Patent Publication Number: US-2022232260-A1

Title: Encoder, a decoder and corresponding methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/119696, filed on Sep. 30, 2020, which claims priority to U.S. Provisional Application No. 62/912,046, filed on Oct. 7, 2019. The disclosures of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present application (disclosure) generally relate to the field of picture processing and more particularly to inter-layer prediction. 
     BACKGROUND 
     Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital TV, video transmission over internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and camcorders of security applications. 
     The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in picture quality are desirable. 
     SUMMARY 
     Embodiments of the present application provide apparatuses and methods for encoding and decoding according to the independent claims. 
     The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures. 
     Particular embodiments are outlined in the attached independent claims, with other embodiments in the dependent claims. 
     According to a first aspect the disclosure relates to a method for decoding a coded video bitstream The method is performed by a decoding device. The method includes: obtaining, from the coded video bitstream, a first syntax element specifying whether the first layer use inter-layer prediction; obtaining, from the coded video bitstream, one or more second syntax elements related to one or more second layers, each second syntax element specifies whether a second layer is a direct reference layer for the first layer; wherein at least one second syntax element of the one or more second syntax elements has a value specifying a second layer is a direct reference layer for the first layer, in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction; performing inter-layer prediction for a picture of the first layer by using a picture of the second layer related to the at least one second syntax element as a reference picture Alternatively, the a first syntax element specifying whether the one or more second syntax elements related to one or more second layers are present in the coded video bitstream. Furthermore, wherein the first syntax element equal to 1 specifies that the one or more second syntax elements related to one or more second layers are not present in the coded video bitstream; or the first syntax element equal to equal to 0 specifies that the one or more second syntax elements related to one or more second layers are present in the coded video bitstream. 
     In an embodiment, a layer comprise a sequence of coded pictures with the same layer index. 
     In an embodiment, the layer indexes of the one or more second layers are less than the layer index of the first layer. 
     In an embodiment, the second layers related to different second syntax element are with different layer index. 
     In an embodiment, the one or more second syntax elements are in one-to-one correspondence with the one or more second layers. 
     In an embodiment, a bitstream is sequence of bits forming one or more coded video sequences (CVSs). 
     In an embodiment, a coded video sequence (CVS) is a sequence of AUs. 
     In an embodiment, a coded layer video sequence (CLVS) is a sequence of PUs with the same value of nuh_layer_id. 
     In an embodiment, an access unit (AU) is a set of PUs that belong to different layers and contain coded pictures associated with the same time for output from the DPB. 
     In an embodiment, a picture unit (PU) is a set of NAL units that are associated with each other according to a specified classification rule, are consecutive in decoding order, and contain exactly one coded picture. 
     In an embodiment, an inter-layer reference picture (ILRP) is a picture in the same AU with the current picture, with nuh_layer_id less than the nuh_layer_id of the current picture. 
     In an embodiment, the SPS is a syntax structure containing syntax elements that apply to zero or more entire CLVSs. 
     In an embodiment, the if layer A use layer B as reference layer, layer B is direct reference layer for layer A; if layer A use layer B as reference layer, layer B use layer C as reference layer, but layer A does not use layer C as reference layer, then layer C is not direct reference layer for layer A. 
     In an embodiment, wherein the first syntax element equal to 1 specifies that the first layer does not use inter-layer prediction; or the first syntax element equal to equal to 0 specifies that the first layer is allowed to use inter-layer prediction. 
     In an embodiment, wherein the second syntax element equal to 0 specifies that the second layer related to the second syntax element is not a direct reference layer for the first layer; or the second syntax element equal to 1 specifies that the second layer related to the second syntax element is a direct reference layer for the first layer. 
     In an embodiment, wherein the obtaining the one or more second syntax elements is performed in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction. 
     In an embodiment, wherein the method further comprises: performing prediction for a picture of the first layer without using a picture of the layer related to the at least one second syntax element as a reference picture, in case that the value of the first syntax element specifies the first layer does not use inter-layer prediction. 
     According to a second aspect the disclosure relates to a method for encoding a coded video bitstream. The method is performed by an encoder. The method comprises: determining whether at least one second layer is a direct reference layer for a first layer; encoding a syntax element into the coded video bitstream, wherein the syntax element specifies whether the first layer use inter-layer prediction; wherein the value of the syntax element specifies the first layer does not use inter-layer prediction, in case that none of the at least one second layer is a direct reference layer for the first layer. 
     In an embodiment, the determining whether at least one second layer is a direct reference layer for a first layer comprises: determining a second layer is a direct reference layer for a first layer based on the determining that a first rate distortion cost is less than or equal to a second rate distortion cost; determining a second layer is not a direct reference layer for a first layer based on the determining that a first rate distortion cost is larger than or equal to a second rate distortion cost; wherein the first rate distortion cost is the cost by using the second layer as a direct reference layer for a first layer, the second rate distortion cost is the cost without using the second layer as a direct reference layer for a first layer. 
     In an embodiment, wherein the value of the syntax element specifies the first layer is allowed to use inter-layer prediction, in case that the at least one second layer is a direct reference layer for the first layer. 
     According to a third aspect the disclosure relates to an apparatus for decoding a coded video bitstream. The apparatus comprises: a obtaining unit configured to obtain, from the coded video bitstream, a first syntax element specifying whether the first layer use inter-layer prediction; the obtaining unit is further configured to obtain, from the coded video bitstream, one or more second syntax elements related to one or more second layers, each second syntax element specifies whether a second layer is a direct reference layer for the first layer; wherein at least one second syntax element of the one or more second syntax elements has a value specifying a second layer is a direct reference layer for the first layer, in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction; and a predicting unit configured to perform inter-layer prediction for a picture of the first layer by using a picture of the second layer related to the at least one second syntax element as a reference picture. 
     In an embodiment, wherein the first syntax element equal to 1 specifies that the first layer does not use inter-layer prediction; or the first syntax element equal to equal to 0 specifies that the first layer is allowed to use inter-layer prediction. 
     In an embodiment, wherein the second syntax element equal to 0 specifies that the second layer related to the second syntax element is not a direct reference layer for the first layer; or the second syntax element equal to 1 specifies that the second layer related to the second syntax element is a direct reference layer for the first layer. 
     In an embodiment, the predicting unit configured to obtain the one or more second syntax elements is performed in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction. 
     According to a fourth aspect the disclosure relates to an apparatus for encoding a coded video bitstream. The apparatus comprises: a determining unit configured to determine whether at least one second layer is a direct reference layer for a first layer; an encoding unit configured to encode a syntax element into the coded video bitstream, wherein the syntax element specifies whether the first layer use inter-layer prediction; wherein the value of the syntax element specifies the first layer does not use inter-layer prediction, in case that none of the at least one second layer is a direct reference layer for the first layer. 
     In an embodiment, wherein the value of the syntax element specifies the first layer is allowed to use inter-layer prediction, in case that the at least one second layer is a direct reference layer for the first layer. 
     The method according to the first aspect of the disclosure can be performed by the apparatus according to the third aspect of the disclosure. Further features and implementation forms of the method according to the third aspect of the disclosure correspond to the features and implementation forms of the apparatus according to the first aspect of the disclosure. 
     The method according to the second aspect of the disclosure can be performed by the apparatus according to the fourth aspect of the disclosure. Further features and implementation forms of the method according to the fourth aspect of the disclosure correspond to the features and implementation forms of the apparatus according to the second aspect of the disclosure. 
     The method according to the second aspect can be extended into implementation forms corresponding to the implementation forms of the first apparatus according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the first apparatus. 
     The advantages of the methods according to the second aspect are the same as those for the corresponding implementation forms of the first apparatus according to the first aspect. 
     According to a fifth aspect the disclosure relates to an apparatus for decoding a video stream includes a processor and a memory. The memory is storing instructions that cause the processor to perform the method according to the first aspect. 
     According to a sixth aspect the disclosure relates to an apparatus for encoding a video stream includes a processor and a memory. The memory is storing instructions that cause the processor to perform the method according to the second aspect. 
     According to a seventh aspect, a computer-readable storage medium having stored thereon instructions that when executed cause one or more processors configured to code video data is proposed. The instructions cause the one or more processors to perform a method according to the first or second aspect or any possible embodiment of the first or second aspect. 
     According to an eighth aspect, the disclosure relates to a computer program comprising program code for performing the method according to the first or second aspect or any possible embodiment of the first or second aspect when executed on a computer. 
     According to an ninth aspect, the disclosure relates to a non-transitory storage medium which includes a coded bitstream to be decoded by an apparatus, the bitstream being generated by dividing a frame of a video signal or an image signal into a plurality blocks, and including a plurality of syntax elements, wherein the plurality of syntax elements comprise a first syntax element specifying whether the first layer use inter-layer prediction and one or more second syntax elements related to one or more second layers, each second syntax element specifies whether a second layer is a direct reference layer for the first layer; wherein at least one second syntax element of the one or more second syntax elements has a value specifying a second layer is a direct reference layer for the first layer, in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction. 
     Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. 
     Furthermore, the following embodiments are provided. 
     In one embodiment, a method of decoding a coded video bitstream is provided, the method comprising: parsing a first syntax element specifying whether the layer with index i use inter-layer prediction, i is integer and i is larger than 0; when a first condition is satisfied, parsing a second syntax element specifying whether the layer with index j is a direct reference layer for the layer with index i, wherein j is integer, and j is less than i and larger than or equal to 0, wherein the first condition comprises the first syntax element specifies that the layer with index i may use inter-layer prediction, j is equal to i−1, and any one of layers with index smaller than j is not a direct reference layer for the layer with index i; predicting a picture of the layer with index i based on the value of the second syntax element. 
     In one embodiment, wherein when the first syntax element specifies that the layer with index i may use inter-layer prediction, the sum of vps_direct_dependency_flag[ i ][ k ] is larger than 0 with k for all of the integers in range of 0 to i−1, wherein vps_direct_dependency_flag equal to 1 specifies the layer with index k is a direct reference layer for the layer with index I, vps_direct_dependency_flag equal to 0 specifies the layer with index k is not a direct reference layer for the layer with index i. 
     In one embodiment, wherein when the first syntax element specifies that the layer with index i may use inter-layer prediction, at least one value of vps_direct_dependency_flag[ i ][ k ] is equal to 1, wherein k is a integer and k is in range of 0 to i−1, wherein vps_direct_dependency_flag equal to 1 specifies the layer with index k is a direct reference layer for the layer with index I, vps_direct_dependency_flag equal to 0 specifies the layer with index k is not a direct reference layer for the layer with index i. 
     In one embodiment, wherein the picture of the layer with index i comprises the picture in the layer with index i or the picture related to the layer with index i. 
     In one embodiment, a method of decoding a coded video bitstream is provided, the method comprising: 
     parsing a syntax element specifying whether the layer with index i use inter-layer prediction, i is integer and i is larger than 0; 
     when a condition is satisfied, predicting a picture of the layer with index i using the layer with index j as a direct reference layer for the layer with index i, wherein j is integer, and j is equal to i−1, wherein the condition comprises the syntax element specifies that the layer with index i may use inter-layer prediction. 
     In one embodiment, wherein the picture of the layer with index i comprises the picture in the layer with index i or the picture related to the layer with index i. 
     In one embodiment, a method of decoding a coded video bitstream is provided, the method comprising: 
     parsing a syntax element specifying whether at least one long-term reference picture (LTRP) is used for inter prediction of any coded picture in the coded video sequence (CVS), wherein each picture of the at least one LTRP is marked as “used for long-term reference”, but not an inter-layer reference picture (ILRP); 
     predicting one or more coded pictures in the CVS based on the value of the syntax element. 
     In one embodiment, a method of decoding a coded video bitstream is provided, the method comprising: determining that whether a condition is satisfied, wherein the condition comprises the layer index of a current layer is larger than a preset value; when the condition is satisfied, parsing a first syntax element specifying whether at least one inter-layer reference picture (ILRP) is used for inter prediction of any coded picture in the coded video sequence (CVS); predicting one or more coded pictures in the CVS based on the value of the first syntax element. 
     In one embodiment, wherein the preset value is 0. 
     In one embodiment, wherein the condition further comprises a second syntax element (for example, sps_video_parameter_set_id) is larger than 0. 
     In one embodiment, a method of decoding a coded video bitstream is provided, the method comprising: determining that whether a condition is satisfied, wherein the condition comprises the layer index of a current layer is larger than a preset value and the current entry in the reference picture list structure is an ILRP entry; when the condition is satisfied, parsing a syntax element specifying the index to the list of directly dependent layers of the current layer; predicting one or more coded pictures in the CVS based on the reference picture list structure the current entry of which the ILRP is obtained using the index to the list of directly dependent layer. 
     In one embodiment, wherein the preset value is 1. 
     In one embodiment, an encoder ( 20 ) is provided, comprising processing circuitry for carrying out the method according to any one of claims  1  to  12 . 
     In one embodiment, a decoder ( 30 ) is provided, comprising processing circuitry for carrying out the method according to any one of claims  1  to  12 . 
     In one embodiment, a computer program product is provided, comprising program code for performing the method according to any one of the preceding claims when executed on a computer or a processor. 
     In one embodiment, a decoder is provided, comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the decoder to carry out the method according to any one of the preceding claims. 
     In one embodiment, an encoder is provided, comprising: one or more processors; and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, wherein the programming, when executed by the processors, configures the encoder to carry out the method according to any one of the preceding claims. 
     In one embodiment, a non-transitory computer-readable medium is provided, carrying a program code which, when executed by a computer device, causes the computer device to perform the method of any one of the preceding claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following embodiments of the disclosure are described in more detail with reference to the attached figures and drawings, in which: 
         FIG. 1A  is a block diagram showing an example of a video coding system configured to implement embodiments of the disclosure; 
         FIG. 1B  is a block diagram showing another example of a video coding system configured to implement embodiments of the disclosure; 
         FIG. 2  is a block diagram showing an example of a video encoder configured to implement embodiments of the disclosure; 
         FIG. 3  is a block diagram showing an example structure of a video decoder configured to implement embodiments of the disclosure; 
         FIG. 4  is a block diagram illustrating an example of an encoding apparatus or a decoding apparatus; 
         FIG. 5  is a block diagram illustrating another example of an encoding apparatus or a decoding apparatus; 
         FIG. 6  is a block diagram showing scalable coding with 2 layer; 
         FIG. 7  is a block diagram showing an example structure of a content supply system  3100  which realizes a content delivery service. 
         FIG. 8  is a block diagram showing a structure of an example of a terminal device. 
         FIG. 9  shows a flow diagram of a decoding method according to one embodiment. 
         FIG. 10  shows a flow diagram of an encoding method according to one embodiment. 
         FIG. 11  is a schematic diagram of an encoder according to one embodiment. 
         FIG. 12  is a schematic diagram of a decoder according to one embodiment. 
       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 disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the disclosure 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 disclosure is defined by the appended claims. 
     For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise. 
     Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term “picture” the term “frame” or “image” may be used as synonyms in the field of video coding. Video coding (or coding in general) comprises two parts video encoding and video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission). Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to “coding” of video pictures (or pictures in general) shall be understood to relate to “encoding” or “decoding” of video pictures or respective video sequences. The combination of the encoding part and the decoding part is also referred to as CODEC (Coding and Decoding). 
     In case of lossless video coding, the original video pictures 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 system  10 , a video encoder  20  and a video decoder  30  are described based on  FIGS. 1 to 3 . 
       FIG. 1A  is a schematic block diagram illustrating an example coding system  10 , e.g. a video coding system  10  (or short coding system  10 ) that may utilize techniques of this present application. Video encoder  20  (or short encoder  20 ) and video decoder  30  (or short decoder  30 ) of video coding system  10  represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present application. 
     As shown in  FIG. 1A , the coding system  10  comprises a source device  12  configured to provide encoded picture data  21  e.g. to a destination device  14  for decoding the encoded picture data  13 . 
     The source device  12  comprises an encoder  20 , and may additionally, i.e. optionally, comprise a picture source  16 , a pre-processor (or pre-processing unit)  18 , e.g. a picture pre-processor  18 , and a communication interface or communication unit  22 . 
     The picture source  16  may comprise or be any kind of picture capturing device, for example a camera for capturing a real-world picture, and/or any kind of a picture generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of other device for obtaining and/or providing a real-world picture, a computer generated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture). The picture source may be any kind of memory or storage storing any of the aforementioned pictures. 
     In distinction to the pre-processor  18  and the processing performed by the pre-processing unit  18 , the picture or picture data  17  may also be referred to as raw picture or raw picture data  17 . 
     Pre-processor  18  is configured to receive the (raw) picture data  17  and to perform pre-processing on the picture data  17  to obtain a pre-processed picture  19  or pre-processed picture data  19 . Pre-processing performed by the pre-processor  18  may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr), color correction, or de-noising. It can be understood that the pre-processing unit  18  may be optional component. 
     The video encoder  20  is configured to receive the pre-processed picture data  19  and provide encoded picture data  21  (further details will be described below, e.g., based on  FIG. 2 ). 
     Communication interface  22  of the source device  12  may be configured to receive the encoded picture data  21  and to transmit the encoded picture data  21  (or any further processed version thereof) over communication channel  13  to another device, e.g. the destination device  14  or any other device, for storage or direct reconstruction. 
     The destination device  14  comprises a decoder  30  (e.g. a video decoder  30 ), and may additionally, i.e. optionally, comprise a communication interface or communication unit  28 , a post-processor  32  (or post-processing unit  32 ) and a display device  34 . 
     The communication interface  28  of the destination device  14  is configured receive the encoded picture data  21  (or any further processed version thereof), e.g. directly from the source device  12  or from any other source, e.g. a storage device, e.g. an encoded picture data storage device, and provide the encoded picture data  21  to the decoder  30 . 
     The communication interface  22  and the communication interface  28  may be configured to transmit or receive the encoded picture data  21  or encoded data  13  via a direct communication link between the source device  12  and the destination device  14 , e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof. 
     The communication interface  22  may be, e.g., configured to package the encoded picture data  21  into an appropriate format, e.g. packets, and/or process the encoded picture data using any kind of transmission encoding or processing for transmission over a communication link or communication network. 
     The communication interface  28 , forming the counterpart of the communication interface  22 , may be, e.g., configured to receive the transmitted data and process the transmission data using any kind of corresponding transmission decoding or processing and/or de-packaging to obtain the encoded picture data  21 . 
     Both, communication interface  22  and communication interface  28  may be configured as unidirectional communication interfaces as indicated by the arrow for the communication channel  13  in  FIG. 1A  pointing from the source device  12  to the destination device  14 , or bi-directional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission. 
     The decoder  30  is configured to receive the encoded picture data  21  and provide decoded picture data  31  or a decoded picture  31  (further details will be described below, e.g., based on  FIG. 3  or  FIG. 5 ). 
     The post-processor  32  of destination device  14  is configured to post-process the decoded picture data  31  (also called reconstructed picture data), e.g. the decoded picture  31 , to obtain post-processed picture data  33 , e.g. a post-processed picture  33 . The post-processing performed by the post-processing unit  32  may comprise, e.g. color format conversion (e.g. from YCbCr to RGB), color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data  31  for display, e.g. by display device  34 . 
     The display device  34  of the destination device  14  is configured to receive the post-processed picture data  33  for displaying the picture, e.g. to a user or viewer. The display device  34  may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD), organic light emitting diodes (OLED) displays, plasma displays, projectors , micro LED displays, liquid crystal on silicon (LCoS), digital light processor (DLP) or any kind of other display. 
     Although  FIG. 1A  depicts the source device  12  and the destination device  14  as separate devices, embodiments of devices may also comprise both or both functionalities, the source device  12  or corresponding functionality and the destination device  14  or corresponding functionality. In such embodiments the source device  12  or corresponding functionality and the destination device  14  or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof. 
     As will be apparent for the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device  12  and/or destination device  14  as shown in  FIG. 1A  may vary depending on the actual device and application. 
     The encoder  20  (e.g. a video encoder  20 ) or the decoder  30  (e.g. a video decoder  30 ) or both encoder  20  and decoder  30  may be implemented via processing circuitry as shown in  FIG. 1B , such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, video coding dedicated or any combinations thereof. The encoder  20  may be implemented via processing circuitry  46  to embody the various modules as discussed with respect to encoder  20  of  FIG. 2  and/or any other encoder system or subsystem described herein. The decoder  30  may be implemented via processing circuitry  46  to embody the various modules as discussed with respect to decoder  30  of  FIG. 3  and/or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform the various operations as discussed later. As shown in  FIG. 5 , if the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Either of video encoder  20  and video decoder  30  may be integrated as part of a combined encoder/decoder (CODEC) in a single device, for example, as shown in  FIG. 1B . 
     Source device  12  and destination device  14  may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers), broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system. In some cases, the source device  12  and the destination device  14  may be equipped for wireless communication. Thus, the source device  12  and the destination device  14  may be wireless communication devices. 
     In some cases, video coding system  10  illustrated in  FIG. 1A  is merely an example and the techniques of the present application may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory. 
     For convenience of description, embodiments of the disclosure 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 disclosure are not limited to HEVC or VVC. 
     Encoder and Encoding Method 
       FIG. 2  shows a schematic block diagram of an example video encoder  20  that is configured to implement the techniques of the present application. In the example of  FIG. 2 , the video encoder  20  comprises an input  201  (or input interface  201 ), a residual calculation unit  204 , a transform processing unit  206 , a quantization unit  208 , an inverse quantization unit  210 , and inverse transform processing unit  212 , a reconstruction unit  214 , a loop filter unit  220 , a decoded picture buffer (DPB)  230 , a mode selection unit  260 , an entropy encoding unit  270  and an output  272  (or output interface  272 ). The mode selection unit  260  may include an inter prediction unit  244 , an intra prediction unit  254  and a partitioning unit  262 . Inter prediction unit  244  may include a motion estimation unit and a motion compensation unit (not shown). A video encoder  20  as shown in  FIG. 2  may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec. 
     The residual calculation unit  204 , the transform processing unit  206 , the quantization unit  208 , the mode selection unit  260  may be referred to as forming a forward signal path of the encoder  20 , whereas the inverse quantization unit  210 , the inverse transform processing unit  212 , the reconstruction unit  214 , the buffer  216 , the loop filter  220 , the decoded picture buffer (DPB)  230 , the inter prediction unit  244  and the intra-prediction unit  254  may be referred to as forming a backward signal path of the video encoder  20 , wherein the backward signal path of the video encoder  20  corresponds to the signal path of the decoder (see video decoder  30  in  FIG. 3 ). The inverse quantization unit  210 , the inverse transform processing unit  212 , the reconstruction unit  214 , the loop filter  220 , the decoded picture buffer (DPB)  230 , the inter prediction unit  244  and the intra-prediction unit  254  are also referred to forming the “built-in decoder” of video encoder  20 . 
     Pictures &amp; Picture Partitioning (Pictures &amp; Blocks) 
     The encoder  20  may be configured to receive, e.g. via input  201 , a picture  17  (or picture data  17 ), e.g. picture of a sequence of pictures forming a video or video sequence. The received picture or picture data may also be a pre-processed picture  19  (or pre-processed picture data  19 ). For sake of simplicity the following description refers to the picture  17 . The picture  17  may also be referred to as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture). 
     A (digital) picture is or 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 encoder  20  may comprise a picture partitioning unit (not depicted in  FIG. 2 ) configured to partition the picture  17  into a plurality of (typically non-overlapping) picture blocks  203 . These blocks may also be referred to as root blocks, macro blocks (H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU) (H.265/HEVC and VVC). The picture partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks. 
     In further embodiments, the video encoder may be configured to receive directly a block  203  of the picture  17 , e.g. one, several or all blocks forming the picture  17 . The picture block  203  may also be referred to as current picture block or picture block to be coded. 
     Like the picture  17 , the picture block  203  again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values), although of smaller dimension than the picture  17 . In other words, the block  203  may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture  17 , or a luma or chroma array in case of a color picture) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture  17 ) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block  203  define the size of block  203 . Accordingly, a block may, for example, an M×N (M-column by N-row) array of samples, or an M×N array of transform coefficients. 
     Embodiments of the video encoder  20  as shown in  FIG. 2  may be configured to encode the picture  17  block by block, e.g. the encoding and prediction is performed per block  203 . 
     Embodiments of the video encoder  20  as shown in  FIG. 2  may be further configured to partition and/or encode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or encoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)). 
     Embodiments of the video encoder  20  as shown in  FIG. 2  may be further configured to partition and/or encode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or encoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks. 
     Residual Calculation 
     The residual calculation unit  204  may be configured to calculate a residual block  205  (also referred to as residual  205 ) based on the picture block  203  and a prediction block  265  (further details about the prediction block  265  are provided later), e.g. by subtracting sample values of the prediction block  265  from sample values of the picture block  203 , sample by sample (pixel by pixel) to obtain the residual block  205  in the sample domain. 
     Transform 
     The transform processing unit  206  may be configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST), on the sample values of the residual block  205  to obtain transform coefficients  207  in a transform domain. The transform coefficients  207  may also be referred to as transform residual coefficients and represent the residual block  205  in the transform domain. 
     The transform processing unit  206  may be configured to apply integer approximations of DCT/DST, such as the transforms specified for H.265/HEVC. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operations, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit  212  (and the corresponding inverse transform, e.g. by inverse transform processing unit  312  at video decoder  30 ) and corresponding scaling factors for the forward transform, e.g. by transform processing unit  206 , at an encoder  20  may be specified accordingly. 
     Embodiments of the video encoder  20  (respectively transform processing unit  206 ) may be configured to output transform parameters, e.g. a type of transform or transforms, e.g. directly or encoded or compressed via the entropy encoding unit  270 , so that, e.g., the video decoder  30  may receive and use the transform parameters for decoding. 
     Quantization 
     The quantization unit  208  may be configured to quantize the transform coefficients  207  to obtain quantized coefficients  209 , e.g. by applying scalar quantization or vector quantization. The quantized coefficients  209  may also be referred to as quantized transform coefficients  209  or quantized residual coefficients  209 . 
     The quantization process may reduce the bit depth associated with some or all of the transform coefficients  207 . For example, an n-bit transform coefficient may be rounded down to an m-bit Transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP). The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and a corresponding and/or the inverse dequantization, e.g. by inverse quantization unit  210 , may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes. 
     Embodiments of the video encoder  20  (respectively quantization unit  208 ) may be configured to output quantization parameters (QP), e.g. directly or encoded via the entropy encoding unit  270 , so that, e.g., the video decoder  30  may receive and apply the quantization parameters for decoding. 
     Inverse Quantization 
     The inverse quantization unit  210  is configured to apply the inverse quantization of the quantization unit  208  on the quantized coefficients to obtain dequantized coefficients  211 , e.g. by applying the inverse of the quantization scheme applied by the quantization unit  208  based on or using the same quantization step size as the quantization unit  208 . The dequantized coefficients  211  may also be referred to as dequantized residual coefficients  211  and correspond—although typically not identical to the transform coefficients due to the loss by quantization—to the transform coefficients  207 . 
     Inverse Transform 
     The inverse transform processing unit  212  is configured to apply the inverse transform of the transform applied by the transform processing unit  206 , e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) or other inverse transforms, to obtain a reconstructed residual block  213  (or corresponding dequantized coefficients  213 ) in the sample domain. The reconstructed residual block  213  may also be referred to as transform block  213 . 
     Reconstruction 
     The reconstruction unit  214  (e.g. adder or summer  214 ) is configured to add the transform block  213  (i.e. reconstructed residual block  213 ) to the prediction block  265  to obtain a reconstructed block  215  in the sample domain, e.g. by adding—sample by sample—the sample values of the reconstructed residual block  213  and the sample values of the prediction block  265 . 
     Filtering 
     The loop filter unit  220  (or short “loop filter”  220 ), is configured to filter the reconstructed block  215  to obtain a filtered block  221 , or in general, to filter reconstructed samples to obtain filtered sample values. The loop filter unit is, e.g., configured to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit  220  may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF), a noise suppression filter (NSF), or any combination thereof. In an example, the loop filter unit  220  may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit  220  is shown in  FIG. 2  as being an in loop filter, in other configurations, the loop filter unit  220  may be implemented as a post loop filter. The filtered block  221  may also be referred to as filtered reconstructed block  221 . 
     Embodiments of the video encoder  20  (respectively loop filter unit  220 ) may be configured to output loop filter parameters (such as SAO filter parameters or ALF filter parameters or LMCS parameters), e.g. directly or encoded via the entropy encoding unit  270 , so that, e.g., a decoder  30  may receive and apply the same loop filter parameters or respective loop filters for decoding. 
     Decoded Picture Buffer 
     The decoded picture buffer (DPB)  230  may be a memory that stores reference pictures, or in general reference picture data, for encoding video data by video encoder  20 . The DPB  230  may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB)  230  may be configured to store one or more filtered blocks  221 . The decoded picture buffer  230  may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks  221 , of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The decoded picture buffer (DPB)  230  may be also configured to store one or more unfiltered reconstructed blocks  215 , or in general unfiltered reconstructed samples, e.g. if the reconstructed block  215  is not filtered by loop filter unit  220 , or any other further processed version of the reconstructed blocks or samples. 
     Mode Selection (Partitioning &amp; Prediction) 
     The mode selection unit  260  comprises partitioning unit  262 , inter-prediction unit  244  and intra-prediction unit  254 , and is configured to receive or obtain original picture data, e.g. an original block  203  (current block  203  of the current picture  17 ), and reconstructed picture data, e.g. filtered and/or unfiltered reconstructed samples or blocks of the same (current) picture and/or from one or a plurality of previously decoded pictures, e.g. from decoded picture buffer  230  or other buffers (e.g. line buffer, not shown). The reconstructed picture data is used as reference picture data for prediction, e.g. inter-prediction or intra-prediction, to obtain a prediction block  265  or predictor  265 . 
     Mode selection unit  260  may be configured to determine or select a partitioning for a current block prediction mode (including no partitioning) and a prediction mode (e.g. an intra or inter prediction mode) and generate a corresponding prediction block  265 , which is used for the calculation of the residual block  205  and for the reconstruction of the reconstructed block  215 . 
     Embodiments of the mode selection unit  260  may be configured to select the partitioning and the prediction mode (e.g. from those supported by or available for mode selection unit  260 ), which provide the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage), or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage), or which considers or balances both. The mode selection unit  260  may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e. select the prediction mode which provides a minimum rate distortion. Terms like “best”, “minimum”, “optimum” etc. in this context do not necessarily refer to an overall “best”, “minimum”, “optimum”, etc. but may also refer to the fulfillment of a termination or selection criterion like a value exceeding or falling below a threshold or other constraints leading potentially to a “sub-optimum selection” but reducing complexity and processing time. 
     In other words, the partitioning unit  262  may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs), and the CTU  203  may be further partitioned into smaller block partitions or sub-blocks (which form again blocks), e.g. iteratively using quad-tree-partitioning (QT), binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g., the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block  203  and the prediction modes are applied to each of the block partitions or sub-blocks. 
     In the following the partitioning (e.g. by partitioning unit  260 ) and prediction processing (by inter-prediction unit  244  and intra-prediction unit  254 ) performed by an example video encoder  20  will be explained in more detail. 
     Partitioning 
     The partitioning unit  262  may be configured to partition a picture from a video sequence into a sequence of coding tree units (CTUs), and the partitioning unit  262  may partition (or split) a coding tree unit (CTU)  203  into smaller partitions, e.g. smaller blocks of square or rectangular size. For a picture that has three sample arrays, a CTU consists of an N×N block of luma samples together with two corresponding blocks of chroma samples. The maximum allowed size of the luma block in a CTU is specified to be 128×128 in the developing versatile video coding (VVC), but it 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 in  FIG. 6 . TT split is also forbidden when either width or height of a chroma coding block is larger than 32. The pipelining design will divide a picture into Virtual pipeline data units 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&#39; sizes. 
     In addition, it should be noted that, when a portion of a tree node block exceeds the bottom or right picture boundary, the tree node block is forced to be split until the all samples of every coded CU are located inside the picture boundaries. 
     As an example, the Intra Sub-Partitions (ISP) tool may divide luma intra-predicted blocks vertically or horizontally into 2 or 4 sub-partitions depending on the block size. 
     In one example, the mode selection unit  260  of video encoder  20  may be configured to perform any combination of the partitioning techniques described herein. 
     As described above, the video encoder  20  is configured to determine or select the best or an optimum prediction mode from a set of (e.g. pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes. 
     Intra-Prediction 
     The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in HEVC, or may comprise 67 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined for VVC. As an example, several conventional angular intra prediction modes are adaptively replaced with wide-angle intra prediction modes for the non-square blocks, e.g. as defined in VVC. As another example, to avoid division operations for DC prediction, only the longer side is used to compute the average for non-square blocks. And, the results of intra prediction of planar mode may be further modified by a position dependent intra prediction combination (PDPC) method. 
     The intra-prediction unit  254  is configured to use reconstructed samples of neighboring blocks of the same current picture to generate an intra-prediction block  265  according to an intra-prediction mode of the set of intra-prediction modes. 
     The intra prediction unit  254  (or in general the mode selection unit  260 ) is further configured to output intra-prediction parameters (or in general information indicative of the selected intra prediction mode for the block) to the entropy encoding unit  270  in form of syntax elements  266  for inclusion into the encoded picture data  21 , so that, e.g., the video decoder  30  may receive and use the prediction parameters for decoding. 
     Inter-Prediction (Comprising Inter-Layer Prediction) 
     The set of (or possible) inter-prediction modes depends on the available reference pictures (i.e. previous at least partially decoded pictures, e.g. stored in DBP  230 ) and other inter-prediction parameters, e.g. whether the whole reference picture or only a part, e.g. a search window area around the area of the current block, of the reference picture is used for searching for a best matching reference block, and/or e.g. whether pixel interpolation is applied, e.g. half/semi-pel, quarter-pel and/or 1/16 pel interpolation, or not. 
     Additional to the above prediction modes, skip mode, direct mode and/or other inter prediction mode may be applied. 
     For example, Extended merge prediction, the merge candidate list of such mode is constructed by including the following five types of candidates in order: Spatial MVP from spatial neighbor CUs, Temporal MVP from collocated CUs, History-based MVP from an FIFO table, Pairwise average MVP and Zero MVs. And a bilateral-matching based decoder side motion vector refinement (DMVR) may be applied to increase the accuracy of the MVs of the merge mode. Merge mode with MVD (MMVD), which comes from merge mode with motion vector differences. A MMVD flag is signaled right after sending a skip flag and merge flag to specify whether MMVD mode is used for a CU. And a CU-level adaptive motion vector resolution (AMVR) scheme may be applied. AMVR allows MVD of the CU to be coded in different precision. Dependent on the prediction mode for the current CU, the MVDs of the current CU 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 unit  244  may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in  FIG. 2 ). The motion estimation unit may be configured to receive or obtain the picture block  203  (current picture block  203  of the current picture  17 ) and a decoded picture  231 , or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures  231 , for motion estimation. E.g. a video sequence may comprise the current picture and the previously decoded pictures  231 , or in other words, the current picture and the previously decoded pictures  231  may be part of or form a sequence of pictures forming a video sequence. 
     The encoder  20  may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit. This offset is also called motion vector (MV). 
     The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block  265 . Motion compensation, performed by the motion compensation unit, may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists. 
     The motion compensation unit may also generate syntax elements associated with the blocks and video slices for use by video decoder  30  in decoding the picture blocks of the video slice. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be generated or used. 
     Entropy Coding 
     The entropy encoding unit  270  is configured to apply, for example, an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, a binarization, a context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) or bypass (no compression) on the quantized coefficients  209 , inter prediction parameters, intra prediction parameters, loop filter parameters and/or other syntax elements to obtain encoded picture data  21  which can be output via the output  272 , e.g. in the form of an encoded bitstream  21 , so that, e.g., the video decoder  30  may receive and use the parameters for decoding. The encoded bitstream  21  may be transmitted to video decoder  30 , or stored in a memory for later transmission or retrieval by video decoder  30 . 
     Other structural variations of the video encoder  20  can be used to encode the video stream. For example, a non-transform based encoder  20  can quantize the residual signal directly without the transform processing unit  206  for certain blocks or frames. In another implementation, an encoder  20  can have the quantization unit  208  and the inverse quantization unit  210  combined into a single unit. 
     Decoder and Decoding Method 
       FIG. 3  shows an example of a video decoder  30  that is configured to implement the techniques of this present application. The video decoder  30  is configured to receive encoded picture data  21  (e.g. encoded bitstream  21 ), e.g. encoded by encoder  20 , to obtain a decoded picture  331 . The encoded picture data or bitstream comprises information for decoding the encoded picture data, e.g. data that represents picture blocks of an encoded video slice (and/or tile groups or tiles) and associated syntax elements. 
     In the example of  FIG. 3 , the decoder  30  comprises an entropy decoding unit  304 , an inverse quantization unit  310 , an inverse transform processing unit  312 , a reconstruction unit  314  (e.g. a summer  314 ), a loop filter  320 , a decoded picture buffer (DBP)  330 , a mode application unit  360 , an inter prediction unit  344  and an intra prediction unit  354 . Inter prediction unit  344  may be or include a motion compensation unit. Video decoder  30  may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder  100  from  FIG. 2 . 
     As explained with regard to the encoder  20 , the inverse quantization unit  210 , the inverse transform processing unit  212 , the reconstruction unit  214 , the loop filter  220 , the decoded picture buffer (DPB)  230 , the inter prediction unit  344  and the intra prediction unit  354  are also referred to as forming the “built-in decoder” of video encoder  20 . Accordingly, the inverse quantization unit  310  may be identical in function to the inverse quantization unit  110 , the inverse transform processing unit  312  may be identical in function to the inverse transform processing unit  212 , the reconstruction unit  314  may be identical in function to reconstruction unit  214 , the loop filter  320  may be identical in function to the loop filter  220 , and the decoded picture buffer  330  may be identical in function to the decoded picture buffer  230 . Therefore, the explanations provided for the respective units and functions of the video  20  encoder apply correspondingly to the respective units and functions of the video decoder  30 . 
     Entropy Decoding 
     The entropy decoding unit  304  is configured to parse the bitstream  21  (or in general encoded picture data  21 ) and perform, for example, entropy decoding to the encoded picture data  21  to obtain, e.g., quantized coefficients  309  and/or decoded coding parameters (not shown in  FIG. 3 ), e.g. any or all of inter prediction parameters (e.g. reference picture index and motion vector), intra prediction parameter (e.g. intra prediction mode or index), transform parameters, quantization parameters, loop filter parameters, and/or other syntax elements. Entropy decoding unit  304  maybe configured to apply the decoding algorithms or schemes corresponding to the encoding schemes as described with regard to the entropy encoding unit  270  of the encoder  20 . Entropy decoding unit  304  may be further configured to provide inter prediction parameters, intra prediction parameter and/or other syntax elements to the mode application unit  360  and other parameters to other units of the decoder  30 . Video decoder  30  may receive the syntax elements at the video slice level and/or the video block level. In addition or as an alternative to slices and respective syntax elements, tile groups and/or tiles and respective syntax elements may be received and/or used. 
     Inverse Quantization 
     The inverse quantization unit  310  may be configured to receive quantization parameters (QP) (or in general information related to the inverse quantization) and quantized coefficients from the encoded picture data  21  (e.g. by parsing and/or decoding, e.g. by entropy decoding unit  304 ) and to apply based on the quantization parameters an inverse quantization on the decoded quantized coefficients  309  to obtain dequantized coefficients  311 , which may also be referred to as transform coefficients  311 . The inverse quantization process may include use of a quantization parameter determined by video encoder  20  for each video block in the video slice (or tile or tile group) to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied. 
     Inverse Transform 
     Inverse transform processing unit  312  may be configured to receive dequantized coefficients  311 , also referred to as transform coefficients  311 , and to apply a transform to the dequantized coefficients  311  in order to obtain reconstructed residual blocks  213  in the sample domain. The reconstructed residual blocks  213  may also be referred to as transform blocks  313 . The transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit  312  may be further configured to receive transform parameters or corresponding information from the encoded picture data  21  (e.g. by parsing and/or decoding, e.g. by entropy decoding unit  304 ) to determine the transform to be applied to the dequantized coefficients  311 . 
     Reconstruction 
     The reconstruction unit  314  (e.g. adder or summer  314 ) may be configured to add the reconstructed residual block  313 , to the prediction block  365  to obtain a reconstructed block  315  in the sample domain, e.g. by adding the sample values of the reconstructed residual block  313  and the sample values of the prediction block  365 . 
     Filtering 
     The loop filter unit  320  (either in the coding loop or after the coding loop) is configured to filter the reconstructed block  315  to obtain a filtered block  321 , e.g. to smooth pixel transitions, or otherwise improve the video quality. The loop filter unit  320  may comprise one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or one or more other filters, e.g. an adaptive loop filter (ALF), a noise suppression filter (NSF), or any combination thereof. In an example, the loop filter unit  220  may comprise a de-blocking filter, a SAO filter and an ALF filter. The order of the filtering process may be the deblocking filter, SAO and ALF. In another example, a process called the luma mapping with chroma scaling (LMCS) (namely, the adaptive in-loop reshaper) is added. This process is performed before deblocking. In another example, the deblocking filter process may be also applied to internal sub-block edges, e.g. affine sub-blocks edges, ATMVP sub-blocks edges, sub-block transform (SBT) edges and intra sub-partition (ISP) edges. Although the loop filter unit  320  is shown in  FIG. 3  as being an in loop filter, in other configurations, the loop filter unit  320  may be implemented as a post loop filter. 
     Decoded Picture Buffer 
     The decoded video blocks  321  of a picture are then stored in decoded picture buffer  330 , which stores the decoded pictures  331  as reference pictures for subsequent motion compensation for other pictures and/or for output respectively display. 
     The decoder  30  is configured to output the decoded picture  311 , e.g. via output  312 , for presentation or viewing to a user. 
     Prediction 
     The inter prediction unit  344  may be identical to the inter prediction unit  244  (in particular to the motion compensation unit) and the intra prediction unit  354  may be identical to the inter prediction unit  254  in function, and performs split or partitioning decisions and prediction based on the partitioning and/or prediction parameters or respective information received from the encoded picture data  21  (e.g. by parsing and/or decoding, e.g. by entropy decoding unit  304 ). Mode application unit  360  may be configured to perform the prediction (intra or inter prediction) per block based on reconstructed pictures, blocks or respective samples (filtered or unfiltered) to obtain the prediction block  365 . 
     When the video slice is coded as an intra coded (I) slice, intra prediction unit  354  of mode application unit  360  is configured to generate prediction block  365  for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current picture. When the video picture is coded as an inter coded (i.e., B, or P) slice, inter prediction unit  344  (e.g. motion compensation unit) of mode application unit  360  is configured to produce prediction blocks  365  for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit  304 . For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder  30  may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB  330 . The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and /or tiles. 
     Mode application unit  360  is configured to determine the prediction information for a video block of the current video slice by parsing the motion vectors or related information and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the mode application unit  360  uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice. The same or similar may be applied for or by embodiments using tile groups (e.g. video tile groups) and/or tiles (e.g. video tiles) in addition or alternatively to slices (e.g. video slices), e.g. a video may be coded using I, P or B tile groups and/or tiles. 
     Embodiments of the video decoder  30  as shown in  FIG. 3  may be configured to partition and/or decode the picture by using slices (also referred to as video slices), wherein a picture may be partitioned into or decoded using one or more slices (typically non-overlapping), and each slice may comprise one or more blocks (e.g. CTUs) or one or more groups of blocks (e.g. tiles (H.265/HEVC and VVC) or bricks (VVC)). 
     Embodiments of the video decoder  30  as shown in  FIG. 3  may be configured to partition and/or decode the picture by using slices/tile groups (also referred to as video tile groups) and/or tiles (also referred to as video tiles), wherein a picture may be partitioned into or decoded using one or more slices/tile groups (typically non-overlapping), and each slice/tile group may comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles, wherein each tile, e.g. may be of rectangular shape and may comprise one or more blocks (e.g. CTUs), e.g. complete or fractional blocks. 
     Other variations of the video decoder  30  can be used to decode the encoded picture data  21 . For example, the decoder  30  can produce the output video stream without the loop filtering unit  320 . For example, a non-transform based decoder  30  can inverse-quantize the residual signal directly without the inverse-transform processing unit  312  for certain blocks or frames. In another implementation, the video decoder  30  can have the inverse-quantization unit  310  and the inverse-transform processing unit  312  combined into a single unit. 
     It should be understood that, in the encoder  20  and the decoder  30 , a processing result of a current step may be further processed and then output to the next step. For example, after interpolation filtering, motion vector derivation or loop filtering, a further operation, such as Clip or shift, may be performed on the processing result of the interpolation filtering, motion vector derivation or loop filtering. 
     It should be noted that further operations may be applied to the derived motion vectors of current block (including but not limit to control point motion vectors of affine mode, sub-block motion vectors in affine, planar, ATMVP modes, temporal motion vectors, and so on). For example, the value of motion vector is constrained to a predefined range according to its representing bit. If the representing bit of motion vector is bitDepth, then the range is −2{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, two methods are provided for constraining the motion vector according to the bitDepth. 
       FIG. 4  is a schematic diagram of a video coding device  400  according to an embodiment of the disclosure. The video coding device  400  is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device  400  may be a decoder such as video decoder  30  of  FIG. 1A  or an encoder such as video encoder  20  of  FIG. 1A . 
     The video coding device  400  comprises ingress ports  410  (or input ports  410 ) and receiver units (Rx)  420  for receiving data; a processor, logic unit, or central processing unit (CPU)  430  to process the data; transmitter units (Tx)  440  and egress ports  450  (or output ports  450 ) for transmitting the data; and a memory  460  for storing the data. The video coding device  400  may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports  410 , the receiver units  420 , the transmitter units  440 , and the egress ports  450  for egress or ingress of optical or electrical signals. 
     The processor  430  is implemented by hardware and software. The processor  430  may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGAs, ASICs, and DSPs. The processor  430  is in communication with the ingress ports  410 , receiver units  420 , transmitter units  440 , egress ports  450 , and memory  460 . The processor  430  comprises a coding module  470 . The coding module  470  implements the disclosed embodiments described above. For instance, the coding module  470  implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module  470  therefore provides a substantial improvement to the functionality of the video coding device  400  and effects a transformation of the video coding device  400  to a different state. Alternatively, the coding module  470  is implemented as instructions stored in the memory  460  and executed by the processor  430 . 
     The memory  460  may comprise one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory  460  may be, for example, volatile and/or non-volatile and may be a read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM). 
       FIG. 5  is a simplified block diagram of an apparatus  500  that may be used as either or both of the source device  12  and the destination device  14  from  FIG. 1  according to an exemplary embodiment. 
     A processor  502  in the apparatus  500  can be a central processing unit. Alternatively, the processor  502  can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor  502 , advantages in speed and efficiency can be achieved using more than one processor. 
     A memory  504  in the apparatus  500  can be a read only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device can be used as the memory  504 . The memory  504  can include code and data  506  that is accessed by the processor  502  using a bus  512 . The memory  504  can further include an operating system  508  and application programs  510 , the application programs  510  including at least one program that permits the processor  502  to perform the methods described here. For example, the application programs  510  can include applications 1 through N, which further include a video coding application that performs the methods described here. 
     The apparatus  500  can also include one or more output devices, such as a display  518 . The display  518  may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display  518  can be coupled to the processor  502  via the bus  512 . 
     Although depicted here as a single bus, the bus  512  of the apparatus  500  can be composed of multiple buses. Further, the secondary storage  514  can be directly coupled to the other components of the apparatus  500  or 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 apparatus  500  can thus be implemented in a wide variety of configurations. 
     Scalable Coding 
     Scalable coding including quality scalable (PSNR scalable), spatial scalable, et.al. For example, as  FIG. 6  shown, a sequence can be down-sampled to a low spatial resolution version. Both the low spatial resolution version and the original spatial resolution (high spatial resolution) version will be encoded. And generally, the low spatial resolution will be coded firstly, and it will be used for reference for the later coded high spatial resolution. 
     To describe the information of the layers (number, dependency, outputting), there is a VPS (Video Parameter Set) defined as following: 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 video_parameter_set_rbsp( ) { 
                   
               
               
                 ... 
               
               
                  vps_max_layers_minus1 
                 u(6) 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) 
               
               
                   vps_all_independent_layers_flag 
                 u(1) 
               
               
                  for( i = 0; i &lt;= vps_max_layers_minus1; i++ ) { 
               
               
                   vps_layer_id[ i ] 
                 u(6) 
               
               
                   if( i &gt; 0 &amp;&amp; !vps_all_independent_layers_flag ) { 
               
               
                    vps_independent_layer_flag[ i ] 
                 u(1) 
               
               
                    if( !vps_independent_layer_flag[ i ] ) 
               
               
                     for( j = 0; j &lt; i; j++ ) 
               
               
                      vps_direct_dependency_flag[ i ][ j ] 
                 u(1) 
               
               
                   } 
               
               
                  } 
               
               
                 ... 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     vps_max_layers_minus1 plus 1 specifies the maximum allowed number of layers in each CVS referring to the VPS. 
     vps_all_independent_layers_flag equal to 1 specifies that all layers in the CVS are independently coded without using inter-layer prediction. vps_all_independent_layers_flag equal to 0 specifies that one or more of the layers in the CVS may use inter-layer prediction. When not present, the value of vps_all_independent_layers_flag is inferred to be equal to 1. When vps_all_independent_layers_flag is equal to 1, the value of vps_independent_layer_flag[ i ] is inferred to be equal to 1. When vps_all_independent_layers_flag is equal to 0, the value of vps_independent_layer_flag[ 0 ] is inferred to be equal to 1. 
     vps_layer_id[ i ] specifies the nuh_layer_id value of the i-th layer. For any two non-negative integer values of m and n, when m is less than n, the value of vps_layer_id[ m ] shall be less than vps_layer_id[ n ]. 
     vps_independent_layer_flag[ i ] equal to 1 specifies that the layer with index i does not use inter-layer prediction. vps_independent_layer_flag[ i ] equal to 0 specifies that the layer with index i may use inter-layer prediction and vps_layer_dependency_flag[ i ] is present in VPS. 
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, it is inferred to be equal to 0. 
     The variable DirectDependentLayerIdx[ i ][ j ], specifying the j-th direct dependent layer of the i-th layer, is derived as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 for( i = 1; i &lt; vps_max_layers_minus1; i− − ) 
                   
               
               
                   
                  if( !vps_independent_layer_flag[ i ] ) 
               
               
                   
                   for( j = i, k = 0; j &gt;= 0; j− − ) 
                 (7-2) 
               
               
                   
                    if( vps_direct_dependency_flag[ i ][ j ] ) 
               
               
                   
                     DirectDependentLayerIdx[ i ][ k++ ] = j 
               
               
                   
                   
               
            
           
         
       
     
     The variable GeneralLayerIdx[ i ], specifying the layer index of the layer with nuh_layer_id equal to vps_layer_id[ i ], is derived as follows: 
       for( i= 0;  i&lt;= vps_max_layers_minus1;  i++ )   (7-3)
 
       GeneralLayerIdx[ vps_layer_id[ i ] ] 32  i
 
     simple description as following: 
     vps_max_layers_minus1 add 1 means the number of the layers 
     vps_all_independent_layers_flag indicate whether all the layers are coded independently 
     vps_layer_id[ i ] indidate the layer ID of the i-th layer. 
     vps_independent_layer_flag[ i ] indidate whether the i-th layer is coded independently. 
     vps_direct_dependency_flag[ i ][ j ] indicate whether the j-th layer is used for refefecne for the i-th layer. 
     DPB Management and Reference Picture Marking. 
     To manage those reference pictures in the decoding process, the decoded pictures are needed to keep in the decoding picture buffer (DPB), for reference usage for the follow picture decoding. To indicate those pictures, their picture order count (POC) information is need to signal in the slice header directly or in directly. Generally, there are two reference picture list, list0 and list1. And, the reference picture index also needed to be included to signal the picture in the list. For uni-prediction, reference pictures are fetched from one reference picture list, for bi-prediction, reference pictures are fetched from two reference picture lists. 
     All the reference pictures are stored in the DPB. All the pictures in the DPB are marked as “used for long-term reference”, “used for short-term reference”, or “unused for reference”, and only one for the three status. Once a picture is marked as “unused for reference”, it will not be used for reference anymore. If it also not needed storing for output, then it can be removed from the DPB. The status of the reference pictures can be signaled in the slice header, or can be derived from the slice header information. 
     A new reference picture management method was proposed, called RPL (reference picture list) method. RPL will proposed whole reference picture set or sets for current coding picture, the reference picture in the reference picture set is used for current picture or future (later, or following) picture decoding. So, RPL reflect the pictures info in the DPB, even a reference picture is not used for reference for current picture, if it will be used for reference for a following picture, it is needed to store in the RPL. 
     After a picture is reconstructed, it will be stored in the DPB, and marked as “used for short-term reference” by default. The DPB management operation will start after parsing the RPL information in the slice header. 
     Reference Picture List Construction. 
     The reference picture information can be signaled via the slice header. Also, there may be some RPL candidates in the Sequence parameters set (SPS), in this case, the slice header may include a RPL index to get the needed RPL information, without signaling a whole RPL syntax structure. Or, a whole RPL syntax structure can be signaled in the slice header. 
     Introduction of RPL Method. 
     To saving the cost bits of RPL signaling, there may be some RPL candidates in the SPS. A picture can use a RPL index (ref_pic_list_idx[ i ]) to get its RPL information from the SPS. RPL candidates are signaled as following: 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                 ... 
               
               
                  rpl1_same_as_rpl0_flag 
                 u(1) 
               
               
                  for( i = 0; i &lt; !rpl1_same_as_rpl0_flag ? 2 : 1; i++ ) { 
               
               
                   num_ref_pic_lists_in_sps[ i ] 
                 ue(v) 
               
               
                   for( j = 0; j &lt; num_ref_pic_lists_in_sps[ i ]; j++) 
               
               
                    ref_pic_list_struct( i, j ) 
               
               
                  } 
               
               
                 ... 
               
               
                   
               
            
           
         
       
     
     The semantics as follow: 
     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) 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) is inferred to be equal to the value of corresponding syntax element in ref_pic_list_struct(0, rplsIdx) 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) 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. 
     Beside get the RPL information based on the RPL index from SPS, the RPL information can be signaled in the slice header. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 slice_header( ) { 
                   
               
               
                 ... 
               
               
                  if( ( nal_unit_type != IDR_W_RADL &amp;&amp; nal_unit_type != 
               
               
                 IDR_N_LP ) || 
               
               
                    sps_idr_rpl_present_flag ) { 
               
               
                   for( i = 0; i &lt; 2; i++ ) { 
               
               
                    if( num_ref_pic_lists_in_sps[ i ] &gt; 0 
               
               
                 &amp;&amp; !pps_ref_pic_list_sps_idc[ i ] &amp;&amp; 
               
               
                         ( i = = 0 || ( i = = 1 &amp;&amp; 
               
               
                 rpl1_idx_present_flag ) ) ) 
               
               
                     ref_pic_list_sps _flag[ i ] 
                 u(1) 
               
               
                    if( ref_pic_list_sps_flag[ i ] ) { 
               
               
                     if( num_ref_pic_lists_in_sps[ i ] &gt; 1 &amp;&amp; 
               
               
                        ( i = = 0 || ( i = = 1 &amp;&amp; 
               
               
                 rpl1_idx_present_flag ) ) ) 
               
               
                       ref_pic_list_idx[ i ] 
                 u(v) 
               
               
                    } else 
               
               
                     ref_pic_list_struct( i, num_ref_pic_lists_in_sps[ i ] ) 
               
               
                    for( j = 0; j &lt; NumLtrpEntries[ i ][ RplsIdx[ i ] ]; j++ ) { 
               
               
                     if( ltrp_in_slice_header_flag[ i ][ RplsIdx[ i ] ] ) 
               
               
                      slice_poc_lsb_lt[ i ][ j ] 
                 u(v) 
               
               
                     delta_poc_msb_present_flag[ i ][ j ] 
                 u(1) 
               
               
                     if( delta_poc_msb_present_flag[ i ][ j ] ) 
               
               
                      delta_poc_msb_cycle_lt[ i ][ j ] 
                 ue(v) 
               
               
                    } 
               
               
                   } 
               
               
                 ... 
               
               
                   
               
            
           
         
       
     
     ref_pic_list_sps_flag[ i ] equal to 1 specifies that reference picture list i of the current slice is derived based on one of the ref_pic_list_struct(listIdx, rplsIdx) syntax structures with listIdx equal to i in the SPS. ref_pic_list_sps_flag[ i ] equal to 0 specifies that reference picture list i of the current slice is derived based on the ref_pic_list_struct(listIdx, rplsIdx) syntax structure with listIdx equal to i that is directly included in the slice headers of the current picture. 
     When ref_pic_list_sps_flag[ i ] is not present, the following applies:
     If num_ref_pic_lists_in_sps[ i ] is equal to 0, the value of ref_pic_list_sps_flag[ i ] is inferred to be equal to 0.   Otherwise (num_ref_pic_lists_in_sps[ i ] is greater than 0), if rpl1 idx_present_flag is equal to 0, the value of ref_pic_list_sps_flag[ 1 ] is inferred to be equal to ref_pic_list_sps_flag[ 0 ].   Otherwise, the value of ref_pic_list_sps_flag[ i ] is inferred to be equal to pps_ref_pic_list_sps_idc[ i ]−1.   

     ref_pic_list_idx[ i ] specifies the index, into the list of the ref_pic_list_struct(listIdx, rplsIdx) syntax structures with listIdx equal to i included in the SPS, of the ref_pic_list_struct(listIdx, rplsIdx) syntax structure with listIdx equal to i that is used for derivation of reference picture list i of the current picture. The syntax element ref_pic_list_idx[ i ] is represented by Ceil(Log2(num_ref_pic_lists_in_sps[ i ])) bits. When not present, the value of ref_pic_list_idx[ i ] is inferred to be equal to 0. The value of ref_pic_list_idx[ i ] shall be in the range of 0 to num_ref_pic_lists_in_sps[ i ]−1, inclusive. When ref_pic_list_sps_flag[ i ] is equal to 1 and num_ref_pic_lists_in_sps[ i ] is equal to 1, the value of ref_pic_list_idx[ i ] is inferred to be equal to 0. When ref_pic_list_sps_flag[ i ] is equal to 1 and rpl1_idx_present_flag is equal to 0, the value of ref_pic_list_idx[ 1 ] is inferred to be equal to ref_pic_list_idx[ 0 ]. 
     The variable RplsIdx[ i ] is derived as follows: 
       RplsIdx[ i ]=ref_pic_list_sps_flag[ i ]? ref_pic_list_idx[ i ]:num_ref_pic_lists_in_sps[ i ]  (7-95)
 
     slice_poc_lsb_lt[ i ][ j ] specifies the value of the picture order count modulo MaxPicOrderCntLsb of the j-th LTRP entry in the i-th reference picture list. The length of the slice_poc_lsb_lt[ i ][ j ] syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. 
     The variable PocLsbLt[ i ][ j ] is derived as follows: 
       PocLsbLt[ i ][ j ]=ltrp_in_slice_header_flag[ i ][ RplsIdx[ i ] ]?slice_poc_lsb lt[ i ][ j ]: rpls_poc_lsb_lt[ listIdx ][ RplsIdx[ i ]][ j ]  (7-96)
 
     delta_poc_msb_present_flag[ i ][ j ] equal to 1 specifies that delta_poc_msb_cycle_lt[ i ][ j ] is present. delta_poc_msb_present_flag[ i ][ j ] equal to 0 specifies that delta_poc_msb_cycle_lt[ i ][ j ] is not present. 
     Let prevTid0Pic be the previous picture in decoding order that has nuh_layer_id the same as the current picture, has TemporalId equal to 0, and is not a RASL or RADL picture. Let setOfPrevPocVals be a set consisting of the following:
     the PicOrderCntVal of prevTid0Pic,   the PicOrderCntVal of each picture that is referred to by entries in RefPicList[ 0 ] or RefPicList[ 1 ] of prevTid0Pic and has nuh_layer_id the same as the current picture,   the PicOrderCntVal of each picture that follows prevTid0Pic in decoding order, has nuh_layer_id the same as the current picture, and precedes the current picture in decoding order.   

     When there is more than one value in setOfPrevPocVals for which the value modulo MaxPicOrderCntLsb is equal to PocLsbLt[ i ][ j ], the value of delta_poc_msb_present_flag[ i ][ j ] shall be equal to 1. 
     delta_poc_msb_cycle_lt[ i ][ j ] specifies the value of the variable FullPocLt[ i ][ j ] as follows: 
       if(j==0)   (7-97)
 
       DeltaPocMsbCycleLt[ i ][ j ]=delta_poc_msb_cycle_lt[ i ][ j ] 
       else 
       DeltaPocMsbCycleLt[  i  ][  j  ]=delta_poc_msb_cycle_lt[  i  ][  j  ]+DeltaPocMsbCycleLt[  i  ][  j− 1 ] 
       FullPocLt[  i  ][  j  ]=PicOrderCntVal−DeltaPocMsbCycleLt[  i  ][  j  ]*MaxPicOrderCntLsb−(PicOrderCntVal &amp; (MaxPicOrderCntLsb−1))+PocLsbLt[  i  ][  j  ]
 
     The value of delta_poc_msb_cycle_lt[ i ][ j ] shall be in the range of 0 to 2 (32−log2_max_pic_order_cnt_lsb_minus4−4) , inclusive. When not present, the value of delta_poc_msb_cycle_lt[ i ][ j ] is inferred to be equal to 0. 
     The syntax structure of RPL as following: 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 ref_pic_list_struct( listIdx, rplsIdx ) { 
                   
               
               
                  num_ref_entries[ listIdx ][ rplsIdx ] 
                 ue(v) 
               
               
                  if( long_term_ref_pics_flag ) 
               
               
                   ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] 
                 u(1) 
               
               
                  for( i = 0, j = 0; i &lt; num_ref_entries[ listIdx ][ rplsIdx ]; i++) { 
               
               
                   if( inter_layer_ref_pics_present_flag ) 
               
               
                    inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                   if( !inter_layer_ref_pics_flag[ listIdx ][ rplsIdx ][ i ] ) { 
               
               
                    if( long_term_ref_pics_flag ) 
               
               
                     st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                    if( st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] ) { 
               
               
                     abs_delta_poc_st[ listIdx ][ rplsIdx ][ i ] 
                 ue(v) 
               
               
                     if( AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ] &gt; 0 ) 
               
               
                      strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                    } else if( !ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] ) 
               
               
                     rpls_poc_lsb_lt[ listIdx ][ rplsIdx ][ j++ ] 
                 u(v) 
               
               
                   } else 
               
               
                    ilrp_idc[ listIdx ][ rplsIdx ][ i ] 
                 ue(v) 
               
               
                  } 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     num_ref_entries[ listIdx ][ rplsIdx ] specifies the number of entries in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure. The value of num_ref_entries[ listIdx ][ rplsIdx ] shall be in the range of 0 to sps_max_dec_pic_buffering_minus1+14, inclusive. 
     ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] equal to 0 specifies that the POC LSBs of the LTRP entries in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure are present in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure. ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] equal to 1 specifies that the POC LSBs of the LTRP entries in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure are not present in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure. 
     inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure is an ILRP entry. inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure is not an ILRP entry. When not present, the value of inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] is inferred to be equal to 0. 
     st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure is an STRP entry. st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure is an LTRP entry. When inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] is equal to 0 and st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] is not present, the value of st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] is inferred to be equal to 1. 
     The variable NumLtrpEntries[ listIdx ][ rplsIdx ] is derived as follows: 
       for( i= 0, NumLtrpEntries[ listIdx ][ rplsIdx ]=0;  i &lt;num_ref_entries[ listIdx ][ rplsIdx ];  i++ ) 
       if(!inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] &amp;&amp; !st_ref_pic_flag[ listIdx ][ rplsI dx ][ i])   (7-120)
 
       NumLtrpEntries[ listIdx ][ rplsIdx ]++ 
     abs_delta_poc_st[ listIdx ][ rplsIdx ][ i ] specifies the value of the variable AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ] as follows: 
       if(sps_weighted_pred_flag || sps_weighted_bipred_flag) AbsDeltaPocSt[ listIdx ][ rplsIdx ][  i  ]=abs_delta_poc_st[ listIdx ][ rplsIdx ][  i  ]  (7-121)
 
       else 
       AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ]=abs_delta_poc_st[ listIdx ][ rplsIdx ][ i ]+1 
     The value of abs_delta_poc_st[ listIdx ][ rplsIdx ][ i ] shall be in the range of 0 to 2 15 −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) has a value greater than or equal to 0. strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] equal to 0 specifies that the i-th entry in the syntax structure ref_pic_list_struct(listIdx, rplsIdx) has a value less than 0. When not present, the value of strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] is inferred to be equal to 1. 
     The list DeltaPocValSt[ listIdx ][ rplsIdx ] is derived as follows: 
       for(i=0; i&lt;num_ref_entries[ listIdx ][ rplsIdx ];  i ++) 
       if(!inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] &amp;&amp; st_ref_pic_flag[ listIdx ][ rplsI dx ][ i])   (7-122)
 
       DeltaPocValSt[ listIdx ][ rplsIdx ][ i ]=(strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i]) ? 
       AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ]: 0−AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ]
 
     rpls_poc_lsb_lt[ listIdx ][ rplsIdx ][ i ] specifies the value of the picture order count modulo MaxPicOrderCntLsb of the picture referred to by the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure. The length of the rpls_poc_lsb_lt[ listIdx ][ rplsIdx ][ i ] syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. 
     Some general description of RPL structure. 
     For each list, there is a RPL structure. First, num_ref_entries[ listIdx ][ rplsIdx ] is signaled to indicate the number of reference pictures in the list. ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] is used indicated whether LSB (Least Significant Bit) information is signaled in the slice header. If current reference picture is not an inter-layer reference picture, then a st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] to indicat whether it is a long-term reference picture. If it is a short-term reference picture, then the POC information(abs_delta_poc_st and strp_entry_sign_flag) is signaled. if ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] is zero, then rpls_poc_lsb_lt[ listIdx ][ rplsIdx ][ j++ ] is used to derived the LSB information of current reference picture. The MSB (Most Significant Bit) can be derived directly, or derived based on the information (delta_poc_msb_present_flag[ i ][ j ] and delta_poc_msb_cycle_lt[ i ][ j ]) in the slice header. 
     Decoding Process for Reference Picture Lists Construction 
     This process is invoked at the beginning of the decoding process for each slice of a non-IDR picture. 
     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 and 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 clause 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 ] may 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 ] may 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( i = 0; i &lt; 2; i++ ) { 
               
               
                  for( j = 0, k = 0, pocBase = PicOrderCntVal; j &lt; num_ref_entries[ i ][ RplsIdx[ i ] ]; 
               
               
                 j++) { 
               
               
                   if( !inter_layer_ref_pic_flag[ i ][ RplsIdx[ i ] ][ j ] ) { 
               
               
                    if( st_ref_pic_flag[ i ][ RplsIdx[ i ] ][ j ] ) { 
               
               
                     RefPicPocList[ i ][ j ] = pocBase − DeltaPocValSt[ i ][ RplsIdx[ i ] ][ j ] 
               
               
                     if( there is a reference picture picA in the DPB with the same nuh_layer_id 
               
               
                 as the current picture 
               
            
           
           
               
               
            
               
                   
                   and PicOrderCntVal equal to RefPicPocList[ i ][ j ] ) 
               
               
                   
                 RefPicList[ i ][ j ] = picA 
               
            
           
           
               
            
               
                     else 
               
            
           
           
               
               
            
               
                   
                 RefPicList[ i ][ j ] = “no reference 
               
               
                 picture” 
                 (8-5) 
               
            
           
           
               
            
               
                     pocBase = RefPicPocList[ i ][ j ] 
               
               
                    } else { 
               
               
                     if( !delta_poc_msb_cycle_lt[ i ][ k ] ) { 
               
            
           
           
               
               
            
               
                   
                 if( there is a reference picA in the DPB with the same nuh_layer_id as 
               
            
           
           
               
            
               
                 the current picture and 
               
            
           
           
               
               
            
               
                   
                    PicOrderCntVal &amp; ( MaxPicOrderCntLsb − 1 ) equal to 
               
            
           
           
               
            
               
                 PocLsbLt[ i ][ k ] ) 
               
            
           
           
               
               
            
               
                   
                  RefPicList[ i ][ j ] = picA 
               
               
                   
                 else 
               
               
                   
                  RefPicList[ i ][ j ] = “no reference picture” 
               
               
                   
                 RefPicLtPocList[ i ][ j ] = PocLsbLt[ i ][ k ] 
               
            
           
           
               
            
               
                     } else { 
               
            
           
           
               
               
            
               
                   
                 if( there is a reference picA in the DPB with the same nuh_layer_id as 
               
            
           
           
               
            
               
                 the current picture and 
               
            
           
           
               
               
            
               
                   
                    PicOrderCntVal equal to FullPocLt[ i ][ k ] ) 
               
               
                   
                  RefPicList[ i ][ j ] = picA 
               
               
                   
                 else 
               
               
                   
                  RefPicList[ i ][ j ] = “no reference picture” 
               
               
                   
                 RefPicLtPocList[ i ][ j ] = FullPocLt[ i ][ k ] 
               
            
           
           
               
            
               
                     } 
               
               
                     k++ 
               
               
                    } 
               
               
                   } else { 
               
               
                    layerIdx = 
               
               
                 DirectDependentLayerIdx[ GeneralLayerIdx[ nuh_layer_id ] ][ ilrp_idc[ i ][ RplsIdx ][ j 
               
               
                  ] ] 
               
               
                    refPicLayerId = vps_layer_id[ layerIdx ] 
               
               
                    if( there is a reference picture picA in the DPB with nuh_layer_id equal to 
               
               
                 refPicLayerId and 
               
            
           
           
               
               
            
               
                   
                  the same PicOrderCntVal as the current picture ) 
               
            
           
           
               
            
               
                     RefPicList[ i ][ j ] = picA 
               
               
                    else 
               
               
                     RefPicList[ i ][ j ] = “no reference picture” 
               
               
                   } 
               
               
                  } 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     After the RPLs are constructed, wherein the refPicLayerId is the layer id of ILRP, PicOrderCntVal is POC value of the picA, the marking process as following: 
     Decoding Process for Reference Picture Marking 
     This process is invoked once per picture, after decoding of a slice header and the decoding process for reference picture list construction for the slice as specified in clause 8.3.2, but prior to the decoding of the slice data. This process may result in one or more reference pictures in the DPB being marked as “unused for reference” or “used for long-term reference”. 
     A decoded picture in the DPB can be marked as “unused for reference”, “used for short-term reference” or “used for long-term reference”, but only one among these three at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly removes another of these markings when applicable. When a picture is referred to as being marked as “used for reference”, this collectively refers to the picture being marked as “used for short-term reference” or “used for long-term reference” (but not both). 
     STRPs and ILRPs are identified by their nuh_layer_id and PicOrderCntVal values. LTRPs are identified by their nuh_layer_id values and the Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values. 
     If the current picture is a CLVSS picture, all reference pictures currently in the DPB (if any) with the same nuh_layer_id as the current picture are marked as “unused for reference”. 
     Otherwise, the following applies:
     For each LTRP entry in RefPicList[ 0 ] or RefPicList[ 1 ], when the referred picture is an STRP with the same nuh_layer_id as the current picture, the picture is marked as “used for long-term reference”.   Each reference picture with the same nuh_layer_id as the current picture in the DPB that is not referred to by any entry in RefPicList[ 0 ] or RefPicList[ 1 ] is marked as “unused for reference”.   For each ILRP entry in RefPicList[ 0 ] or RefPicList[ 1 ], the referred picture is marked as “used for long-term reference”   

     Here note that, ILRP (inter-layer reference picture) is marked as “used for long-term reference”. 
     There are two syntax in the SPS which are relative to the inter-layer reference information. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                   
                 ... 
               
               
                   
                  sps_video_parameter_set_id 
                 u(4) 
               
               
                   
                 ... 
               
               
                   
                  long_term_ref_pics_flag 
                 u(1) 
               
               
                   
                  inter_layer_ref_pics_present_flag 
                 u(1) 
               
               
                   
                  sps_idr_rpl_present_flag 
                 u(1) 
               
               
                   
                  rpl1_same_as_rpl0_flag 
                 u(1) 
               
               
                   
                 ... 
               
               
                   
                   
               
            
           
         
       
     
     sps_video_parameter_set_id, when greater than 0, specifies the value of vps_video_parameter_set_id for the VPS referred to by the SPS. When sps_video_parameter_set_id is equal to 0, the SPS does not refer to a VPS and no VPS is referred to when decoding each CVS referring to the SPS. 
     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. 
     inter_layer_ref_pics_present_flag equal to 0 specifies that no ILRP is used for inter prediction of any coded picture in the CVS. inter_layer_ref_pics_flag equal to 1 specifies that ILRPs may be used for inter prediction of one or more coded pictures in the CVS. When sps_video_parameter_set_id is equal to 0, the value of inter_layer_ref_pics_present_flag is inferred to be equal to 0. 
     Simple description as below: 
     long_term_ref_pics_flag is used to indicate whether LTRP can be used in the decoding process. 
     inter_layer_ref_pics_present_flag is used to indicate whether ILRP can be used in the decoding process. 
     So, when inter_layer_ref_pics_present_flag equal to 1, there may be an ILRP which is used in decoding process, and it is marked as “used for long-term reference”. In this case, there is an LTRP is used in decoding process, even the long_term_ref_pics_flag equal to 0. So there is an inconsistent with the semantic of long_term_ref_pics_flag. 
     In the existing method, some syntax elements for inter-layer reference information are signaled always, without considering the index of current layer. This disclosure propose to add some conditions to the syntax elements to improve the signaling efficiency. 
     Since long_term_ref_pics_flag only used to control parsing of ltrp_in_slice_header_flag and st_ref_pic_flag, the semantic is modified to control the parsing of the flags parsing in the RPL. 
     Syntax elements for inter-layer reference information are signaled considering the index of current layer. If the information can be derived by the index of current layer, the information is not needed to siganled. 
     Since long_term_ref_pics_flag only used to control parsing of ltrp_in_slice_header_flag and st_ref_pic_flag, the semantic is modified to control the parsing of the flags parsing in the RPL. 
     Syntax elements for inter-layer reference information are signaled considering the index of current layer. If the information can be derived by the index of current layer, the information is not needed to signaled. 
     The first embodiment of the present disclosure modifies the semantic of long_term_ref_pics_flag to remove the inconsistent of LTRP and ILRP. 
     Since long_term_ref_pics_flag only used to control parsing of ltrp_in_slice_header_flag and st_ref_pic_flag, the semantic is modified as follows: 
     long_term_ref_pics_flag equal to 1, specifies that ltrp_in_slice_header_flag, and st_ref_pic_flag are present in the syntax structures ref_pic_list_struct(listIdx, rplsIdx). long_term_ref_pics_flag equal to 0 specifies that these syntax elements are not present in the syntax structures ref_pic_list_struct(listIdx, rplsIdx). 
     Also, the semantic can be modified to exclude the ILRP as follows: 
     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. Here the LTRP doesn&#39;t include ILRP (inter-layer reference picture). 
     The second embodiment of the present disclosure provides conditional signaling of vps_direct_dependency_flag[ i ][ j ] (the inter-layer reference information is signaled considering the index of current layer, to remove the redundancy information signaling, to improve the coding efficiency.). 
     Option 1.A: 
     Here note that, when i equal to 1, which means that layer1 need to refer to other layer. While only the layer0 can be the reference layer, so, vps_direct_dependency_flag[ i ][ j ] does not need to be signaled. Only when i larger than 1, vps_direct_dependency_flag[ i ][ j ] need to be signaled. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 video_parameter_set_rbsp( ) { 
                   
               
               
                  vps_video_parameter_set_id 
                 u(4) 
               
               
                  vps_max_layers_minus1 
                 u(6) 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) 
               
               
                   vps_all_independent_layers_flag 
                 u(1) 
               
               
                  for( i = 0; i &lt;= vps_max_layers_minus1; i++ ) { 
               
               
                   vps_layer_id[ i ] 
                 u(6) 
               
               
                   if( i &gt; 0 &amp;&amp; !vps_all_independent_layers_flag ) { 
               
               
                    vps_independent_layer_flag[ i ] 
                 u(1) 
               
               
                    if( i &gt; 1 &amp;&amp; !vps_independent_layer_flag[ i ] ) 
               
               
                     for( j = 0; j &lt; i; j++ ) 
               
               
                      vps_direct_dependency_flag[ i ][ j ] 
                 u(1) 
               
               
                   } 
               
               
                  } 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) { 
               
               
                 ... 
               
               
                   
               
            
           
         
       
     
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, if i equal to 1 and vps_independent_layer_flag[ i ] equal to 0, vps_direct_dependency_flag[ i ][ j ] is inferred to be equal to 1, otherwise, it is inferred to be equal to 0. 
     Option 1.B: 
     Besides the implementation method above (Option 1.A), there is another method Option 1.B. which means, for i and j in the range of 0 to i−1, inclusive, and when vps_independent_layer_flag[ i ] equal to 0, and all the value of vps_direct_dependency_flag[ i ][ j ] equal to 0 for j in the range of 0 to i−2, inclusive, then the value of vps_direct_dependency_flag[ i ][ i−1 ] is not needed to signal, and it is inferred to be equal to 1. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 video_parameter_set_rbsp( ) { 
                   
               
               
                  vps_video_parameter_set_id 
                 u(4) 
               
               
                  vps_max_layers_minus1 
                 u(6) 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) 
               
               
                   vps_all_independent_layers_flag 
                 u(1) 
               
               
                  for( i = 0; i &lt;= vps_max_layers_minus1; i++ ) { 
               
               
                   vps_layer_id[ i ] 
                 u(6) 
               
               
                   if( i &gt; 0 &amp;&amp; !vps_all_independent_layers_flag ) { 
               
               
                    vps_independent_layer_flag[ i ] 
                 u(1) 
               
               
                    if(!vps_independent_layer_flag[ i ] ) 
               
               
                     for(j = 0, SumDependencyFlag=0; j &lt; i; j++ ) { 
               
               
                       if( !(j = = i−1 &amp;&amp; SumDependencyFlag = = 0) ) 
               
               
                      vps_direct_dependency_flag[ i ][ j ] 
                 u(1) 
               
               
                       SumDependencyFlag+= 
               
               
                       vps_direct_dependency_flag[ i ][ j ] 
               
               
                     } 
               
               
                   } 
               
               
                  } 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) { 
               
               
                 ... 
               
               
                   
               
            
           
         
       
     
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, if vps_independent_layer_flag[ i ] equal to 0, and j equal to i−1 and the value of SumDependencyFlag equal to 0, then vps_direct_dependency_flag[ i ][ j ] is inferred to be equal to 1, otherwise, it is inferred to be equal to 0. 
     Constraints on the Semantics of vps_direct_dependency_flag[ i ][ j ] 
     Also, in an embodiment, a constraint can be added to the semantic of vps_direct_dependency_flag[ i ][ j ], without changing the syntax signaling method, or the syntax table. Basically, for i, if layer with index i is a dependent layer (vps_independent_layer_flag[ i ] equal to 0), at least one value of vps_direct_dependency_flag[ i ][ j ], j in the range of 0 to i−1, is equal to 1. Alternatively, the sum of vps_direct_dependency_flag[ i ][ j ], j in the range of 0 to i−1, should not equal to 0. Or, should larger than or equal to 1. (e.g. &gt;=1). Or, should larger than 0 (e.g. &gt;0). 
     Option 2.A: 
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, it is inferred to be equal to 0. Here for i and j in the range of 0 to i−1, inclusive, and when vps_independent_layer_flag[ i ] equal to 0, the sum of vps_direct_dependency_flag[ i ][ j ] should larger than 0. 
     Option 2.B: 
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, it is inferred to be equal to 0. Here, for i and j in the range of 0 to i−1, inclusive, and when vps_independent_layer_flag[ i ] equal to 0, at least one value of vps_direct_dependency_flag[ i ][ j ] should equal to 1. 
     Option 3 
     In some embodiments, the Option1 and Option2 can be combined to be other implementation method. 
     Like Operation1.B+Operation2.B. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 video_parameter_set_rbsp( ) { 
                   
               
               
                  vps_video_parameter_set_id 
                 u(4) 
               
               
                  vps_max_layers_minus1 
                 u(6) 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) 
               
               
                   vps_all_independent_layers_flag 
                 u(1) 
               
               
                  for( i = 0; i &lt;= vps_max_layers_minus1; i++ ) { 
               
               
                   vps_layer_id[ i ] 
                 u(6) 
               
               
                   if( i &gt; 0 &amp;&amp; !vps_all_independent_layers_flag ) { 
               
               
                    vps_independent_layer_flag[ i ] 
                 u(1) 
               
               
                    if(!vps_independent_layer_flag[ i ] ) 
               
               
                     for(j = 0, SumDependencyFlag=0; j &lt; i; j++ ) { 
               
               
                       if( !(j = = i−1 &amp;&amp; SumDependencyFlag = = 0) ) 
               
               
                      vps_direct_dependency_flag[ i ][ j ] 
                 u(1) 
               
               
                       SumDependencyFlag+= 
               
               
                       vps_direct_dependency_flag[ i ][ j ] 
               
               
                     } 
               
               
                   } 
               
               
                  } 
               
               
                  if( vps_max_layers_minus1 &gt; 0 ) { 
               
               
                 ... 
               
               
                   
               
            
           
         
       
     
     vps_direct_dependency_flag[ i ][ j ] equal to 0 specifies that the layer with index j is not a direct reference layer for the layer with index i. vps_direct_dependency_flag [ i ][ j ] equal to 1 specifies that the layer with index j is a direct reference layer for the layer with index i. When vps_direct_dependency_flag[ i ][ j ] is not present for i and j in the range of 0 to vps_max_layers_minus1, inclusive, if vps_independent_layer_flag[ i ] equal to 0, and j equal to i−1 and the value of SumDependencyFlag equal to 0, then vps_direct_dependency_flag[ i ][ j ] is inferred to be equal to 1, otherwise, it is inferred to be equal to 0. Here, for i and j in the range of 0 to i−1, inclusive, and when vps_independent_layer_flag[ i ] equal to 0, at least one value of vps_direct_dependency_flag[ i ][ j ] should equal to 1. 
     The combination method is not limited here, it can also be 
     Like Operation1.A+Operation2.B. 
     Like Operation1.A+Operation2.A. 
     Like Operation1.B+Operation2.A. 
     The third embodiment of the present disclosure provides the inter-layer reference information is signaled considering the index of current layer, to remove the redundancy information signaling, to improve the coding efficiency. 
     Here, note that if sps_video_parameter_set_id is equal to 0, then it means that there is no multiple layers, so there is no need to signal inter_layer_ref_pics_flag, and the flag is 0 by default. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                   
                 ... 
               
               
                   
                  sps_video_parameter_set_id 
                 u(4) 
               
               
                   
                 ... 
               
               
                   
                  long_term_ref_pics_flag 
                 u(1) 
               
               
                   
                  if( sps_video_parameter_set_id &gt; 0) 
               
               
                   
                   inter_layer_ref_pics_present_flag 
                 u(1) 
               
               
                   
                  sps_idr_rpl_present_flag 
                 u(1) 
               
               
                   
                  rpl1_same_as_rpl0_flag 
                 u(1) 
               
               
                   
                 ... 
               
               
                   
                   
               
            
           
         
       
     
     inter_layer_ref_pics_present_flag equal to 0 specifies that no ILRP is used for inter prediction of any coded picture in the CVS. inter_layer_ref_pics_flag equal to 1 specifies that ILRPs may be used for inter prediction of one or more coded pictures in the CVS. When inter_layer_ref_pics_flag is not present, it is inferred to be equal to 0. 
     Here note that, when GeneralLayerIdx[ nuh_layer_id ] equal to 0, then current layer is the 0-th layer, it cannot refer to any other layer. So, there is no need to signal inter_layer_ref_pics_present_flag, and the value is 0 by default. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                   
                 ... 
               
               
                   
                  sps_video_parameter_set_id 
                 u(4) 
               
               
                   
                 ... 
               
               
                   
                  long_term_ref_pics_flag 
                 u(1) 
               
               
                   
                  if(GeneralLayerIdx[ nuh_layer_id ] &gt; 0) 
               
               
                   
                   inter_layer_ref_pics_present_flag 
                 u(1) 
               
               
                   
                  sps_idr_rpl_present_flag 
                 u(1) 
               
               
                   
                  rpl1_same_as_rpl0_flag 
                 u(1) 
               
               
                   
                 ... 
               
               
                   
                   
               
            
           
         
       
     
     inter_layer_ref_pics_present_flag equal to 0 specifies that no ILRP is used for inter prediction of any coded picture in the CVS. inter_layer_ref_pics_flag equal to 1 specifies that ILRPs may be used for inter prediction of one or more coded pictures in the CVS. When inter_layer_ref_pics_flag is not present, it is inferred to be equal to 0. 
     Coding both case mentioned above, another application example is shown below: 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 seq_parameter_set_rbsp( ) { 
                   
               
               
                   
                 ... 
               
               
                   
                  sps_video_parameter_set_id 
                 u(4) 
               
               
                   
                 ... 
               
               
                   
                  long_term_ref_pics_flag 
                 u(1) 
               
               
                   
                  if( sps_video_parameter_set_id &gt; 0 &amp;&amp; 
               
               
                   
                  GeneralLayerIdx[ nuh_layer_id ] &gt; 
               
               
                   
                 0) 
               
               
                   
                   inter_layer_ref_pics_present_flag 
                 u(1) 
               
               
                   
                  sps_idr_rpl_present_flag 
                 u(1) 
               
               
                   
                  rpl1_same_as_rpl0_flag 
                 u(1) 
               
               
                   
                 ... 
               
               
                   
                   
               
            
           
         
       
     
     inter_layer_ref_pics_present_flag equal to 0 specifies that no ILRP is used for inter prediction of any coded picture in the CVS. inter_layer_ref_pics_flag equal to 1 specifies that ILRPs may be used for inter prediction of one or more coded pictures in the CVS. When inter_layer_ref_pics_flag is not present, it is inferred to be equal to 0. 
     The fourth embodiment of the present disclosure 
     Here note that, when GeneralLayerIdx[ nuh_layer_id ] is equal to 1, then current layer is layer1, and it only can refer to layer0 while the ilrp_idc of layer0 must be 0. So, there is no need to signal ilrp_idc in this case. 
     
       
         
           
               
               
             
               
                   
                   
               
               
                   
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 ref_pic_list_struct( listIdx, rplsIdx ) { 
                   
               
               
                  num_ref_entries[ listIdx ][ rplsIdx ] 
                 ue(v) 
               
               
                  if( long_term_ref_pics_flag ) 
               
               
                   ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] 
                 u(1) 
               
               
                  for( i = 0, j = 0; i &lt; num_ref_entries[ listIdx ][ rplsIdx ]; i++) { 
               
               
                   if( inter_layer_ref_pics_present_flag ) 
               
               
                    inter_layer_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                   if( !inter_layer_ref_pics_flag[ listIdx ][ rplsIdx ][ i ] ) { 
               
               
                    if( long_term_ref_pics_flag ) 
               
               
                     st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                    if( st_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] ) { 
               
               
                     abs_delta_poc_st[ listIdx ][ rplsIdx ][ i ] 
                 ue(v) 
               
               
                     if( AbsDeltaPocSt[ listIdx ][ rplsIdx ][ i ] &gt; 0 ) 
               
               
                      strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] 
                 u(1) 
               
               
                    } else if( !ltrp_in_slice_header_flag[ listIdx ][ rplsIdx ] ) 
               
               
                     rpls_poc_lsb_lt[ listIdx ][ rplsIdx ][ j++ ] 
                 u(v) 
               
               
                   } else if( GeneralLayerIdx[ nuh_layer_id ] &gt; 1 ) 
               
               
                    ilrp_idc[ listIdx ][ rplsIdx ][ i ] 
                 ue(v) 
               
               
                  } 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     ilrp_idc[ listIdx ][ rplsIdx ][ i ] specifies the index, to the list of directly dependent layers, of the ILRP of i-th entry in ref_pic_list_struct(listIdx, rplsIdx) syntax structure to the list of directly dependent layers. The value of ilrp_idc[ listIdx ][ rplsIdx ][ i ] shall be in the range of 0 to the GeneralLayerIdx[ nuh_layer_id ]−1, inclusive. When GeneralLayerIdx[ nuh_layer_id ] is equal to 1, the value of ilrp_idc[ listIdx ][ rplsIdx ][ i ] is inferred to be equal to 0 
     The fifth embodiment of the present disclosure 
     Here note that part or all of the above embodiments can be combined to form a new embodiment. 
     For example, embodiment1+embodiment2+embodiment3+embodiment4, or embodiment2+embodiment3+embodiment4, or other combinations. 
     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. 7  is a block diagram showing a content supply system  3100  for realizing content distribution service. This content supply system  3100  includes capture device  3102 , terminal device  3106 , and optionally includes display  3126 . The capture device  3102  communicates with the terminal device  3106  over communication link  3104 . The communication link may include the communication channel  13  described above. The communication link  3104  includes but not limited to WIFI, Ethernet, Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, or the like. 
     The capture device  3102  generates data, and may encode the data by the encoding method as shown in the above embodiments. Alternatively, the capture device  3102  may distribute the data to a streaming server (not shown in the Figures), and the server encodes the data and transmits the encoded data to the terminal device  3106 . The capture device  3102  includes but not limited to camera, smart phone or Pad, computer or laptop, video conference system, PDA, vehicle mounted device, or a combination of any of them, or the like. For example, the capture device  3102  may include the source device  12  as described above. When the data includes video, the video encoder  20  included in the capture device  3102  may actually perform video encoding processing. When the data includes audio (i.e., voice), an audio encoder included in the capture device  3102  may actually perform audio encoding processing. For some practical scenarios, the capture device  3102  distributes the encoded video and audio data by multiplexing them together. For other practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. Capture device  3102  distributes the encoded audio data and the encoded video data to the terminal device  3106  separately. 
     In the content supply system  3100 , the terminal device  310  receives and reproduces the encoded data. The terminal device  3106  could be a device with data receiving and recovering capability, such as smart phone or Pad  3108 , computer or laptop  3110 , network video recorder (NVR)/digital video recorder (DVR)  3112 , TV  3114 , set top box (STB)  3116 , video conference system  3118 , video surveillance system  3120 , personal digital assistant (PDA)  3122 , vehicle mounted device  3124 , or a combination of any of them, or the like capable of decoding the above-mentioned encoded data. For example, the terminal device  3106  may include the destination device  14  as described above. When the encoded data includes video, the video decoder  30  included in the terminal device is prioritized to perform video decoding. When the encoded data includes audio, an audio decoder included in the terminal device is prioritized to perform audio decoding processing. 
     For a terminal device with its display, for example, smart phone or Pad  3108 , computer or laptop  3110 , network video recorder (NVR)/digital video recorder (DVR)  3112 , TV  3114 , personal digital assistant (PDA)  3122 , or vehicle mounted device  3124 , the terminal device can feed the decoded data to its display. For a terminal device equipped with no display, for example, STB  3116 , video conference system  3118 , or video surveillance system  3120 , an external display  3126  is contacted therein to receive and show the decoded data. 
     When each device in this system performs encoding or decoding, the picture encoding device or the picture decoding device, as shown in the above-mentioned embodiments, can be used. 
       FIG. 8  is a diagram showing a structure of an example of the terminal device  3106 . After the terminal device  3106  receives stream from the capture device  3102 , the protocol proceeding unit  3202  analyzes the transmission protocol of the stream. The protocol includes but not limited to Real Time Streaming Protocol (RTSP), Hyper Text Transfer Protocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH, Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP), or any kind of combination thereof, or the like. 
     After the protocol proceeding unit  3202  processes the stream, stream file is generated. The file is outputted to a demultiplexing unit  3204 . The demultiplexing unit  3204  can separate the multiplexed data into the encoded audio data and the encoded video data. As described above, for some practical scenarios, for example in the video conference system, the encoded audio data and the encoded video data are not multiplexed. In this situation, the encoded data is transmitted to video decoder  3206  and audio decoder  3208  without through the demultiplexing unit  3204 . 
     Via the demultiplexing processing, video elementary stream (ES), audio ES, and optionally subtitle are generated. The video decoder  3206 , which includes the video decoder  30  as explained in the above mentioned embodiments, decodes the video ES by the decoding method as shown in the above-mentioned embodiments to generate video frame, and feeds this data to the synchronous unit  3212 . The audio decoder  3208 , decodes the audio ES to generate audio frame, and feeds this data to the synchronous unit  3212 . Alternatively, the video frame may store in a buffer (not shown in FIG. Y) before feeding it to the synchronous unit  3212 . Similarly, the audio frame may store in a buffer (not shown in FIG. Y) before feeding it to the synchronous unit  3212 . 
     The synchronous unit  3212  synchronizes the video frame and the audio frame, and supplies the video/audio to a video/audio display  3214 . For example, the synchronous unit  3212  synchronizes the presentation of the video and audio information. Information may code in the syntax using time stamps concerning the presentation of coded audio and visual data and time stamps concerning the delivery of the data stream itself. 
     If subtitle is included in the stream, the subtitle decoder  3210  decodes the subtitle, and synchronizes it with the video frame and the audio frame, and supplies the video/audio/subtitle to a video/audio/subtitle display  3216 . 
     The present disclosure 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 multiplication   x y  Exponentiation. 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 is intended.       

     
       
         
           
             x 
             y 
           
         
       
         
         
           
             Used to denote division in mathematical equations where no truncation or rounding is intended. 
           
         
       
    
     
       
         
           
             
               ∑ 
               
                 i 
                 = 
                 x 
               
               y 
             
             ⁢ 
             
               f 
               ⁡ 
               
                 ( 
                 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&gt;=0 and y&gt;0. 
           
         
       
    
     Logical Operators 
     The following logical operators are defined as follows:
         x &amp;&amp; y Boolean logical “and” of x and y   x||y Boolean logical “or” of x and y   ! Boolean logical “not”   x?y:z If x is TRUE or not equal to 0, evaluates to the value of y; otherwise, evaluates to the value of z.       

     Relational Operators 
     The following relational operators are defined as follows:
         &gt; Greater than   &gt;= Greater than or equal to   &lt; Less than   &lt;= 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:
         &amp; Bit-wise “and”. When operating on integer arguments, operates on a two&#39;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&#39;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.   {circumflex over ( )} Bit-wise “exclusive or”. When operating on integer arguments, operates on a two&#39;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 &gt;&gt;y Arithmetic right shift of a two&#39;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&lt;&lt;y Arithmetic left shift of a two&#39;s complement integer representation of x by y binary digits. This function is defined only for non-negative integer values of y. Bits shifted into the least significant bits (LSBs) as a result of the left shift have a value equal to 0.       

     Assignment Operators 
     The following arithmetic operators are defined as follows:
         = Assignment operator   ++ Increment, i.e., x ++  is equivalent to x=x+1; when used in an array index, evaluates to the value of the variable prior to the increment operation.   −− Decrement, i.e., x −−  is equivalent to x=x−1; when used in an array index, evaluates to the value of the variable prior to the decrement operation.   += Increment by amount specified, i.e., x+=3 is equivalent to x=x+3, and x+=(−3) is equivalent to x=x+(−3).   −= Decrement by amount specified, i.e., x−=3 is equivalent to x=x−3, and x−=(−3) is equivalent to x=x−(−3).       

     Range Notation 
     The following notation is used to specify a range of values:
         x=y . . . z x takes on integer values starting from y to z, inclusive, with x, y, and z being integer numbers and z being greater than y.       

     Mathematical Functions 
     The following mathematical functions are defined: 
     
       
         
           
             
               Abs 
               ⁡ 
               
                 ( 
                 x 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       x 
                       ; 
                     
                   
                   
                     
                       x 
                       &gt;= 
                       0 
                     
                   
                 
                 
                   
                     
                       
                         - 
                         x 
                       
                       ; 
                     
                   
                   
                     
                       x 
                       &lt; 
                       0 
                     
                   
                 
               
             
           
         
       
         
         
           
             Asin(x) the trigonometric inverse sine function, operating on an argument x that is in the range of −1.0 to 1.0, inclusive, with an output value in the range of −π÷2 to π÷2, inclusive, in units of radians 
             Atan(x) the trigonometric inverse tangent function, operating on an argument x, with an output value in the range of −π÷2 to π÷2, inclusive, in units of radians 
           
         
       
    
     
       
         
           
             
               A 
               ⁢ 
               tan 
               ⁢ 
               2 
               ⁢ 
               
                 ( 
                 
                   y 
                   , 
                   x 
                 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       
                         A 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           tan 
                           ⁢ 
                           
                               
                           
                           ( 
                           
                             y 
                             x 
                           
                           ) 
                         
                       
                       ; 
                     
                   
                   
                     
                       x 
                       &gt; 
                       0 
                     
                   
                 
                 
                   
                     
                       
                         
                           A 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             tan 
                             ⁢ 
                             
                                 
                             
                             ( 
                             
                               y 
                               x 
                             
                             ) 
                           
                         
                         + 
                         π 
                       
                       ; 
                     
                   
                   
                     
                       
                           
                       
                       ⁢ 
                       
                         
                           
                             
                               
                                 x 
                                 &lt; 
                                 0 
                               
                               ⁢ 
                               
                                   
                               
                               &amp; 
                             
                             &amp; 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           y 
                         
                         &gt;= 
                         0 
                       
                     
                   
                 
                 
                   
                     
                       
                         
                           A 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             tan 
                             ⁢ 
                             
                                 
                             
                             ( 
                             
                               y 
                               x 
                             
                             ) 
                           
                         
                         - 
                         π 
                       
                       ; 
                     
                   
                   
                     
                       
                         x 
                         &lt; 
                         0 
                       
                       ⁢ 
                       
                           
                       
                       &amp;&amp; 
                       
                           
                       
                       ⁢ 
                       
                         y 
                         &lt; 
                         0 
                       
                     
                   
                 
                 
                   
                     
                       
                         + 
                         
                           π 
                           2 
                         
                       
                       ; 
                     
                   
                   
                     
                       
                         
                           
                             x 
                             == 
                             
                               0 
                               ⁢ 
                               
                                   
                               
                               &amp; 
                             
                           
                           &amp; 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         y 
                       
                       &gt;= 
                       0 
                     
                   
                 
                 
                   
                     
                       
                         - 
                         
                             
                         
                         ⁢ 
                         
                           π 
                           2 
                         
                       
                       ; 
                     
                   
                   
                     otherwise 
                   
                 
               
             
           
         
       
         
         
           
             Ceil(x) the smallest integer greater than or equal to x. 
           
         
       
    
     
       
         
           
             
               Clip 
               ⁢ 
               
                   
               
               ⁢ 
               
                 1 
                 Y 
               
               ⁢ 
               
                 ( 
                 x 
                 ) 
               
             
             = 
             
               Clip 
               ⁢ 
               
                   
               
               ⁢ 
               3 
               ⁢ 
               
                 ( 
                 
                   0 
                   , 
                   
                     
                       ( 
                       
                         1 
                         ⪡ 
                         
                           BitDepth 
                           Y 
                         
                       
                       ) 
                     
                     - 
                     1 
                   
                   , 
                   x 
                 
                 ) 
               
             
           
         
       
       
         
           
             
               Clip 
               ⁢ 
               
                   
               
               ⁢ 
               
                 1 
                 C 
               
               ⁢ 
               
                 ( 
                 x 
                 ) 
               
             
             = 
             
               Clip 
               ⁢ 
               
                   
               
               ⁢ 
               3 
               ⁢ 
               
                 ( 
                 
                   0 
                   , 
                   
                     
                       ( 
                       
                         1 
                         ⪡ 
                         
                           BitDepth 
                           C 
                         
                       
                       ) 
                     
                     - 
                     1 
                   
                   , 
                   x 
                 
                 ) 
               
             
           
         
       
       
         
           
             
               Clip 
               ⁢ 
               
                   
               
               ⁢ 
               3 
               ⁢ 
               
                 ( 
                 
                   x 
                   , 
                   y 
                   , 
                   z 
                 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       x 
                       ; 
                     
                   
                   
                     
                       z 
                       &lt; 
                       x 
                     
                   
                 
                 
                   
                     
                       y 
                       ; 
                     
                   
                   
                     
                       z 
                       &gt; 
                       y 
                     
                   
                 
                 
                   
                     
                       z 
                       ; 
                     
                   
                   
                     otherwise 
                   
                 
               
             
           
         
       
         
         
           
             Cos(x) the trigonometric cosine function operating on an argument x in units of radians. 
             Floor(x) the largest integer less than or equal to x. 
           
         
       
    
     
       
         
           
             
               GetCurrMsb 
               ⁡ 
               
                 ( 
                 
                   a 
                   , 
                   b 
                   , 
                   c 
                   , 
                   d 
                 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       
                         c 
                         + 
                         d 
                       
                       ; 
                     
                   
                   
                     
                       
                         b 
                         - 
                         a 
                       
                       ⁢ 
                       
                           
                       
                       &gt;= 
                       
                         d 
                         / 
                         2 
                       
                     
                   
                 
                 
                   
                     
                       
                         c 
                         - 
                         d 
                       
                       ; 
                     
                   
                   
                     
                       
                         a 
                         - 
                         b 
                       
                       &gt; 
                       
                         d 
                         / 
                         2 
                       
                     
                   
                 
                 
                   
                     
                       c 
                       ; 
                     
                   
                   
                     otherwise 
                   
                 
               
             
           
         
       
         
         
           
             Ln(x) the natural logarithm of x (the base-e logarithm, where e is the natural logarithm base constant 2.718 281 828 . . . ). 
             Log2(x) the base-2 logarithm of x. 
             Log10(x) the base-10 logarithm of x. 
           
         
       
    
     
       
         
           
             
               Min 
               ⁡ 
               
                 ( 
                 
                   x 
                   , 
                   y 
                 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       
                         
                           x 
                           ; 
                         
                       
                       
                         
                           x 
                           &lt;= 
                           y 
                         
                       
                     
                     
                       
                         
                           y 
                           ; 
                         
                       
                       
                         
                           x 
                           &gt; 
                           y 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     Max 
                     ⁡ 
                     
                       ( 
                       
                         x 
                         , 
                         y 
                       
                       ) 
                     
                   
                 
                 = 
                 
                   { 
                   
                     
                       
                         
                           
                             
                               x 
                               ; 
                             
                           
                           
                             
                               x 
                               &gt;= 
                               y 
                             
                           
                         
                         
                           
                             
                               y 
                               ; 
                             
                           
                           
                             
                               x 
                               &lt; 
                               y 
                             
                           
                         
                       
                       ⁢ 
                       
                         
 
                       
                       ⁢ 
                       
                         Round 
                         ⁡ 
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                     = 
                     
                       
                         
                           Sign 
                           ⁡ 
                           
                             ( 
                             x 
                             ) 
                           
                         
                         * 
                         
                           Floor 
                           ⁡ 
                           
                             ( 
                             
                               
                                 Abs 
                                 ⁡ 
                                 
                                   ( 
                                   x 
                                   ) 
                                 
                               
                               + 
                               0.5 
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           
 
                         
                         ⁢ 
                         
                           Sign 
                           ⁡ 
                           
                             ( 
                             x 
                             ) 
                           
                         
                       
                       = 
                       
                         { 
                         
                           
                             
                               
                                 1 
                                 ; 
                               
                             
                             
                               
                                 x 
                                 &gt; 
                                 0 
                               
                             
                           
                           
                             
                               
                                 0 
                                 ; 
                               
                             
                             
                               
                                 x 
                                 == 
                                 0 
                               
                             
                           
                           
                             
                               
                                 
                                   - 
                                   1 
                                 
                                 ; 
                               
                             
                             
                               
                                 x 
                                 &lt; 
                                 0 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
         
         
           
             Sin(x) the trigonometric sine function operating on an argument x in units of radians 
             Sqrt(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) 
               
               
                 operations (with operands x, y, and z) 
               
               
                   
               
             
            
               
                 ″x++″, ″x− −″ 
               
               
                 ″!x″, ″−x″ (as a unary prefix operator) 
               
               
                 x y   
               
               
                 ″x * y″, ″x/y″, ″x ÷ y″, ″ x/y″, ″x % y″ 
               
               
                 ″x + y″, ″x − y″(as a two-argument operator), 
               
               
                   
               
               
                 
                   
                     
                       
                         
                           
                               
                           
                           ″ 
                         
                         ⁢ 
                         
                           
                             
                               ∑ 
                               y 
                             
                             
                               i 
                               = 
                               x 
                             
                           
                           ⁢ 
                           
                             
                               f 
                               ⁡ 
                               
                                 ( 
                                 i 
                                 ) 
                               
                             
                             ″ 
                           
                         
                       
                     
                   
                 
               
               
                   
               
               
                 ″x &lt;&lt; y″, ″x &gt;&gt; y ″ 
               
               
                 ″x &lt; y″, ″x &lt;= y″, ″x &gt; y″, ″x &gt;= y″ 
               
               
                 ″x = = y″, ″x != y″ 
               
               
                 ″x &amp; y″ 
               
               
                 ″x | y″ 
               
               
                 ″x &amp;&amp; y″ 
               
               
                 ″x ∥ y″ 
               
               
                 ″x ? y : z″ 
               
               
                 ″x . . . y″ 
               
               
                 ″x = y″, ″x += y″, ″x −= y″ 
               
               
                   
               
            
           
         
       
     
     Text Description of Logical Operations 
     In the text, a statement of logical operations as would be described mathematically in the following form: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 if( condition 0 ) 
               
               
                  statement 0 
               
               
                 else if( condition 1 ) 
               
               
                  statement 1 
               
               
                 ... 
               
               
                 else /* informative remark on remaining condition */ 
               
               
                  statement n 
               
               
                   may be described in the following manner: 
               
               
                  ... as follows / ... the following applies: 
               
               
                  - If condition 0, statement 0 
               
               
                  - Otherwise, if condition 1, statement 1 
               
               
                  - ... 
               
               
                  - Otherwise (informative remark on remaining condition), statement n 
               
               
                   
               
            
           
         
       
     
     Each “If . . . Otherwise, if . . . Otherwise, ...” statement in the text is introduced with “. . . as follows” or “. . . the following applies” immediately followed by “If . . . ”. The last condition of the “If . . . Otherwise, if . . . Otherwise, ...” is always an “Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . . Otherwise, ...” statements can be identified by matching “. . . as follows” or “. . . the following applies” with the ending “Otherwise, . . . ”. 
     In the text, a statement of logical operations as would be described mathematically in the following form: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 if( condition 0a &amp;&amp; condition 0b ) 
               
               
                  statement 0 
               
               
                 else if( condition 1a || condition 1b ) 
               
               
                  statement 1 
               
               
                 ... 
               
               
                 else 
               
               
                  statement n 
               
               
                   may be described in the following manner: 
               
               
                 ... as follows / ... the following applies: 
               
            
           
           
               
               
            
               
                  - 
                 If all of the following conditions are true, statement 0: 
               
               
                   
                 - condition 0a 
               
               
                   
                 - condition 0b 
               
               
                  - 
                 Otherwise, if one or more of the following conditions are true, 
               
               
                   
                 statement 1: 
               
               
                   
                 - condition 1a 
               
               
                   
                 - condition 1b 
               
               
                  - 
                 ... 
               
               
                  - 
                 Otherwise, statement n 
               
               
                   
               
            
           
         
       
     
     In the text, a statement of logical operations as would be described mathematically in the following form:
         if(condition 0)   statement 0   if(condition 1)   statement 1       

     may be described in the following manner:
         When condition 0, statement 0   When condition 1, statement 1       

     Although embodiments of the disclosure have been primarily described based on video coding, it should be noted that embodiments of the coding system  10 , encoder  20  and decoder  30  (and correspondingly the system  10 ) 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 units  244  (encoder) and  344  (decoder) may not be available in case the picture processing coding is limited to a single picture  17 . All other functionalities (also referred to as tools or technologies) of the video encoder  20  and video decoder  30  may equally be used for still picture processing, e.g. residual calculation  204 / 304 , transform  206 , quantization  208 , inverse quantization  210 / 310 , (inverse) transform  212 / 312 , partitioning  262 / 362 , intra-prediction  254 / 354 , and/or loop filtering  220 ,  320 , and entropy coding  270  and entropy decoding  304 . 
     Embodiments, e.g. of the encoder  20  and the decoder  30 , and functions described herein, e.g. with reference to the encoder  20  and the decoder  30 , may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over communication media as one or more instructions or code and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium. 
     In particular, it is provided a method of decoding a coded video bitstream implemented in an decoder as illustrated in  FIG. 9 , the method comprising: S 901 , obtaining, from the coded video bitstream, a first syntax element (i.e. vps_independent_layer_flag[ i ]) specifying whether the first layer use inter-layer prediction. S 902 , obtaining, from the coded video bitstream, one or more second syntax elements (i.e. vps_direct_dependency_flag[ i ][ j ]) related to one or more second layers, each second syntax element specifies whether a second layer is a direct reference layer for the first layer; wherein at least one second syntax element of the one or more second syntax elements has a value specifying a second layer is a direct reference layer for the first layer, in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction. and S 903 , performing inter-layer prediction for a picture of the first layer by using a picture of the second layer related to the at least one second syntax element as a reference picture. 
     Similarly, it is provided a method of encoding a video bitstream comprising coded data for a implemented in an encoder as illustrated in  FIG. 10 , the method comprising: S 1001 , determining whether at least one second layer is a direct reference layer for a first layer; S 1003 , encoding a syntax element into the coded video bitstream, wherein the syntax element specifies whether the first layer use inter-layer prediction; wherein the value of the syntax element specifies the first layer does not use inter-layer prediction, in case that none of the at least one second layer is a direct reference layer for the first layer. 
       FIG. 11  illustrates a decoder  1100  configured for decoding a video bitstream comprising coded data for a plurality of pictures. The decoder  1100  according to the shown example comprises: a obtaining unit  1110  configured to obtain, from the coded video bitstream, a first syntax element specifying whether the first layer use inter-layer prediction; the obtaining unit  1110  is further configured to obtain, from the coded video bitstream, one or more second syntax elements related to one or more second layers, each second syntax element specifies whether a second layer is a direct reference layer for the first layer; wherein at least one second syntax element of the one or more second syntax elements has a value specifying a second layer is a direct reference layer for the first layer, in case that the value of the first syntax element specifies the first layer is allowed to use inter-layer prediction; and a predicting unit  1120  configured to perform inter-layer prediction for a picture of the first layer by using a picture of the second layer related to the at least one second syntax element as a reference picture. 
     Wherein the unit may be a software module for execution by the processors, or processing circuitry. 
     Wherein the obtaining unit  1110  may be entropy decoding unit  304 . The predicting unit  1120  may be inter prediction unit  344 . The decoder  1100  may be the destination device  14 , the decoder  30 , the apparatus  500 , the video decoder  3206  or the terminal device  3106 . 
     Similarly, it is provided an encoder  1200  configured for encoding a video bitstream comprising coded data for a plurality of pictures as illustrated in  FIG. 12 . The encoder  1200  comprises: a determining unit  1210  configured to determine whether at least one second layer is a direct reference layer for a first layer; an encoding unit  1220  configured to encode a syntax element into the coded video bitstream, wherein the syntax element specifies whether the first layer use inter-layer prediction; wherein the value of the syntax element specifies the first layer does not use inter-layer prediction, in case that none of the at least one second layer is a direct reference layer for the first layer. 
     Wherein the unit may be a software module for execution by the processors, or processing circuitry. 
     Wherein the first encoding unit  1210  and the second encoding unit  1220  may be Entropy 
     encoding unit  270 . The determining unit may be mode selection unit  260 . The encoder  1200  may be the source device  12 , the encoder  20 , or the apparatus  500 . 
     By way of example, and not limiting, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.