Reference picture management methods for video coding

Reference picture management scheme is provided in the context of video coding. A method of decoding an encoded video sequence, comprising obtaining a value of a reference picture list (RPL) syntax element from a bitstream of the encoded video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream, when the RPL syntax element specifies that the syntax elements related to the reference picture lists are present in the bitstream, obtaining, from the bitstream, values of the syntax elements related to the reference picture lists; and constructing at least one reference picture list for inter prediction using the obtained values of the syntax elements related to the reference picture lists.

TECHNICAL FIELD

Embodiments of the present application generally relate to the field of picture processing and more particularly to video coding.

BACKGROUND

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

Particularly, efficient implementation of reference picture management schemes in the context of inter prediction processing still poses a demanding problem in view of an efficient handling of and selection from different schemes that, in principle, may be made available.

SUMMARY

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

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

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

According to one aspect, it is provided a method of decoding an encoded video sequence, the method comprising

obtaining a value of a reference picture list (RPL) syntax element (e.g. sps_rpl_flag) from a bitstream of the video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream;

when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream: a) obtaining, from the bitstream, values of the syntax elements related to reference picture lists and b)

constructing at least one reference picture list for inter prediction using the obtained values of the syntax elements related to reference picture lists.

In an embodiment, it is provided a method of decoding an encoded video sequence, the method comprising

obtaining a value of a reference picture list (RPL) syntax element from a bitstream of the video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream; and

when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, obtaining, from the bitstream, values of the syntax elements related to reference picture lists.

The value of the RPL syntax element may be obtained by parsing the bitstream. Different from the art, a syntax element (RPL syntax element) is provided that allows to detect (for example, by a decoding device) whether or not syntax related to reference picture lists is present in the bitstream and, thus, whether a reference picture lists method can be used for an inter prediction process or not. Thereby, the management of the inter prediction process, particularly, the reference picture management can be efficiently controlled.

According to an embodiment, the method further comprises, when the RPLsyntax element specifies that the syntax elements related to reference picture lists are not present in the bitstream, constructing at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream. Construction of at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream may comprise performing a sliding window method to construct at least one reference picture list for inter prediction.

Thus, reference picture list management that is not based on reference picture list can be performed. In this case, a sliding window method may be performed. Accordingly, an efficient management of different reference picture management schemes including reference picture lists management as utilized by VVC, on the one hand, and a sliding window method as utilized by AVC, on the other hand, can be provided.

According to an embodiment, the method further comprises, when the RPL syntax element specifies that the syntax elements related to reference picture lists are not present in the bitstream, obtaining, from the bitstream, a value of a second syntax element (e.g. max_num_tid0_ref_pics) related to reference picture marking (as it is utilized by AVC). The reference picture marking may provide information on a maximum number of reference pictures (in temporal layer 0) usable for inter prediction of pictures of the video sequence. This information can be readily used to determine the size of the Decoded Picture Buffer.

According to an embodiment, the syntax elements related to reference picture lists are first syntax elements related to reference picture lists constructing (as it is utilized by VVC). These first syntax elements related to reference picture lists constructing may be included in at least one reference picture list syntax structure, wherein each reference picture list syntax structure is used to construct one (single) reference picture list. Employment of such a reference picture list syntax structure allows for an efficient coding of the information necessary for the construction of the reference picture lists.

According to an embodiment, the RPL syntax element is a flag (for example, named “sps_rpl_flag”, see also detailed description below) wherein a first value (for example, 1) of the flag specifies that syntax related to reference picture lists is present in the bitstream and a second value (for example, 0) of the flag different from the first value specifies that syntax related to reference picture lists is not present in the bitstream. Detecting/signalling of whether or not syntax related to reference picture lists is present in the bitstream by means of such a flag is very efficient in terms of the bit size of the coding.

In principle, the value of the RPL syntax element may be obtained from one of a sequence parameter set, a picture parameter set and a slice header. Thus, signalling on different hierarchy levels of parameter sets is envisaged.

According to an embodiment, the syntax elements related to reference picture lists are obtained from a sequence parameter set and/or a slice header. Again, different hierarchy levels of parameter sets may suitably be used.

According to an embodiment the method of decoding comprises, when the RPL syntax element specifies that syntax related to reference picture lists is present in the bitstream, obtaining a value of a at least one third syntax element (e.g. ref_pic_list_sps_flag) from a slice header specifying whether the syntax elements related to reference picture lists are obtainable from a sequence parameter set or a slice header. Thereby, the management of the inter prediction process based on reference picture lists can be efficiently implemented.

According to an embodiment, the at least one third syntax element comprises two third syntax elements, wherein the value of one of the two third syntax elements is obtained for a first reference picture list and, in case that a fourth syntax element (e.g. rpl1_idx_present_flag) obtained from the bitstream indicates that another third syntax element is present in the bitstream, the value of the other one of the two third syntax elements is obtained for a second reference list.

The fourth syntax element may be another flag, a value of 1 of the other flag indicating that the second reference list is present in the bitstream. Employment of such a flag allows for an efficient signalling in terms of the bit size of the coding.

According to an embodiment, the at least one value of the third syntax element is obtained in case that there is at least one reference picture list syntax structure signalled at sequence parameter set level in the bitstream, wherein each reference picture list syntax structure is used to construct one reference picture list.

The at least one value of the third syntax element may be obtained from a slice header comprising

According to another embodiment, the at least one value of the third syntax element is obtained from a slice header comprising

According to a second aspect, a method of encoding a video sequence is provided corresponding to the above-described decoding method and providing the same or similar advantages as discussed above. The method of encoding a video sequence according to the second aspect comprises

determining whether values of syntax elements related to reference picture lists are to be used for construction (by a decoding device) of at least one reference picture list for inter prediction;

generating a bitstream comprising a RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream, wherein the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream in case that it is determined that the values of the syntax elements related to reference picture lists are to be used (by the decoding device) for construction of at least one reference picture list for inter prediction.

According to an embodiment, the bitstream comprises a second syntax element related to reference picture marking when it is determined that values of syntax elements related to reference picture lists are not to be used for construction of at least one reference picture list for inter prediction.

The syntax elements related to reference picture lists may be first syntax elements related to reference picture lists constructing.

The first syntax elements related to reference picture lists constructing may be included in at least one reference picture list syntax structure, wherein each reference picture list syntax structure is used for construction of one reference picture list.

According to an embodiment, the second syntax element related to reference picture marking provides information on a maximum number of reference pictures (in temporal layer 0) usable for inter prediction of pictures of the video sequence.

According to an embodiment, the RPL syntax element is a flag and a first value (for example 1) of the flag specifies that syntax related to reference picture lists is present in the bitstream and a second value (for example, 0) of the flag different from the first value specifies that syntax related to reference picture lists is not present in the bitstream.

The syntax elements related to reference picture lists may be comprised in a sequence parameter set and/or a slice header.

According to an embodiment, at least one third syntax element is signalled in a slice header specifying whether the syntax elements related to reference picture lists are obtainable from a sequence parameter set or a slice header, when it is determined that values of syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction.

According to an embodiment, the bitstream comprises a fourth syntax element and the at least one third syntax element comprises two third syntax elements, wherein one of the two third syntax elements is for a first reference picture list and the other one of the two third syntax elements is for a second reference list in case that a value of the fourth syntax element indicates that the other third syntax element is present in the bitstream.

The fourth syntax element may be another flag, a value of 1 of the other flag indicating that the other third syntax element is present in the bitstream.

According to an embodiment, the at least one reference picture list syntax structure is signalled at sequence parameter set level in the bitstream, wherein each reference picture list syntax structure is used for construction of one reference picture list.

The third syntax element may be signalled in a slice header comprising

According to another embodiment the third syntax element is signalled in a slice header comprising

Furthermore, a decoder configured for performing the above-described embodiments of the inventive decoding method and an encoder configured for performing the above-described embodiments of the inventive encoding method are provided. Particularly, it is provided an decoder comprising processing circuitry for carrying out the above-described embodiments of the inventive decoding method and an encoder comprising processing circuitry for carrying out the above-described embodiments of the inventive encoding method.

Further, it is provided a computer program product comprising program code for performing the methods described above when executed on a computer or a processor.

A decoder is provided that comprises one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the methods described above.

An encoder is provided that comprises one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the methods described above.

Further, it is provided a non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the methods described above.

Furthermore, the following decoding and encoding devices are provided that provide the same or similar advantages as discussed above.

According to another aspect, it is provided a decoding device for decoding an encoded video sequence, comprising:

an obtaining unit configured for obtaining a value of a reference picture list (RPL) syntax element from a bitstream of the video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream and,

when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, obtaining, from the bitstream, values of the syntax elements related to reference picture lists; and

a RPL construction unit for, when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, constructing at least one reference picture list for inter prediction using the obtained values of the syntax elements related to reference picture lists.

Particularly, it is provided a decoding device for decoding an encoded video sequence, comprising an obtaining unit configured for obtaining a value of a reference picture list (RPL) syntax element from a bitstream of the video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream and,

when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, obtaining, from the bitstream, values of the syntax elements related to reference picture lists.

According to an embodiment, the RPL construction unit is configured for, when the RPL syntax element specifies that the syntax elements related to reference picture lists are not present in the bitstream, constructing at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream.

The constructing at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream may comprise performing a sliding window method to construct at least one reference picture list for inter prediction.

According to an embodiment, the obtaining unit is configured for, when the RPL syntax element specifies that the syntax elements related to reference picture lists are not present in the bitstream, obtaining, from the bitstream, a value of a second syntax element related to reference picture marking.

The syntax elements related to reference picture lists may be first syntax elements related to reference picture lists constructing.

According to an embodiment, the first syntax elements related to reference picture lists constructing are included in at least one reference picture list syntax structure, and the RPL construction unit is configured for using each reference picture list syntax structure to construct one reference picture list.

The second syntax element related to reference picture marking may provide information on a maximum number of reference pictures usable for inter prediction of pictures of the video sequence.

The RPL syntax element may be a flag wherein a first value (for example, 1) of the flag specifies that syntax related to reference picture lists is present in the bitstream and a second value (for example, 0) of the flag different from the first value specifies that syntax related to reference picture lists is not present in the bitstream.

According to an embodiment, the obtaining unit is configured for obtaining the value of the RPS syntax element from one of a sequence parameter set, picture parameter set and slice header.

According to an embodiment, the obtaining unit is configured for obtaining the syntax elements related to reference picture lists from a sequence parameter set and/or a slice header.

According to an embodiment, the obtaining unit is configured for, when the RPL syntax element specifies that syntax related to reference picture lists is present in the bitstream, obtaining a value of at least one third syntax element from a slice header specifying whether the syntax elements related to reference picture lists are obtainable from a sequence parameter set or a slice header.

According to an embodiment, the at least one third syntax element comprises two third syntax elements, wherein the obtaining unit is configured for obtaining the value of one of the two third syntax elements for a first reference picture list and, in case that a fourth syntax element obtained from the bitstream indicates that another third syntax element is present in the bitstream, the value of the other one of the two third syntax elements for a second reference list.

48. The decoding device of claim47, wherein the fourth syntax element is another flag, a value of 1 of the other flag indicating that the other third syntax element is present in the bitstream.

According to an embodiment, the obtaining unit is configured for obtaining the at least one value of the third syntax element in case that there is at least one reference picture list syntax structure signalled at sequence parameter set level in the bitstream, and wherein the RPL construction unit is configured for using each reference picture list syntax structure to construct one reference picture list.

According to an embodiment, the obtaining unit is configured for obtaining the at least one value of the third syntax element from a slice header comprising

Moreover, the obtaining unit may be configured for obtaining the at least one value of the third syntax element from a slice header comprising

According to another aspect, it is provided an encoding device for encoding a video sequence, comprising:

a determining unit for determining whether values of syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction;

a bitstream generation unit configured for generating a bitstream comprising a RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream, wherein the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream in case that it is determined by the determining unit that the values of the syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction.

The bitstream may comprise a second syntax element related to reference picture marking, when it is determined by the determining unit that values of syntax elements related to reference picture lists are not to be used for construction of at least one reference picture list for inter prediction.

The syntax elements related to reference picture lists may be first syntax elements related to reference picture lists constructing.

According to an embodiment, the first syntax elements related to reference picture lists constructing are included in at least one reference picture list syntax structure, wherein each reference picture list syntax structure is used for construction of one reference picture list.

According to an embodiment, the second syntax element related to reference picture marking provides information on a maximum number of reference pictures usable for inter prediction of pictures of the video sequence

According to an embodiment, the RPL syntax element is a flag and a first value (for example, 1) of the flag specifies that syntax related to reference picture lists is present in the bitstream and a second value (for example, 0) of the flag different from the first value specifies that syntax related to reference picture lists is not present in the bitstream.

The syntax elements related to reference picture lists may be comprised in a sequence parameter set and/or a slice header.

According to an embodiment, at least one third syntax element is comprised in a slice header specifying whether the syntax elements related to reference picture lists are obtainable from a sequence parameter set or a slice header, when it is determined by the determining unit that values of syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction.

According to an embodiment, the bitstream comprises a fourth syntax element and the at least one third syntax element comprises two third syntax elements, wherein one of the two third syntax elements is for a first reference picture list and the other one of the two third syntax elements is for a second reference list in case that a value of the fourth syntax element indicates that the other third syntax element is present in the bitstream.

The fourth syntax element may be another flag, a value of 1 of the other flag indicating that the other third syntax element is present in the bitstream.

According to an embodiment, at least one reference picture list syntax structure is comprised in a sequence parameter set, wherein each reference picture list syntax structure is used for construction of one reference picture list.

The third syntax element may be comprised in a slice header comprising

The third syntax element may be comprised in a slice header comprising

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

DETAILED DESCRIPTION OF THE EMBODIMENTS

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

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

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

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

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

In the following embodiments of a video coding system10, a video encoder20and a video decoder30are described based onFIGS.1to3.

FIG.1Ais a schematic block diagram illustrating an example coding system10, e.g. a video coding system10(or short coding system10) that may utilize techniques of this present application. Video encoder20(or short encoder20) and video decoder30(or short decoder30) of video coding system10represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application.

As shown inFIG.1A, the coding system10comprises a source device12configured to provide encoded picture data21e.g. to a destination device14for decoding the encoded picture data13.

The source device12comprises an encoder20, and may additionally comprise a picture source16, a pre-processor (or pre-processing unit)18, e.g. a picture pre-processor18, and a communication interface or communication unit22.

The picture source16may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture). The picture source may be any kind of memory or storage storing any of the aforementioned pictures.

In distinction to the pre-processor18and the processing performed by the pre-processing unit18, the picture or picture data17may also be referred to as raw picture or raw picture data17.

Pre-processor18is configured to receive the (raw) picture data17and to perform pre-processing on the picture data17to obtain a pre-processed picture19or pre-processed picture data19. Pre-processing performed by the pre-processor18may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr), color correction, or de-noising. It can be understood that the pre-processing unit18may be an optional component in some embodiments.

The video encoder20is configured to receive the pre-processed picture data19and provide encoded picture data21(further details will be described below, e.g., based onFIG.2).

Communication interface22of the source device12may be configured to receive the encoded picture data21and to transmit the encoded picture data21(or any further processed version thereof) over communication channel13to another device, e.g. the destination device14or any other device, for storage or direct reconstruction.

The destination device14comprises a decoder30(e.g. a video decoder30), and may additionally comprise a communication interface or communication unit28, a post-processor32(or post-processing unit32) and a display device34.

The communication interface28of the destination device14is configured receive the encoded picture data21(or any further processed version thereof), e.g. directly from the source device12or from any other source, e.g. a storage device, e.g. an encoded picture data storage device, and provide the encoded picture data21to the decoder30.

The communication interface22and the communication interface28may be configured to transmit or receive the encoded picture data21or encoded data13via a direct communication link between the source device12and the destination device14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof.

The communication interface22may be, e.g., configured to package the encoded picture data21into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a communication link or communication network.

The communication interface28, forming the counterpart of the communication interface22, may be, e.g., configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data21.

Both, communication interface22and communication interface28may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel13inFIG.1Apointing from the source device12to the destination device14, or bi-directional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission.

The decoder30is configured to receive the encoded picture data21and provide decoded picture data31or a decoded picture31(further details will be described below, e.g., based onFIG.3orFIG.5).

The post-processor32of destination device14is configured to post-process the decoded picture data31(also called reconstructed picture data), e.g. the decoded picture31, to obtain post-processed picture data33, e.g. a post-processed picture33. The post-processing performed by the post-processing unit32may comprise, e.g. color format conversion (e.g. from YCbCr to RGB), color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data31for display, e.g. by display device34.

The display device34of the destination device14is configured to receive the post-processed picture data33for displaying the picture, e.g. to a user or viewer. The display device34may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD), organic light emitting diodes (OLED) displays, plasma displays, projectors, micro LED displays, liquid crystal on silicon (LCoS), digital light processor (DLP) or any kind of other display.

AlthoughFIG.1Adepicts the source device12and the destination device14as separate devices, embodiments of devices may also comprise both or both functionalities, the source device12or corresponding functionality and the destination device14or corresponding functionality. In such embodiments the source device12or corresponding functionality and the destination device14or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device12and/or destination device14as shown inFIG.1Amay vary depending on the actual device and application.

The encoder20(e.g. a video encoder20) or the decoder30(e.g. a video decoder30) or both encoder20and decoder30may be implemented via processing circuitry as shown inFIG.1B, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, video coding dedicated or any combinations thereof. The encoder20may be implemented via processing circuitry46to embody the various modules as discussed with respect to encoder20ofFIG.2and/or any other encoder system or subsystem described herein. The decoder30may be implemented via processing circuitry46to embody the various modules as discussed with respect to decoder30ofFIG.3and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. As shown inFIG.5, if the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Either of video encoder20and video decoder30may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown inFIG.1B.

Source device12and destination device14may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers), broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system. In some cases, the source device12and the destination device14may be equipped for wireless communication. Thus, the source device12and the destination device14may be wireless communication devices.

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

Encoder and Encoding Method

FIG.2shows a schematic block diagram of an example video encoder20that is configured to implement the techniques of the present application. In the example ofFIG.2, the video encoder20comprises an input201(or input interface201), a residual calculation unit204, a transform processing unit206, a quantization unit208, an inverse quantization unit210, and inverse transform processing unit212, a reconstruction unit214, a loop filter unit220, a decoded picture buffer (DPB)230, a mode selection unit260, an entropy encoding unit270and an output272(or output interface272). The mode selection unit260may include an inter prediction unit244, an intra prediction unit254and a partitioning unit262. Inter prediction unit244may include a motion estimation unit and a motion compensation unit (not shown). A video encoder20as shown inFIG.2may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

The residual calculation unit204, the transform processing unit206, the quantization unit208, the mode selection unit260may be referred to as forming a forward signal path of the encoder20, whereas the inverse quantization unit210, the inverse transform processing unit212, the reconstruction unit214, the buffer216, the loop filter220, the decoded picture buffer (DPB)230, the inter prediction unit244and the intra-prediction unit254may be referred to as forming a backward signal path of the video encoder20, wherein the backward signal path of the video encoder20corresponds to the signal path of the decoder (see video decoder30inFIG.3). The inverse quantization unit210, the inverse transform processing unit212, the reconstruction unit214, the loop filter220, the decoded picture buffer (DPB)230, the inter prediction unit244and the intra-prediction unit254are also referred to forming the “built-in decoder” of video encoder20.

High Level Syntax (HLS)

There are several high level sets of syntax elements which are designed to transmit different high level syntax elements such as tools' control flags, video sequence specific parameters (e.g. resolution, external and internal bitdepth, etc.) and some codec routines, that can be reused, e.g. by specific pictures, slices or blocks of the picture.

In modern codecs such as VVC and EVC the following 3 parameter sets are normally used: 1) sequence parameter set (SPS); 2) picture parameter set (PPS); and 3) slice header (SH). SPS is the most general set and includes information, which does not change for or within several coded pictures, e.g. video resolution, internal and external bitdepth are normally signalled in an SPS (or at SPS level). PPS includes an information, which may change from picture to picture, e.g. tiles or PPS level delta QP information. SH contains information that can change from slice to slice, as well as such picture related information that is relatively small or relevant only for certain slice or picture types. SPS, PPS and SH may be considered forming a hierarchy of high level syntax sets, wherein SPS defines the highest level, PPS a next lower level and SH a further lower level within such a hierarchy of levels. Embodiments may be configured to implement these three parameter sets and further parameter sets.

The encoder20may be configured to receive, e.g. via input201, a picture17(or picture data17), e.g. picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture19(or pre-processed picture data19). For sake of simplicity the following description refers to the picture17. The picture17may also be referred to as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture).

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

Embodiments of the video encoder20may comprise a picture partitioning unit (not depicted inFIG.2) configured to partition the picture17into a plurality of (typically non-overlapping) picture blocks203. These blocks may also be referred to as root blocks, macro blocks (H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and VVC). The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receive directly a block203of the picture17, e.g. one, several or all blocks forming the picture17. The picture block203may also be referred to as current picture block or picture block to be coded.

Like the picture17, the picture block203again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although of smaller dimension than the picture17. In other words, the block203may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture17, or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture17) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block203define the size of block203. Accordingly, a block may, for example, an M×N (M-column by N-row) array of samples, or an M×N array of transform coefficients.

Embodiments of the video encoder20as shown inFIG.2may be configured to encode the picture17block by block, e.g. the encoding and prediction is performed per block203.

Embodiments of the video encoder20as shown inFIG.2may be further configured to partition and/or encode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or encoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video encoder20as shown inFIG.2may be further configured to partition and/or encode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or encoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Residual Calculation

The residual calculation unit204may be configured to calculate a residual block205(also referred to as residual205) based on the picture block203and a prediction block265(further details about the prediction block265are provided later), e.g. by subtracting sample values of the prediction block265from sample values of the picture block203, sample by sample (pixel by pixel) to obtain the residual block205in the sample domain.

Transform

The transform processing unit206may be configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block205to obtain transform coefficients207in a transform domain. The transform coefficients207may also be referred to as transform residual coefficients and represent the residual block205in the transform domain.

The transform processing unit206may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and embodiment costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit212(and the corresponding inverse transform, e.g. by inverse transform processing unit312at video decoder30) and corresponding scaling factors for the forward transform, e.g. by transform processing unit206, at an encoder20may be specified accordingly.

Embodiments of the video encoder20(respectively transform processing unit206) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g. directly or encoded or compressed via the entropy encoding unit270, so that, e.g., the video decoder30may receive and use the transform parameters for decoding.

Quantization

The quantization unit208may be configured to quantize the transform coefficients207to obtain quantized coefficients209, e.g. by applying scalar quantization or vector quantization. The quantized coefficients209may also be referred to as quantized transform coefficients209or quantized residual coefficients209.

The quantization process may reduce the bit depth associated with some or all of the transform coefficients207. For example, an n-bit transform coefficient may be rounded down to an m-bit Transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit210, may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In an embodiment, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

Embodiments of the video encoder20(respectively quantization unit208) may be configured to output quantization parameters (QP), e.g. directly or encoded via the entropy encoding unit270, so that, e.g., the video decoder30may receive and apply the quantization parameters for decoding.

Inverse Quantization

The inverse quantization unit210is configured to apply the inverse quantization of the quantization unit208on the quantized coefficients to obtain dequantized coefficients211, e.g. by applying the inverse of the quantization scheme applied by the quantization unit208based on or using the same quantization step size as the quantization unit208. The dequantized coefficients211may also be referred to as dequantized residual coefficients211and correspond—although typically not identical to the transform coefficients due to the loss by quantization—to the transform coefficients207.

Inverse Transform

The inverse transform processing unit212is configured to apply the inverse transform of the transform applied by the transform processing unit206, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block213(or corresponding dequantized coefficients213) in the sample domain. The reconstructed residual block213may also be referred to as transform block213.

Reconstruction

The reconstruction unit214(e.g. adder or summer214) is configured to add the transform block213(i.e. reconstructed residual block213) to the prediction block265to obtain a reconstructed block215in the sample domain, e.g. by adding—sample by sample—the sample values of the reconstructed residual block213and the sample values of the prediction block265.

Filtering

The loop filter unit220(or short “loop filter”220), is configured to filter the reconstructed block215to obtain a filtered block221, or in general, to filter reconstructed samples to obtain filtered sample values. The loop filter unit is, e.g., configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit220may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF), a noise suppression filter (NSF), or any combination thereof. In an example, the loop filter unit220may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit220is shown inFIG.2as being an in loop filter, in other configurations, the loop filter unit220may be implemented as a post loop filter. The filtered block221may also be referred to as filtered reconstructed block221.

Embodiments of the video encoder20(respectively loop filter unit220) may be configured to output loop filter parameters (such as SAO filter parameters or ALF filter parameters or LMCS parameters), e.g. directly or encoded via the entropy encoding unit270, so that, e.g., a decoder30may receive and apply the same loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB)230may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder20. The DPB230may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB)230may be configured to store one or more filtered blocks221. The decoded picture buffer230may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks221, of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The decoded picture buffer (DPB)230may be also configured to store one or more unfiltered reconstructed blocks215, or in general unfiltered reconstructed samples, e.g. if the reconstructed block215is not filtered by loop filter unit220, or any other further processed version of the reconstructed blocks or samples.

In a video codec specification, pictures are identified for multiple purposes, including for use as a reference picture in inter-prediction, for output of pictures from the decoded picture buffer (DPB), for scaling of motion vectors, for weighted prediction, etc. In AVC and HEVC, pictures can be identified by picture order count (POC). In AVC and HEVC, pictures in the DPB can be marked as “used for short-term reference,” “used for long-term reference,” or “unused for reference.” Once a picture has been marked “unused for reference,” the picture can no longer be used for prediction. When the picture is no longer needed for output, the picture can be removed from the DPB.

In AVC, there are two types of reference pictures, short-term and long-term. A reference picture may be marked as “unused for reference” when it becomes no longer needed for prediction reference. The conversion among these three statuses (short-term, long-term, and unused for reference) is controlled by the decoded reference picture marking process. There are two alternative decoded reference picture marking mechanisms, the implicit sliding window process and the explicit memory management control operation (MMCO) process. The sliding window process marks a short-term reference picture as “unused for reference” when the number of reference frames is equal to a given maximum number (max_num_ref_frames in the sequence parameter set (SPS)). The short-term reference pictures are stored in a first-in, first-out manner so that the most recently decoded short-term pictures are kept in the DPB.

The explicit MMCO process may include multiple MMCO commands. An MMCO command may mark one or more short-term or long-term reference pictures as “unused for reference,” may mark all the pictures as “unused for reference,” or may mark the current reference picture or an existing short-term reference picture as long-term and then assign a long-term picture index to that long-term reference picture.

In AVC, the reference picture marking operations as well as the processes for output and removal of pictures from the DPB are performed after a picture has been decoded. Embodiments of the invention may be configured to implement any of these methods and may be configured to use the implicit sliding window process, the explicit memory management control operation (MMCO), or both.

Another method for reference pictures management is used in VVC. It is called an Reference Picture Lists (RPL) method and includes the following aspects, each of which can be applied individually, and some of which can be applied in combination. 1) Reference picture marking is directly based on the two reference picture lists, namely reference picture list 0 and reference picture list 1. 1a) Information for derivation of the two reference picture lists is signaled based on syntax elements and syntax structures in the SPS, PPS, and/or the slice header. 1b) Each of the two reference picture lists for a picture is signaled explicitly in a reference picture list structure. 1b.i) One or more reference picture list structures can be signaled in SPS and each of them can be referred to by an index from the slice header. 1b.ii) Each of the reference picture list 0 and 1 can be signaled directly in the slice header. 2) Information for derivation of the two reference picture lists is signaled for all types of slices, i.e., B (bi-predictive), P (uni-predictive), and I (intra) slices. The term slice refers to a collection of coding tree units such as a slice in HEVC or the latest VVC WD or EVC WD; it may also refer to some other collection of coding tree units such as a tile in HEVC. 3) The two reference picture lists are generated for all types of slices, i.e., B, P, and I slices. 4) The two reference picture lists are directly constructed without using a reference picture list initialization process and a reference picture list modification process. 5) In each of the two reference picture lists, reference pictures that may be used for inter prediction of the current picture can only be referred to by a number of entries at the beginning of the list. These entries are referred to as the active entries in the list, while other entries are referred to as the inactive entries in the list. The number of the total entries and the number of the active entries in the list can both be derived. 6) The picture referred to by an inactive entry in a reference picture list is disallowed to be referred to by another entry in the reference picture list or any entry in the other reference picture list. 7) Long-term reference pictures are only identified by a certain number of POC LSBs, where this number may be greater than the number of POC LSBs signaled in the slice headers for derivation of POC values, and this number is indicated in the SPS. 8) Reference picture list structures are signaled only in slice headers, both short-term reference pictures and long-term reference pictures are identified by their POC LSBs, which may be represented by numbers of bits that are different from the number of bits used for representing the POC LSBs signaled in slice headers for derivation of POC values, and the numbers of bits used to represent the POC LSBs for identifying short-term reference pictures and long-term reference pictures may be different. 9) Reference picture list structures are signaled only in slice headers, no distinction is made between short-term and long-term reference pictures, all reference pictures are just named reference pictures, and reference pictures are identified by their POC LSBs, which may be represented by a number of bits that is different from number of bits used for representing the POC LSBs signaled in slice headers for derivation of POC values. Embodiments of the invention may be configured to implement any of these methods.

An embodiment of RPL method assumes that the following syntax elements are present in the bitstream.

Where the semantics on newly added syntax elements related to RPL is given below. rpl1_same_as_rp10_flag equal to 1 specifies that the syntax structures num_ref_pic_lists_in_sps[1] and ref_pic_list_struct(1, rplsIdx, ltrpFlag) are not present.

rpl1_idx_present_flag equal to 0 specifies that ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not present in slice headers. rpl1_idx_present_flag equal to 1 specifies that ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] may be present in slice headers.

ref_pic_list_sps_flag[i] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures with listIdx equal to i in the active SPS. ref_pic_list_sps_flag[i] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure with listIdx equal to i that is directly included in the slice headers of the current picture. When num_ref_pic_lists_in_sps[i] is equal to 0, the value of ref_pic_list_sps_flag[i] shall be equal to 0. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] is present, the value of ref_pic_list_sps_flag[1] is inferred to be equal to ref_pic_list_sps_flag[0]. When not present, the value of rep_pic_list_sps_flag[i] is inferred to be equal to 0.

The variable NumEntriesInList[listIdx][rplsIdx] is derived as follows:
NumEntriesInList[listIdx][rplsIdx]=num_strp_entries[listIdx][rplsIdx]+num_ltrp_entries[listIdx][rplsIdx]  (123)

The value of NumEntriesInList[listIdx][rplsIdx] shall be in the range of 0 to sps_max_dec_pic_buffering_minus1, inclusive.

It ref_pic_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure is an LTRP entry. It ref_pic_flag[listIdx][rplsIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure is an STRP entry. When not present, the value of lt_ref_pic_flag[listIdx][rplsIdx][i] is inferred to be equal to 0. The sum of lt_ref_pic_flag[listIdx][rplsIdx][i] for all values of i in the range of 0 to NumEntriesInList[listIdx][rplsIdx]−1, inclusive, shall be equal to num_ltrp_entries[listIdx][rplsIdx].

The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of −215 to 215-1, inclusive.

strp_entry_sign_flag[listIdx][rplsIdx][i] equal to 1 specifies that i-th entry in the syntax structure ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) has a value greater than or equal to 0. strp_entry_sign_flag[listIdx][rplsIdx] equal to 0 specifies that the i-th entry in the syntax structure ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) has a value less than 0. When not present, the value of strp_entry_sign_flag[i][j] is inferred to be equal to 1.

The list DeltaPocSt[listIdx][rplsIdx] is derived as follows:

Embodiments of the invention may be configured to implement any of these methods.

The mode selection unit260comprises partitioning unit262, inter-prediction unit244and intra-prediction unit254, and is configured to receive or obtain original picture data, e.g. an original block203(current block203of the current picture17), and reconstructed picture data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from decoded picture buffer230or other buffers (e.g. line buffer, not shown). The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block265or predictor265.

Mode selection unit260may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra or inter prediction mode) and generate a corresponding prediction block265, which is used for the calculation of the residual block205and for the reconstruction of the reconstructed block215.

Embodiments of the mode selection unit260may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit260), which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit260may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion. Terms like “best”, “minimum”, “optimum” etc. in this context do not necessarily refer to an overall “best”, “minimum”, “optimum”, etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a “sub-optimum selection” but reducing complexity and processing time.

In other words, the partitioning unit262may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs), and the CTU203may be further partitioned into smaller block partitions or sub-blocks (which form again blocks), e.g. iteratively using quad-tree-partitioning (QT), binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g., the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block203and the prediction modes are applied to each of the block partitions or sub-blocks.

In the following the partitioning (e.g. by partitioning unit260) and prediction processing (by inter-prediction unit244and intra-prediction unit254) performed by an example video encoder20will be explained in more detail.

Partitioning

The partitioning unit262may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs), and the partitioning unit262may partition (or split) a coding tree unit (CTU)203into smaller partitions, e.g. smaller blocks of square or rectangular size. For a picture that has three sample arrays, a CTU consists of an N×N block of luma samples together with two corresponding blocks of chroma samples. The maximum allowed size of the luma block in a CTU is specified to be 128×128 in the developing versatile video coding (VVC), but it can be specified to be value rather than 128×128 in the future, for example, 256×256. The CTUs of a picture may be clustered/grouped as slices/tile groups, tiles or bricks. A tile covers a rectangular region of a picture, and a tile can be divided into one or more bricks. A brick consists of a number of CTU rows within a tile. A tile that is not partitioned into multiple bricks can be referred to as a brick. However, a brick is a true subset of a tile and is not referred to as a tile. There are two modes of tile groups are supported in VVC, namely the raster-scan slice/tile group mode and the rectangular slice mode. In the raster-scan tile group mode, a slice/tile group contains a sequence of tiles in tile raster scan of a picture. In the rectangular slice mode, a slice contains a number of bricks of a picture that collectively form a rectangular region of the picture. The bricks within a rectangular slice are in the order of brick raster scan of the slice. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to tree-partitioning or hierarchical tree-partitioning, wherein a root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0), may be recursively partitioned, e.g. partitioned into two or more blocks of a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level 1, depth 1), wherein these blocks may be again partitioned into two or more blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioning is terminated, e.g. because a termination criterion is fulfilled, e.g. a maximum tree depth or minimum block size is reached. Blocks which are not further partitioned are also referred to as leaf-blocks or leaf nodes of the tree. A tree using partitioning into two partitions is referred to as binary-tree (BT), a tree using partitioning into three partitions is referred to as ternary-tree (TT), and a tree using partitioning into four partitions is referred to as quad-tree (QT).

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

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

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

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

As an example, the Intra Sub-Partitions (ISP) tool may divide luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size.

In one example, the mode selection unit260of video encoder20may be configured to perform any combination of the partitioning techniques described herein.

As described above, the video encoder20is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

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

The intra-prediction unit254is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block265according to an intra-prediction mode of the set of intra-prediction modes.

The intra prediction unit254(or in general the mode selection unit260) is further configured to output intra-prediction parameters (or in general information indicative of the selected intra prediction mode for the block) to the entropy encoding unit270in form of syntax elements266for inclusion into the encoded picture data21, so that, e.g., the video decoder30may receive and use the prediction parameters for decoding.

The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP230) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel, quarter-pel and/or 1/16 pel interpolation, or not.

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

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

The inter prediction unit244may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown inFIG.2). The motion estimation unit may be configured to receive or obtain the picture block203(current picture block203of the current picture17) and a decoded picture231, or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures231, for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures231, or in other words, the current picture and the previously decoded pictures231may be part of or form a sequence of pictures forming a video sequence.

The encoder20may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists.

The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder30in decoding the picture blocks of the video slice. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit270is configured to apply, for example, an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients209, inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data21which can be output via the output272, e.g. in the form of an encoded bitstream21, so that, e.g., the video decoder30may receive and use the parameters for decoding, The encoded bitstream21may be transmitted to video decoder30, or stored in a memory for later transmission or retrieval by video decoder30.

Other structural variations of the video encoder20can be used to encode the video stream. For example, a non-transform based encoder20can quantize the residual signal directly without the transform processing unit206for certain blocks or frames. In another embodiment, an encoder20can have the quantization unit208and the inverse quantization unit210combined into a single unit.

Decoder and Decoding Method

FIG.3shows an example of a video decoder30that is configured to implement the techniques of this present application. The video decoder30is configured to receive encoded picture data21(e.g. encoded bitstream21), e.g. encoded by encoder20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice (and/or tile groups or tiles) and associated syntax elements.

In the example ofFIG.3, the decoder30comprises an entropy decoding unit304, an inverse quantization unit310, an inverse transform processing unit312, a reconstruction unit314(e.g. a summer314), a loop filter320, a decoded picture buffer (DBP)330, a mode application unit360, an inter prediction unit344and an intra prediction unit354. Inter prediction unit344may be or include a motion compensation unit. Video decoder30may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder100fromFIG.2.

As explained with regard to the encoder20, the inverse quantization unit210, the inverse transform processing unit212, the reconstruction unit214, the loop filter220, the decoded picture buffer (DPB)230, the inter prediction unit344and the intra prediction unit354are also referred to as forming the “built-in decoder” of video encoder20. Accordingly, the inverse quantization unit310may be identical in function to the inverse quantization unit110, the inverse transform processing unit312may be identical in function to the inverse transform processing unit212, the reconstruction unit314may be identical in function to reconstruction unit214, the loop filter320may be identical in function to the loop filter220, and the decoded picture buffer330may be identical in function to the decoded picture buffer230. Therefore, the explanations provided for the respective units and functions of the video20encoder apply correspondingly to the respective units and functions of the video decoder30.

Entropy Decoding

The entropy decoding unit304is configured to parse the bitstream21(or in general encoded picture data21) and perform, for example, entropy decoding to the encoded picture data21to obtain, e.g., quantized coefficients309and/or decoded coding parameters (not shown inFIG.3), e.g. any or all of inter prediction parameters (e.g. reference picture index and motion vector), intra prediction parameter (e.g. intra prediction mode or index), transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. Entropy decoding unit304maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit270of the encoder20. Entropy decoding unit304may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode application unit360and other parameters to other units of the decoder30. Video decoder30may receive the syntax elements at the video slice level and/or the video block level. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used.

Inverse Quantization

The inverse quantization unit310may be configured to receive quantization parameters (QP) (or in general information related to the inverse quantization) and quantized coefficients from the encoded picture data21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit304) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients309to obtain dequantized coefficients311, which may also be referred to as transform coefficients311. The inverse quantization process may include use of a quantization parameter determined by video encoder20for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse Transform

Inverse transform processing unit312may be configured to receive dequantized coefficients311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients311in order to obtain reconstructed residual blocks213in the sample domain. The reconstructed residual blocks213may also be referred to as transform blocks313. The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit312may be further configured to receive transform parameters or corresponding information from the encoded picture data21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit304) to determine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit314(e.g. adder or summer314) may be configured to add the reconstructed residual block313, to the prediction block365to obtain a reconstructed block315in the sample domain, e.g. by adding the sample values of the reconstructed residual block313and the sample values of the prediction block365.

Filtering

The loop filter unit320(either in the coding loop or after the coding loop) is configured to filter the reconstructed block315to obtain a filtered block321, e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit320may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF), a noise suppression filter (NSF), or any combination thereof. In an example, the loop filter unit220may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit320is shown inFIG.3as being an in loop filter, in other configurations, the loop filter unit320may be implemented as a post loop filter.

Decoded Picture Buffer

The decoded video blocks321of a picture are then stored in decoded picture buffer330, which stores the decoded pictures331as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display.

The decoder30is configured to output the decoded picture311, e.g. via output312, for presentation or viewing to a user.

Prediction

The inter prediction unit344may be identical to the inter prediction unit244(in particular to the motion compensation unit) and the intra prediction unit354may be identical to the inter prediction unit254in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit304). Mode application unit360may be configured to perform the prediction (intra or inter prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block365.

When the video slice is coded as an intra coded (I) slice, intra prediction unit354of mode application unit360is configured to generate prediction block365for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter coded (i.e., B, or P) slice, inter prediction unit344(e.g. motion compensation unit) of mode application unit360is configured to produce prediction blocks365for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder30may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB330. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Mode application unit360is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors or related information and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the mode application unit360uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles.

Embodiments of the video decoder30as shown inFIG.3may be configured to partition and/or decode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)).

Embodiments of the video decoder30as shown inFIG.3may be configured to partition and/or decode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or decoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder30can be used to decode the encoded picture data21. For example, the decoder30can produce the output video stream without the loop filtering unit320. For example, a non-transform based decoder30can inverse-quantize the residual signal directly without the inverse-transform processing unit312for certain blocks or frames. In another embodiment, the video decoder30can have the inverse-quantization unit310and the inverse-transform processing unit312combined into a single unit.

It should be understood that, in the encoder20and the decoder30, a processing result of a current operation may be further processed and then output to the next operation. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering.

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

FIG.4is a schematic diagram of a video coding device400according to an embodiment of the disclosure. The video coding device400is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device400may be a decoder such as video decoder30ofFIG.1Aor an encoder such as video encoder20ofFIG.1A.

The video coding device400comprises ingress ports410(or input ports410) and receiver units (Rx)420for receiving data; a processor, logic unit, or central processing unit (CPU)430to process the data; transmitter units (Tx)440and egress ports450(or output ports450) for transmitting the data; and a memory460for storing the data. The video coding device400may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports410, the receiver units420, the transmitter units440, and the egress ports450for egress or ingress of optical or electrical signals.

The processor430is implemented by hardware and software. The processor430may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor430is in communication with the ingress ports410, receiver units420, transmitter units440, egress ports450, and memory460. The processor430comprises a coding module470. The coding module470implements the disclosed embodiments described above. For instance, the coding module470implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module470therefore provides a substantial improvement to the functionality of the video coding device400and effects a transformation of the video coding device400to a different state. Alternatively, the coding module470is implemented as instructions stored in the memory460and executed by the processor430.

FIG.5is a simplified block diagram of an apparatus500that may be used as either or both of the source device12and the destination device14fromFIG.1according to an exemplary embodiment.

A processor502in the apparatus500can be a central processing unit. Alternatively, the processor502can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed embodiments be practiced with a single processor as shown, e.g., the processor502, advantages in speed and efficiency can be achieved using more than one processor.

A memory504in the apparatus500can be a read only memory (ROM) device or a random access memory (RAM) device in an embodiment. Any other suitable type of storage device can be used as the memory504. The memory504can include code and data506that is accessed by the processor502using a bus512. The memory504can further include an operating system508and application programs510, the application programs510including at least one program that permits the processor502to perform the methods described here. For example, the application programs510can include applications1through N, which further include a video coding application that performs the methods described here.

The apparatus500can also include one or more output devices, such as a display518. The display518may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display518can be coupled to the processor502via the bus512.

Although depicted here as a single bus, the bus512of the apparatus500can be composed of multiple buses. Further, the secondary storage514can be directly coupled to the other components of the apparatus500or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus500can thus be implemented in a wide variety of configurations.

Embodiments of the current invention allow to implement two or more reference picture management schemes (e.g. implicit sliding window method (e.g. as used in AVC) and reference picture list (RPL) management method (e.g. VVC) inside one codec.

In a first embodiment of the current invention, implicit sliding window method and Reference Picture Lists (RPL) methods are combined into one codec and any of these two methods can be selected, e.g., for usage at the sequence (SPS) level.

The following table provides a snippet of a SPS syntax table specifying the reference picture management method switch.

Descriptorseq_parameter_set_rbsp( ) {...sps_rpl_flagu(l)...}
sps_rpl_flag equal to 1 specifies that syntax related to reference picture lists is present and RPL method is used; sps_rpl_flag equal to 0 specifies that syntax related to reference picture lists is not present and AVC method is used.

The following table provides an example of signalling reference pictures syntax related to AVC or RPL methods.

The syntax parameter (or flag) sps_rpl_flag is, e.g., sent at SPS level (in further embodiment it might be sent at PPS or slice header) and indicates whether RPL shall be used for reference picture management (flag value “1” indicates RPL to be used, flag value “0” indicates that RPL is not to be used but the implicit sliding window mechanism).

If RPL method is not enabled (sps_rpl_flag equal to 0), only max_num_tid0_ref_pics is signalled for the implicit sliding window reference picture management method.

max_num_tid0_ref_pics specifies the maximum number of reference pictures in temporal layer 0 that may be used by the decoding process for inter prediction (implicit sliding window reference picture management method) of any picture in the CVS (Coding Video sequence). The value of max_num_tid0_ref_pics is also used to determine the size of the Decoded Picture Buffer. The value of max_num_tid0_ref_pics is typically in the range of 0 to 5. When not present, the value of max_num_tid0_ref_pics is inferred, e.g., to be equal to 0.

long_term_ref_pics_flag equal to 0 specifies that no LTRP is used for inter prediction of any coded picture in the CVS. long_term_ref_pics_flag equal to 1 specifies that LTRPs may be used for inter prediction of one or more coded pictures in the CVS. When not present, the value of long_term_ref_pics_flag is inferred to be equal to 0.
rpl1_same_as_rpl0_flag equal to 1 specifies that the syntax structures num_ref_pic_lists_in_sps[1] and ref_pic_list_struct(1, rplsIdx, ItrpFlag) are not present and the following applies:The value of num_ref_pic_lists_in_sps[1] is inferred to be equal to the value of num_ref_pic_lists_in_sps[0].The value of each of syntax elements in ref_pic_list_struct(1, rplsIdx, ltrpFlag) is inferred to be equal to the value of corresponding syntax element in ref_pic_list_struct(0, rplsIdx, ltrpFlag) for rplsIdx ranging from 0 to num_ref_pic_lists_in_sps[0]−1.
num_ref_pic_lists_in_sps[i] specifies the number of the ref_pic_list_struct(listIdx, rplsIdx, ItrpFlag) syntax structures with listIdx equal to i included in the SPS. The value of num_ref_pic_lists_in_sps[i] shall be in the range of 0 to 64, inclusive. When not present, the value of num_ref_pic_lists_in_sps[i] is inferred to be equal to 0.

NOTE For each value of listIdx (equal to 0 or 1), a decoder must allocate memory for a total number of num_ref_pic_lists_in_sps[i]+1 ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures since there can be one ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure directly signalled in the slice headers of a current picture.

If RPL method is enabled (sps_rpl_flag equal to 1), the following RPL syntax is signalled at the slice level.

According to the slice header syntax table, there is a syntax element (e.g. ref_pic_list_sps_flag[i]) specifying whether reference picture list is signalled in the slice header or some of reference picture lists that are already signalled at SPS level, are used in the current slice.

In the current embodiment ref_pic_list_sps_flag[i] is always signalled in the slice header for list0 and also signalled for list1 only if rpl1_idx_present_flag is equal to 1.

In another embodiment similar to the first embodiment, if RPL method is enabled (sps_rpl_flag equal to 1), the following RPL syntax is signalled at the slice level.

In this embodiment signalling of ref_pic_list_sps_flag[i] element is not performed if number of RPL lists inside SPS is equal 0.

ref_pic_list_sps_flag[i] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures with listIdx equal to i in the active SPS. ref_pic_list_sps_flag[i] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure with listIdx equal to i that is directly included in the slice headers of the current picture. When num_ref_pic_lists_in_sps[i] is equal to 0, the value of ref_pic_list_sps_flag[i] shall be equal to 0. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] is present, the value of ref_pic_list_sps_flag[1] is inferred to be equal to ref_pic_list_sps_flag[0]. When not present, the value of rep_pic_list_sps_flag[i] is inferred to be equal to 0.

Following is an explanation of the applications of the encoding method as well as the decoding method as shown in the above-mentioned embodiments, and a system using them.

FIG.6is a block diagram showing a content supply system3100for realizing content distribution service. This content supply system3100includes capture device3102, terminal device3106, and may include display3126. The capture device3102communicates with the terminal device3106over communication link3104. The communication link may include the communication channel13described above. The communication link3104includes but not limited to WIFI, Ethernet, Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, or the like.

The capture device3102generates data, and may encode the data by the encoding method as shown in the above embodiments. Alternatively, the capture device3102may distribute the data to a streaming server (not shown in the Figures), and the server encodes the data and transmits the encoded data to the terminal device3106. The capture device3102includes but not limited to camera, smart phone or Pad, computer or laptop, video conference system, PDA, vehicle mounted device, or a combination of any of them, or the like. For example, the capture device3102may include the source device12as described above. When the data includes video, the video encoder20included in the capture device3102may actually perform video encoding processing. When the data includes audio (i.e., voice), an audio encoder included in the capture device3102may actually perform audio encoding processing. For some practical scenarios, the capture device3102distributes the encoded video and audio data by multiplexing them together. For other practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. Capture device3102distributes the encoded audio data and the encoded video data to the terminal device3106separately.

In the content supply system3100, the terminal device310receives and reproduces the encoded data. The terminal device3106could be a device with data receiving and recovering capability, such as smart phone or Pad3108, computer or laptop3110, network video recorder (NVR)/digital video recorder (DVR)3112, TV3114, set top box (STB)3116, video conference system3118, video surveillance system3120, personal digital assistant (PDA)3122, vehicle mounted device3124, or a combination of any of them, or the like capable of decoding the above-mentioned encoded data. For example, the terminal device3106may include the destination device14as described above. When the encoded data includes video, the video decoder30included in the terminal device is prioritized to perform video decoding. When the encoded data includes audio, an audio decoder included in the terminal device is prioritized to perform audio decoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop3110, network video recorder (NVR)/digital video recorder (DVR)3112, TV3114, personal digital assistant (PDA)3122, or vehicle mounted device3124, the terminal device can feed the decoded data to its display. For a terminal device equipped with no display, for example, STB3116, video conference system3118, or video surveillance system3120, an external display3126is contacted therein to receive and show the decoded data.

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

FIG.7is a diagram showing a structure of an example of the terminal device3106. After the terminal device3106receives stream from the capture device3102, the protocol proceeding unit3202analyzes the transmission protocol of the stream. The protocol includes but not limited to Real Time Streaming Protocol (RTSP), Hyper Text Transfer Protocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH, Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP), or any kind of combination thereof, or the like.

After the protocol proceeding unit3202processes the stream, stream file is generated. The file is outputted to a demultiplexing unit3204. The demultiplexing unit3204can separate the multiplexed data into the encoded audio data and the encoded video data. As described above, for some practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. In this situation, the encoded data is transmitted to video decoder3206and audio decoder3208without through the demultiplexing unit3204.

Via the demultiplexing processing, video elementary stream (ES), audio ES, and subtitle (which may be optional in some embodiments) are generated. The video decoder3206, which includes the video decoder30as explained in the above mentioned embodiments, decodes the video ES by the decoding method as shown in the above-mentioned embodiments to generate video frame, and feeds this data to the synchronous unit3212. The audio decoder3208, decodes the audio ES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG.7) before feeding it to the synchronous unit3212. Similarly, the audio frame may store in a buffer (not shown inFIG.7) before feeding it to the synchronous unit3212.

The synchronous unit3212synchronizes the video frame and the audio frame, and supplies the video/audio to a video/audio display3214. For example, the synchronous unit3212synchronizes the presentation of the video and audio information. Information may code in the syntax using time stamps concerning the presentation of coded audio and visual data and time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder3210decodes the subtitle, and synchronizes it with the video frame and the audio frame, and supplies the video/audio/subtitle to a video/audio/subtitle display3216.

In accordance with the description above, in particular, the following embodiments are provided.FIG.8illustrates a method of decoding an encoded video sequence according to an embodiment. The method illustrated inFIG.8comprises the operation of obtaining810(for example, by parsing) a value of a reference picture list (RPL) syntax element (e.g. sps_rpl_flag) from a bitstream of the video sequence. The RPL syntax element specifies whether syntax elements related to reference picture lists are present in the bitstream. The method, further, comprises, when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, obtaining820, from the bitstream, values of the syntax elements related to reference picture lists. At least one reference picture list for inter prediction using the obtained values of the syntax elements related to reference picture lists is constructed830, when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream.

The method may further comprise, when the RPL syntax element specifies that the syntax elements related to reference picture lists are not present in the bitstream, constructing at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream. In this case, construction of at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream may comprise performing a sliding window method to construct at least one reference picture list for inter prediction.

Thus, reference picture list management that is based and that is not based on reference picture list can be performed. By means of the RPL syntax element (for example, an “sps_rpl_flag”), whether a reference picture lists method can be used for an inter prediction process or not, and, thus, the management of the inter prediction process, particularly, the reference picture management, can be efficiently controlled.

The operations of constructing the at least one reference picture list for inter prediction using the obtained values of the syntax elements related to reference picture lists and at least one reference picture list for inter prediction without further obtaining values of syntax elements from the bitstream, respectively, can be performed in accordance with the EVC standard known to the skilled person. With reference to that standard, when at least one reference picture list for inter prediction using the obtained values of the syntax elements related to reference picture lists is constructed the following applies for the construction process:

“Reference pictures are addressed through reference indices. A reference index is an index into a reference picture list. When decoding an I slice, no reference picture list is used in decoding of the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used in decoding of the slice data. When decoding a B slice, both reference picture list 0 (i.e., RefPicList[0]) and the reference picture list 1 (i.e., RefPicList[1]) are used in decoding of the slice data.

At the beginning of the decoding process for each slice of a non-IDR picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used in marking of reference pictures as specified in subclause 8.3.3 or in decoding of the slice data.

NOTE For an I slice of a non-IDR picture that it is not the first slice of the picture, RefPicList[0] and RefPicList[1] can be derived for bitstream conformance checking purpose, but their derivation is not necessary for decoding of the current picture or pictures following the current picture in decoding order. For a P slice that it is not the first slice of a picture, RefPicList[1] can be derived for bitstream conformance checking purpose, but its derivation is not necessary for decoding of the current picture or pictures following the current picture in decoding order.

The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

For each i equal to 0 or 1, the following applies:The first NumRefIdxActive[i] entries in RefPicList[i] are referred to as the active entries in RefPicList[i], and the other entries in RefPicList[i] are referred to as the inactive entries in RefPicList[i].Each entry in RefPicList[i][j] for j in the range of 0 to NumEntriesInList[i][SliceRplsIdx[i]]−1, inclusive, is referred to as an STRP entry if lt_ref_pic_flag[i][SliceRplsIdx[i]][j] is equal to 0, and as an LTRP entry otherwise.”

With continued reference to that standard, when at least one reference picture list for inter prediction not using the obtained values of the syntax elements related to reference picture lists is constructed the following applies for the construction process:

1) The decoding process for filling a reference picture list with lower PicOrderCntVal in subclause 8.3.2.2.2 is invoked with i set equal to 0 and startIdx set equal to 0, and the output is the variable nextIdx.2) When nextIdx is less than NumRefIdxActive[0], the decoding process for filling a reference picture list with higher PicOrderCntVal in subclause 8.3.2.2.3 is invoked with i set equal to 0 and startIdx set equal to nextIdx, and the output is the variable nextIdx.3) When nextIdx is less than NumRefIdxActive[0], NumRefIdxActive[0] is set equal to nextIdx.
For B slices, the reference picture list RefPicList[1] is constructed as follows:1) The decoding process for filling a reference picture list with higher PicOrderCntVal in subclause 8.3.2.2.3 is invoked with i set equal to 1 and startIdx set equal to 0, and the output is the variable nextIdx.2) When nextIdx is less than NumRefIdxActive[1], the decoding process for filling a reference picture list with lower PicOrderCntVal in subclause 8.3.2.2.2 is invoked with i set equal to 1 and startIdx set equal to nextIdx, and the output is the variable nextIdx.3) When nextIdx is less than NumRefIdxActive[1], NumRefIdxActive[1] is set equal to nextIdx.”
8.3.2.2.2 Decoding Process for Filling a Reference Picture List with Lower PicOrderCntVal Pictures

Inputs to this process are:a reference picture list identifier i, anda start index position startIdx.
Output of this process is the variable nextIdx representing the number of positions filled in the reference picture list.
The variable nextIdx is set equal to startIdx.
The variable nextTemporalId is set equal to Max(TemporalId−1, 0).
Let minPoc be set equal to the lowest value of PictureOrderCountVal of all reference pictures in the DPB.
The reference picture list RefPicList[i] is filled with lower PicOrderCntVal pictures as follows:

for j = PicOrderCntVal; j >= minPoc && nextIdx < NumRefIdxActive[ i ]; j− − ) {if( there is a reference picture picA in the DPB with PicOrderCntVal equal to j andwith TemporalId <= nextTemporalId ) {RefPicList[ i ][ nextIdx++ ] = picA(167)nextTemporalId = Max( TemporalId of picA − 1, 0 )}}
8.3.2.2.3 Decoding Process for Filling a Reference Picture List with Higher PicOrderCntVal Inputs to this Process are:a reference picture list identifier i, anda start index position startIdx.
Output of this process is the variable nextIdx representing the number of positions filled in the reference picture list.
The variable nextIdx is set equal to startIdx.
The variable nextTemporalId is set equal to Max(Temporalld−1, 0).
Let maxPoc be set equal to the highest value of PictureOrderCountVal of all reference pictures in the DPB.
The reference picture list RefPicList[i] is filled with higher PicOrderCntVal pictures as follows:

According to another embodiment, it is provided a method of encoding a video sequence corresponding to the above-described decoding method and as illustrated inFIG.9. The method of encoding a video sequence illustrated inFIG.9comprises the operation of determining910whether values of syntax elements related to reference picture lists are to be used for construction (by a decoding device) of at least one reference picture list for inter prediction. Further, this method comprises generating920a bitstream comprising a RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream, wherein the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream in case that it is determined that the values of the syntax elements related to reference picture lists are to be used (by the decoding device) for construction of at least one reference picture list for inter prediction.

The above-described methods may be implemented in a decoding device or encoding device, respectively, as described in the following.

As shown inFIG.10it is provided, according to an embodiment, a decoding device1000for decoding an encoded video sequence. The decoding device comprises an obtaining unit1010configured for obtaining a value of a reference picture list (RPL) syntax element from a bitstream of the video sequence, the RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream and, when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, obtaining, from the bitstream, values of the syntax elements related to reference picture lists. Further, the decoding device1000comprises a RPL construction unit1020for, when the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream, constructing at least one reference picture list for inter prediction using the values of the syntax elements related to reference picture lists provided by the obtaining unit1010.

Similarly, it is provided an encoding device for encoding a video sequence as shown inFIG.11. The encoding device shown inFIG.11comprises a determining unit1110for determining whether values of syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction. Further, the encoding device1100comprises a bitstream generation unit1120configured for generating a bitstream comprising a RPL syntax element specifying whether syntax elements related to reference picture lists are present in the bitstream, wherein the RPL syntax element specifies that the syntax elements related to reference picture lists are present in the bitstream in case that it is determined by the determining unit1110that the values of the syntax elements related to reference picture lists are to be used for construction of at least one reference picture list for inter prediction.

The decoding device1000shown inFIG.10may be or may be comprised by the decoder30shown inFIG.1A,1B,3and the video decoder3206shown inFIG.7. Further, the decoding device1000may be comprised by the video coding device400shown inFIG.4, the apparatus500shown inFIG.5and the terminal device3106shown inFIG.6. The encoding device1100shown inFIG.11may be or may be comprised by the encoder20shown inFIGS.1A,1B and3. Further, the encoding device1100may be comprised by the video coding device400shown inFIG.4, the apparatus500shown inFIG.5and the capture device3102shown inFIG.6.

Furthermore, the following embodiments are provided herein.

1. A method for decoding (e.g. a video), e.g. implemented by a decoding device, comprising:

3. The method of embodiment 1 or 2, wherein the syntax (syntax information or syntax parameters) representing the reference picture lists is signalled at a sequence parameter set level (SPS) (at SPS level e.g. rpl1_same_as_rpl0_flag and num_ref_pic_lists_in_sps[i], where “i” is a number of reference picture list, e.g. value “0” corresponds to list0 and value “1” corresponds to list1) and/or a slice header (SH) level (at SH level e.g. ref_pic_list_sps_flag[i] and ref_pic_list_idx[i], where “i” is a number of reference picture list, e.g. value “0” corresponds to list0 and value “1” corresponds to list1).

4. The method of any of the preceding embodiments, wherein a syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level (or in a slice header), specifies whether the reference picture lists (see e.g. syntax table ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag)) that are signalled at SPS level, are used in or for the current slice (to which the slice header belongs to).

5. The method of embodiment 4, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at slice header level, specifying whether the reference picture lists that are signalled at SPS level are used in the current slice, is always signalled for a first reference list (e.g. list0) and also signalled for a second reference list (e.g. list1) only if rpl1_idx_present_flag is equal to 1 (or in general only if a syntax element, .e.g a second flag, indicating whether a second reference list is signaled in the bitstream has a predetermined value, e.g. 1).

6. The method of embodiment 5, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level (or in a slice header), specifying whether the reference picture lists that are signalled at SPS level, are used in the current slice (to which the slice header belongs to), is signalled at the slice header according to the following table snippet.

7. The method of embodiment 4, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at a slice header level (or in a slice header), which specifies whether the reference picture lists that are signalled at SPS level are used in or for the current slice, is not signalled if there are no reference picture lists signalled at SPS level.

8. The method of embodiment 7, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level, which specifies whether the reference picture lists that are signalled at SPS level are used in the current slice, is signalled for list0 and signalled for list1 only if rpl1_idx_present_flag is equal to 1 (or in general only if a syntax element, .e.g. a second flag, indicating whether a second reference list is signaled in the bitstream has a predetermined value, e.g. 1).

9. The method of embodiment 7 or embodiment 8, wherein the syntax element specifying which reference picture list is used is signalled at the slice header according to the following table snippet.

10. A method for encoding (e.g. a video), e.g. implemented by an encoding device, comprising:

generating a bitstream (e.g. representing an encoded version of the video);

adding (to the bitstream) a flag (e.g. sps_rpl_flag or some other parameter) specifying whether syntax (e.g. syntax information or syntax parameters) related to reference picture lists (e.g. RPL) is present (or is added) in a bitstream;if the flag (e.g. sps_rpl_flag) specifying whether syntax (e.g. syntax information or syntax parameters) related to reference picture lists (e.g. RPL) is present in the bitstream, is equal to 1 (or in general, if the flag value is set to a first value, e.g. 1 or 0, indicating that RPL shall be used, wherein a second opposite/inverse value, e.g. 0 or 1, indicates that RPL shall not be used)adding the syntax elements representing (or defining) the reference picture lists to the bitstream;otherwise,adding no or other syntax to enable the decoder to perform a different reference picture list management (e.g. a reference picture management using an implicit sliding window method, e.g. using syntax element max_num_tid0_ref_pics).

11. The method of embodiment 10, wherein the flag (e.g. sps_rpl_flag) specifying whether syntax related to reference picture lists (e.g. RPL) is present in a bitstream is signaled at a SPS level.

12. The method of embodiment 10 or 11, wherein the syntax (syntax information or syntax parameters) representing the reference picture lists is signalled at a sequence parameter set level (SPS) (e.g. at SPS level rpl1_same_as_rpl0_flag and num_ref_pic_lists_in_sps[i], where “i” is a number of reference picture list, e.g. value “0” corresponds to list0 and value “1” corresponds to list1) and/or a slice header (SH) level (at SH level e.g. ref_pic_list_sps_flag[i] and ref_pic_list_idx[i], where “i” is a number of reference picture list, e.g. value “0” corresponds to list0 and value “1” corresponds to list1).

13. The method of any of the embodiments 10 to 12, wherein a syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level (or in a slice header), specifies whether the reference picture lists (see e.g. syntax table ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag)) that are signalled at SPS level, are used in or for the current slice (to which the slice header belongs to).

14. The method of embodiment 13, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at slice header level, specifying whether the reference picture lists that are signalled at SPS level are used in the current slice, is always signalled for a first reference list (e.g. list0) and also signalled for a second reference list (e.g. list1) only if rpl1_idx_present_flag is equal to 1 (or in general only if a syntax element, .e.g a second flag, indicating whether a second reference list is signaled in the bitstream has a predetermined value, e.g. 1).

15. The method of embodiment 14, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level (or in a slice header), specifying whether the reference picture lists that are signalled at SPS level are used in the current slice (to which the slice header belongs to), is signalled at the slice header according to the following table snippet.

16. The method of embodiment 15, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at a slice header level (or in a slice header), which specifies whether the reference picture lists that are signalled at SPS level, are used in or for the current slice, is not signalled if there are no reference picture lists signalled at SPS level.

17. The method of embodiment 16, wherein the syntax element (e.g. ref_pic_list_sps_flag[i]), signalled at the slice header level, which specifies whether the reference picture lists that are signalled at SPS level are used in the current slice, is signalled for list0 and signalled for list1 only if rpl1_idx_present_flag is equal to 1 (or in general only if a syntax element, .e.g. a second flag, indicating whether a second reference list is signaled in the bitstream has a predetermined value, e.g. 1).

18. The method of embodiment 16 or embodiment 17, wherein the syntax element specifying which reference picture list is used is signalled at the slice header according to the following table snippet.

19. An encoder (20) comprising processing circuitry for carrying out the method according to any of embodiments 10 to 18.

20. A decoder (30) comprising processing circuitry for carrying out the method according to any of embodiments 1 to 9.

21. A computer program product comprising program code for performing the method according to any one of the embodiments 1 to 18 when executed on a computer or a processor.

one or more processors; and

a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to any one of the embodiments 1 to 9.

one or more processors; and

a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to any one of the embodiments 10 to 18.

24. A non-transitory computer-readable medium carrying a program code which, when executed by a computer device, causes the computer device to perform the method of any one of the embodiments 1 to 18.

Furthermore, it is provided:

1. A method of coding implemented by a decoding device, comprising:

obtaining a flag specifying whether syntax related to reference picture lists is present in a bitstream by parsing the bitstream;

In condition that syntax related to reference picture lists is present, obtaining the syntax related to reference picture lists by parsing the bitstream; Predicting pictures related to the flag, based on the syntax related to reference picture lists.

2. A method of coding implemented by an encoding device, comprising:

Determining whether syntax related to reference picture lists is present in a bitstream by parsing the bitstream;

In condition that syntax related to reference picture lists is present, encoding the syntax related to reference picture lists and a flag specifying the syntax related to reference picture lists is present in the bitstream into the bitstream.

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

Mathematical Operators

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

Arithmetic Operators

The following arithmetic operators are defined as follows:

+ Addition− Subtraction (as a two-argument operator) or negation (as a unary prefix operator)* Multiplication, including matrix multiplicationxYExponentiation. Specifies x to the power of y. In other contexts, such notation is used for superscripting not intended for interpretation as exponentiation./ Integer division with truncation of the result toward zero. For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4 are truncated to −1.÷ Used to denote division in mathematical equations where no truncation or rounding

xy
Used to denote division in mathematical equations where no truncation or rounding is intended.

∑i=xyf⁡(i)
The summation of f(i) with i taking all integer values from x up to and including y.x % y Modulus. Remainder of x divided by y, defined only for integers x and y with x>=0 and y>0.
Logical Operators
The following logical operators are defined as follows:x && y Boolean logical “and” of x and yx∥y Boolean logical “or” of x and y! Boolean logical “not”x ? y: z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z.
Relational Operators
The following relational operators are defined as follows:> Greater than>=Greater than or equal to< Less than<=Less than or equal to==Equal to!= Not equal to
When a relational operator is applied to a syntax element or variable that has been assigned the value “na” (not applicable), the value “na” is treated as a distinct value for the syntax element or variable. The value “na” is considered not to be equal to any other value.
Bit-Wise Operators
The following bit-wise operators are defined as follows:& Bit-wise “and”. When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.| Bit-wise “or”. When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.Â Bit-wise “exclusive or”. When operating on integer arguments, operates on a two's complement representation of the integer value. When operating on a binary argument that contains fewer bits than another argument, the shorter argument is extended by adding more significant bits equal to 0.x>>y Arithmetic right shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the most significant bits (MSBs) as a result of the right shift have a value equal to the MSB of x prior to the shift operation.x<<y Arithmetic left shift of a two's complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.
Assignment Operators
The following arithmetic operators are defined as follows:= Assignment operator++ Increment, i.e., x++ is equivalent to x=x+1; when used in an array index, evaluates to the value of the variable prior to the increment operation.−− Decrement, i.e., x−−3 is equivalent to x=x−1; when used in an array index, evaluates to the value of the variable prior to the decrement operation.+=Increment by amount specified, i.e., x+=3 is equivalent to x=x+3, and x+=(−3) is equivalent to x=x+(−3).−= Decrement by amount specified, i.e., x−=3 is equivalent to x=x−3, and x−=(−3) is equivalent to x=x−(−3).
Range Notation
The following notation is used to specify a range of values:x=y . . . z x takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y.
Mathematical Functions
The following mathematical functions are defined:

Abs⁡(x)={x;x>=0-x;x<0A sin(x) the trigonometric inverse sine function, operating on an argument x that is in the range of −1.0 to 1.0, inclusive, with an output value in the range of −π+2 to π+2, inclusive, in units of radiansA tan(x) the trigonometric inverse tangent function, operating on an argument x, with an output value in the range of −π+2 to π+2, inclusive, in units of radians

Atan⁢2⁢(y,x)={Atan⁡(yx);x>0Atan⁢(yx)+π;x<0&&y>=0Atan⁢(yx)-π;x<0&&y<0+π2;x==0&&y>=0-π2;otherwiseCeil(x) the smallest integer greater than or equal to x.Clip1y(x)=Clip3(0, (1<<BitDepthY)−1, x)Clip1c(x)=Clip3(0, (1<<BitDepthC)−1, x)

Clip⁢3(x,y,z)={x;z<xy;z>yz;otherwiseCos(x) the trigonometric cosine function operating on an argument x in units of radians.Floor(x) the largest integer less than or equal to x.

GetCurrMsb⁢(a,b,c,d)={c+d;b-a>=d/2c-d;a-b>d/2c;otherwiseLn(x) the natural logarithm of x (the base-e logarithm, where e is the natural logarithm base constant 2.718 281 828 . . . ).Log 2(x) the base-2 logarithm of x.Log 10(x) the base-10 logarithm of x.

Sign(x)={1;x>00;x==0-1;x<0Sin(x) the trigonometric sine function operating on an argument x in units of radiansSqrt(x)=√{square root over (x)}Swap(x, y)=(y, x)Tan(x) the trigonometric tangent function operating on an argument x in units of radians
Order of Operation Precedence
When an order of precedence in an expression is not indicated explicitly by use of parentheses, the following rules apply:Operations of a higher precedence are evaluated before any operation of a lower precedence.Operations of the same precedence are evaluated sequentially from left to right.
The table below specifies the precedence of operations from highest to lowest; a higher position in the table indicates a higher precedence.
For those operators that are also used in the C programming language, the order of precedence used in this Specification is the same as used in the C programming language.
Table: Operation precedence from highest (at top of table) to lowest (at bottom of table)

Although embodiments of the invention have been primarily described based on video coding, it should be noted that embodiments of the coding system10, encoder20and decoder30(and correspondingly the system10) and the other embodiments described herein may also be configured for still picture processing or coding, i.e. the processing or coding of an individual picture independent of any preceding or consecutive picture as in video coding. In general only inter-prediction units244(encoder) and344(decoder) may not be available in case the picture processing coding is limited to a single picture17. All other functionalities (also referred to as tools or technologies) of the video encoder20and video decoder30may equally be used for still picture processing, e.g. residual calculation204/304, transform206, quantization208, inverse quantization210/310, (inverse) transform212/312, partitioning262/362, intra-prediction254/354, and/or loop filtering220,320, and entropy coding270and entropy decoding304.