal device (140), including, for example, wired (wired) and/or wireless communication networks. The communication network (150) may exchange data in circuit-switched and/or packet-switched channels. The network may include a telecommunications network, a local area network, a wide area network, and/or the internet. For purposes of this application, the architecture and topology of the network (150) may be immaterial to the operation disclosed herein, unless explained below.

By way of example, fig. 2 illustrates the placement of a video encoder and a video decoder in a streaming environment. The subject matter disclosed herein is equally applicable to other video-enabled applications including, for example, video conferencing, digital TV, storing compressed video on digital media including CDs, DVDs, memory sticks, and the like.

The streaming system may include an acquisition subsystem (213), which may include a video source (201), such as a digital camera, that creates an uncompressed video picture stream (202). In an embodiment, the video picture stream (202) includes samples taken by a digital camera. The video picture stream (202) is depicted as a thick line to emphasize a high data amount video picture stream compared to the encoded video data (204) (or the encoded video codestream), the video picture stream (202) being processable by an electronic device (220), the electronic device (220) comprising a video encoder (203) coupled to a video source (201). The video encoder (203) may comprise hardware, software, or a combination of hardware and software to implement or embody aspects of the disclosed subject matter as described in more detail below. The encoded video data (204) (or encoded video codestream (204)) is depicted as a thin line to emphasize the lower data amount of the encoded video data (204) (or encoded video codestream (204)) as compared to the video picture stream (202), which may be stored on the streaming server (205) for future use. One or more streaming client subsystems, such as client subsystem (206) and client subsystem (208) in fig. 2, may access streaming server (205) to retrieve copies (207) and copies (209) of encoded video data (204). The client subsystem (206) may include, for example, a video decoder (210) in an electronic device (230). The video decoder (210) decodes incoming copies (207) of the encoded video data and generates an output video picture stream (211) that may be presented on a display (212), such as a display screen, or another presentation device (not depicted). In some streaming systems, encoded video data (204), video data (207), and video data (209), such as video streams, may be encoded according to certain video encoding/compression standards. Examples of such standards include ITU-T H.265. In an embodiment, the Video Coding standard under development is informally referred to as next generation Video Coding (VVC), and the present application may be used in the context of the VVC standard.

It should be noted that electronic device (220) and electronic device (230) may include other components (not shown). For example, the electronic device (220) may include a video decoder (not shown), and the electronic device (230) may also include a video encoder (not shown).

Fig. 3 is a block diagram of a video decoder (310) according to an embodiment of the present disclosure. The video decoder (310) may be disposed in an electronic device (330). The electronic device (330) may include a receiver (331) (e.g., a receive circuit). The video decoder (310) may be used in place of the video decoder (210) in the fig. 2 embodiment.

The receiver (331) may receive one or more encoded video sequences to be decoded by the video decoder (310); in the same or another embodiment, the encoded video sequences are received one at a time, wherein each encoded video sequence is decoded independently of the other encoded video sequences. The encoded video sequence may be received from a channel (301), which may be a hardware/software link to a storage device that stores encoded video data. The receiver (331) may receive encoded video data as well as other data, e.g. encoded audio data and/or auxiliary data streams, which may be forwarded to their respective usage entities (not indicated). The receiver (331) may separate the encoded video sequence from other data. To prevent network jitter, a buffer memory (315) may be coupled between the receiver (331) and the entropy decoder/parser (320) (hereinafter "parser (320)"). In some applications, the buffer memory (315) is part of the video decoder (310). In other cases, the buffer memory (315) may be disposed external (not labeled) to the video decoder (310). While in other cases a buffer memory (not labeled) is provided external to the video decoder (310), e.g., to prevent network jitter, and another buffer memory (315) may be configured internal to the video decoder (310), e.g., to handle playout timing. The buffer memory (315) may not be required to be configured or may be made smaller when the receiver (331) receives data from a store/forward device with sufficient bandwidth and controllability or from an isochronous network. Of course, for use over traffic packet networks such as the internet, a buffer memory (315) may also be required, which may be relatively large and may be of adaptive size, and may be implemented at least partially in an operating system or similar element (not labeled) external to video decoder (310).

The video decoder (310) may include a parser (320) to reconstruct symbols (321) from the encoded video sequence. The categories of these symbols include information for managing the operation of the video decoder (310), as well as potential information to control a display device, such as a display screen (312), that is not an integral part of the electronic device (330), but may be coupled to the electronic device (330), as shown in fig. 3. The control Information for the display device may be a parameter set fragment (not shown) of Supplemental Enhancement Information (SEI message) or Video Usability Information (VUI). The parser (320) may parse/entropy decode the received encoded video sequence. Encoding of the encoded video sequence may be performed in accordance with video coding techniques or standards and may follow various principles, including variable length coding, Huffman coding, arithmetic coding with or without contextual sensitivity, and so forth. A parser (320) may extract a subgroup parameter set for at least one of the subgroups of pixels in the video decoder from the encoded video sequence based on at least one parameter corresponding to the group. A subgroup may include a Group of Pictures (GOP), a picture, a tile, a slice, a macroblock, a Coding Unit (CU), a block, a Transform Unit (TU), a Prediction Unit (PU), and so on. The parser (320) may also extract information from the encoded video sequence, such as transform coefficients, quantizer parameter values, motion vectors, and so on.

The parser (320) may perform entropy decoding/parsing operations on the video sequence received from the buffer memory (315), thereby creating symbols (321).

The reconstruction of the symbol (321) may involve a number of different units depending on the type of the encoded video picture or a portion of the encoded video picture (e.g., inter and intra pictures, inter and intra blocks), among other factors. Which units are involved and the way in which they are involved can be controlled by subgroup control information parsed from the coded video sequence by the parser (320). For the sake of brevity, such a subgroup control information flow between parser (320) and the following units is not described.

In addition to the functional blocks already mentioned, the video decoder (310) may be conceptually subdivided into several functional units as described below. In a practical embodiment operating under business constraints, many of these units interact closely with each other and may be integrated with each other. However, for the purposes of describing the disclosed subject matter, a conceptual subdivision into the following functional units is appropriate.

The first unit is a sealer/inverse transform unit (351). A sealer/inverse transform unit (351) receives the quantized transform coefficients as symbols (321) from the parser (320) along with control information including which transform scheme to use, block size, quantization factor, quantization scaling matrix, etc. The scaler/inverse transform unit (351) may output a block comprising sample values, which may be input into the aggregator (355).

In some cases, the output samples of sealer/inverse transform unit (351) may belong to an intra-coded block; namely: predictive information from previously reconstructed pictures is not used, but blocks of predictive information from previously reconstructed portions of the current picture may be used. Such predictive information may be provided by an intra picture prediction unit (352). In some cases, the intra picture prediction unit (352) generates a surrounding block of the same size and shape as the block being reconstructed using the reconstructed information extracted from the current picture buffer (358). For example, the current picture buffer (358) buffers a partially reconstructed current picture and/or a fully reconstructed current picture. In some cases, the aggregator (355) adds the prediction information generated by the intra prediction unit (352) to the output sample information provided by the scaler/inverse transform unit (351) on a per sample basis.

In other cases, the output samples of sealer/inverse transform unit (351) may belong to inter-coded and potential motion compensated blocks. In this case, the motion compensated prediction unit (353) may access the reference picture memory (357) to fetch samples for prediction. After motion compensating the extracted samples according to the sign (321), the samples may be added to the output of the scaler/inverse transform unit (351), in this case referred to as residual samples or residual signals, by an aggregator (355), thereby generating output sample information. The fetching of prediction samples by the motion compensated prediction unit (353) from addresses within the reference picture memory (357) may be controlled by motion vectors, and the motion vectors are used by the motion compensated prediction unit (353) in the form of the symbols (321), the symbols (321) for example comprising X, Y and reference picture components. Motion compensation may also include interpolation of sample values fetched from reference picture store (357), motion vector prediction mechanisms, etc., when using sub-sample exact motion vectors.

The output samples of the aggregator (355) may be employed in a loop filter unit (356) by various loop filtering techniques. The video compression techniques may include in-loop filter techniques that are controlled by parameters included in the encoded video sequence (also referred to as an encoded video bitstream) and that are available to the loop filter unit (356) as symbols (321) from the parser (320). However, in other embodiments, the video compression techniques may also be responsive to meta-information obtained during decoding of previous (in decoding order) portions of the encoded picture or encoded video sequence, as well as to sample values previously reconstructed and loop filtered.

The output of the loop filter unit (356) may be a sample stream that may be output to a display device (312) and stored in a reference picture memory (357) for subsequent inter picture prediction.

Once fully reconstructed, some of the coded pictures may be used as reference pictures for future prediction. For example, once the encoded picture corresponding to the current picture is fully reconstructed and the encoded picture is identified (by, e.g., parser (320)) as a reference picture, current picture buffer (358) may become part of reference picture memory (357) and a new current picture buffer may be reallocated before reconstruction of a subsequent encoded picture begins.

The video decoder (310) may perform decoding operations according to predetermined video compression techniques, such as in the ITU-T h.265 standard. The encoded video sequence may conform to the syntax specified by the video compression technique or standard used, in the sense that the encoded video sequence conforms to the syntax of the video compression technique or standard and the configuration files recorded in the video compression technique or standard. In particular, the configuration file may select certain tools from all tools available in the video compression technology or standard as the only tools available under the configuration file. For compliance, the complexity of the encoded video sequence is also required to be within the limits defined by the level of the video compression technique or standard. In some cases, the hierarchy limits the maximum picture size, the maximum frame rate, the maximum reconstruction sampling rate (measured in units of, e.g., mega samples per second), the maximum reference picture size, and so on. In some cases, the limits set by the hierarchy may be further defined by a Hypothetical Reference Decoder (HRD) specification and metadata signaled HRD buffer management in the encoded video sequence.

In an embodiment, receiver (331) may receive additional (redundant) data along with the encoded video. The additional data may be part of an encoded video sequence. The additional data may be used by the video decoder (310) to properly decode the data and/or more accurately reconstruct the original video data. The additional data may be in the form of, for example, a temporal, spatial, or signal-to-noise ratio (SNR) enhancement layer, a redundant slice, a redundant picture, a forward error correction code, and so forth.

Fig. 4 is a block diagram of a video encoder (403) according to an embodiment of the disclosure. The video encoder (403) is disposed in an electronic device (420). The electronic device (420) includes a transmitter (440) (e.g., a transmission circuit). The video encoder (403) may be used in place of the video encoder (203) in the embodiment of fig. 2.

Video encoder (403) may receive video samples from a video source (401) (not part of electronics (420) in the fig. 4 embodiment) that may capture video images to be encoded by video encoder (403). In another embodiment, the video source (401) is part of an electronic device (420).

The video source (401) may provide a source video sequence in the form of a stream of digital video samples to be encoded by the video encoder (403), which may have any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit … …), any color space (e.g., bt.601Y CrCB, RGB … …), and any suitable sampling structure (e.g., Y CrCB 4:2:0, Y CrCB 4:4: 4). In the media service system, the video source (401) may be a storage device that stores previously prepared video. In a video conferencing system, the video source (401) may be a camera that captures local image information as a video sequence. Video data may be provided as a plurality of individual pictures that are given motion when viewed in sequence. The picture itself may be constructed as an array of spatial pixels, where each pixel may comprise one or more samples, depending on the sampling structure, color space, etc. used. The relationship between pixels and samples can be readily understood by those skilled in the art. The following text focuses on describing the samples.

According to an embodiment, the video encoder (403) may encode and compress pictures of a source video sequence into an encoded video sequence (443) in real-time or under any other temporal constraints required by the application. It is a function of the controller (450) to implement the appropriate encoding speed. In some embodiments, the controller (450) controls and is functionally coupled to other functional units as described below. For simplicity, the couplings are not labeled in the figures. The parameters set by the controller (450) may include rate control related parameters (picture skip, quantizer, lambda value of rate distortion optimization technique, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (450) may be used to have other suitable functions relating to the video encoder (403) optimized for a certain system design.

In some embodiments, the video encoder (403) operates in an encoding loop. As a brief description, in an embodiment, an encoding loop may include a source encoder (430) (e.g., responsible for creating symbols, such as a symbol stream, based on input pictures and reference pictures to be encoded) and a (local) decoder (433) embedded in a video encoder (403). The decoder (433) reconstructs the symbols to create sample data in a manner similar to the way a (remote) decoder creates sample data (since any compression between symbols and encoded video streams is lossless in the video compression techniques considered herein). The reconstructed sample stream (sample data) is input to a reference picture memory (434). Since the decoding of the symbol stream produces bit accurate results independent of decoder location (local or remote), the content in the reference picture store (434) also corresponds bit accurately between the local encoder and the remote encoder. In other words, the reference picture samples that the prediction portion of the encoder "sees" are identical to the sample values that the decoder would "see" when using prediction during decoding. This reference picture synchronization philosophy (and the drift that occurs if synchronization cannot be maintained due to, for example, channel errors) is also used in some related techniques.

The operation of the "local" decoder (433) may be the same as a "remote" decoder, such as that which has been described in detail above in connection with fig. 3 for the video decoder (310). However, referring briefly also to fig. 3, when symbols are available and the entropy encoder (445) and parser (320) are able to losslessly encode/decode the symbols into an encoded video sequence, the entropy decoding portion of the video decoder (310), including the buffer memory (315) and parser (320), may not be fully implemented in the local decoder (433).

At this point it can be observed that any decoder technique other than the parsing/entropy decoding present in the decoder must also be present in the corresponding encoder in substantially the same functional form. For this reason, the present application focuses on decoder operation. The description of the encoder techniques may be simplified because the encoder techniques are reciprocal to the fully described decoder techniques. A more detailed description is only needed in certain areas and is provided below.

During operation, in some embodiments, the source encoder (430) may perform motion compensated predictive coding. The motion compensated predictive coding predictively codes an input picture with reference to one or more previously coded pictures from the video sequence that are designated as "reference pictures". In this way, an encoding engine (432) encodes differences between pixel blocks of an input picture and pixel blocks of a reference picture, which may be selected as a prediction reference for the input picture.

The local video decoder (433) may decode encoded video data for a picture that may be designated as a reference picture based on symbols created by the source encoder (430). The operation of the encoding engine (432) may be a lossy process. When the encoded video data can be decoded at a video decoder (not shown in fig. 4), the reconstructed video sequence may typically be a copy of the source video sequence with some errors. The local video decoder (433) replicates a decoding process that may be performed on reference pictures by the video decoder, and may cause reconstructed reference pictures to be stored in a reference picture cache (434). In this way, the video encoder (403) may locally store a copy of the reconstructed reference picture that has common content (no transmission errors) with the reconstructed reference picture to be obtained by the remote video decoder.

The predictor (435) may perform a prediction search for the coding engine (432). That is, for a new picture to be encoded, predictor (435) may search reference picture memory (434) for sample data (as candidate reference pixel blocks) or some metadata, such as reference picture motion vectors, block shapes, etc., that may be referenced as appropriate predictions for the new picture. The predictor (435) may operate on a block-by-block basis of samples to find a suitable prediction reference. In some cases, from search results obtained by predictor (435), it may be determined that the input picture may have prediction references taken from multiple reference pictures stored in reference picture memory (434).

The controller (450) may manage the encoding operations of the source encoder (430), including, for example, setting parameters and subgroup parameters for encoding the video data.

The outputs of all of the above functional units may be entropy encoded in an entropy encoder (445). The entropy encoder (445) losslessly compresses the symbols generated by the various functional units according to techniques such as huffman coding, variable length coding, arithmetic coding, etc., to convert the symbols into an encoded video sequence.

The transmitter (440) may buffer the encoded video sequence created by the entropy encoder (445) in preparation for transmission over a communication channel (460), which may be a hardware/software link to a storage device that will store the encoded video data. The transmitter (440) may combine the encoded video data from the video encoder (403) with other data to be transmitted, such as encoded audio data and/or an auxiliary data stream (sources not shown).

The controller (450) may manage the operation of the video encoder (403). During encoding, the controller (450) may assign a certain encoded picture type to each encoded picture, but this may affect the encoding techniques applicable to the respective picture. For example, pictures may be generally assigned to any of the following picture types:

intra pictures (I pictures), which may be pictures that can be encoded and decoded without using any other picture in the sequence as a prediction source. Some video codecs tolerate different types of intra pictures, including, for example, Independent Decoder Refresh ("IDR") pictures. Those skilled in the art are aware of variants of picture I and their corresponding applications and features.

Predictive pictures (P pictures), which may be pictures that may be encoded and decoded using intra prediction or inter prediction that uses at most one motion vector and reference index to predict sample values of each block.

Bi-predictive pictures (B-pictures), which may be pictures that can be encoded and decoded using intra-prediction or inter-prediction that uses at most two motion vectors and reference indices to predict sample values of each block. Similarly, multiple predictive pictures may use more than two reference pictures and associated metadata for reconstructing a single block.

A source picture may typically be spatially subdivided into blocks of samples (e.g., blocks of 4 x 4, 8 x 8, 4 x 8, or 16 x 16 samples) and encoded block-wise. These blocks may be predictively encoded with reference to other (encoded) blocks that are determined according to the encoding allocation applied to their respective pictures. For example, a block of an I picture may be non-predictive encoded, or the block may be predictive encoded (spatial prediction or intra prediction) with reference to an already encoded block of the same picture. The pixel block of the P picture can be prediction-coded by spatial prediction or by temporal prediction with reference to one previously coded reference picture. A block of a B picture may be prediction coded by spatial prediction or by temporal prediction with reference to one or two previously coded reference pictures.

The video encoder (403) may perform encoding operations according to a predetermined video encoding technique or standard, such as the ITU-T h.265 recommendation. In operation, the video encoder (403) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. Thus, the encoded video data may conform to syntax specified by the video coding technique or standard used.

In an embodiment, the transmitter (440) may transmit the additional data while transmitting the encoded video. The source encoder (430) may take such data as part of an encoded video sequence. The additional data may include temporal/spatial/SNR enhancement layers, redundant pictures and slices, among other forms of redundant data, SEI messages, VUI parameter set segments, and the like.

The captured video may be provided as a plurality of source pictures (video pictures) in a time sequence. Intra-picture prediction, often abbreviated as intra-prediction, exploits spatial correlation in a given picture, while inter-picture prediction exploits (temporal or other) correlation between pictures. In an embodiment, the particular picture being encoded/decoded, referred to as the current picture, is partitioned into blocks. When a block in a current picture is similar to a reference block in a reference picture that has been previously encoded in video and is still buffered, the block in the current picture may be encoded by a vector called a motion vector. The motion vector points to a reference block in a reference picture, and in the case where multiple reference pictures are used, the motion vector may have a third dimension that identifies the reference picture.

In some embodiments, bi-directional prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture that are both prior to the current picture in video in decoding order (but may be past and future, respectively, in display order). A block in a current picture may be encoded by a first motion vector pointing to a first reference block in a first reference picture and a second motion vector pointing to a second reference block in a second reference picture. In particular, the block may be predicted by a combination of a first reference block and a second reference block.

Furthermore, merge mode techniques may be used in inter picture prediction to improve coding efficiency.

According to some embodiments disclosed herein, prediction such as inter-picture prediction and intra-picture prediction is performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned into Coding Tree Units (CTUs) for compression, the CTUs in the pictures having the same size, e.g., 64 × 64 pixels, 32 × 32 pixels, or 16 × 16 pixels. In general, a CTU includes three Coding Tree Blocks (CTBs), which are one luminance CTB and two chrominance CTBs. Further, each CTU may be further split into one or more Coding Units (CUs) in a quadtree. For example, a 64 × 64-pixel CTU may be split into one 64 × 64-pixel CU, or 432 × 32-pixel CUs, or 16 × 16-pixel CUs. In an embodiment, each CU is analyzed to determine a prediction type for the CU, such as an inter prediction type or an intra prediction type. Furthermore, depending on temporal and/or spatial predictability, a CU is split into one or more Prediction Units (PUs). In general, each PU includes a luma Prediction Block (PB) and two chroma blocks PB. In an embodiment, a prediction operation in encoding (encoding/decoding) is performed in units of prediction blocks. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values (e.g., luma values), such as 8 × 8 pixels, 16 × 16 pixels, 8 × 16 pixels, 16 × 8 pixels, and so on.

Fig. 5 is a diagram of a video encoder (503) according to another embodiment of the present disclosure. A video encoder (503) is used to receive a processing block (e.g., a prediction block) of sample values within a current video picture in a sequence of video pictures and encode the processing block into an encoded picture that is part of an encoded video sequence. In this embodiment, a video encoder (503) is used in place of the video encoder (203) in the embodiment of fig. 2.

In an HEVC embodiment, a video encoder (503) receives a matrix of sample values for a processing block, e.g., a prediction block of 8 × 8 samples, etc. A video encoder (503) determines whether to encode the processing block using intra mode, inter mode, or bi-directional prediction mode using, for example, rate-distortion (RD) optimization. When encoding a processing block in intra mode, video encoder (503) may use intra prediction techniques to encode the processing block into an encoded picture; and when the processing block is encoded in inter mode or bi-prediction mode, video encoder (503) may encode the processing block into the encoded picture using inter prediction or bi-prediction techniques, respectively. In some video coding techniques, the merge mode may be an inter-picture prediction sub-mode, in which motion vectors are derived from one or more motion vector predictors without resorting to coded motion vector components outside of the predictors. In some other video coding techniques, there may be motion vector components that are applicable to the subject block. In an embodiment, the video encoder (503) includes other components, such as a mode decision module (not shown) for determining a processing block mode.

In the embodiment of fig. 5, the video encoder (503) includes an inter encoder (530), an intra encoder (522), a residual calculator (523), a switch (526), a residual encoder (524), a general purpose controller (521), and an entropy encoder (525) coupled together as shown in fig. 5.

The inter encoder (530) is used to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures), generate inter prediction information (e.g., redundant information descriptions, motion vectors, merge mode information according to inter coding techniques), and calculate inter prediction results (e.g., predicted blocks) using any suitable technique based on the inter prediction information. In some embodiments, the reference picture is a decoded reference picture that is decoded based on encoded video information.

An intra encoder (522) is used to receive samples of a current block (e.g., a processing block), in some cases compare the block to a block already 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 an embodiment, the intra encoder (522) also calculates an intra prediction result (e.g., a predicted block) based on the intra prediction information and a reference block in the same picture.

A general purpose controller (521) is used to determine general purpose control data and control other components of the video encoder (503) based on the general purpose control data. In an embodiment, a general purpose controller (521) determines a mode of a block and provides a control signal to a switch (526) based on the mode. For example, when the mode is intra mode, the general purpose controller (521) controls the switch (526) to select an intra mode result for use by the residual calculator (523) and controls the entropy encoder (525) to select and add intra prediction information in the code stream; and when the mode is an inter mode, the general purpose controller (521) controls the switch (526) to select an inter prediction result for use by the residual calculator (523), and controls the entropy encoder (525) to select and add inter prediction information in the code stream.

A residual calculator (523) is used to calculate the difference (residual data) between the received block and the prediction result selected from the intra encoder (522) or the inter encoder (530). A residual encoder (524) is operative based on the residual data to encode the residual data to generate transform coefficients. In an embodiment, a residual encoder (524) is used to convert residual data from the time domain to the frequency domain and generate transform coefficients. The transform coefficients are then subjected to a quantization process to obtain quantized transform coefficients. In various embodiments, the video encoder (503) also includes a residual decoder (528). A residual decoder (528) is used to perform the inverse transform and generate decoded residual data. The decoded residual data may be suitably used by the intra (522) and inter (530) encoders. For example, inter encoder (530) may generate a decoded block based on decoded residual data and inter prediction information, and intra encoder (522) may generate a decoded block based on decoded residual data and intra prediction information. The decoded blocks are processed appropriately to generate a decoded picture, and in some embodiments, the decoded picture may be buffered in a memory circuit (not shown) and used as a reference picture.

An entropy encoder (525) is used to format the codestream to produce encoded blocks. The entropy encoder (525) generates various information according to a suitable standard such as the HEVC standard. In an embodiment, the entropy encoder (525) is used to obtain general control data, selected prediction information (e.g., intra prediction information or inter prediction information), residual information, and other suitable information in the code stream. It should be noted that, according to the disclosed subject matter, there is no residual information when a block is encoded in the merge sub-mode of the inter mode or bi-prediction mode.

Fig. 6 is a diagram of a video decoder (610) according to another embodiment of the present disclosure. A video decoder (610) is used to receive an encoded image that is part of an encoded video sequence and decode the encoded image to generate a reconstructed picture. In an embodiment, video decoder (610) is used in place of video decoder (210) in the fig. 2 embodiment.

In the fig. 6 embodiment, video decoder (610) includes an entropy decoder (671), an inter-frame decoder (680), a residual decoder (673), a reconstruction module (674), and an intra-frame decoder (672) coupled together as shown in fig. 6.

An entropy decoder (671) is operable to reconstruct from an encoded picture certain symbols representing syntax elements constituting the encoded picture. Such symbols may include, for example, a mode used to encode the block (e.g., intra mode, inter mode, bi-prediction mode, a merge sub-mode of the latter two, or another sub-mode), prediction information (e.g., intra prediction information or inter prediction information) that may identify certain samples or metadata for use by intra decoder (672) or inter decoder (680), respectively, residual information in the form of, for example, quantized transform coefficients, and so forth. In an embodiment, when the prediction mode is inter or bi-directional prediction mode, inter prediction information is provided to an inter decoder (680); and providing the intra prediction information to an intra decoder (672) when the prediction type is an intra prediction type. The residual information may be inverse quantized and provided to a residual decoder 673.

An inter-frame decoder (680) is configured to receive inter-frame prediction information and generate an inter-frame prediction result based on the inter-frame prediction information.

An intra decoder (672) is configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

A residual decoder (673) is used to perform inverse quantization to extract dequantized transform coefficients and to process the dequantized transform coefficients to convert the residual from the frequency domain to the spatial domain. The residual decoder (673) may also need some control information (to obtain the quantizer parameter QP) and that information may be provided by the entropy decoder (671) (data path not labeled as this is only low-level control information).

The reconstruction module (674) is configured to combine in the spatial domain the residuals output by the residual decoder (673) with the prediction results (which may be output by the inter prediction module or the intra prediction module) to form a reconstructed block, which may be part of a reconstructed picture, which in turn may be part of a reconstructed video. It should be noted that other suitable operations, such as deblocking operations, may be performed to improve visual quality.

It should be noted that video encoder (203), video encoder (403), and video encoder (503) as well as video decoder (210), video decoder (310), and video decoder (610) may be implemented using any suitable techniques. In an embodiment, video encoder (203), video encoder (403), and video encoder (503) and video decoder (210), video decoder (310), and video decoder (610) may be implemented using one or more integrated circuits. In another embodiment, the video encoder (203), the video encoder (403), and the video encoder (503) and the video decoder (210), the video decoder (310), and the video decoder (610) may be implemented using one or more processors executing software instructions.

Aspects of the present disclosure provide entropy encoding techniques for transform coefficients in hybrid video coding techniques. In some embodiments, entropy encoding techniques may change the coding order of syntax elements related to transform coefficients. In general, a Transform Unit (TU) may be partitioned into sub-blocks, such as Coefficient Groups (CGs), each of which is 4 x 4 in size. In some examples, the transform coefficients are coded coefficient group by coefficient group (also referred to as CG level). The present disclosure may provide entropy encoding techniques that operate an encoding pass at a TU level instead of a CG level.

In some examples, such as VVC, entropy encoding techniques for transform coefficients are employed.

Fig. 7 shows an example of an encoded block (700) corresponding to a transform unit. The coding block (700) is 8 × 8 in size and is partitioned into sub-blocks (710), (720), (730), and (740). Each of the sub-blocks (710), (720), (730), and (740) has a size of 4 × 4, and corresponds to a coefficient group. The transform coefficients in each of the sub-blocks (710), (720), (730), and (740) are encoded according to a predefined scan order. In an example, transform coefficients in a sub-block (740) are first encoded; then encoding the transform coefficients in the sub-block (730); then encoding the transform coefficients in the sub-block (720); and finally encoding the transform coefficients in the sub-blocks (710).

According to one aspect of the present disclosure, for sub-blocks (corresponding to CGs) having at least one non-zero transform coefficient, encoding of the transform coefficients may be divided into a plurality of scan passes (e.g., four passes) and encoding of the transform coefficients uses the plurality of scan passes. For example, absLevel represents the absolute value of the current transform coefficient. In a first pass, encoding syntax elements sig _ coeff _ flag (which indicates that absLevel is greater than 0), par _ level _ flag (which indicates parity of absLevel), and rem _ abs _ gt1_ flag (which indicates that (absLevel-1) > >1 is greater than 0, which also indicates that absLevel is greater than 2); in a second pass, syntax element rem _ abs _ gt2_ flag (which indicates that absLevel is greater than 4) is encoded; in a third pass, the remaining values of the transform coefficient levels (called abs _ remaining) are called, if necessary; in the fourth pass, symbol information is encoded.

According to another aspect of the disclosure, transform coefficients may be context coded. For example, in order to exploit the correlation between transform coefficients, previously encoded transform coefficients covered by a local template may be used in the context selection of the current transform coefficient. In the example of fig. 7, the current transform coefficient (711) is located as shown by the black area in the coding block (700), and the local template (750) for the current transform coefficient (711) covers five adjacent coefficients located as shown by the slanted line areas in the coding block (700). Let absLevel1[ x ] [ y ] denote the partially reconstructed absolute level of the transform coefficient at position (x, y) after the first pass, d denotes the diagonal position of the current coefficient (d ═ x + y), numSig denotes the number of non-zero coefficients in the local template, and sumAbs1 denotes the sum of the partially reconstructed absolute levels absLevel1[ x ] [ y ] of the transform coefficients covered by the local template (750).

In some examples, when coding sig _ coeff _ flag for the current coefficient, the context model index is selected according to sumAbs1 and diagonal position d. More specifically, in an example, for the luma component, the context model index is determined according to:

ctxSig＝18×max(0,state-1)+min(sumAbs1,5)+(d<2？12:(d<5？6:0))

(equation 1)

In some examples, the context model index is determined based on a combination of a cardinality (context model index cardinality) and an offset (context model index offset). Then, in the example, (equation 1) is equivalent to (equation 2) and (equation 3):

ctxIdBase ═ 18 × max (0, state-1) + (d <2

ctxSig sigtable [ min (sumAbs1,5) ] + ctxIdBase (equation 3)

For the chroma component, the context model index is determined according to (equation 4):

ctxSig ═ 12 xmax (0, state-1) + min (sumAbs1,5) + (d <2

Note that in the example of the cardinality and offset, (equation 4) is equivalent to (equation 5) and (equation 6):

ctxIdBase ═ 12 xmax (0, state-1) + (d <2

ctxSig sigtable [ min (sumAbs1,5) ] + ctxIdBase (equation 6)

Wherein if dependent quantization is enabled, the state specifies the scalar quantizer used and the state transformation process is used to derive the state; the table ctxIdSigTable stores context model index offsets, ctxIdSigTable [ 0-5 ] ═ 0,1,2,3,4,5 }.

When coding par level flag of the current coefficient, a context model index is selected according to the sumAbs1, numSig, and diagonal position d. More specifically, in some examples, for the luminance component, the context model index is determined according to (equation 7):

ctxPar ═ 1+ min (sumAbs 1-numSig, 4) + (d ═ 0

In some examples, (equation 7) is equivalent to (equation 8) and (equation 9) in terms of cardinality and offset:

ctxIdBase ═ 0

ctxPar ═ 1+ ctxidTable [ min (sumAbs 1-numTig, 4) ] + ctxidBase (equation 9)

For the chroma component, the context model index is determined according to (equation 10):

ctxPar ═ 1+ min (sumAbs 1-numSig, 4) + (d ═ 0

In some examples, (equation 10) is equivalent to (equation 11) and (equation 12) in terms of cardinality and offset:

ctxIdBase ═ (d ═ 0

ctxPar ═ 1+ ctxIdTable [ min (sumAbs 1-numSig, 4) ] + ctxIdBase (equation 12), where the table ctxIdTable stores context model index offsets, ctxIdTable [ 0-4 ] ═ 0,1,2,3,4 }.

When encoding the rem _ abs _ 1_ flag and the rem _ abs _ 2_ flag of the current coefficient, their context model indices are determined in a similar manner to par _ level _ flag, for example:

ctxGt1 ═ ctxPar and ctxGt2 ═ ctxPar

It should be noted that different sets of context models are used for rem _ abs _ gt1_ flag and rem _ abs _ gt2_ flag. This means that the context model for rem _ abs _ gt1_ flag is different from that of rem _ abs _ gt2_ flag, even though ctxGt1 is equal to ctxGt 2.

According to some aspects of the present disclosure, entropy encoding may also be used to transform coded residuals in a skip mode (TSM) and/or a block-based residual differential pulse code modulation mode (residual domain BDPCM). Certain coding techniques, such as bypass coding, context coding, etc., may be used to encode the residual in the TSM and BDPCM. In an example, bypass coding refers to a technique that directly encodes the residual without using context coding.

In some embodiments, in order to adapt the residual coding to the statistics and signal characteristics of the transform skip mode and the BDPCM residual level representing the quantized prediction residual (spatial domain), the coding scheme for the above-mentioned transform coefficients is modified and applied to the TSM and BDPCM modes as described below.

In some embodiments, three encoding passes are used in residual encoding for TSM and BDPCM. In some examples, the coefficients in the TSM and BDPCM modes may correspond to a residual. For example, absLevel is the absolute value of the current residual. In the example, in the first encoding pass, sig _ coeff _ flag (which is used to indicate that absLevel is greater than 0), coeff _ sign _ flag (which is used to indicate the sign of the residual), abs _ level _ gt1_ flag (which is used to indicate that absLevel is greater than 2), par _ level _ flag (which is used to indicate the parity of absLevel) are encoded. In the second pass, the pair abs _ level _ gtX _ flag (which is used to indicate that abs level is greater than 2)^X) Encoding is performed, where X can be 3, 5, 7, etc. In the third pass, the abs _ remaining (which is used to indicate the remainder of the residual level) is encoded. The encoding pass is operated at the Coefficient Group (CG) level. For each CG (e.g., 4 × 4 residual), three encoding passes are performed.

In some embodiments, entropy encoding of the residual is free of encoding of the last significant (e.g., non-zero) scan position. In particular, since the residual signal reflects the spatial residual after prediction and no energy compression by transform is performed for the TSM, no higher probability of trailing a zero or invalid level at the lower right corner of the transform block is given anymore. Therefore, the last active scan position signaling is omitted in this case. Instead, the first sub-block to be processed is the bottom-most-right sub-block within the transform block.

In some embodiments, certain signaling techniques for sub-block Coded Block Flag (CBF) are used. Since there is no last valid scan position signaling, the sub-block CBF signaling with coded _ sub _ block _ flag for the TSM can be modified based on triple considerations.

Based on the first reconsideration, the aforementioned invalid sequence may still occur locally within the transform block due to quantization. Therefore, the last valid scan position is removed as described above, and a coded _ sub _ block _ flag is encoded for all subblocks.

Based on the second consideration, coded _ sub _ block _ flag for a subblock covering a DC frequency position (upper left subblock) represents a special case. In an example, a coded _ sub _ block _ flag for the sub-block is not signaled, and is always inferred to be equal to 1. When the last valid scan position is located in another sub-block, this means that there is at least one valid level outside the DC sub-block. Thus, a DC sub-block may contain only zero/non-significance levels, although the coded sub-block flag for that sub-block is inferred to be equal to 1. In the case where the last scan position information does not exist in the TS, coded _ sub _ block _ flag for each subblock is signaled. This also includes a coded sub block flag for the DC sub block, except when all other coded sub block flag syntax elements have been equal to 0. In this case, DC coded _ sub _ block _ flag is inferred to be equal to 1(inferDcSbCbf 1). Since there must be at least one level of significance in this DC sub-block, if all other sig _ coeff _ flag syntax elements in this DC sub-block are equal to 0, the sig _ coeff _ flag syntax element of the first position at (0, 0) is not signaled and is not derived to be equal to 1 (interferesbdcsigcoefflag ═ 1).

Based on a third consideration, the context modeling for the coded _ sub _ block _ flag is changed. The context model index is calculated as the sum of the coded _ sub _ block _ flag to the right of the current subblock and the coded _ sub _ block _ flag below the current subblock, rather than as a logical disjunction of both.

According to one aspect of the present disclosure, sig _ coeff _ flag context modeling is used. In an example, the local template in sig _ coeff _ flag context modeling is modified to include only the neighborhood to the right of the current scan position (NB)₀) And a Neighborhood (NB) below the current scan position₁). The context model offset is exactly the valid neighbor position sig _ coeff _ flag NB₀]+sig_coeff_flag[NB₁]The number of (2). Thus, the selection of a different context set depending on the diagonal d within the current transform block is removed. This results in three context models and a single set of context models for coding sig _ coeff _ flag.

According to an aspect of the present disclosure, abs _ level _ 1_ flag and par _ level _ flag context modeling may be performed using a single context model for abs _ level _ 1_ flag and par _ level _ flag.

According to one aspect of the present disclosure, certain abs _ remaining encoding techniques are used. Although the empirical distribution of transform skip residual absolute levels still generally fits the laplacian or geometric distribution, there is greater instability than the transform coefficient absolute levels. In particular, for residual absolute levels, the variance within the window of continuous implementation is higher. Thus, the following two modifications of abs _ remaining syntax binarization and context modeling can be performed.

In a first modification, a higher cutoff value in binarization is used. For example, adding the cutoff value of the transition point from the encoding with sig _ coeff _ flag, abs _ level _ gt1_ flag, par _ level _ flag, and abs _ level _ gt3_ flag to the rice code for abs _ remaining, and a dedicated context model for each bin position may yield higher compression efficiency. Increasing the cutoff value may result in more "greater than X" flags, e.g., introducing abs _ level _ gt5_ flag, abs _ level _ gt7_ flag, etc., until the cutoff value is reached. In some examples, the cutoff value itself is fixed to 5(numGtFlags ═ 5).

In a second modification, the template used for rice parameter derivation is modified, i.e. only the neighborhood to the left of the current scan position and the neighborhood below the current scan position are considered similar to the local template used for sig _ coeff _ flag context modeling.

According to one aspect of the present disclosure, a coeff _ sign _ flag context modeling technique is used. Due to the instability within the sequence of symbols and the fact that the prediction residuals are often biased, the symbols can be encoded using a context model even when the global empirical distribution is almost evenly distributed. The symbols are encoded using a single dedicated context model and parsed after sig _ coeff _ flag to keep all context encoded bins together.

According to one aspect of the disclosure, a restriction technique of context-coded bins is used. In some examples, the total number of context-coded bins per TU is limited to the TU region size multiplied by 2. For example, for a 16 × 8TU, the maximum number of context coded bins is 16 × 8 × 2 — 256. The budget of context-coded bins is consumed at the TU level, that is, all CGs within the current TU share one budget of context-coded bins, unlike the separate budget of context-coded bins for each CG.

Fig. 8A-8B illustrate tables of residual coding syntax for transform skip mode used in some examples. This table of residual coding syntax implements some of the features described above.

According to some aspects of the disclosure, context-coded bins contribute different coding gains to different syntax elements compared to bypass coding. In an example, context-coded bins contribute more coding gain to sig _ coeff _ flag than abs _ level _ gtX _ flag. However, in some examples, since the total budget for context-coded bins is specified for the current TU, but the encoding pass is performed at the CG level, some of the sig _ coeff _ flags in the CG that are later encoded for the current TU may not have an opportunity to be context-coded because all syntax elements in the previous CG consume all of the budget for context-coded bins, which may not be optimal in terms of encoding performance.

Aspects of the present disclosure provide entropy coding techniques of transform coefficients and residual coding of TSMs, as well as residual coding of BDPCM modes. Entropy coding techniques may prioritize syntax elements with higher context coding gain for context coding at the TU level and use the context coding budget in an optimal manner to improve coding efficiency.

According to an aspect of the present disclosure, entropy encoding of syntax elements related to transform coefficients is performed using a TU-level coding pass scheme. In particular, in some examples, all syntax elements are first divided into different groups, namely syntax element Groups (GSEs). Then, the coding order of the different groups of syntax elements is defined. Further, GSEs are encoded at TU level and on a GSE-by-GSE basis, following a given encoding order. For example, after all syntax elements within the current GSE are encoded for the current TU, entropy encoding for the next GSE may begin. When all GSEs have been encoded, the entropy encoding of the transform coefficients is complete. Meanwhile, the total number of context-coded bins for the current TU is limited to a predefined number.

In some examples, syntax elements are grouped and ordered to prioritize certain syntax elements with higher context coding gain. Thus, when the budget of the total number of context-coded bins for the current TU is a predefined number, certain syntax elements with higher context coding gain have more opportunities to be context-coded in the TU-level coding pass than in the CG-level coding pass.

According to an aspect of the disclosure, various techniques may be used to define the syntax element Groups (GSEs).

In an embodiment, each GSE includes only one syntax element.

In another embodiment, the GSE may comprise a single or a combination of the following syntax elements: sig _ coeff _ flag, coeff _ sign _ flag, abs _ level _ 1_ flag, par _ level _ flag, abs _ level _ gtX _ flag (where X is 3, 5, 7, …), and abs _ remaining.

In some examples, the first GSE comprises sig _ coeff _ flag; the second GSE comprises abs _ level _ gt1_ flag; the third GSE comprises coeff _ sign _ flag; the fourth GSE comprises abs _ level _ gtX _ flag; the fifth GSE comprises par _ level _ flag; and the sixth GSE comprises abs _ remaining. In an example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, third, fourth, fifth, and sixth GSEs. In another example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, third, second, fourth, fifth, and sixth GSEs.

In some examples, the first GSE comprises sig _ coeff _ flag; the second GSE comprises abs _ level _ gt1_ flag; the third GSE comprises par _ level _ flag; the fourth GSE comprises abs _ level _ gtX _ flag; the fifth GSE comprises coeff _ sign _ flag; and the sixth GSE comprises abs _ remaining. In an example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, third, fourth, fifth, and sixth GSEs. In another example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, fourth, third, fifth, and sixth GSEs.

In some examples, the first GSE comprises sig _ coeff _ flag; the second GSE comprises abs _ level _ gt1_ flag; the third GSE comprises abs _ level _ gtX _ flag; the fourth GSE comprises par _ level _ flag; the fifth GSE comprises abs _ remaining; and the sixth GSE comprises coeff _ sign _ flag. In an example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, third, fourth, fifth, and sixth GSEs. In another example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, third, second, fourth, fifth, and sixth GSEs.

In some examples, the first GSE comprises sig _ coeff _ flag; the second GSE comprises abs _ level _ gt1_ flag; the third GSE comprises par _ level _ flag; the fourth GSE comprises abs _ level _ gtX _ flag; the fifth GSE comprises abs _ remaining; and the sixth GSE comprises coeff _ sign _ flag. In an example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, third, fourth, fifth, and sixth GSEs. In another example, the GSEs may be encoded in a TU-level encoding pass in an order of the first, second, fourth, third, fifth, and sixth GSEs.

In one embodiment, the GSE may be defined differently in different modes. In one example, a first set of GSEs (one or more GSEs) is defined for residual coding of TSM mode and a second set of GSEs (one or more GSEs) is defined for residual coding of non-TSM mode. The first set of GSEs is defined differently than the second set of GSEs.

In another example, a first set of GSEs (one or more GSEs) is defined for residual coding of BDPCM and a second set of GSEs (one or more GSEs) is defined for residual coding of non-BDPCM modes. The first set of GSEs is defined differently than the second set of GSEs.

In another example, a first set of GSEs (one or more GSEs) is defined for residual encoding of TSM and BDPCM, and a second set of GSEs (one or more GSEs) is defined for residual encoding of non-TSM and non-BDPCM modes. The first set of GSEs is defined differently than the second set of GSEs.

In another embodiment, the coding order of the GSE may be different for different modes. In one example, multiple GSEs are defined for residual coding of TSM and non-TSM modes. The coding order of the GSE of the TSM mode is different from the coding order of the GSE of the non-TSM mode.

In one example, multiple GSEs are defined for residual coding of BDPCM and non-BDPCM modes. The encoding order of the GSEs of a BDPCM mode is different from the encoding order of the GSEs of a non-BDPCM mode.

In one example, multiple GSEs are defined for residual coding of TSM, BDPCM, non-TSM and non-BDPCM modes. The coding order of the GSEs of the TM and BDPCM modes is different from the coding order of the GSEs of the non-TSM and non-BDPCM modes.

In one embodiment, entropy encoding of each GSE may be performed using a predefined scan order, such as diagonal scan, zig-zag scan, horizontal scan, vertical scan, and the like. Furthermore, different GSEs may use different scan orders.

In some examples, entropy encoding of a particular GSE may be performed CG-by-CG, and within each CG, the relevant syntax elements within the particular GSE are encoded using a predefined CG-level scan order (e.g., diagonal scan, zig-zag scan, horizontal scan, vertical scan, etc.).

Fig. 9 shows an example of scan orders in an encoding pass for encoding GSEs of 8 × 8 TUs (900). The scan order is a raster scan of the CGs, and within each CG, the coefficients (residuals) are scanned using a diagonal scan order. Specifically, the TU (900) is divided into CGs (910), (920), (930), and (940). After (910), (920), (930), and (940), the GSE is encoded in the raster scan order of the CGs. Within each of CGs (910), (920), (930), and (940), the GSE is encoded using a diagonal scanning order. The scanning sequence is illustrated by the arrows in fig. 9.

According to one aspect of the disclosure, a limit on the total number of context-coded bins is defined for a current TU. When a bin in a GSE reaches that number, all subsequent bins and all bins of subsequent GSEs are encoded using bypass encoding.

Fig. 10 shows a flowchart outlining a process (1000) according to an embodiment of the present disclosure. The process (1000) may be used in the reconstruction of a block to generate a prediction block for the block in reconstruction. In various embodiments, process (1000) is performed by processing circuitry, such as processing circuitry in terminal devices (110), (120), (130), and (140), processing circuitry that performs the functions of video encoder (203), processing circuitry that performs the functions of video decoder (210), processing circuitry that performs the functions of video decoder (310), processing circuitry that performs the functions of video encoder (403), and so forth. In some embodiments, process (1000) is implemented in software instructions, such that when the software instructions are executed by the processing circuitry, the processing circuitry performs process (1000). The process starts at (S1001) and proceeds to (S1010).

At (S1010), in a first encoding pass that scans coding positions within a transform block, a first syntax element at a coding position within the transform block of the current block is decoded. For example, the first encoding pass scans the encoding positions in one of a diagonal scan order, a zig-zag scan order, a horizontal scan order, a vertical scan order, and the like.

At (S1020), a second syntax element at a coding position within the transform block is decoded in a second coding pass in which the coding position is scanned within the transform block. For example, the second encoding pass scans the encoding positions in one of a diagonal scan order, a zig-zag scan order, a horizontal scan order, a vertical scan order, and the like.

In some embodiments, the first syntax element may obtain a higher coding gain than the second syntax element when context coded. In some examples, a budget of context-coded bins is provided for each transform block. In one example, the first syntax element has priority at the transform block level, so the first syntax element at all coding positions in the transform block is coded before any second syntax element, and higher coding gain can be achieved under the limited budget of context-coded bins. In some embodiments, the counter is reset to a number that is a limited number of context-encoded bins (also referred to as the budget of the context-encoded bins in the transform block level). The counter may count down in response to each decoded bit of the syntax element until exhausted. Before the budget is exhausted, the syntax element may be decoded based on the context model; and when the budget is exhausted, syntax elements can be decoded based on bypass coding.

According to some aspects of the disclosure, syntax elements for transform coefficients or residuals may be partitioned into syntax element groups and the syntax element groups are encoded in coding order at the transform block level (also referred to as TU level). In one example, the coding order may be defined based on context coding gains. In some examples, after all syntax elements within a set of syntax elements are encoded for a current TU, entropy encoding for a next set of syntax elements is started.

It should be noted that any suitable encoding order may be used.

In some embodiments, the syntax element groups may be defined differently for different modes. For example, the definition of the first set of syntax elements of the transform skip mode is different from the definition of the second set of syntax elements of the BDPCM mode.

In some embodiments, the coding order of the syntax element groups may be different for different modes. For example, the same syntax element group is defined for the transform skip mode and the BDPCM mode. However, in the transform skip mode, syntax element groups are encoded in a different order from the BDPCM mode.

Various scan orders, such as diagonal scan order, zig-zag scan order, horizontal scan order, vertical scan order, etc., may be used to scan the encoded positions in the transform block. In one example, a transform block is divided into sub-blocks, e.g., 4 x 4 sub-blocks also referred to as coefficient groups, and then the sub-blocks are scanned one by one in the scanning order. In each sub-block, the scan order may be any one of a diagonal scan order, a zigzag scan order, a horizontal scan order, and a vertical scan order.

At (S1030), a residual in the transform block is determined based on the decoded first syntax element and the decoded second syntax element at the coding position within the transform block.

At (S1040), samples of the current block are reconstructed based on the residue in the transformed block. Then, the process proceeds to S1099 and terminates.

An embodiment of the present application further provides a video decoding apparatus, including:

a first decoding module for decoding a first syntax element at an encoding position within a transform block of a current block in a first encoding pass that scans the encoding position within the transform block;

a second decoding module for decoding, in a second coding pass, second syntax elements at the coding positions within the transform blocks, the second coding pass following the first coding pass and scanning the coding positions within the transform blocks;

a determination module to determine a residual in the transform block based at least on the decoded first syntax element and the decoded second syntax element at the coding position in the transform block; and

a reconstruction module to reconstruct samples of the current block based on the residual in the transformed block.

The embodiments of the present application further provide a computer device, which includes one or more processors and one or more memories, where at least one instruction is stored in the one or more memories, and the at least one instruction is loaded and executed by the one or more processors to implement the method according to any of the embodiments of the present application.

Embodiments of the present application also provide a non-transitory computer-readable medium having instructions stored thereon, which when executed by a computer, cause the computer to perform the method according to any of the embodiments of the present application.

The techniques described above may be implemented as computer software via computer readable instructions and physically stored in one or more computer readable media. For example, fig. 11 illustrates a computer system (1100) suitable for implementing certain embodiments of the disclosed subject matter.

The computer software may be encoded in any suitable machine code or computer language, and by assembly, compilation, linking, etc., mechanisms create code that includes instructions that are directly executable by one or more computer Central Processing Units (CPUs), Graphics Processing Units (GPUs), etc., or by way of transcoding, microcode, etc.

The instructions may be executed on various types of computers or components thereof, including, for example, personal computers, tablets, servers, smartphones, gaming devices, internet of things devices, and so forth.

The components illustrated in FIG. 11 for the computer system (1100) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing embodiments of the application. Neither should the configuration of components be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary embodiments of the computer system 1100.

The computer system (1100) may include some human interface input devices. The human interface input device may respond to input from one or more human users through tactile input (e.g., keyboard input, swipe, data glove movement), audio input (e.g., sound, applause), visual input (e.g., gestures), olfactory input (not shown). The human interface device may also be used to capture certain media that are not necessarily directly related to human conscious input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from still-image cameras), video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

The human interface input device may include one or more of the following (only one of which is depicted): keyboard (1101), mouse (1102), touch pad (1103), touch screen (1110), data glove (not shown), joystick (1105), microphone (1106), scanner (1107), camera (1108).

The computer system (1100) may also include certain human interface output devices. The human interface output device may stimulate the senses of one or more human users through, for example, tactile output, sound, light, and smell/taste. The human 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 are not input devices), audio output devices (e.g., speakers (1109), headphones (not shown)), visual output devices (e.g., screens (1110) including cathode ray tube screens, liquid crystal screens, plasma screens, organic light emitting diode screens, each with or without touch screen input functionality, tactile feedback functionality-some of which may output two-dimensional visual output or more than three-dimensional output through means such as stereoscopic visual output; virtual reality glasses (not shown), holographic displays, and smoke boxes (not shown)), and printers (not shown).

The computer system (1100) may also include human-accessible storage devices and their associated media such as optical media including media (1121) such as CD/DVD ROM/RW (1120) with CD/DVD, thumb drives (1122), removable hard or solid state drives (1123), conventional magnetic media such as magnetic tapes and floppy disks (not shown), ROM/ASIC/PLD based application specific devices such as security dongle (not shown), and the like.

Those skilled in the art will also appreciate that the term "computer-readable medium" used in connection with the subject matter of this application does not include transmission media, carrier waves, or other transitory signals.

The computer system (1100) may also include an interface to one or more communication networks. For example, the network may be wireless, wired, optical. The network may also be a local area network, a wide area network, a metropolitan area network, a vehicular network, an industrial network, a real-time network, a delay tolerant network, and so forth. The network also includes ethernet, wireless local area networks, local area networks such as cellular networks (GSM, 3G, 4G, 5G, LTE, etc.), television wired or wireless wide area digital networks (including cable, satellite, and terrestrial broadcast television), automotive and industrial networks (including CANBus), and so forth. Certain networks typically require external network interface adapters connected to certain general purpose data ports or peripheral buses (1149), such as USB ports of computer system (1100); other systems are typically integrated into the core of the computer system (1100) by connecting to a system bus as described below (e.g., an ethernet interface to a PC computer system or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (1100) may communicate with other entities. The communication may be unidirectional, for reception only (e.g., wireless television), unidirectional for transmission only (e.g., CAN bus to certain CAN bus devices), or bidirectional, for example, to other computer systems over a local or wide area digital network. Each of the networks and network interfaces described above may use certain protocols and protocol stacks.

The aforementioned human interface device, human accessible storage device, and network interface may be connected to the core (1140) of the computer system (1100).

The cores (1140) may include one or more Central Processing Units (CPUs) (1141), Graphics Processing Units (GPUs) (1142), special purpose programmable processing units in the form of Field Programmable Gate Arrays (FPGAs) (1143), hardware accelerators (1144) for specific tasks, and so forth. The devices may be connected via a system bus (1148) to Read Only Memory (ROM) (1145), random access memory (1146), internal mass storage (e.g., internal non-user accessible hard disk drives, SSDs, etc.) (1147), and the like. In some computer systems, the system bus (1148) may be accessed in the form of one or more physical plugs, to extend through additional central processing units, graphics processing units, and the like. The peripheral devices may be attached directly to the system bus (1148) of the core or connected through a peripheral bus (1149). The architecture of the peripheral bus includes peripheral controller interface PCI, universal serial bus USB, etc.

The CPU (1141), GPU (1142), FPGA (1143), and accelerator (1144) may execute certain instructions, which in combination may constitute the computer code. The computer code may be stored in ROM (1145) or RAM (1146). Transitional data may also be stored in RAM (1146), while persistent data may be stored in, for example, internal mass storage (1147). Fast storage and retrieval of any memory device may be achieved through the use of a cache, which may be closely associated with one or more of CPU (1141), GPU (1142), mass storage (1147), ROM (1145), RAM (1146), and the like.

The computer-readable medium may have computer code thereon for performing various computer-implemented operations. The media and computer code may be those specially designed and constructed for the purposes of the present application, or they may be of the kind well known and available to those having skill in the computer software arts.

By way of example, and not limitation, a computer system having an architecture (1100), and in particular a core (1140), may provide functionality as a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be media associated with user-accessible mass storage as described above, as well as specific memory of the kernel (1140) having non-transitory nature, such as kernel internal mass storage (1147) or ROM (1145). Software implementing various embodiments of the present application may be stored in such a device and executed by the kernel (1140). The computer-readable medium may include one or more memory devices or chips, according to particular needs. The software may cause the core (1140), and particularly the processors therein (including CPUs, GPUs, FPGAs, etc.), to perform certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (1146) and modifying such data structures according to software-defined processes. Additionally or alternatively, the computer system may provide functionality that is logically hardwired or otherwise embodied in circuitry (e.g., accelerator (1144)) that may operate in place of or in conjunction with software to perform certain processes or certain portions of certain processes described herein. Where appropriate, reference to software may include logic and vice versa. Where appropriate, reference to a computer-readable medium may include circuitry (e.g., an Integrated Circuit (IC)) storing executable software, circuitry comprising executable logic, or both. The present application includes any suitable combination of hardware and software.

Appendix A: acronym

JEM: joint exploration model

VVC: universal video coding

BMS: reference setting

MV: motion vector

HEVC: efficient video coding

SEI: supplemental enhancement information

VUI: video usability information

GOPs: picture group

TUs: a transformation unit for transforming the image data into a plurality of image data,

and (4) PUs: prediction unit

CTUs: coding tree unit

CTBs: coding tree block

PBs: prediction block

HRD: hypothetical reference decoder

SNR: signal to noise ratio

CPUs: central processing unit

GPUs: graphics processing unit

CRT: cathode ray tube having a shadow mask with a plurality of apertures

LCD: liquid crystal display device with a light guide plate

An OLED: organic light emitting diode

CD: optical disk

DVD: digital video CD

ROM: read-only memory

RAM: random access memory

ASIC: application specific integrated circuit

PLD: programmable logic device

LAN: local area network

GSM: global mobile communication system

LTE: long term evolution

CANBus: controller area network bus

USB: universal serial bus

PCI: peripheral device interconnect

FPGA: field programmable gate array

SSD: solid state drive

IC: integrated circuit with a plurality of transistors

CU: coding unit

TSM: transition skip mode

IBC: intra-block replication

DPCM: differential pulse code modulation

BDPCM: block-based DPCM

Plural in this application means two or more. While the present application has described several exemplary embodiments, various alterations, permutations, and various substitutions of the embodiments are within the scope of the present application. It will thus be appreciated that those skilled in the art will be able to devise various systems and methods which, although not explicitly shown or described herein, embody the principles of the application and are thus within its spirit and scope.

Claims (13)

1. A video decoding method, comprising:

in a first encoding pass, decoding a first syntax element at an encoding position within a transform block of a current block, the first encoding pass scanning the encoding position within the transform block;

decoding, in a second coding pass, a second syntax element at the coding position within the transform block, the second coding pass following the first coding pass and scanning the coding position within the transform block;

determining a residual in the transform block based at least on the decoded first syntax element and the decoded second syntax element at the coding position in the transform block; and

reconstructing samples of the current block based on the residual in the transform block.

2. The method of claim 1, further comprising:

in the first encoding pass, decoding a first set of syntax elements that includes the first syntax element; and

in the second encoding pass, a second set of syntax elements comprising the second syntax elements is decoded.

3. The method of claim 1 or 2, further comprising:

decoding each set of a plurality of sets of syntax elements in a respective coding pass that scans the coding positions within the transform block, each set of the plurality of sets of syntax elements comprising one or more syntax elements.

4. The method of claim 3, wherein each of the plurality of sets of syntax elements comprises one syntax element.

5. The method of claim 3, further comprising:

decoding a first plurality of sets of syntax elements defined for a transform skip mode in response to the transform block being encoded in the transform skip mode; and

decoding a second plurality of sets of syntax elements defined for a block-Based Differential Pulse Code Modulation (BDPCM) mode in response to the transform block being encoded in the BDPCM mode.

6. The method of claim 3, further comprising:

in response to the transform block being encoded in transform skip mode, decoding the plurality of sets of syntax elements in a first coding pass order; and

decoding the sets of syntax elements in a second encoding pass order in response to the transform block encoded in a block-Based Differential Pulse Code Modulation (BDPCM) mode.

7. The method of claim 3, further comprising:

decoding each set of the plurality of sets of syntax elements in the respective coding pass that scans the coding positions within the transform block in one of a diagonal scan order, a zig-zag scan order, a horizontal scan order, and a vertical scan order.

8. The method of claim 3, further comprising:

decoding each set of the plurality of sets of syntax elements in an encoding pass that scans sub-blocks in the transform block and encoding positions within the sub-blocks in one of a diagonal scan order, a zig-zag scan order, a horizontal scan order, and a vertical scan order.

9. The method of claim 3, further comprising:

determining, using a counter, a residual budget for context-encoded bins of syntax elements in the transform block;

decoding the syntax element by using a context model when the residual budget exists; and

when the residual budget is exhausted, syntax elements are decoded without using a context model.

10. The method of claim 1, wherein the first syntax element comprises one or more of sig _ coeff _ flag, coeff _ sign _ flag, par _ level _ flag, abs _ level _ 1_ flag, abs _ level _ 3_ flag, abs _ level _ 5_ flag, abs _ level _ 7_ flag, and abs _ remaining.

11. A video decoding apparatus, comprising:

a first decoding module for decoding a first syntax element at an encoding position within a transform block of a current block in a first encoding pass that scans the encoding position within the transform block;

a second decoding module for decoding, in a second coding pass, second syntax elements at the coding positions within the transform blocks, the second coding pass following the first coding pass and scanning the coding positions within the transform blocks;

a determination module to determine a residual in the transform block based at least on the decoded first syntax element and the decoded second syntax element at the coding position in the transform block; and

a reconstruction module to reconstruct samples of the current block based on the residual in the transformed block.

12. A computer device comprising one or more processors and one or more memories having at least one instruction stored therein, the at least one instruction being loaded and executed by the one or more processors to implement the method of any of claims 1-10.

13. A non-transitory computer-readable medium having instructions stored thereon, wherein the instructions, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 10.

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