Improving lossless encoding and decoding efficiency in video encoding and decoding

Abstract

An electronic device performs a method for decoding video data in the following manner: receiving a first indication associated with a first segmentation level of the hierarchical structure from a video bitstream having a hierarchical structure; based on determining that the first indication indicates that a lossless mode is enabled at the first segmentation level: configuring one or more codec tools according to the lossless mode; and using the configured one or more coding tools to decode a codec block at or below the first segmentation level.

Description

Technical Field

[0001] The present application relates generally to video data encoding and decoding, and in particular, to a system and method for improving lossless encoding and decoding efficiency in video encoding and decoding. Background Art

[0002] Various electronic devices (such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video game consoles, smart phones, video teleconferencing devices, video streaming devices, etc.) support digital video. Electronic devices send, receive, encode, decode and / or store digital video data by implementing video compression / decompression standards such as those defined by MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4Part 10, Advanced Video Codec (AVC), High Efficiency Video Codec (HEVC) and General Video Codec (VVC) standards. Video compression typically includes performing spatial (intra-frame) prediction and / or temporal (inter-frame) prediction to reduce or remove the redundancy inherent in video data. For block-based video codecs, a video frame is divided into one or more strips, each strip having multiple video blocks, which may also be referred to as codec tree units (CTUs). Each CTU may contain a codec unit (CU), or may be recursively split into smaller CUs until a predefined minimum CU size is reached. Each CU (also called leaf-CU) contains one or more transform units (TUs), and each CU also contains one or more prediction units (PUs). Each CU can be coded and decoded in intra mode, inter mode, or IBC mode. Video blocks in an intra-coded (I) slice of a video frame are encoded using spatial prediction, which is about reference samples in neighboring blocks within the same video frame. Video blocks in an inter-coded (P or B) slice of a video frame can use spatial prediction or temporal prediction, where spatial prediction is about reference samples in neighboring blocks within the same video frame, and temporal prediction is about reference samples in other previous and / or future reference video frames.

[0003] A prediction block for the current video block to be coded is derived based on spatial prediction or temporal prediction of a reference block (e.g., a neighboring block) that has been previously coded. The process of finding the reference block can be accomplished by a block matching algorithm. The residual data representing the pixel difference between the current block to be coded and the prediction block is called a residual block or prediction error. Inter-coded blocks are coded according to motion vectors and residual blocks, and the motion vectors point to reference blocks in a reference frame that form the prediction block. The process of determining motion vectors is generally referred to as motion estimation. Intra-coded blocks are coded according to intra-prediction modes and residual blocks. For further compression, the residual block is transformed from the pixel domain to the transform domain (e.g., the frequency domain), thereby deriving residual transform coefficients, which can then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, can be scanned to produce a one-dimensional vector of transform coefficients and then entropy encoded into a video bitstream to achieve even greater compression.

[0004] The coded video bitstream is then stored in a computer-readable storage medium (e.g., a flash memory) for access by another electronic device with digital video capabilities, or is directly sent to the electronic device by wire or wirelessly. The electronic device then performs video decompression (which is the reverse process of the video compression described above), for example, by parsing the coded video bitstream to obtain syntax elements from the bitstream, and reconstructing digital video data from the coded video bitstream to its original format based at least in part on the syntax elements obtained from the bitstream, and the electronic device presents the reconstructed digital video data on a display of the electronic device.

[0005] As digital video quality changes from HD to 4K×2K or even 8K×4K, the amount of video data to be encoded / decoded increases exponentially. How to encode / decode video data more efficiently while maintaining the image quality of the decoded video data is an ongoing challenge. Summary of the invention

[0006] The present application describes embodiments related to video data encoding and decoding, and more particularly, the embodiments relate to systems and methods for improving lossless encoding and decoding efficiency during video encoding and decoding.

[0007] According to a first aspect of the present application, a method for decoding video data is performed at an electronic device in the following manner: receiving a first indication associated with a first segmentation level of the hierarchical structure from a video bitstream having a hierarchical structure; based on determining that the first indication indicates that a lossless mode is enabled at the first segmentation level: configuring one or more codec tools according to the lossless mode; and using the configured one or more encoding tools to decode a codec block at or below the first segmentation level.

[0008] According to a second aspect of the present application, an electronic device includes one or more processors, a memory, and a plurality of programs stored in the memory. When the programs are executed by the one or more processors, the electronic device performs the operations described above.

[0009] According to a third aspect of the present application, a non-transitory computer-readable storage medium stores a plurality of programs for execution by an electronic device having one or more processors. When the programs are executed by the one or more processors, the electronic device performs the operations described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification, illustrate the described embodiments and together with the description serve to explain the basic principles. Like reference numerals designate corresponding parts.

[0011] Figure 1 is a block diagram illustrating an exemplary video encoding and decoding system according to some embodiments of the present disclosure.

[0012] Figure 2 is a block diagram illustrating an exemplary video encoder according to some embodiments of the present disclosure.

[0013] Figure 3 is a block diagram illustrating an exemplary video decoder according to some embodiments of the present disclosure.

[0014] FIG. 4A to FIG. 4E is a block diagram illustrating how a frame may be recursively partitioned into multiple video blocks of different sizes and shapes according to some embodiments of the present disclosure.

[0015] Figure 5A and Figure 5B is a block diagram illustrating an exemplary video frame segmentation scheme according to some embodiments of the present disclosure.

[0016] Figure 6 is a flow chart illustrating an exemplary process by which a video codec implements techniques for improving lossless encoding and decoding efficiency according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0017] Reference will now be made in detail to specific embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth to aid in understanding the subject matter presented herein. However, it will be apparent to one of ordinary skill in the art that various alternatives may be used without departing from the scope of the claims, and that the subject matter may be practiced without these specific details. For example, it will be apparent to one of ordinary skill in the art that the subject matter presented herein may be implemented on many types of electronic devices having digital video capabilities.

[0018] Figure 1 is a block diagram illustrating an exemplary system 10 for encoding and decoding video blocks in parallel according to some embodiments of the present disclosure. Figure 1 As shown in , system 10 includes a source device 12 that generates and encodes video data that is subsequently decoded by a destination device 14. Source device 12 and destination device 14 may include any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, etc. In some implementations, source device 12 and destination device 14 are equipped with wireless communication capabilities.

[0019] In some embodiments, the target device 14 may receive the encoded video data to be decoded via the link 16. The link 16 may include any type of communication medium or device capable of moving the encoded video data from the source device 12 to the target device 14. In one example, the link 16 may include a communication medium that enables the source device 12 to directly send the encoded video data to the target device 14 in real time. The encoded video data may be modulated according to a communication standard (such as a wireless communication protocol) and sent to the target device 14. The communication medium may include any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form a portion of a packet-based network (such as a local area network, a wide area network, or a global network, such as the Internet). The communication medium may include a router, a switch, a base station, or any other equipment that may be beneficial to facilitate communication from the source device 12 to the target device 14.

[0020] In some other embodiments, the encoded video data may be sent from the output interface 22 to the storage device 32. Subsequently, the encoded video data in the storage device 32 may be accessed by the target device 14 via the input interface 28. The storage device 32 may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, a Blu-ray disc, a DVD, a CD-ROM, a flash memory, a volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In a further example, the storage device 32 may correspond to a file server or another intermediate storage device that may hold the encoded video data generated by the source device 12. The target device 14 may access the stored video data from the storage device 32 via streaming or downloading. The file server may be any type of computer capable of storing encoded video data and sending the encoded video data to the target device 14. Exemplary file servers include a web server (e.g., for a website), an FTP server, a network attached storage (NAS) device, or a local disk drive. The target device 14 may access the encoded video data through any standard data connection suitable for accessing encoded video data stored on a file server, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both. The transmission of the encoded video data from the storage device 32 may be a streaming transmission, a download transmission, or a combination of both.

[0021] like Figure 1 As shown in , source device 12 includes video source 18, video encoder 20 and output interface 22. Video source 18 may include sources such as or a combination of such sources: a video capture device (e.g., a camera), a video archive containing previously captured video, a video feed interface for receiving video from a video content provider, and / or a computer graphics system for generating computer graphics data as source video. As an example, if video source 18 is a camera of a security monitoring system, source device 12 and target device 14 may form a camera phone or a video phone. However, the embodiments described in the present application may be generally applicable to video encoding and decoding, and may be applied to wireless and / or wired applications.

[0022] The captured video, pre-captured video, or computer-generated video may be encoded by the video encoder 20. The encoded video data may be sent directly to the target device 14 via the output interface 22 of the source device 12. The encoded video data may also be stored on a storage device 32 for later access by the target device 14 or other devices for decoding and / or playback. The output interface 22 may further include a modem and / or a transmitter.

[0023] Target device 14 includes input interface 28, video decoder 30, and display device 34. Input interface 28 may include a receiver and / or a modem and receives encoded video data via link 16. Encoded video data communicated via link 16 or provided on storage device 32 may include various syntax elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such syntax elements may be included in encoded video data sent over a communication medium, encoded video data stored on a storage medium, or encoded video data stored on a file server.

[0024] In some implementations, the target device 14 may include a display device 34, which may be an integrated display device and an external display device that is configured to communicate with the target device 14. The display device 34 displays the decoded video data to a user and may include any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0025] The video encoder 20 and the video decoder 30 can operate according to a proprietary standard or an industry standard (such as VVC, HEVC, MPEG-4 Part 10, Advanced Video Codec AVC) or an extension of such a standard. It should be understood that the present application is not limited to a specific video codec / decoding standard and can be applied to other video codec / decoding standards. It is generally believed that the video encoder 20 of the source device 12 can be configured to encode video data according to any of these current standards or future standards. Similarly, it is also generally believed that the video decoder 30 of the target device 14 can be configured to decode video data according to any of these current standards or future standards.

[0026] The video encoder 20 and the video decoder 30 can be implemented as any of a variety of suitable encoder circuit systems, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. When partially implemented in software, the electronic device can store instructions for the software in a suitable non-transitory computer-readable medium, and use one or more processors to execute the instructions in the hardware to perform the video encoding / decoding operations disclosed in the present disclosure. Each of the video encoder 20 and the video decoder 30 can be included in one or more encoders or decoders, and either of the encoders or decoders can be integrated as part of a combined encoder / decoder (CODEC) in the corresponding device.

[0027] Figure 2 2 is a block diagram illustrating an exemplary video encoder 20 according to some embodiments described herein. The video encoder 20 may perform intra-frame prediction codecs and inter-frame prediction codecs for video blocks within a video frame. Intra-frame prediction codecs rely on spatial predictions to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter-frame prediction codecs rely on temporal predictions to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.

[0028] like Figure 2 As shown in , the video encoder 20 includes a video data memory 40, a prediction processing unit 41, a decoded picture buffer (DPB) 64, an adder 50, a transform processing unit 52, a quantization unit 54, and an entropy coding unit 56. The prediction processing unit 41 further includes a motion estimation unit 42, a motion compensation unit 44, a segmentation unit 45, an intra-frame prediction processing unit 46, and an intra-frame block copy (BC) unit 48. In some embodiments, the video encoder 20 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and an adder 62 for video block reconstruction. A deblocking filter (not shown) may be located between the adder 62 and the DPB 64 to filter the block boundaries to remove block effects from the reconstructed video. In addition to the deblocking filter, a loop filter (not shown) may also be used to filter the output of the adder 62. The video encoder 20 may take the form of a fixed hardware unit or a programmable hardware unit, or may be dispersed in one or more of the fixed hardware units or programmable hardware units described.

[0029] The video data memory 40 may store video data to be encoded by the components of the video encoder 20. The video data in the video data memory 40 may be obtained, for example, from the video source 18. The DPB 64 is a buffer that stores reference video data, which is used by the video encoder 20 (e.g., in an intra-frame or inter-frame prediction codec mode) when encoding the video data. The video data memory 40 and the DPB 64 may be formed by any of a variety of memory devices. In various examples, the video data memory 40 may be on-chip with other components of the video encoder 20, or off-chip relative to those components.

[0030] like Figure 2As shown in , after receiving the video data, the segmentation unit 45 within the prediction processing unit 41 segments the video data into video blocks. This segmentation may also include segmenting the video frame into strips, tiles, or other larger codec units (CUs) according to a predefined splitting structure associated with the video data (such as a quadtree structure). The video frame may be divided into a plurality of video blocks (or a set of video blocks referred to as tiles, each tile being defined as a rectangular area of ​​a picture, the rectangular area including a sequence of codec tree units). A tile group contains a plurality of tiles of a picture. The prediction processing unit 41 may select one of a plurality of possible prediction codec modes for the current video block based on error results (e.g., codec rate and distortion level), such as one of a plurality of intra-frame prediction codec modes or one of a plurality of inter-frame prediction codec modes. The prediction processing unit 41 may provide the resulting intra-frame or inter-frame prediction codec block to an adder 50 to generate a residual block, and to an adder 62 to reconstruct the coded block to be subsequently used as part of a reference frame. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit 56 .

[0031] In order to select an appropriate intra-frame prediction codec mode for the current video block, intra-frame prediction processing unit 46 within prediction processing unit 41 may perform intra-frame prediction codec of the current video block relative to one or more neighboring blocks to provide spatial prediction, the one or more neighboring blocks being in the same frame as the current block to be coded. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter-frame prediction codec of the current video block relative to one or more prediction blocks in one or more reference frames to provide temporal prediction. Video encoder 20 may perform multiple codec passes, for example, to select an appropriate codec mode for each block of video data.

[0032] In some embodiments, the motion estimation unit 42 determines the inter-prediction mode for the current video frame by generating a motion vector according to a predetermined pattern within the sequence of video frames, the motion vector indicating the displacement of a prediction unit (PU) of a video block within the current video frame relative to a prediction block within a reference video frame. Motion estimation performed by the motion estimation unit 42 is the process of generating a motion vector, which estimates the motion for a video block. The motion vector may, for example, indicate the displacement of a PU of a video block within the current video frame or picture relative to a prediction block (or other coded unit) within a reference frame, the prediction block being relative to a current block (or other coded unit) being coded within the current frame. The predetermined pattern may designate the video frames in the sequence as P frames or B frames. The intra BC unit 48 may determine a vector (e.g., a block vector) for intra BC coding in a manner similar to how the motion estimation unit 42 determines a motion vector for inter prediction, or may utilize the motion estimation unit 42 to determine the block vector.

[0033] A prediction block is a block of a reference frame that is considered to closely match the PU of the video block to be encoded in terms of pixel differences, which may be determined by the sum of absolute differences (SAD), the sum of squared differences (SSD), or other difference metrics. In some embodiments, the video encoder 20 may calculate values ​​for sub-integer pixel positions of reference frames stored in the DPB 64. For example, the video encoder 20 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference frame. Thus, the motion estimation unit 42 may perform a motion search relative to full pixel positions and fractional pixel positions, and output a motion vector with fractional pixel accuracy.

[0034] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-prediction codec frame by comparing the position of the PU with the position of a prediction block of a reference frame selected from a first reference frame list (list 0) or a second reference frame list (list 1), each of which identifies one or more reference frames stored in DPB 64. Motion estimation unit 42 sends the calculated motion vector to motion compensation unit 44 and then to entropy encoding unit 56.

[0035] The motion compensation performed by the motion compensation unit 44 may involve extracting or generating a prediction block based on the motion vector determined by the motion estimation unit 42. Upon receiving the motion vector for the PU of the current video block, the motion compensation unit 44 may locate the prediction block pointed to by the motion vector in one of the reference frame lists, retrieve the prediction block from the DPB 64, and forward the prediction block to the adder 50. The adder 50 then forms a residual video block of pixel difference values ​​by subtracting the pixel values ​​of the prediction block provided by the motion compensation unit 44 from the pixel values ​​of the current video block being encoded and decoded. The pixel difference values ​​forming the residual video block may include a luminance difference component or a chrominance difference component or both. The motion compensation unit 44 may also generate syntax elements associated with the video block of the video frame for use by the video decoder 30 when decoding the video block of the video frame. The syntax elements may include, for example, syntax elements defining a motion vector for identifying the prediction block, any flag indicating a prediction mode, or any other syntax information described herein. Note that the motion estimation unit 42 and the motion compensation unit 44 may be highly integrated, but are described separately for conceptual purposes.

[0036] In some embodiments, the intra BC unit 48 may generate vectors and extract prediction blocks in a similar manner to that described above in conjunction with the motion estimation unit 42 and the motion compensation unit 44, but these prediction blocks are in the same frame as the current block being encoded and decoded, and these vectors are referred to as block vectors rather than motion vectors. Specifically, the intra BC unit 48 may determine the intra prediction mode to be used to encode the current block. In some examples, the intra BC unit 48 may encode the current block using various intra prediction modes, for example, during multiple separate encoding passes, and test their performance through rate-distortion analysis. Next, the intra BC unit 48 may select a suitable intra prediction mode to use from among the various tested intra prediction modes, and generate an intra mode indicator accordingly. For example, the intra BC unit 48 may calculate rate-distortion values ​​for various tested intra prediction modes using rate-distortion analysis, and select an intra prediction mode with the best rate-distortion characteristics from among the tested modes as a suitable intra prediction mode to use. The rate-distortion analysis typically determines the amount of distortion (or error) between a coded block and the original uncoded block (which was encoded to produce the coded block), and the bit rate (i.e., the number of bits) used to produce the coded block. Intra BC unit 48 may calculate ratios from the distortions and rates for the various coded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

[0037] In other examples, intra BC unit 48 may use, in whole or in part, motion estimation unit 42 and motion compensation unit 44 to perform such functions for intra BC prediction in accordance with embodiments described herein. In either case, for intra block copying, the prediction block may be a block that is considered to closely match the block to be encoded and decoded in terms of pixel differences, which may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics, and identification of the prediction block may include calculating values ​​for sub-integer pixel positions.

[0038] Regardless of whether the prediction block is from the same frame according to intra-frame prediction or from a different frame according to inter-frame prediction, the video encoder 20 can form a residual video block by subtracting the pixel values ​​of the prediction block from the pixel values ​​of the current video block being decoded. The pixel difference values ​​forming the residual video block may include both luma component differences and chroma component differences.

[0039] As an alternative to the inter-frame prediction performed by the motion estimation unit 42 and the motion compensation unit 44 or the intra-frame block copy prediction performed by the intra BC unit 48 as described above, the intra-frame prediction processing unit 46 can perform intra-frame prediction on the current video block. Specifically, the intra-frame prediction processing unit 46 can determine the intra-frame prediction mode for encoding the current block. To do so, the intra-frame prediction processing unit 46 can use various intra-frame prediction modes to encode the current block, for example, during multiple separate encoding passes, and the intra-frame prediction processing unit 46 (or in some examples, the mode selection unit) can select a suitable intra-frame prediction mode from the tested intra-frame prediction modes to use. The intra-frame prediction processing unit 46 can provide information indicating the intra-frame prediction mode selected for the block to the entropy coding unit 56. The entropy coding unit 56 can encode the information indicating the selected intra-frame prediction mode in the bitstream.

[0040] After prediction processing unit 41 determines a prediction block for the current video block via inter-prediction or intra-prediction, adder 50 forms a residual video block by subtracting the prediction block from the current video block. The residual video data in the residual block may be included in one or more transform units (TUs) and provided to transform processing unit 52. Transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform (such as a discrete cosine transform DCT or a conceptually similar transform).

[0041] Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of the matrix including the quantized transform coefficients. Optionally, entropy encoding unit 56 may perform the scan.

[0042] After quantization, entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, for example, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy coding method or technique. The encoded bitstream may then be sent to video decoder 30, or archived in storage device 32 for later sending to or retrieval by video decoder 30. Entropy encoding unit 56 may also entropy encode motion vectors and other syntax elements for the current video frame being encoded or decoded.

[0043] Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual video block in the pixel domain to generate a reference block for predicting other video blocks. As noted above, motion compensation unit 44 may generate a motion compensated prediction block from one or more reference blocks of a frame stored in DPB 64. Motion compensation unit 44 may also apply one or more interpolation filters to the prediction block to calculate sub-integer pixel values ​​for use in motion estimation.

[0044] Adder 62 adds the reconstructed residual block to the motion compensated prediction block produced by motion compensation unit 44 to produce a reference block for storage in DPB 64. The reference block may then be used as a prediction block by intra BC unit 48, motion estimation unit 42, and motion compensation unit 44 to inter-predict another video block in a subsequent video frame.

[0045] Figure 3 30 is a block diagram showing an exemplary video decoder 30 according to some embodiments of the present application. The video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, an adder 90, and a DPB 92. The prediction processing unit 81 further includes a motion compensation unit 82, an intra-frame prediction unit 84, and an intra-frame BC unit 85. The video decoder 30 can perform a decoding process, and the decoding process is combined with the above Figure 2The encoding process described with respect to video encoder 20 is generally reciprocal. For example, motion compensation unit 82 may generate prediction data based on motion vectors received from entropy decoding unit 80, while intra-prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 80.

[0046] In some examples, units of the video decoder 30 may be tasked to perform embodiments of the present application. In addition, in some examples, embodiments of the present disclosure may be dispersed in one or more of the multiple units of the video decoder 30. For example, the intra BC unit 85 may perform embodiments of the present application alone or in combination with other units of the video decoder 30 (such as the motion compensation unit 82, the intra prediction unit 84, and the entropy decoding unit 80). In some examples, the video decoder 30 may not include the intra BC unit 85, and the functions of the intra BC unit 85 may be performed by other components of the prediction processing unit 81 (such as the motion compensation unit 82).

[0047] The video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by other components of the video decoder 30. The video data stored in the video data memory 79 may be obtained, for example, from the storage device 32, from a local video source (such as a camera), via a wired or wireless network communication of video data, or by accessing a physical data storage medium (e.g., a flash drive or hard disk). The video data memory 79 may include a codec picture buffer (CPB) that stores encoded video data from an encoded video bitstream. A decoded picture buffer (DPB) 92 of the video decoder 30 stores reference video data for use by the video decoder 30 when decoding video data (e.g., in intra-frame or inter-frame prediction codec mode). The video data memory 79 and the DPB 92 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. For illustrative purposes, the video data memory 79 and the DPB 92 are stored in a plurality of memory devices. Figure 3 92 as two different components of the video decoder 30. However, it will be apparent to those skilled in the art that the video data memory 79 and the DPB 92 may be provided by the same memory device or multiple separate memory devices. In some examples, the video data memory 79 may be on-chip with other components of the video decoder 30, or off-chip relative to those components.

[0048] During the decoding process, the video decoder 30 receives an encoded video bitstream, which represents video blocks and associated syntax elements of the encoded video frames. The video decoder 30 may receive syntax elements at the video frame level and / or the video block level. The entropy decoding unit 80 of the video decoder 30 entropy decodes the bitstream to generate quantization coefficients, motion vectors or intra-frame prediction mode indicators, and other syntax elements. The entropy decoding unit 80 then forwards the motion vectors and other syntax elements to the prediction processing unit 81.

[0049] When a video frame is encoded and decoded as an intra-frame prediction codec (I) frame or an intra-frame prediction block in another type of frame, the intra-frame prediction unit 84 of the prediction processing unit 81 can generate prediction data for a video block of the current video frame based on the intra-frame prediction mode transmitted by the signal and the reference data from the previously decoded block of the current frame.

[0050] When the video frame is encoded as an inter-frame prediction codec (i.e., B or P) frame, the motion compensation unit 82 of the prediction processing unit 81 generates one or more prediction blocks for the video block of the current video frame based on the motion vectors and other syntax elements received from the entropy decoding unit 80. Each of the prediction blocks can be generated from a reference frame in one of the reference frame lists. The video decoder 30 can construct the reference frame lists, List 0 and List 1, using a default construction technique based on the reference frames stored in the DPB 92.

[0051] In some examples, when the video block is encoded and decoded according to the intra BC mode described herein, intra BC unit 85 of prediction processing unit 81 generates a prediction block for the current video block based on the block vector and other syntax elements received from entropy decoding unit 80. The prediction block may be within a reconstructed region of the same picture as the current video block defined by video encoder 20.

[0052] The motion compensation unit 82 and / or the intra BC unit 85 determine prediction information for a video block of the current video frame by parsing the motion vector and other syntax elements, and then use the prediction information to generate a prediction block for the current video block being decoded. For example, the motion compensation unit 82 uses some of the received syntax elements to determine a prediction mode (e.g., intra prediction or inter prediction) for encoding and decoding a video block of a video frame, an inter prediction frame type (e.g., B or P), construction information for one or more reference frame lists in a reference frame list for a frame, motion vectors for each inter prediction coded video block of a frame, inter prediction states for each inter prediction coded video block of a frame, and other information for decoding a video block in the current video frame.

[0053] Similarly, the intra BC unit 85 may use some of the received syntax elements, such as flags, to determine whether the current video block is predicted using intra BC mode, construction information of which video blocks of the frame are within the reconstruction region and should be stored in the DPB 92, block vectors for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information for decoding video blocks in the current video frame.

[0054] Motion compensation unit 82 may also perform interpolation using interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values ​​for sub-integer pixels of reference blocks. In this case, motion compensation unit 82 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use these interpolation filters to produce the prediction blocks.

[0055] Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80, using the same quantization parameters calculated by video encoder 20 for each video block in the video frame to determine the degree of quantization. Inverse transform processing unit 88 applies an inverse transform (e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process) to the transform coefficients to reconstruct the residual block in the pixel domain.

[0056] After the motion compensation unit 82 or the intra BC unit 85 generates a prediction block for the current video block based on the vector and other syntax elements, the adder 90 reconstructs the decoded video block for the current video block by adding the residual block from the inverse transform processing unit 88 to the corresponding prediction block generated by the motion compensation unit 82 and the intra BC unit 85. A loop filter (not shown) may be located between the adder 90 and the DPB 92 to further process the decoded video block. The decoded video blocks in a given frame are then stored in the DPB 92, which stores reference frames for subsequent motion compensation of the next video block. The DPB 92 or a memory device separate from the DPB 92 may also store the decoded video for later presentation on a display device such as a video display. Figure 1 on a display device 34).

[0057] In a typical video encoding and decoding process, a video sequence usually includes an ordered set of frames or pictures. Each frame may include three sample arrays, denoted as SL, SCb, and SCr. SL is a two-dimensional array of luma samples. SCb is a two-dimensional array of Cb chroma samples. SCr is a two-dimensional array of Cr chroma samples. In other cases, a frame may be monochrome and therefore include only a two-dimensional array of luma samples.

[0058] like Figure 4AAs shown in , the video encoder 20 (or more specifically, the segmentation unit 45) generates an encoded representation of a frame by first segmenting the frame into a set of codec tree units (CTUs). A video frame may include an integer number of CTUs ordered consecutively from left to right and from top to bottom in a raster scan order. Each CTU is the largest logical codec unit, and the width and height of the CTU are signaled by the video encoder 20 in a sequence parameter set so that all CTUs in a video sequence have the same size, one of 128×128, 64×64, 32×32, and 16×16. It should be noted, however, that the present application is not necessarily limited to a particular size. As Figure 4B As shown in , each CTU may include one codec tree block (CTB) of luma samples, two corresponding codec tree blocks of chroma samples, and syntax elements for encoding and decoding the samples of the codec tree blocks. The syntax elements describe the properties of different types of units of codec pixel blocks and how the video sequence can be reconstructed at the video decoder 30, including inter-frame prediction or intra-frame prediction, intra-frame prediction mode, motion vectors, and other parameters. In a monochrome picture or a picture with three separate color planes, a CTU may include a single codec tree block and syntax elements for encoding and decoding the samples of the codec tree block. The codec tree block may be an N×N sample block.

[0059] To achieve better performance, the video encoder 20 may recursively perform tree partitioning, such as binary tree partitioning, ternary tree partitioning, quadtree partitioning, or a combination of both, on the codec tree block of the CTU and divide the CTU into smaller codec units (CUs). Figure 4C As depicted in , a 64×64 CTU 400 is first divided into four smaller CUs, each CU having a block size of 32×32. Among the four smaller CUs, CU 410 and CU 420 are respectively divided into four CUs with a block size of 16×16. Two 16×16 CUs 430 and CU 440 are further divided into four CUs with a block size of 8×8. Figure 4D Depicts a quadtree data structure showing Figure 4C The final result of the partitioning process of the CTU 400 depicted in FIG. 4 is that each leaf node of the quadtree corresponds to a CU of various sizes ranging from 32×32 to 8×8. Figure 4B Each CU may include a codec block (CB) of luma samples and two corresponding codec blocks of chroma samples of the same size frame, and syntax elements for encoding and decoding the samples of the codec block. In a monochrome picture or a picture with three separate color planes, a CU may include a single codec block and syntax structures for encoding and decoding the samples of the codec block. It should be noted that Figure 4C and Figure 4DThe quadtree partitioning depicted in FIG. 1 is for illustrative purposes only, and one CTU may be split into multiple CUs based on quadtree partitioning / ternary tree partitioning / binary tree partitioning to adapt to varying local characteristics. In a multi-type tree structure, one CTU is partitioned by a quadtree structure, and each quadtree leaf CU may be further partitioned by a binary tree structure and a ternary tree structure. Figure 4E As shown in , there are five possible partition types for a codec block with width W and height H, namely, quadruple partition, horizontal binary partition, vertical binary partition, horizontal ternary partition, and vertical ternary partition.

[0060] In some embodiments, the video encoder 20 may further partition the codec block of the CU into one or more M×N prediction blocks (PBs). A prediction block is a rectangular (square or non-square) block of samples to which the same prediction (inter or intra) is applied. The prediction unit (PU) of a CU may include a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements for predicting the prediction blocks. In a monochrome picture or a picture with three separate color planes, a PU may include a single prediction block and a syntax structure for predicting the prediction block. The video encoder 20 may generate a predicted luma block, a predicted Cb block, and a predicted Cr block for the luma prediction block, the Cb prediction block, and the Cr prediction block of each PU of the CU.

[0061] Video encoder 20 may use intra prediction or inter prediction to generate a prediction block for a PU. If video encoder 20 uses intra prediction to generate a prediction block for a PU, video encoder 20 may generate the prediction block for the PU based on decoded samples of a frame associated with the PU. If video encoder 20 uses inter prediction to generate a prediction block for a PU, video encoder 20 may generate the prediction block for the PU based on decoded samples of one or more frames other than the frame associated with the PU.

[0062] After the video encoder 20 generates the predicted luma block, the predicted Cb block, and the predicted Cr block for one or more PUs of a CU, the video encoder 20 may generate a luma residual block for the CU by subtracting the predicted luma block of the CU from its original luma codec block, so that each sample in the luma residual block of the CU indicates the difference between a luma sample in one of the predicted luma blocks of the CU and a corresponding sample in the original luma codec block of the CU. Similarly, the video encoder 20 may generate a Cb residual block and a Cr residual block for the CU, respectively, so that each sample in the Cb residual block of the CU indicates the difference between a Cb sample in one of the predicted Cb blocks of the CU and a corresponding sample in the original Cb codec block of the CU, and each sample in the Cr residual block of the CU may indicate the difference between a Cr sample in one of the predicted Cr blocks of the CU and a corresponding sample in the original Cr codec block of the CU.

[0063] In addition, if Figure 4C As shown in , the video encoder 20 can use quadtree partitioning to decompose the luma residual block, Cb residual block and Cr residual block of the CU into one or more luma transform blocks, Cb transform blocks and Cr transform blocks. A transform block is a rectangular (square or non-square) sample block to which the same transform is applied. The transform unit (TU) of the CU may include a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements for transforming the transform block samples. Therefore, each TU of the CU may be associated with a luma transform block, a Cb transform block and a Cr transform block. In some examples, the luma transform block associated with the TU may be a sub-block of the luma residual block of the CU. The Cb transform block may be a sub-block of the Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU. In a monochrome picture or a picture with three separate color planes, a TU may include a single transform block and a syntax structure for transforming the samples of the transform block.

[0064] The video encoder 20 may apply one or more transforms to the luma transform block of the TU to generate a luma coefficient block for the TU. The coefficient block may be a two-dimensional array of transform coefficients. The transform coefficient may be a scalar. The video encoder 20 may apply one or more transforms to the Cb transform block of the TU to generate a Cb coefficient block for the TU. The video encoder 20 may apply one or more transforms to the Cr transform block of the TU to generate a Cr coefficient block for the TU.

[0065] After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block, or a Cr coefficient block), the video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. After the video encoder 20 quantizes the coefficient block, the video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, the video encoder 20 may perform context-adaptive binary arithmetic coding (CABAC) on the syntax elements indicating the quantized transform coefficients. Finally, the video encoder 20 may output a bitstream including a sequence of bits forming a representation of a coded frame and associated data, and the bitstream is stored in the storage device 32 or sent to the target device 14.

[0066] After receiving the bitstream generated by the video encoder 20, the video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. The video decoder 30 may reconstruct a frame of video data based at least in part on the syntax elements obtained from the bitstream. The process of reconstructing video data is generally inverse to the encoding process performed by the video encoder 20. For example, the video decoder 30 may perform an inverse transform on a coefficient block associated with a TU of the current CU to reconstruct a residual block associated with the TU of the current CU. The video decoder 30 also reconstructs the codec block of the current CU by adding samples of the prediction block for the PU of the current CU to corresponding samples of the transform block of the TU of the current CU. After reconstructing the codec block for each CU of the frame, the video decoder 30 may reconstruct the frame.

[0067] Figure 5A and Figure 5B is a block diagram illustrating an exemplary video frame segmentation scheme according to some embodiments of the present disclosure.

[0068] Figure 5A An exemplary raster scan stripe partitioning (eg, raster scan stripe pattern) of a video frame 502 is shown. The video frame 502 is a rectangular region including 12×18 CTUs (eg, CTU 504a, CTU 504b, etc.) and is partitioned into three stripes (eg, Figure 5A 508a, stripe 508b, and stripe 508c with different fill patterns in the video frame 502. A stripe in a raster scan stripe partitioning scheme is defined as a set of consecutive tiles (e.g., in raster scan order) in a video frame. For example, stripe 508a includes two tiles, namely tile 506a and tile 506b, stripe 508b includes five consecutive tiles of video frame 502 in raster scan order, and stripe 508c includes another five tiles of video frame 502 in raster scan order. Each tile is a rectangular area of ​​multiple CTUs. Thus, video frame 502 includes twelve tiles, each of which includes 3×6 CTUs.

[0069] Figure 5B An exemplary rectangular slice partitioning (eg, rectangular slice pattern) of a video frame 510 is shown. The video frame 510 is a rectangular region including 12×18 CTUs (eg, CTU 512a, CTU 512b, etc.) and is partitioned into nine slices (eg, Figure 5B 516a, 516b, 516c, etc. having different fill patterns. Figure 5AUnlike the raster scan strip segmentation shown in , the strips in the video frame 510 (e.g., strips 516a, strips 516b, strips 516c) are rectangular areas including multiple tiles. For example, strip 516a is a rectangular area including two tiles (tile 514a and tile 514b), and strip 516b is a square area including four tiles. In some embodiments, the tiles within each strip are arranged in a raster scan order. The video frame 510 includes 24 tiles of equal size (e.g., tile 514a, tile 514b, etc.), each tile including 3×3 CTUs.

[0070] In some embodiments, a slice consists of an integer number of complete tiles of a picture, or an integer number of consecutive complete CTU rows within a tile of a picture. Therefore, each vertical slice boundary is always also a vertical tile boundary. It is possible that the horizontal boundaries of a slice are not tile boundaries, but consist of horizontal CTU boundaries within a tile; this occurs when a tile is split into multiple rectangular strips, each of which consists of an integer number of consecutive complete CTU rows within a tile. Two striping modes are supported, namely raster scan striping mode (e.g., Figure 5A ) and rectangular strip patterns (e.g. Figure 5B ). In raster scan strip mode, a strip contains a complete sequence of tiles of a picture raster scanned in tile order. In rectangular strip mode, a strip contains multiple complete tiles that together form a rectangular area of ​​a picture, or multiple consecutive complete CTU rows of a tile that together form a rectangular area of ​​a picture. Tiles within a rectangular strip are scanned in tile raster scan order within the rectangular area corresponding to the strip.

[0071] Therefore, in a raster scan strip segmentation scheme or a rectangular strip segmentation scheme, the video frame is segmented in a nested manner at different levels. For example, a video frame can be segmented into multiple strips, multiple tiles within each strip, and multiple CTUs within each tile. In some embodiments, each segmentation is associated with a parameter set that includes instructions for encoding and decoding the corresponding segmentation. For example, a video sequence including video frame 502 (or video frame 510) can be associated with a sequence parameter set (SPS), and each video frame 502 (or video frame 510) can be further associated with a picture parameter set (PPS). Each slice (e.g., slice 508a or slice 516a) may be associated with a respective slice parameter set (e.g., within a slice header), and each tile (e.g., tile 506a or tile 514a) may be associated with a respective tile parameter set (e.g., within a tile header), each CTU (e.g., CTU 504a or CTU 512a) may be associated with a respective CTU parameter set (CTU header), and each CU may be associated with a respective CU parameter set (CU header). The respective parameter set for the partition may include information for encoding and decoding the respective partition in (i) a lossy mode or (ii) a lossless mode (in which operations such as transform / inverse transform, quantization / dequantization, and loop filtering are skipped).

[0072] Traditionally (e.g., in HEVC), lossless codec is enabled through a two-flag signaling mechanism. A first flag (e.g., "transquant_bypass_enabled_flag") is signaled only at the video frame level (e.g., included in the PPS associated with the video frame) to indicate whether lossless mode is enabled in the video frame, and a second flag (e.g., "cu_transquant_bypass_flag") is signaled only at the CU level to indicate whether the corresponding CU is encoded and decoded in lossless mode or lossy mode. For example, if transquant_bypass_enabled_flag is set to a Boolean value of "1" for a video frame, lossless mode is enabled for the video frame, and further signaling through the second flag at the CU level is required. On the other hand, if transquant_bypass_enabled_flag is set to a Boolean value of "0" for a video frame, lossless mode is not enabled and no further signaling through the second flag at the CU level is required (i.e., all CUs in the video frame are encoded and decoded in lossy mode). In other words, the first flag transquant_bypass_enabled_flag is used to turn on the syntax signaling of the second flag cu_transquant_bypass_flag. When transquant_bypass_enabled_flag is set to "1" for a video frame, cu_transquant_bypass_flag needs to be signaled for each CU in the video frame to indicate whether the respective CU is encoded and decoded in lossless mode (e.g., cu_transquant_bypass_flag is set to "1") or in lossy mode (e.g., cu_transquant_bypass_flag is set to "0"). In lossless mode, the transform / inverse transform process, quantization / dequantization process, and loop filtering process are skipped for each CU, and the prediction residual value is directly encoded and decoded by the entropy encoding and decoding unit 56.

[0073] This two-flag signaling mechanism provides greater control granularity for enabling lossless mode in video codecs, but incurs excessive signaling overhead. For example, if the entire video frame or a desired portion of a video frame is to be encoded and decoded in lossless mode (e.g., in applications where high-definition images such as telemedicine, remote sensing need to be transmitted, or in applications where images including high-definition portions such as slides in video conferencing or license plates in traffic surveillance videos need to be transmitted) with transquant_bypass_enabled_flag set to "1", then cu_transquant_bypass_flag must be signaled for each CU in the video frame, thereby incurring excessive signaling overhead. In addition, the two-flag signaling mechanism is too rigid because the flag can only be set at two predefined partition levels (e.g., video frame level and CU level). Therefore, a more flexible signaling mechanism is highly desirable to indicate the codec mode (e.g., lossless or lossy) at any partition level (e.g., video sequence level, video frame level, slice level, tile level, CTU level, or CU level).

[0074] In some embodiments, the first syntax element can be signaled at any partition level (e.g., video sequence level, video frame level, slice level, tile level, CTU level, or CU level) to turn on syntax signaling of lossless mode or lossy mode. If the first syntax element is set to "0" at the first partition level, all CUs at or below the first partition level are encoded and decoded in lossy mode (e.g., the corresponding second syntax element for each CU at and below the first partition level is implicitly interpreted as "0" to indicate that lossy mode is used). For example, if the first syntax element is set to "0" at the first partition level, all CUs at or below the first partition level are encoded and decoded in lossy mode. Figure 5B If the first syntax element is set to "0" in the slice header of the slice 516a of the slice 516a, all CTUs (e.g., CTU 512a, CTU 512b, etc.) within the slice 516a are encoded and decoded in the lossy mode (e.g., no further signaling of the corresponding second syntax element for each CU within the slice 516a is required). On the other hand, if Figure 5B If the first syntax element is set to "1" in the slice header of the slice 516a of the first partitioning level, all CTUs at or below the first partitioning level can be encoded or decoded in lossless mode or lossy mode, and further signaling through respective second syntax elements is required. Figure 5BIf the first syntax element is set to "1" in the slice header of the slice 516a of the same tile, further syntax signaling through the corresponding second syntax element is required at a lower level (such as a tile level). If the corresponding second syntax element for tile 514a is set to "0", all nine CTUs within tile 514a are encoded and decoded in lossy mode (e.g., further signaling of the corresponding second syntax element for each CU within tile 514a is no longer required). If the corresponding second syntax element for tile 514b is set to "1", further signaling through the corresponding third syntax element is required for each CTU within tile 514b. Therefore, syntax signaling can be performed in a hierarchical or cascaded manner, and the presence of lower-level syntax signaling depends on the value of higher-level syntax signaling.

[0075] In the embodiments described above, the lossy mode is signaled in a bit-saving manner (e.g., a syntax element "0" at a partition level will cause all lower partition levels to be encoded and decoded in lossy mode, and no further syntax signaling is required). In some optional embodiments, the lossless mode is implicitly signaled instead of the lossy mode based on the signaling of the lossless mode at a higher partition level. For example, if the first syntax element is set to "1" in the PPS of the video frame 510, all CTUs within the video frame 510 are encoded and decoded using the lossless mode, and no further signaling through the second syntax element is required. If the first syntax element is set to "0" in the PPS of the video frame 510 (e.g., indicating that not all CUs in the video frame 510 are encoded and decoded in lossless mode), further signaling through the second syntax element at the lower slice level is required. Further signaling (e.g., through the second, third, fourth, etc. syntax elements) can be performed at the lower partition levels in a hierarchical or cascaded manner. For example, if the second syntax element is set to "0" in the slice header for the slice 516a, further syntax signaling is required for all tiles (e.g., tile 514a and tile 514b) within the slice 516a (e.g., through respective third syntax elements, which may indicate lossless mode or lossy mode). If the second syntax element is set to "1" in the slice header for the slice 516a, no further syntax signaling is required at any partitioning level within the slice 516a, and all CTUs within the slice 516a are in lossless mode.

[0076] Between the lossless mode and the lossy mode, different codec tools suitable for different codec modes have been developed. For example, in the lossy mode, the video codec (video encoder 20 or video decoder 30) needs to use various transform-related codec tools to perform transform / inverse transform on the residual block, and the transform-related codec tools include, for example, a multiple transform selection (MTS) scheme, sub-block transform (SBT), transform skip and secondary transform for residual encoding and decoding of both inter-frame codec blocks and intra-frame codec blocks. However, as pointed out above, these transform-related codec tools will not be used when the video codec performs lossless encoding and decoding, because the residual block is directly encoded and decoded by the entropy codec unit 56. Similarly, when the video codec performs lossless encoding and decoding, other tools for, for example, quantization / inverse quantization process, loop filtering process, adaptive loop filtering process, deblocking filtering process, sample adaptive offset filtering process, luminance mapping and chrominance scaling process, intra-frame sub-division process, and joint encoding and decoding process of chrominance residual should not be available. Therefore, in some embodiments, when the video codec performs lossless coding, those codec tools that are not required for the lossless coding are disabled.

[0077] As a result, signaling of these codec tools by video encoder 20 is not required, and video decoder 30 may assign values ​​to syntax elements related to these codec tools based on signaling or signaling indication of the lossless mode.

[0078] In one example, it is proposed to avoid signaling control flags for codecs that may not be able to losslessly reconstruct the current block for a CU that is losslessly coded (e.g., when cu_transquant_bypass_flag is equal to 1). These codecs include, but are not limited to, joint coding of intra subpartitioning and chroma residual. In other words, when the current block is coded in lossless mode (i.e., cu_transquant_bypass_flag is equal to 1), intra_subpartitions_mode_flag is not signaled.

[0079] In another example, codec tools and their signaling that do not efficiently provide codec performance gain for losslessly coded blocks are disabled. Such codec tools include, but are not limited to, decoder-side motion vector refinement (DMVR), bidirectional optical flow (BDOF), sub-block-based temporal motion vector prediction (SbTMVP), adaptive motion vector resolution (AMVR), combined inter- and intra-frame prediction (CIIP), multiple reference line (MRL) intra-frame prediction, and separate block trees for luma and chroma (or referred to as dual-tree codec for luma and chroma components). In yet another example, it is proposed to avoid signaling incremental QP, transform skip, or symbol data hiding for CUs coded as lossless mode.

[0080] In some embodiments, when the width or height of a CU is greater than 64, its TU is implicitly split into two smaller TUs with half the size for the sides greater than 64. For example, a 128×64 CU corresponds to 2 64×64 TUs, and a 128×128 CU corresponds to 4 64×64 TUs. However, this implicit TU splitting is disabled for losslessly coded CUs because no transform is deployed in losslessly coded CUs.

[0081] In some embodiments, the intra prediction results of the planar mode are refined by a position-dependent intra prediction combination (PDPC) method. PDPC is a method that calls for a combination of intra prediction using unfiltered boundary reference samples and intra prediction using filtered boundary reference samples. However, PDPC may not benefit the codec efficiency for lossless coded blocks and is therefore disabled for lossless coded blocks. In addition, filtering of intra reference samples may also be disabled for lossless coded blocks.

[0082] Figure 6 is a flow chart illustrating an exemplary process 600 according to some embodiments of the present disclosure, by which a video codec (e.g., Figure 3 The video decoder 30 of the embodiment of the present invention implements the technology of improving the efficiency of lossless coding. In some embodiments, the video codec skips the transformation (e.g., by Figure 3 ), quantization (e.g., by Figure 3 The operation performed by the inverse quantization unit 86 of the quantization unit 86) and the loop filter (deblocking filter, sample adaptive offset, adaptive loop filter, etc.) to perform lossless coding and decoding. As a result, the prediction residual value is obtained by the entropy coding and decoding module (for example, Figure 3 For convenience, process 600 is described as being performed by a video codec (e.g., Figure 3 The video decoder 30) is executed.

[0083] In a first step, a video codec extracts a video bitstream having a hierarchical structure (e.g., in Figure 1 ), receiving a first indication associated with a first segmentation level of a hierarchical structure (605). For example, the one or more pictures may be a video frame or a video sequence and will be reconstructed by a video codec on the target device. In some embodiments, the hierarchical structure includes multiple groups at different segmentation levels. For example, the one or more pictures may have been divided into multiple slices (e.g., Figure 5A 508a to 508c), and each stripe may have been further divided into multiple tiles (e.g., Figure 5A 506a and tile 506b within stripe 508a), and each tile may have been divided into multiple CTUs (e.g., Figure 5A In the example, the first partitioning level may correspond to the video sequence level, the second partitioning level may correspond to the picture level (one or more pictures within the video sequence), the third partitioning level may correspond to the slice level, the fourth partitioning level may correspond to the tile level, the fifth partitioning level may correspond to the CTU level, and the sixth partitioning level may correspond to the CU level.

[0084] The video codec then checks a first indication associated with the first segmentation level to determine whether the lossless mode is enabled at the first segmentation level. In some embodiments, the first indication is a one-bit flag dedicated to indicating the lossless mode (e.g., transquant_bypass_enabled_flag is equal to a Boolean value of "1"). In some other embodiments, the first indication is a combination of multiple parameters, each parameter having a corresponding value, and the combination of the corresponding values ​​of the multiple parameters corresponds to the lossless mode. For example, a combination of a syntax element indicating that transform_skip is activated and a value of a quantization parameter (QP) at a certain level (e.g., 4) can be interpreted as indicating that the lossless mode is enabled for codec blocks at or below the first segmentation level. Note that the fact that the first indication is a combination of multiple parameters indicates that none of the parameters has a dedicated relationship to the lossless mode like the one-bit flag transquant_bypass_enabled_flag, and when one of the multiple parameters does not have a value corresponding to the lossless mode, at least one of the multiple parameters and its associated value can be used in the lossy mode.

[0085] After the video decoder 30 determines that the lossless mode is enabled, the video decoder 30 configures one or more codec tools under its control according to the lossless mode (610), and then uses the configured one or more codec tools to decode the codec block at or below the first segmentation level (615). As noted above, there are codec tools that are incompatible with the lossless mode, and they are disabled when the video decoder 30 decodes the current block according to the lossless mode. Since these codec tools are disabled, the video decoder 30 does not need to find their corresponding syntax elements in the video bitstream, because they may not exist in the bitstream at all. Even if any of them exists, the video decoder 30 will skip it. As noted above, the lossless mode requires disabling transform codec tools including multiple transform selection (MTS), sub-block transform (SBT), intra-frame sub-segmentation (ISP), secondary transform, etc. In some embodiments, the lossless mode also requires disabling signal data hiding.

[0086] Next, video decoder 30 receives from the video bitstream a second indication associated with a second segmentation level below the first segmentation level of the hierarchical structure (620), and determines whether the codec block at or below the second segmentation level is to be decoded in lossless mode or lossy mode. Note that sub-blocks within a large codec block marked with lossless mode can still be encoded and decoded using lossless mode or lossy mode because lossy mode has lower requirements than lossless mode. For example, Figure 5B The strip 516a in can be marked as lossless mode, while the tile 514a can still be marked as lossy mode. In contrast, if the strip 516a has been marked as lossy mode, the tile 514a must also be marked as lossy mode. If the second indication indicates that the lossy mode is enabled at the second segmentation level, the video decoder 30 then changes the configuration of one of the one or more codec tools according to the lossy mode (625), and uses the configured one or more codec tools to decode the codec block (630) at or below the second segmentation level. In some embodiments, the video decoder 30 changes the configuration of the codec tool based on the syntax elements corresponding to the codec tool in the video bitstream. For example, the syntax elements can indicate that MTS or SBT is enabled at the second segmentation level or lower. As noted above, all codec blocks at or below the second segmentation level will be considered to be decoded according to the lossy mode.

[0087] In one or more examples, the functions described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored on or transmitted by a computer-readable medium as one or more instructions or codes, and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium or a communication medium, and a computer-readable storage medium corresponds to a tangible medium such as a data storage medium, and a communication medium includes any medium that facilitates the transfer of a computer program from one place to another (e.g., according to a communication protocol). In this way, a computer-readable medium can generally correspond to (1) a non-transient tangible computer-readable storage medium, or (2) a communication medium, such as a signal or carrier wave. A data storage medium can be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures for implementing the embodiments described in this application. A computer program product may include a computer-readable medium.

[0088] The terms used in the description of the embodiments herein are only used for the purpose of describing specific embodiments and are not intended to limit the scope of the claims. As used in the description of the embodiments and the appended claims, the singular forms "a", "an" and "the" are intended to also include plural forms unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and covers any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "including" and / or "including" when used in this specification specify the presence of stated features, elements and / or components, but do not exclude the presence or addition of one or more other features, elements, components and / or groups thereof.

[0089] It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the embodiment, the first electrode may be referred to as the second electrode, and similarly, the second electrode may be referred to as the first electrode. Both the first electrode and the second electrode are electrodes, but they are not the same electrode.

[0090] The description of the present application has been presented for the purpose of illustration and description, and is not intended to be exhaustive or limited to the invention in the disclosed form. With the benefit of the teachings presented in the foregoing description and the associated drawings, many modifications, variations and alternative embodiments will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to best explain the principles of the invention, the practical application, and to enable other persons skilled in the art to understand the invention for various embodiments, and to best utilize the basic principles and various embodiments with various modifications suitable for the intended specific use. Therefore, it will be understood that the scope of the claims is not limited to the specific examples of the disclosed embodiments, and modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A method for decoding video data, the method comprising: receiving, from a video bitstream having a hierarchical structure, a first indication associated with a first segmentation level of the hierarchical structure; According to determining that the first indication indicates that the lossless mode is enabled at the first segmentation level: configuring one or more codecs according to the lossless mode; as well as decoding codec blocks at or below the first segmentation level using the configured one or more codec tools, The first indication is a combination of multiple parameters, each parameter has a corresponding value, the combination of the values ​​of the multiple parameters corresponds to the lossless mode, and each parameter has no dedicated relationship with the lossless mode.

2. The method of claim 1, wherein configuring one or more codec tools according to the lossless mode further comprises: Transform codecs are disabled according to the lossless mode.

3. The method of claim 2, wherein no syntax elements related to the transform codec tool are present in the video bitstream.

4. The method according to claim 2, wherein the transform coding tool includes multiple transform selection (MTS), sub-block transform (SBT), intra-frame sub-partitioning (ISP), and secondary transform.

5. The method of claim 1, wherein configuring one or more codec tools according to the lossless mode further comprises: Symbol data hiding is disabled according to the lossless mode. 6 . The method of claim 1 , wherein when one of the plurality of parameters does not have a value corresponding to the lossless mode, at least one of the plurality of parameters and its associated value can be used in the lossy mode.

7. The method according to any one of claims 1 to 6, further comprising: receiving from the video bitstream a second indication associated with a second level of segmentation below the first level of segmentation of the hierarchical structure; According to determining that the second indication indicates that the lossy mode is enabled at the second segmentation level: changing a configuration of one of the one or more codec tools according to the lossy mode; and Codec blocks at or below the second partitioning level are decoded using the codec tool having the changed configuration.

8. An electronic device comprising one or more processors, a memory, and a plurality of programs, wherein the plurality of programs are stored in the memory, wherein the plurality of programs, when executed by the one or more processors, causes the electronic device to execute the method of any one of claims 1 to 7.

9. A non-transitory computer-readable storage medium storing a plurality of programs for execution by an electronic device having one or more processors, wherein the plurality of programs, when executed by the one or more processors, causes the electronic device to execute the method of any one of claims 1 to 7.

10. A computer program product, comprising a plurality of programs, the plurality of programs being executed by an electronic device having one or more processors, wherein the plurality of programs, when executed by the one or more processors, causes the electronic device to perform the method of any one of claims 1 to 7.

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