System and method for switching interpolation filters

Abstract

Systems, methods, and devices are provided for adaptively switching interpolation filters during encoding of video data or decoding of a video bitstream. In various implementations, a set of interpolation filters can be defined and made available to a coding device. The coding device can select an interpolation filter for a given coding unit. The interpolation filter can be selected based on, for example, a coding level of the coding unit, among other possibilities. In some examples, signaling of the selected interpolation filter can be simplified by selecting a subset of the set of interpolation filters for a given coding scenario. An index of the interpolation filter from the subset can then be signaled. Alternatively, a decoder can derive the identification of the interpolation filter from data provided by a bitstream, in which case the index need not be explicitly signaled in the bitstream.

Description

Technical Field

[0001] This application relates to switching interpolation filters used in motion estimation (ME) and motion compensation (MC) processes within the context of an advanced video codec, including code developed in a Joint Exploratory Model (JEM). For example, the proposed method improves inter-layer prediction performance by adaptively employing multiple interpolation filters. Background Technology

[0002] Video decoding standards include ITU-T H.261, ISO / IEC MPEG-1 Visual, ITU-T H.262 or ISO / IEC MPEG-2 Visual, ITU-T H.263, ISO / IEC MPEG-4 Visual, and ITU-T H.264 (also known as ISO / IEC MPEG-4 AVC), which include their Scalable Video Decoding (SVC) and Multi-View Video Decoding (MVC) extensions.

[0003] In addition, the ITU-T Video Decoding Experts Group (VCEG) and the ISO / IEC Animation Experts Group (MPEG) Joint Collaborative Working Group on Video Decoding (JCT-VC) and the Joint Collaborative Working Group on 3D Video Decoding Extensions (JCT-3V) have recently developed a new video decoding standard, namely High Efficiency Video Decoding (HEVC) or ITU-T H.265, which includes its scope and screen content decoding extensions, 3D video decoding (3D-HEVC) and multi-view extensions (MV-HEVC), and scalable extensions (SHVC).

[0004] In 2016, MPEG and ITU-T VCEG formed the Joint Video Exploration Team (JVET) to explore new decoding tools for next-generation video decoding standards. The reference software is known as the Joint Exploration Model (JEM). Summary of the Invention

[0005] Video compression techniques perform spatial and temporal predictions to reduce or remove redundancy inherent in the input video signal. To reduce temporal redundancy (i.e., visual similarity between adjacent frames), motion estimation is performed to track object movement in the video. Motion vectors can indicate displacement in pixel units. In some cases, motion vectors can have a level of accuracy higher than integer pixel precision, such as half-pixel, quarter-pixel, or 1 / 16th of a pixel distance. This finer level of precision allows video decoders to track motion fields more accurately and thus achieve better predictions.

[0006] According to at least one example, a method for encoding video data is provided, comprising obtaining the video data. The method further comprises determining a subset of interpolation filters from an interpolation filter set for a decoding unit, wherein the subset of interpolation filters is determined based on information in the video data associated with the decoding unit. The method further comprises encoding the decoding unit, wherein encoding the decoding unit includes selecting interpolation filters for motion estimation and motion compensation for the decoding unit, wherein the interpolation filters are selected from the subset of interpolation filters. The method further comprises generating an encoded video bitstream, wherein the encoded video bitstream includes the encoded decoding unit.

[0007] In another example, an apparatus is provided comprising: a memory configured to store video data; and a processor. The processor is configured to access the video data. The processor is configured to determine a subset of interpolation filters from a set of interpolation filters for a decoding unit, wherein the subset of interpolation filters is determined based on information in the video data associated with the decoding unit. The processor is configured to encode the decoding unit, wherein encoding the decoding process includes selecting interpolation filters for motion estimation and motion compensation, wherein the interpolation filters are selected from the subset of interpolation filters. The processor is configured to generate an encoded video bitstream, wherein the encoded video bitstream includes the encoded decoding unit.

[0008] In another example, a computer-readable medium is provided having instructions stored thereon that, when executed by a processor, perform a method comprising: acquiring video data. The method further comprises determining a subset of interpolation filters from a set of interpolation filters for a decoding unit, wherein the subset of interpolation filters is determined based on information in the video data associated with the decoding unit. The method further comprises an encoding-decoding unit, wherein encoding the decoding unit includes selecting interpolation filters for motion estimation and motion compensation for the decoding unit, wherein the interpolation filters are selected from the set of interpolation filters. The method further comprises generating an encoded video bitstream, wherein the encoded video bitstream includes the encoded-decoding unit.

[0009] In another example, an apparatus is provided that includes means for acquiring video data. The apparatus further includes means for determining a subset of interpolation filters from a set of interpolation filters for a decoding unit, wherein the subset of interpolation filters is determined based on information in the video data associated with the decoding unit. The apparatus further includes means for encoding the decoding unit, wherein encoding the decoding unit includes selecting interpolation filters for motion estimation and motion compensation for the decoding unit, wherein the interpolation filters are selected from the subset of interpolation filters. The apparatus further includes means for generating an encoded video bitstream, wherein the encoded video bitstream includes the encoded decoding unit.

[0010] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on the decoding level of the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0011] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on a prediction mode for the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0012] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on the motion information, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0013] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on a decoding tool used to decode the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0014] In some aspects, the interpolation filter is selected from previously decoded blocks. In some aspects, the interpolation filter is selected from adjacent blocks of the decoding unit.

[0015] In some aspects, the methods, apparatus, and computer-readable media described above further include merging the interpolation filter with a second interpolation filter, wherein the resulting merged interpolation filter is used for the motion estimation.

[0016] In some aspects, the interpolation filter is associated with a second interpolation filter, wherein the interpolation filter is used for integer pixel locations and wherein the second interpolation filter is used for fractional pixel locations.

[0017] In some respects, the interpolation filter and the second interpolation filter have different cutoff frequencies.

[0018] In some respects, the encoded video bitstream includes values ​​that identify the interpolation filter.

[0019] In some aspects, the encoded video bitstream is not used to signal the set of interpolation filters, and the identifier of the interpolation filters can be implied from the encoded video bitstream.

[0020] In some respects, devices such as those described above may include a camera for capturing images.

[0021] According to at least one example, a method for decoding video data is provided, comprising obtaining an encoded video bitstream. The method further comprises determining a reference frame from the encoded video bitstream for a decoding unit in a current frame. The method further comprises determining a subset of interpolation filters from a set of interpolation filters, wherein the subset of interpolation filters is determined based on information associated with the decoding unit in the encoded video bitstream. The method further comprises determining interpolation filters from the subset of interpolation filters. The method further comprises using the reference frame and the interpolation filters to reconstruct the decoding unit.

[0022] In another example, an apparatus is provided comprising: a memory configured to store video data; and a processor. The processor is configured to obtain an encoded video bitstream. The processor is configured to determine, from the encoded video bitstream, a reference frame for a decoding unit in a current frame. The processor is further configured to determine a subset of interpolation filters from a set of interpolation filters, wherein the subset of interpolation filters is determined based on information associated with the decoding unit in the encoded video bitstream. The processor is configured to determine interpolation filters from the subset of interpolation filters. The processor is configured to use the reference frame and the interpolation filters to reconstruct the decoding unit.

[0023] In another example, a computer-readable medium is provided having instructions stored thereon that, when executed by a processor, perform a method comprising: obtaining an encoded video bitstream. The method further comprises determining, from the encoded video bitstream, a reference frame for a decoding unit in a current frame. The method further comprises determining, from a set of interpolation filters, a subset of interpolation filters, wherein the subset of interpolation filters is determined based on information associated with the decoding unit in the encoded video bitstream. The method further comprises determining interpolation filters from the set of interpolation filters. The method further comprises using the reference frame and the interpolation filters to reconstruct the decoding unit.

[0024] In another example, an apparatus is provided that includes means for obtaining an encoded video bitstream. The apparatus further includes means for determining a reference frame from the encoded video bitstream for a decoding unit in a current frame. The apparatus further includes means for determining a subset of interpolation filters from a set of interpolation filters, wherein the subset of interpolation filters is determined based on information associated with the decoding unit in the encoded video bitstream. The apparatus further includes means for determining interpolation filters from the subset of interpolation filters. The apparatus further includes means for reconstructing the decoding unit using the reference frame and the interpolation filters.

[0025] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on the decoding level of the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0026] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on a prediction mode for the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0027] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on motion information, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0028] In some aspects, the methods, apparatus, and computer-readable media described above further include determining a subset of interpolation filters from the set of interpolation filters, wherein the subset of interpolation filters is determined based on a decoding tool used to decode the decoding unit, and wherein the interpolation filters are determined from the subset of interpolation filters.

[0029] In some aspects, the interpolation filter is selected from previously decoded blocks. In some aspects, the interpolation filter is selected from adjacent blocks.

[0030] In some aspects, the methods, apparatus, and computer-readable media described above further include merging the interpolation filter with a second interpolation filter, wherein the resulting merged interpolation filter is used to reconstruct the prediction unit.

[0031] In some aspects, the interpolation filter is associated with a second interpolation filter, wherein the interpolation filter is used for integer pixel locations and the second interpolation filter is used for fractional pixel locations. In some aspects, the interpolation filter and the second interpolation filter have different cutoff frequencies.

[0032] In some respects, the encoded video bitstream includes values ​​that identify the interpolation filter.

[0033] In some aspects, the methods, apparatus, and computer-readable media described above further include using the encoded video bitstream to derive the identifier of the interpolation filter.

[0034] In some aspects, the device as described above may include a camera for capturing images. In some aspects, the device may include a display for displaying video data. Attached Figure Description

[0035] The following illustrative embodiments of the invention are described in detail with reference to the accompanying drawings:

[0036] Figure 1 A block diagram illustrating an example of an encoding device and a decoding device.

[0037] Figure 2 This illustrates an instance of the encoding process used for the current block from the current frame.

[0038] Figure 3 Plot an example of fractional pixel positions.

[0039] Figure 4 Draw an example of the motion estimation steps in the encoding process.

[0040] Figure 5 An example of the motion estimation step in the decoding process is illustrated.

[0041] Figure 6 To plot the frequency response graphs of three example filters F0, F1, and F2.

[0042] Figure 7 An example is illustrated of the process used to switch interpolation filters during the encoding process.

[0043] Figure 8 This is an example of a process used to switch interpolation filters during decoding.

[0044] Figure 9 A block diagram illustrating the example encoding device.

[0045] Figure 10 A block diagram illustrating an example video decoding device. Detailed Implementation

[0046] Certain aspects and embodiments of the invention are provided below. Some of these aspects and embodiments may be applied independently, and some may be applied in combination, as will be apparent to those skilled in the art. In the following description, specific details are set forth for illustrative purposes in order to provide a thorough understanding of embodiments of the invention. However, it will be apparent that various embodiments may be practiced without these specific details. The figures and descriptions are not intended to be limiting.

[0047] The following description provides exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the subsequent description of the exemplary embodiments will provide those skilled in the art with an open description for carrying out the exemplary embodiments. It should be understood that various changes can be made to the function and arrangement of the elements without departing from the spirit and scope of the invention as set forth in the appended claims.

[0048] Specific details are set forth in the following description to provide a thorough understanding of the embodiments. However, those skilled in the art will understand that the embodiments can be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may be shown as block diagrams to avoid obscuring the embodiments with unnecessary details. In other cases, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary details to avoid obscuring the embodiments.

[0049] Furthermore, it should be noted that individual embodiments can be described as processes depicted as flowcharts, flow diagrams, data flow diagrams, structure diagrams, or block diagrams. Although flowcharts may describe operations as sequential processes, many operations may be performed in parallel or simultaneously. Additionally, the order of operations can be rearranged. A process terminates when its operations are completed, but may have additional steps not included in the diagram. A process may correspond to a method, function, procedure, subroutine, subroutine, etc. When a process corresponds to a function, its termination may correspond to the function returning to the calling function or the main function.

[0050] The term "computer-readable media" includes, but is not limited to, portable or non-portable storage devices, optical storage devices, and various other media capable of storing, containing, or carrying instructions and / or data. Computer-readable media may include non-transitory media, in which data may be stored, and which do not contain carrier waves and / or transient electronic signals propagated wirelessly or via wired connections. Examples of non-transitory media include, but are not limited to, magnetic disks or magnetic tapes, optical storage media such as compact optical discs (CDs) or digital versatile optical discs (DVDs), flash memory, memory, or memory devices. Computer-readable media may store code and / or machine-executable instructions, which may represent procedures, functions, subroutines, programs, routines, subroutines, modules, software packages, classes, or any combination of instructions, data structures, or program statements. A segment of code can be coupled to another segment of code or hardware circuitry by transmitting and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc., can be transmitted, forwarded, or transferred via any suitable means, including memory sharing, messaging, token passing, network transmission, etc.

[0051] Furthermore, embodiments may be implemented using hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented as software, firmware, middleware, or microcode, program code or code segments (e.g., computer program products) used to perform the necessary tasks may be stored in computer-readable or machine-readable media. The processor may perform the necessary tasks.

[0052] As more devices and systems provide users with access to digital video data, the need for efficient video decoding technologies becomes more critical. Video decoding is required to reduce the storage and transmission requirements necessary to handle the large amounts of data present in digital video data. Various video decoding technologies can be used to compress video data into a form that maintains high video quality while using a lower bit rate. As used herein, "decoding" refers to either "encoding" or "decoding".

[0053] Figure 1This is a block diagram illustrating an example of a video decoding system 100 including an encoding device 104 and a decoding device 112. The encoding device 104 may be part of a source device, and the decoding device 112 may be part of a receiving device. The source device and / or receiving device may include electronic devices such as mobile or static telephones (e.g., smartphones, cellular phones, etc.), desktop computers, laptops or notebook computers, tablet computers, set-top boxes, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, Internet Protocol (IP) cameras, or any other suitable electronic devices. In some instances, the source device and receiving device may include one or more wireless transceivers for wireless communication. The decoding techniques described herein are applicable to video decoding in a variety of multimedia applications, including streaming video transmission (e.g., via the Internet), television broadcasting or transmission, encoding of digital video stored on data storage media, decoding of digital video stored on data storage media, or other applications. In some instances, system 100 may support one-way or two-way video transmission to support applications such as video conferencing, video streaming, video playback, video broadcasting, gaming, and / or video telephony.

[0054] Encoding device 104 (or encoder) can be used to encode video data using video decoding standards or protocols to produce an encoded video bitstream. Examples of video decoding standards include ITU-T H.261, ISO / IEC MPEG-1 Visual, ITU-T H.262 or ISO / IEC MPEG-2 Visual, ITU-T H.263, ISO / IEC MPEG-4 Visual, ITU-T H.264 (also known as ISO / IEC MPEG-4 AVC), including its Scalable Video Decoding (SVC) and Multi-View Video Decoding (MVC) extensions, and High Efficiency Video Decoding (HEVC) or ITU-T H.265. Various HEVC extensions exist involving multi-layer video decoding, including range and screen content decoding extensions, 3D video decoding (3D-HEVC) and multi-view extensions (MV-HEVC), and Scalable Extensions (SHVC). The ITU-T Video Decoding Experts Group (VCEG) and the ISO / IEC Animation Experts Group (MPEG) Joint Collaborative Working Group on Video Decoding (JCT-VC) and the Joint Collaborative Working Group on 3D Video Decoding Extensions (JCT-3V) have developed HEVC and its extensions. MPEG and ITU-T VCEG have also formed the Joint Exploratory Video Working Group (JVET) to explore new decoding tools for next-generation video decoding standards. The reference software is known as the Joint Exploratory Model (JEM).

[0055] Many of the examples described herein provide examples using the JEM model, the HEVC standard, and / or its extensions. However, the techniques and systems described herein are also applicable to other decoding standards, such as AVC, MPEG, their extensions, or other suitable decoding standards, whether currently existing or future. Therefore, while the techniques and systems described herein may be described with reference to specific video decoding standards, those skilled in the art should understand that the descriptions should not be construed as applicable only to those specific standards.

[0056] See Figure 1 Video source 102 can provide video data to encoding device 104. Video source 102 may be part of a source device or part of a device other than a source device. Video source 102 may include video capture devices (e.g., video cameras, camera phones, video phones, etc.), video archives containing stored video, video servers or content providers that provide video data, video feed interfaces that receive video from video servers or content providers, computer graphics systems for generating computer graphics video data, combinations of such sources, or any other suitable video source.

[0057] Video data from video source 102 may contain one or more input pictures or frames. The pictures or frames of the video are still images of the scene. Encoder engine 106 (or encoder) of encoding device 104 encodes the video data to produce an encoded video bitstream. In some instances, the encoded video bitstream (or “video bitstream” or “bitstream”) is a series of one or more decoded video sequences. A decoded video sequence (CVS) contains a series of access units (AUs) that begin with an AU having a random access point picture in the base layer and possessing certain attributes, and continue until, and do not contain, the next AU having a random access point picture in the base layer and possessing certain attributes. For example, certain attributes of the random access point picture that begins the CVS may include a RASL flag equal to 1 (e.g., NoRaslOutputFlag). Otherwise, a random access point picture (with a RASL flag equal to 0) will not begin the CVS. An access unit (AU) contains one or more decoded pictures and control information corresponding to decoded pictures sharing the same output time. The decoded slices of an image are encapsulated into data units called Network Abstraction Layer (NAL) units at the bitstream level. For example, an HEVC video bitstream may contain one or more CVSs, and one or more CVSs contain NAL units. Each NAL unit has a NAL unit header. In one instance, the header is one byte for H.264 / AVC (but not multi-layer extensions) and two bytes for HEVC. The syntax elements in the NAL unit header are specified bits and are therefore visible to all kinds of systems and transport layers, such as transport streams, Real-Time Transport (RTP) protocols, file formats, etc.

[0058] Two types of NAL units exist in the HEVC standard: Video Decoding Layer (VCL) NAL units and non-VCL NAL units. A VCL NAL unit contains a slice or fragment of decoded image data (described below), while a non-VCL NAL unit contains control information about one or more decoded images. In some cases, NAL units may be referred to as data packets. A HEVC AU contains VCL NAL units with decoded image data and corresponding non-VCL NAL units (if present) for the decoded image data.

[0059] NAL units may contain decoded bit sequences that form video data (e.g., encoded video bitstreams, CVS of bitstreams, etc.), such as decoded representations of images in a video. Encoder engine 106 generates decoded representations of images by dividing each image into multiple slices. Each slice is independent of other slices, such that information in the slice is decoded without depending on data from other slices within the same image. A slice contains one or more segments, which contain independent segments and, if present, one or more dependent segments that depend on previous segments. The slices are then divided into decoder tree blocks (CTBs) of luma and chroma samples. The CTBs of luma samples and one or more CTBs of chroma samples, together with the syntax used for the samples, are called decoder tree units (CTUs). CTUs are the basic processing units for HEVC encoding. A CTU may be split into multiple decoder units (CUs) of different sizes. A CU contains an array of luma and chroma samples called a decoder block (CB).

[0060] The luma and chroma blocks (CBs) can be further subdivided into prediction blocks (PBs). A PB is a block of samples of the luma or chroma components that uses the same motion parameters for inter-frame prediction or intra-block copy prediction (when available or enabled for use). The luma PB and one or more chroma PBs, together with the associated syntax, form a prediction unit (PU). For inter-frame prediction, a set of motion parameters (e.g., one or more motion vectors, reference indices, etc.) is signaled in the bitstream for each PU and used for inter-frame prediction of the luma PB and one or more chroma PBs. Motion parameters can also be referred to as motion information. CBs can also be subdivided into one or more transform blocks (TBs). A TB represents a square block of samples of the color components, to which the same two-dimensional transform is applied for decoding the predicted residual signal. A transform unit (TU) represents a TB of luma and chroma samples, and the corresponding syntax element.

[0061] The size of a CU corresponds to the size of the decoding mode and can be square. For example, the size of a CU can be 8×8 samples, 16×16 samples, 32×32 samples, 64×64 samples, or any other suitable size up to the size of the corresponding CTU. The phrase "N×N" is used herein to refer to the pixel dimensions of a video block in both the vertical and horizontal dimensions (e.g., 8 pixels × 8 pixels). Pixels in a block can be arranged in rows and columns. In some instances, a block may not have the same number of pixels in the horizontal direction as it does in the vertical direction. The syntax data associated with a CU may describe, for example, the division of the CU into one or more PUs. The division mode may differ between intra-frame prediction mode encoding and inter-frame prediction mode encoding of the CU. PUs can be divided into non-square shapes. The syntax data associated with a CU may also describe, for example, the division of the CU into one or more TUs according to the CTU. TUs can be square or non-square.

[0062] According to the HEVC standard, transform units (TUs) can be used to perform transforms. TUs can vary for different core cells (CUs). The size of a TU can be determined based on the size of a function unit (PU) within a given CU. A TU can be the same size as or smaller than a PU. In some instances, a quadtree structure called a residual quadtree (RQT) can be used to further divide the residual samples corresponding to the CU into smaller units. The leaf nodes of the RQT can correspond to TUs. The pixel differences associated with the TU can be transformed to produce transform coefficients. The transform coefficients can then be quantized by the encoder engine 106.

[0063] Once the video data is segmented into Units (CUs), the encoder engine 106 uses a prediction mode to predict each Unit (PU). The prediction unit or block is then subtracted from the original video data to obtain the residual (described below). For each CU, the prediction mode can be signaled within the bitstream using syntax data. The prediction mode can include intra-frame prediction (or intra-picture prediction) or inter-frame prediction (or inter-picture prediction). Intra-frame prediction utilizes the correlation between spatially adjacent samples within a picture. For example, when using intra-frame prediction, DC prediction is used to determine the average value of the PU, planar prediction is used to fit a planar surface to the PU, orientation prediction is used to extrapolate from adjacent data, or any other suitable type of prediction is used to predict each PU from adjacent image data in the same picture. Inter-frame prediction uses the temporal correlation between pictures to derive motion-compensated predictions for blocks of image samples. For example, when using inter-frame prediction, motion-compensated prediction is used to predict each PU from image data in one or more reference pictures (in the output order before or after the current picture). The decision to use inter-picture prediction or intra-picture prediction to decode a picture region can be made, for example, at the CU level.

[0064] In some instances, one or more slices of an image are assigned slice types. Slice types include I-slices, P-slices, and B-slices. An I-slice (internal frame, independently decodable) is a slice of an image that is decoded solely by intra-frame prediction, and is therefore independently decodable because an I-slice only requires intra-frame data to predict any prediction unit or prediction block of the slice. A P-slice (one-way prediction frame) is a slice of an image that can be decoded using both intra-frame prediction and one-way inter-frame prediction. Each prediction unit or prediction block within a P-slice is decoded using either intra-frame or inter-frame prediction. When inter-frame prediction is applicable, the prediction unit or prediction block is predicted by only one reference image, and therefore the reference sample comes from only one reference region within a frame. A B-slice (two-way prediction frame) is a slice of an image that can be decoded using both intra-frame prediction and inter-frame prediction (e.g., two-way or one-way prediction). Prediction units or blocks of B-slices can be bidirectionally predicted from two reference images, where each image contributes to a reference region, and the sample sets of the two reference regions are weighted (e.g., using equal weights or different weights) to generate the prediction signal for the bidirectional prediction block. As explained above, slices of an image are decoded independently. In some cases, an image can be decoded as a single slice.

[0065] A prediction unit (PU) may contain data related to the prediction process (such as motion parameters or other suitable data). For example, when encoding a PU using intra-frame prediction, the PU may contain data describing the intra-frame prediction mode used for the PU. As another example, when encoding a PU using inter-frame prediction, the PU may contain data defining the motion vectors used for the PU. The data defining the motion vectors used for the PU may describe, for example, the horizontal component (Δx) of the motion vector, the vertical component (Δy) of the motion vector, the resolution of the motion vector (e.g., integer precision, quarter-pixel precision, or eighth-pixel precision), the reference picture to which the motion vector points, the reference index, a list of reference pictures for the motion vector (e.g., list 0, list 1, or list C), or any combination thereof.

[0066] Encoding device 104 can then perform transformation and quantization. For example, after prediction, encoder engine 106 can calculate a residual value corresponding to the PU. The residual value can include the pixel difference between the current block (PU) of the pixel being decoded and the prediction block used to predict the current block (e.g., a predicted version of the current block). For example, after generating a prediction block (e.g., issuing inter-frame prediction or intra-frame prediction), encoder engine 106 can generate a residual block by subtracting the prediction block generated by the prediction unit from the current block. The residual block contains a set of pixel difference values ​​that quantize the differences between the pixel values ​​of the current block and the pixel values ​​of the prediction block. In some instances, the residual block can be represented in a two-dimensional block format (e.g., a two-dimensional matrix or array of pixel values). In such instances, the residual block is a two-dimensional representation of the pixel values.

[0067] Block transforms are used to transform any residual data remaining after prediction is performed. These block transforms can be based on discrete cosine transform, discrete sine transform, integer transform, wavelet transform, other suitable transform functions, or any combination thereof. In some cases, one or more block transforms (e.g., sizes 32×32, 16×16, 8×8, 4×4, etc.) can be applied to the residual data in each CU. In some instances, TUs can be used for the transform and quantization process implemented by encoder engine 106. A given CU with one or more PUs may also contain one or more TUs. As described in further detail below, block transforms can be used to transform residual values ​​into transform coefficients, and then TUs can be used to quantize and scan the residual values ​​to produce serialized transform coefficients for entropy decoding.

[0068] In some instances, after intra-frame predictive or inter-frame predictive decoding using the PU of the CU, the encoder engine 106 may compute residual data for the TU of the CU. The PU may include pixel data in the spatial domain (or pixel domain). After applying the block transform, the TU may include coefficients in the transform domain. As previously mentioned, the residual data may correspond to the pixel difference between the pixels of the uncoded image and the predicted value corresponding to the PU. The encoder engine 106 may form a TU containing the residual data for the CU, and then transform the TU to produce transform coefficients for the CU.

[0069] The encoder engine 106 performs quantization of the transform coefficients. Quantization provides further compression by reducing the amount of data used to represent the coefficients. For example, quantization can reduce the bit depth associated with some or all of the coefficients. In one instance, a coefficient with an n-bit value can be rounded down to an m-bit value during quantization, where n is greater than m.

[0070] Once quantization is performed, the decoded video bitstream contains quantized transform coefficients, prediction information (e.g., prediction modes, motion vectors, block vectors, etc.), segmentation information, and any other suitable data such as other syntax data. The different elements of the decoded video bitstream can then be entropy encoded by encoder engine 106. In some instances, encoder engine 106 may use a predefined scan order to scan the quantized transform coefficients to produce a serialized vector that can be entropy encoded. In some instances, encoder engine 106 may perform adaptive scanning. After scanning the quantized transform coefficients to form a vector (e.g., a one-dimensional vector), encoder engine 106 can entropy encode the vector. For example, encoder engine 106 may use context-adaptive variable-length decoding, context-adaptive binary arithmetic decoding, syntax-based context-adaptive binary arithmetic decoding, probabilistic interval segmentation entropy decoding, or another suitable entropy coding technique.

[0071] As previously described, the HEVC bitstream comprises a group of NAL units, which includes VCL NAL units and non-VCL NAL units. VCL NAL units contain decoded picture data that forms the decoded video bitstream. For example, the bit sequence forming the decoded video bitstream is retransmitted in a VCL NAL unit. Non-VCL NAL units may also contain parameter sets with higher-level information related to the encoded video bitstream, plus other information. For example, parameter sets may include a Video Parameter Set (VPS), a Sequence Parameter Set (SPS), and a Picture Parameter Set (PPS). Instances of objectives for parameter sets include bit rate efficiency, error resiliency, and providing a system-level interface. Each slice references a single active PPS, SPS, and VPS to access information that can be used by the decoding device 112 to decode the slice. An identifier (ID) can be decoded for each parameter set, including a VPS ID, an SPS ID, and a PPS ID. An SPS includes an SPS ID and a VPS ID. A PPS includes a PPS ID and an SPS ID. Each slice header contains a PPS ID. When using the ID, the set of active parameters can be identified for a given slice.

[0072] A PPS contains information applicable to all slices within a given image. Thus, all slices within an image reference the same PPS. Slices in different images can also reference the same PPS. An SPS contains information applicable to all images within the same decoded video sequence (CVS) or bitstream. As previously described, a decoded video sequence is a series of access units (AUs) that begins with a random access point image (e.g., an instantaneous decode reference (IDR) image or a broken link access (BLA) image, or other suitable random access point image) in the base layer and has certain properties (described above), until and does not contain the next AU (or the end of the bitstream) with a random access point image in the base layer and having certain properties. The information in the SPS may not change with different images within the decoded video sequence. Images within a decoded video sequence can use the same SPS. A VPS contains information applicable to all layers within the decoded video sequence or bitstream. A VPS contains a syntax structure with syntax elements applicable to the entire decoded video sequence. In some instances, a VPS, SPS, or PPS can be transmitted within a frequency band using a coded bitstream. In some instances, VPS, SPS, or PPS can be transmitted out of band in a separate transmission compared to NAL units containing decoded video data.

[0073] Video bitstreams may also include Supplemental Enhancement Information (SEI) messages. For example, an SEI NAL unit may be part of the video bitstream. In some cases, SEI messages may contain information not required for the decoding process. For instance, the information in an SEI message may not be necessary for the decoder to decode video images in the bitstream, but the decoder can use the information to improve the display or processing of the images (e.g., the decoded output). The information in an SEI message may be embedded metadata. In one illustrative example, the information in an SEI message may be used by a decoder-side entity to improve the viewability of the content. In some cases, certain application standards may mandate the presence of such SEI messages in the bitstream so that all devices conforming to the application standard can benefit from improved quality (e.g., the carrying of frame-wrapped SEI messages for frame-compatible planar stereoscopic 3DTV video formats, where an SEI message is carried for each frame of the video; the handling of recovery point SEI messages; the use of pull-scan rectangle SEI messages in DVB; and many other examples).

[0074] The output 110 of the encoding device 104 can transmit the NAL units constituting the encoded video data to the decoding device 112 of the receiving device via the communication link 120. The input 114 of the decoding device 112 can receive the NAL units. The communication link 120 may include a channel provided by a wireless network, a wired network, or a combination of wired and wireless networks. The wireless network may include any wireless interface or combination of wireless interfaces, and may include any suitable wireless network (e.g., the Internet or other wide area networks, packet-based networks, WiFi™, radio frequency (RF), UWB, WiFi-Direct, cellular, LTE, WiMax™, etc.). The wired network may include any wired interface (e.g., fiber optic, Ethernet, powerline Ethernet, Ethernet via coaxial cable, digital signal line (DSL), etc.). Various devices such as base stations, routers, access points, bridges, gateways, switches, etc., can be used to implement wired and / or wireless networks. The encoded video data can be modulated according to a communication standard such as a wireless communication protocol and transmitted to the receiving device.

[0075] In some instances, encoding device 104 may store encoded video data in storage device 108. Output 110 may retrieve encoded video data from encoder engine 106 or from storage device 108. Storage device 108 may comprise any of a variety of distributed or locally accessed data storage media. For example, storage device 108 may comprise a hard disk drive, optical disk drive, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0076] Input 114 of decoding device 112 receives encoded video bitstream data and can provide the video bitstream data to decoder engine 116 or to storage device 118 for later use by decoder engine 116. Decoder engine 116 decodes the encoded video bitstream data by entropy decoding (e.g., using an entropy decoder) and extracting elements that make up one or more decoded video sequences of the encoded video data. Decoder engine 116 can then rescale the encoded video bitstream data and perform an inverse transform on it. The residual data is then passed to the prediction stage of decoder engine 116. Decoder engine 116 then predicts pixel blocks (e.g., PUs). In some instances, the prediction is added to the output of the inverse transform (residual data).

[0077] Decoding device 112 can output decoded video to a video destination device, which may include a display or other output device for displaying the decoded video data to a user of the content. In some aspects, video destination device 122 may be part of a receiving device that includes decoding device 112. In some aspects, video destination device 122 may be part of a separate device other than a receiving device.

[0078] In some instances, video encoding device 104 and / or video decoding device 112 may be integrated with audio encoding device and audio decoding device, respectively. Video encoding device 104 and / or video decoding device 112 may also include other hardware or software necessary for implementing the decoding techniques described above, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware, or any combination thereof. Video encoding device 104 and video decoding device 112 may be integrated as part of a combined encoder / decoder (codec) in the respective device. References below... Figure 9 Examples describing specific details of the encoding device 104. See below for reference. Figure 10 Examples describing specific details of the decoding device 112.

[0079] Extensions to the HEVC standard include the Multi-View Video Decoding Extension, known as MV-HEVC, and the Scalable Video Decoding Extension, known as SHVC. Both MV-HEVC and SHVC extensions share the concept of layered decoding, where different layers are contained within the encoded video bitstream. Each layer in the decoded video sequence is addressed by a unique layer identifier (ID). The layer ID may exist in the header of a NAL unit to identify the layer associated with that NAL unit. In MV-HEVC, different layers typically represent different views of the same scene in the video bitstream. In SHVC, different scalable layers are provided to represent the video bitstream at different spatial resolutions (or picture resolutions) or different reconstruction fidelities. A scalable layer may contain a base layer (where layer ID = 0) and one or more enhancement layers (where layer IDs = 1, 2, ..., n). The base layer may conform to the first version of the HEVC profile and represents the lowest available layer in the bitstream. Compared to the base layer, enhancement layers have increased spatial resolution, temporal resolution, or frame rate, and / or reconstruction fidelity (or quality). Enhancement layers are organized hierarchically and may (or may not) depend on lower layers. In some instances, a single standard codec can be used to decode different layers (e.g., using HEVC, SHVC, or other decoding standards to encode all layers). In other instances, multiple standard codecs can be used to decode different layers. For example, AVC can be used to decode the base layer, while SHVC and / or MV-HEVC extensions to the HEVC standard can be used to decode one or more enhancement layers.

[0080] Video compression techniques perform spatial and temporal prediction to reduce or remove inherent redundancy in the input video signal. To reduce temporal redundancy (i.e., visual similarity in adjacent frames), motion estimation is performed to track object movement in the video. Motion estimation is the process of identifying the best-matching (e.g., most similar) pixel block in a reference frame (or two reference frames used for bidirectional prediction) for a given pixel block from the current frame. One or more reference indices can be used to identify one or more reference frames for the current block. Pixel blocks in the reference frames can be called candidate blocks, predictors, or prediction blocks. The size of the blocks can vary. The offset between the current block from the current frame and the candidate block from the reference frames can be characterized as a motion vector, which indicates the degree and direction of displacement.

[0081] Motion vectors indicate displacement in pixels. In some cases, motion vectors can have a level of precision higher than integer pixel accuracy, such as half-pixel, quarter-pixel, or 1 / 16th of a pixel distance. This higher level of precision allows video decoders to track motion fields more accurately and thus achieve better predictions.

[0082] When a video decoder is reconstructing a frame using fractional pixel values ​​and encounters a motion vector, it can perform interpolation to produce fractional pixel values. For example, and as further discussed below, the video decoder can apply an interpolation filter to available pixels to produce interpolated pixels for half-pixel, quarter-pixel, or some other fractional pixel location.

[0083] Many video codecs use fixed interpolation filters. With fixed interpolation filters, both the encoder and decoder can be provided with filter coefficients in advance, and these coefficients do not need to be provided in the encoded bitstream.

[0084] However, motion estimation and motion compensation can be optimized by using an optimal interpolation filter instead of a fixed filter. The optimal filter for a given situation tends to be highly localized and content-dependent. Using the optimal filter can therefore increase encoder complexity and / or significantly increase signal transmission overhead, as filter coefficients will need to be transferred from the encoder to the decoder.

[0085] In various implementations, systems and methods are provided in which different interpolation filters can be applied to different decoding units and can be signaled with minimal additional increase in the size of the decoded bitstream. For example, for HEVC, a specific set of filter candidates may be available when the decoding unit is at the sequence level, picture level, coding tree unit level, decoding unit level, transform unit level, or prediction unit level, etc. Additionally, for JEM, a specific set of filter candidates may be available at the quadtree plus binary tree (QTBT) level, etc. In this document, a decoding unit may also be referred to as a block. In these and other instances, the video decoder can switch between interpolation filters while encoding video or decoding the bitstream.

[0086] In various implementations, a set of N filters can be defined, each with different characteristics (e.g., filter length, cutoff frequency, transition band, or ripple, and other characteristics). For blocks at different decoding levels, subsets of the N filter set can be defined. Using various criteria, the encoder can select filters from the filter subset. The selected filters can then be explicitly or implicitly signaled or indicated to the decoder. The subset of filters applied at a given level can vary based on, for example, the hit rate of filters in previous decoded blocks and other criteria. In some implementations, similar mechanisms can also be used to implicitly or implicitly signal filter selection for chroma components or integer pixel locations.

[0087] Figure 2 This illustrates an example of the encoding process 200 for the current block 236 from the current frame. The current block 236 can also be referred to as a decoding unit. The current block 236 may be smaller than the entire current frame.

[0088] In this example, encoding process 200 first performs motion estimation 242 on the current block 236. Motion estimation 242 may involve identifying one or more reference frames from the available reference frames 264. Reference frames may include frames that appear before or after the current frame in time. Performing motion estimation 242 may involve searching for a search region in the reference frames to find the “best” match for the current block 236. The best match may be determined, for example, by subtracting the candidate region from the current block 236 to determine the residual energy. In this example, the candidate region with the lowest residual energy may be selected as the best match.

[0089] Motion estimation 242 further includes generating a motion vector 243 that estimates the direction and extent of movement of the current block 236 relative to a reference frame. In most cases, one or more reference indices are associated with the motion vector, where the reference indices identify the reference frame used to determine the motion vector. In some cases, after motion estimation, a rate distortion model, for example, can be used to select the optimal motion vector.

[0090] Motion compensation 244 may include generating a prediction block 245 by performing motion compensation using an optimal motion vector. The prediction block 245 is a block selected from a reference frame using the optimal motion vector. The prediction block 245 may be subtracted from the current block 236 to generate a residual block 251. A block transform 252 may be applied to the residual block 251. The resulting transform coefficients may undergo quantization 254 to generate quantized coefficients 255. Entropy decoding 256 may be applied to the quantized coefficients 255 to further reduce the bit rate and generate an encoded bitstream 210.

[0091] The quantization coefficients 255 can also be input into inverse quantization 258, and then into inverse transform 260. Inverse quantization 258 and inverse transform 260 are the reverse of block transform 252 and quantization 254, and produce a reconstructed residual block 261. The reconstructed residual block 261 can be added to the predicted block 245 to produce a reconstructed block 253. The reconstructed block 253 is substantially the same as the current block 236. The reconstructed video block 253 can be included in a reference frame for encoding additional blocks.

[0092] Example procedure 200 primarily describes temporal motion estimation. In other examples, such as the H.264 / AVC and HEVC coding processes, spatial prediction can also be performed to generate intra-frame decoded blocks. (Regarding...) Figure 9 To describe the encoding process in more detail.

[0093] As previously mentioned, the best-match reference block for the current block can be at a full-pixel offset from the current block or at a fractional-pixel offset. When motion information indicates that the best match is at a fractional-pixel position, the video decoder can reconstruct the block by interpolating the pixels at the fractional position from the pixels in the reference block.

[0094] Figure 3 Plot an example of fractional pixel positions. In Figure 3 In this example, block 300 from the reference frame is drawn, with a width of three pixels and a height of three pixels. Integer pixel positions (e.g., A) are represented using uppercase letters with shading. 0,0 A 1,0 A 0,1 A -1,0 A 0,-1 A 1,1 A 1,-1 A -1,1 and A -1,-1 Use lowercase letters to represent the quarter-pixel position, also referred to as the subpixel position in this article (e.g., a). 0,0 b 0,0 c 0,0 (etc.). In this example, there are 15 sub-pixel positions per pixel location, labeled a to r (note that "l" and "o" are omitted for clarity).

[0095] Various methods can be used to derive samples for sub-pixel locations. For example, half-pixel location b 0,0 The sample at location A can be obtained by taking the sample at location A. 0,0 and A 1,0 This is generated by averaging the pixels at that location. As another example, it comes from location A-1 of a neighboring block. ,0 A 1,0 A 0,0 and A 2,0 The pixels at location b can be averaged to produce a value for location b. 0,0 The sample.

[0096] In HEVC, the value for position a can be derived by applying an 8-pin filter to the sample closest to the integer position. 0,0 b 0,0 and c 0,0 Horizontal sub-pixel samples and used for position d 0,0 h 0,0 and n 0,0 The vertical sub-pixel samples. This can be achieved by applying an 8-pin filter to position a. 0,i b 0,i and c 0,i The sample at location e is used to derive the value for location e. 0,0 i 0,0 p 0,0 f 0,0 j 0,0 q 0,0 g 0,0 k 0,0 and r 0,0The samples are given, where i = -3…4. Table 1 shows examples of 8-tap brightness interpolation filters.

[0097] Table 1

[0098] Phase shift Coefficient 0 {0,0,0,64,0,0,0,0}, 1 {-1,4,-10,58,17,-5,1,0}, 2 {-1,4,-11,40,40,-11,4,-1}, 3 {0,1,-5,17,58,-10,4,-1},

[0099] Table 1 contains eight coefficients per phase shift and one coefficient per tap. Each phase shift corresponds to a quarter-pixel position. For example, a phase shift of 1 could correspond to sub-pixel position a. 0,0 and d 0,0 Phase shift 2 can correspond to sub-pixel position b 0,0 and h 0,0 And so on. In other instances, filters with longer taps (e.g., more coefficients) can be applied. Filters with longer taps can have different characteristics compared to 8-tap filters, and may require more complex calculations when applied.

[0100] In other video codecs that incorporate the codecs under development in JEM, 1 / 16 subpixel motion vector resolution can be enabled. For a 1 / 16 subpixel position, a filter with 16 phases can be used for interpolation. Example filters with 16 phases are provided in Table 2. However, in JEM, an 8-pin filter with fixed coefficients is used.

[0101] Table 2

[0102] Phase shift Coefficient 0 {0,0,0,64,0,0,0,0}, 1 {0,1,-3,63,4,-2,1,0}, 2 {-1,2,-5,62,8,-3,1,0}, 3 {-1,3,-8,60,13,-4,1,0}, 4 {-1,4,-10,58,17,-5,1,0}, 5 {-1,4,-11,52,26,-8,3,-1}, 6 {-1,3,-9,47,31,-10,4,-1}, 7 {-1,4,-11,45,34,-10,4,-1}, 8 {-1,4,-11,40,40,-11,4,-1}, 9 {-1,4,-10,34,45,-11,4,-1}, 10 {-1,4,-10,31,47,-9,3,-1}, 11 {-1,3,-8,26,52,-11,4,-1}, 12 {0,1,-5,17,58,-10,4,-1}, 13 {0,1,-4,13,60,-8,3,-1}, 14 {0,1,-3,8,62,-5,2,-1}, 15 {0,1,-2,4,63,-3,1,0}

[0103] See Figure 2 Content Adaptive Binary Arithmetic Decoding (CABAC) is a system that can be used for entropy decoding 256 to encode and decode syntax elements in a bitstream. CABAC achieves good compression performance by: selecting a probabilistic model for each syntax element, using the context of the element; adapting probability estimates based on local statistics; and using arithmetic decoding instead of variable-length decoding.

[0104] CABAC uses binary arithmetic decoding, meaning that only binary decisions (1 or 0) are encoded. Non-binary value symbols (such as transform coefficients or motion vectors, or any symbol with two or more possible values) are "binarized" or converted to binary code before arithmetic decoding. For each bit of the binaryized symbol, a context model is then selected. The context model is a probability model for one or more bits of the binaryized symbol. The context model is selected from available models based on statistics of the most recently decoded data symbols. The context model stores the probability of each bit as "1" or "0". The arithmetic decoder then encodes each bit according to the selected probability model. The selected context model is then updated based on the actual decoded value (e.g., if the bit value is "1", then the frequency count of "1" is incremented).

[0105] As an example, three candidate context models named skip_flag_C[0], skip_flag_C[1], and skip_flag_C[2] can be used to decode the syntax element cu_skip_flag. To select the appropriate context from the three candidates, the selection value x is calculated as:

[0106] x=(cu_skip_flag[xNbL][yNbL]&&availableL)+(cu_skip_flag[xNbA][yNbA]&&availableA)

[0107] For the above equations, the context model to be used can be determined as follows:

[0108] (x0, y0) specifies the position of the top left luminance sample of the current luminance block relative to the top left sample of the current image.

[0109] The position (xNbL, yNbL) can be set to (x0-1, y0), and the variable availableL can indicate the availability of the block located directly to the left of the current block.

[0110] The position (xNbA, yNbA) can be set to equal (x0, y0-1), and the variable availableA can specify the availability of the decoded block located directly above the current block.

[0111] cu_skip_flag[xNbL][yNbL] and cu_skip_flag[xNbA][yNbA] can represent the cu_skip_flag used for the first block (block L) and the second block (block A), respectively.

[0112] As mentioned above, the HEVC and codec implemented by JEM use a fixed interpolation filter when enabling subpixel motion vectors. For any given situation, the interpolation filter may not be optimal. For example, when the decoding unit has more detail, a filter with a higher cutoff frequency may be more appropriate, allowing for detail saving during interpolation. Conversely, when the processing unit has less detail, a filter with a lower cutoff frequency may be more appropriate, allowing the decoding unit to use fewer bits to be decoded.

[0113] Motion estimation and motion compensation can be optimized by using an optimal interpolation filter instead of a fixed filter. The optimal filter for a given situation tends to be highly localized and content-dependent. Using the optimal filter can therefore increase encoder complexity and / or significantly increase signal transmission overhead, as filter coefficients will need to be transferred from the encoder to the decoder.

[0114] In various implementations, the video decoder can be configured to switch between available interpolation filters when performing motion estimation and motion compensation for different prediction units. In some cases, interlayer prediction can be improved by adaptively selecting interpolation filters. In various implementations, a set of N filters can be defined, each having characteristics such as filter length, cutoff frequency, transition band, ripple, and / or combinations of characteristics.

[0115] f 400. Figure 4 The diagram also illustrates filter set 410, representing all filters defined for use by the codec. As discussed above, in motion estimation step 444, a reference block from reference frame 464 is determined. The reference block is the portion of reference frame 464 that best matches (e.g., is most similar to) the decoding unit 402 in appearance. In this example, decoding unit 402 can be a sequence, picture, slice, coding tree unit, decoding unit, transform unit, prediction unit, or some other video data block. When using the reference block, motion estimation 444 determines motion information 406 for decoding unit 402. Motion information 406 can include one or more motion vectors, and indices that can be used to identify the reference frame, etc.

[0116] exist Figure 4In this example, the motion estimation step 444 may also determine filter selection criteria 414. Filter selection criteria 414 can be used to select a subset 412 of filters (also referred to herein as filter candidates) suitable for a particular decoding unit 402. For example, in some embodiments, filter selection criteria 414 may be the decoding level of the decoding unit 402 (e.g., sequence level, picture level, slice level, coding tree unit level, decoding unit level, transform unit level, prediction unit level, etc.). In this example, the subset 412 of filters may be selected based on the decoding level of the decoding unit 402. For example, the specific filters in the subset and the number of filters in the subset may vary across different processing levels.

[0117] In various implementations, motion estimation 444 may select the optimal interpolation filter from the filter subset 412. For example, motion estimation 444 may use rate distortion optimization to determine which filter in the filter subset 412 provides the best compression. Various other methods may be used to select the optimal filter.

[0118] In various implementations, filter index 408 can be used to identify the selected filter. Filter index 408 can identify filters selected from filter subset 412. For example, possible indices can be 0, 1, or 2 (for F1, F3, and F9 respectively in the illustrated examples), and filter index 408 can be "0" when filter F1 is selected. In some cases, filter index 408 may be included in the output bit stream 420 along with motion information 406. In these implementations, filter index 408 may be explicitly signaled in the bit stream 420.

[0119] In some cases, filter index 408 may be implicitly transmitted via signaling; that is, filter index 408 is not included in bitstream 420 and may instead be derived by the decoder when decoding bitstream 420. For example, in some cases, filter selection criterion 414 results in a filter subset 412 containing only one filter. As another example, in some cases, filter subset 412 may contain multiple filters, but motion estimation 444 determines to use a default filter (e.g., filter F1 is always selected for time-combining candidates). In other instances, factors such as decoding level, prediction mode, and / or one or more of the decoding tools being used may be used by the decoder to derive appropriate filters.

[0120] In some implementations, motion estimation 444 may select filters based on static data derived from previous decoded blocks. For example, some filters from filter subset 412 may never be used in previous decoded blocks due to poor performance. In this example, motion estimation 444 may eliminate poorly performing filters when selecting filters for a particular current decoder 402. Conversely, when a particular filter has been used very frequently in previous decoded blocks, motion estimation 444 may prioritize that filter when selecting filters for a particular decoder 402.

[0121] In some implementations, motion estimation 444 may select a filter from neighboring blocks, such as spatial or temporal neighbors. For example, in some situations, decoding unit 402 may copy motion vectors from neighboring blocks. In this example, decoding unit 402 may also borrow filter indices from the same neighboring block. As another example, when several neighboring blocks use the same filter, motion estimation 444 may determine that decoding unit 402 should use the same filter.

[0122] In some implementations, filter selection criterion 414 may be based on various factors. For example, filters in filter subset 412 may be selected based on the prediction mode used for the current block (e.g., inter-frame prediction, intra-frame prediction, etc.), the resolution or difference of the motion vectors, the decoding tool being used (e.g., bidirectional optical flow), and / or pixels in overlapping block motion compensation. As another example, filters in filter subset 412 may be selected based on the size and / or shape of the current block, the resolution of the current frame, the distance between the current frame and the reference frame, and / or the quantization parameter (QP) value used for the reference image.

[0123] As an example, when decoding unit 402 is a large data set, such as a frame or slice, or when decoding unit 402 has very little detail, the filters in filter subset 412 can be filters with low cutoff frequencies. Filters with low cutoff frequencies tend to eliminate details, so when decoding unit 402 has very little detail, no data will be lost by using filters with low cutoff frequencies. As another example, when decoding unit 402 is a small data set, such as a decoding unit, or when decoding unit 402 has a high degree of detail, filter subset 412 can contain filters with high cutoff frequencies. Filters with high cutoff frequencies can preserve high-frequency components in decoding unit 402, and thus conserve detail.

[0124] In some implementations, additional filter candidates can be generated by merging filters from filter subset 412. For example, given two filter candidates, a third candidate can be generated by merging the even phase shift from the first candidate filter with the odd phase shift from the second candidate. As another example, a fourth candidate can be constructed by combining the odd phase shift from the first candidate with the even phase shift from the second candidate.

[0125] In some implementations, interpolation filters can be coupled. For example, interpolation filters for integer samples can be counted down to interpolation filters for fractional samples. In this example, the filter for integer samples may have a higher cutoff frequency compared to the filter with the smallest non-zero phase shift from the filter for fractional samples. Alternatively, the filter for integer samples may have a lower cutoff frequency compared to the filter for fractional samples.

[0126] In some implementations, the decoding tool is also associated with a filter. For example, a gradient filter can be used for bidirectional optical flow, and an improved filter can be used for frame rate upconversion. In some implementations, a tool-specific filter can be generated based on each filter candidate in the filter subset 412. For example, given three interpolation filter candidates, three gradient filters can be derived for bidirectional optical flow. In these implementations, by deriving the tool-specific filter, it is not necessary to describe the tool-specific filter in the output bitstream 420.

[0127] In some instances, when a filter is applied to both integer pixel locations and fractional pixel locations, the filter for the integer pixel locations can be applied first. The filtered integer samples can then be used as input for further interpolation to derive the fractional pixel samples.

[0128] In some instances, when a filter is applied to both integer pixel locations and fractional pixel locations, the filter for the integer pixel locations may only be applicable if the associated motion vector has integer-level precision. In these instances, unfiltered pixels at integer locations can be used as input to derive fractional pixel samples.

[0129] Figure 5 This diagram illustrates an example of motion estimation step 544 in the decoding process 500. Figure 5The diagram also illustrates a filter set 510, representing all filters defined for use by the codec. In the decoder process 500, motion estimation 544 can be used to reconstruct or predict prediction unit 502. For prediction unit 502 in the current frame, the coded bitstream 520 may contain motion information 506. Motion information 506 may include, for example, one or more motion vectors and an index to a reference frame 564. Using motion information 506, motion estimation 544 can identify reference blocks in the reference frame 564 and predict or generate prediction unit 502.

[0130] In some implementations, motion estimation 544 may also determine filter selection criteria 514. Filter selection criteria 514 can be used to select a subset 512 of filters suitable for prediction unit 502. For example, filter selection criteria 514 may be based on the decoding level of prediction unit 502, prediction mode, and / or the decoding tool being used. The specific filters in the subset and the number of filters in the subset may change as the decoded bitstream 520 is processed and as different situations arise.

[0131] In some cases, bitstream 520 includes an explicit filter index 508 that can be used to select a filter from filter subset 512. In various embodiments, filter index 508 may be associated with motion information 506. When filter index 508 is included in bitstream 520, filter index 508 is said to be explicitly signaled. Filter index 508 can identify the filter to be used for interpolation from filter subset 512. For example, possible indices may be 0, 1, or 2 (for F1, F3, and F9 respectively in the illustrated examples), and filter index 508 may be "0" when filter F1 is selected.

[0132] In some cases, the decoder process 500 may derive a filter index 508. For example, in some cases, the filter selection criterion 514 produces a filter subset 512 containing only one filter. As another example, in some cases, the filter subset 512 may contain multiple filters, but motion estimation 544 determines to use a default filter (e.g., filter F1 is always selected for time-combining candidates). In other instances, one or more factors, such as the decoding level, prediction mode, and / or the decoding tool being used, may be used by the decoder to derive the appropriate filter. Because the decoder should use the same filter determined by the encoder, the filter identifier will be signaled in the bit stream 520 if the decoder cannot deterministically derive the filter identifier.

[0133] Various methods can be used to determine the interpolation filter for use when the filter index is implicit. In some instances, the interpolation filter can be determined by other blocks encoded before the current block. For example, blocks that meet certain conditions can determine the filter by inferring or inheriting the filters selected for other blocks. For instance, when deriving the current motion vector from a previously decoded block (e.g., spatial merge candidate, affine merge candidate, and other candidates), the interpolation filter selected for the block from which the motion vector was derived can be used for the current block. In this instance, it may not be necessary to explicitly signal the filter index because: once the decoder has determined the motion vector, it can derive the filter for the current block without any additional information.

[0134] In some instances, the interpolation filter used for certain blocks may always be selected, or sometimes a predetermined default filter may be selected. In these instances, there is no need to search for or inherit filters from another block. In some situations, once determined, the default filter is applied at all decoding levels. In some instances, a subset of filters may be biased towards selecting specific filters. For example, filters may be tested sequentially, and a particular filter may be set as the first candidate for deriving motion vectors from frame rate upconversion, Temporal Motion Vector Prediction (TMVP), Advanced Motion Vector Prediction (AMVP), or zero motion vector merging candidates. In some instances, the default filter may change across frames and / or slices. For example, a frequently selected filter from a previous picture and / or slice may be set as the default filter for all blocks belonging to the current picture or slice. Because the decoder can emulate the same procedure without any side information from the encoder, it may not be necessary to explicitly signal the filter index.

[0135] If necessary, the filter index can be explicitly included in the bitstream in other ways. In some instances, a syntax element, which may be called "interpolation_filter_index", can be signaled by the encoder to the decoder to indicate the interpolation filter selected for blocks where the filter cannot be implicitly selected. Signaling means that interpolation_filter_index can be included in the bitstream for the decoder to read.

[0136] In some instances, the value of `interpolation_filter_index` can be binary-coded using, for example, fixed-length code, exponential Golomb code, unary code, or truncated unary code. For instance, when there are three filters in the filter subset, truncated unary code can be used to indicate `interpolation_filter_index`. In this example, two flags (e.g., FLAG0 and FLAG1) can be used to decode the three possible indices 0, 1, and 2 for the three filters in the subset. For example, the three indices can be decoded as (0, N / A), (1, 0), and (1, 1), respectively. In this example, only one flag (FLAG0) can be used to indicate `interpolation_filter_index = 0`.

[0137] In some instances, certain context models may be associated with `interpolation_filter_index`, which can be used when encoding `interpolation_filter_index`. For example, X number of context models may be associated with `interpolation_filter_index`, named, for example, `interpolation_filter_index_C[0]`, `interpolation_filter_index_C[1]`, ..., `interpolation_filter_index_C[X-1]`. In this instance, the context model `interpolation_filter_index_C[x]` with index x from these context models may be selected as the context for decoding the `interpolation_filter_index` used for the current block.

[0138] In some instances, when two flags (e.g., FLAG0 and FLAG1) can be used to represent the interpolation_filter_index, a certain number of context models may exist associated with each flag. For example, there may be Y context models associated with FLAG0, named interpolation_filter_index_C[0], interpolation_filter_index_C[1], ..., interpolation_filter_index_C[Y-1]. In this instance, when FLAG0 is set, the context model interpolation_filter_index_C[x] with index x may be selected as the context for decoding the interpolation_filter_index of the current block. In this instance, FLAG1 may not be set, or FLAG1 may be irrelevant. As another instance, there may be Z context models associated with FLAG1, named interpolation_filter_index_C[0], interpolation_filter_index_C[1], ..., interpolation_filter_index_C[Z-1]. In this example, when FLAG1 is set, the context model `interpolation_filter_index_C[x]` with index `x` is selected as the context for decoding the `interpolation_filter_index` of the current block. In this example, FLAG0 may not be set, or FLAG0 may be irrelevant.

[0139] In the examples above, x can be selected based on various criteria. For example, x can be based on the size of the current block, the shape of the current block, the resolution of the current frame, the inter-frame prediction direction, the motion vector used for the current block, the motion vector difference used for the current block, the reference frame used for the current block, the interpolation_filter_index of the neighboring blocks of the current block, some other criteria, or a combination of criteria. In various examples, a function can be used to produce the value of x, wherein the function can take one or more of the criteria in the examples above as input. In some examples, different functions can be used for different frame resolutions.

[0140] In some instances, a threshold P can be used to determine the value of x when it is based on the size of the current block. For example, x can be 0 if the size of the current block is less than P; otherwise, x can be 1. The threshold P can be an integer. The size of the current block can be calculated as M×N, where M and N are the width and height of the current block in pixels.

[0141] In some instances, when x is based on the size of the current block, the value of x can be determined from an integer array {a K}, where the array is sorted in ascending order. For example, when a K-1 <= S < a K , x can be equal to K, where S is the size of the current block. In this instance, S can be the number of pixels in the current block, calculated as M × N, where M and N are the width and height of the current block, in pixels.

[0142] In some instances, when x is based on the shape of the current block, the value of x can be determined from the relationship between the height and width of the block. For example, given the height M and width N of the current block, when M < N, x can be equal to 0; when M = N, x can be equal to 1; and when M > N, x can be equal to 2.

[0143] In some instances, when x is based on the prediction direction of the current block, the value of x can be determined from the prediction direction. For example, when using uni - directional inter - frame prediction to decode the current block, x can be equal to 0, and when using bi - directional inter - frame prediction to decode the current block, x can be equal to 1. As another example, the value of x can be based on the value InterDir, where when using uni - directional inter - frame prediction from reference list 0 to decode the current block, InterDir is 1; when using uni - directional inter - frame prediction from reference list 1 to decode the current block, InterDir is 2; and when using bi - directional inter - frame prediction to decode the current block, InterDir is 3. In this instance, x can be equal to InterDir - 1.

[0144] In some instances, when x is based on the interpolation_filter_index of adjacent blocks, the value of x can be determined from the interpolation_filter_index of one or more adjacent blocks. For example, the value of x can be determined by the function f(left_idx, top_idx), where left_idx is the interpolation_filter_index of the left adjacent block, and top_idx is the interpolation_filter_index of the top adjacent block. The function f can be any function. In some instances, different functions can be used for different frame resolutions. Alternatively or additionally, the value of x can be equal to a + b, where a is equal to 1 when the interpolation_filter_index of the left adjacent block is available and greater than zero (otherwise a is equal to 0), and b is equal to 1 when the interpolation_filter_index of the top adjacent block is available and greater than zero (otherwise b is equal to 0).

[0145] In some instances, a combination of factors can be considered when determining the value of x. For example, the size of the current block can be used to select the interpolation_filter_index value from neighboring blocks. For instance, when the size of the current image is less than a threshold P, x can be equal to the result of f(left_idx, top_idx), where P is an integer and the size of the current block is calculated as M×N, where M and N are the width and height of the current block in pixels. When the size of the current block is greater than or equal to P, x can be equal to the output of the function g(left_idx, top_idx).

[0146] Now, we will describe an example application of switching interpolation filters. As mentioned above, the optimal filter can be selected for each of N filters that may have different characteristics. For example, rate distortion optimization or some other selection mechanism can be used to select the optimal filter.

[0147] To reduce encoder complexity, the best filter can be inherited from a previously decoded block, reused from a previous decision, or fixed without evaluating the performance of all available filters. To reduce signal transmission overhead, a fixed set of filters can be determined in advance, and the encoder can transmit filter indices to the decoder as signals instead of filter coefficients.

[0148] The following example uses JEM3.0 based on HM16.6 to illustrate the application of switching interpolation filters. JEM is a project of the International Telecommunication Union Video Decoding Experts Group (ITU-VCEG) and the International Organization for Standardization / International Electrotechnical Commission Animation Experts Group (ISO / IEC MPEG). JEM provides reference software for a platform to research and potentially standardize video decoding technologies with better compression capabilities than HEVC.

[0149] In the following examples, the decoding unit is a block defined in a QTBT structure implemented on JEM3.0. In other examples, the decoding unit can be a larger structure, such as a QTBT block, CTU, slice, image, sequence, or a collection of other suitable decoding units. It should be noted that the examples only show interpolation filters for the luma component, and switching interpolation filters can be extended to the chroma component and integer samples.

[0150] In this example, the interpolation filter candidate set contains three filters with different characteristics: one 12-tap filter (F0) and two 8-tap filters (F1 and F2). Filter F0 is plotted in Table 3, filter F1 in Table 4, and filter F2 in Table 5. In this example, the filter candidate set remains consistent across different images and / or slices. Because JEM3.0 supports motion vector resolution up to 1 / 16, each filter candidate is constructed with 16 different phase shifts, as shown in the following tables.

[0151] Table 3

[0152] Phase shift Coefficient (F0) 0 {0,0,0,0,0,256,0,0,0,0,0,0}, 1 {-1,2,-4,7,-14,254,16,-7,4,-2,1,0}, 2 {-1,4,-7,12,-27,249,35,-15,8,-4,2,0}, 3 {-2,5,-10,17,-36,241,54,-22,12,-6,3,0}, 4 {-2,6,-12,21,-44,232,75,-30,16,-9,4,-1}, 5 {-2,7,-13,24,-49,215,97,-36,19,-10,5,-1}, 6 {-2,7,-14,26,-51,198,119,-42,22,-12,6,-1}, 7 {-2,7,-14,26,-52,183,140,-47,24,-13,6,-2}, 8 {-2,7,-14,26,-50,161,161,-50,26,-14,7,-2}, 9 {-2,6,-13,24,-47,140,183,-52,26,-14,7,-2}, 10 {-1,6,-12,22,-42,119,198,-51,26,-14,7,-2}, 11 {-1,5,-10,19,-36,97,215,-49,24,-13,7,-2}, 12 {-1,4,-9,16,-30,75,232,-44,21,-12,6,-2}, 13 {0,3,-6,12,-22,54,241,-36,17,-10,5,-2}, 14 {0,2,-4,8,-15,35,249,-27,12,-7,4,-1}, 15 {0,1,-2,4,-7,16,254,-14,7,-4,2,-1},

[0153] Table 4

[0154]

[0155]

[0156] Table 5

[0157] Phase shift Coefficient (F2) 0 {0,0,0,256,0,0,0,0,}, 1 {1,15,61,97,70,17,-3,-2,}, 2 {0,13,58,96,73,20,-2,-2,}, 3 {0,11,55,95,75,23,-1,-2,}, 4 {0,10,51,94,77,26,0,-2,}, 5 {0,8,48,92,80,29,1,-2,}, 6 {-1,7,45,90,82,32,2,-1,}, 7 {-1,5,41,88,86,35,3,-1,}, 8 {-1,4,38,87,87,38,4,-1,}, 9 {-1,3,35,86,88,41,5,-1,}, 10 {-1,2,32,82,90,45,7,-1,}, 11 {-2,1,29,80,92,48,8,0,}, 12 {-2,0,26,77,94,51,10,0,}, 13 {-2,-1,23,75,95,55,11,0,}, 14 {-2,-2,20,73,96,58,13,0,}, 15 {-2,-3,17,70,97,61,15,1,},

[0158] Figure 6 The frequency response graphs for three example filters, F0, F1, and F2, are plotted. Each curve corresponds to the same phase shift of 8 for each filter. As illustrated in this example, filter F0 has a high cutoff frequency, while filter F2 has a low cutoff frequency. Filter F1 has a fairly neutral cutoff frequency.

[0159] Continuing with the example, for a given decoding unit, one of filters F0, F1, and F2 can be selected. The selected filter can be implicitly or explicitly transmitted via a signal.

[0160] In this example, because the decoder can mimic the same procedure performed by the encoder to determine candidates for merging motion vectors without any side information from the encoder, an implicit signaling of the filter index is enabled for the merging mode. For example, the interpolation filter for the decoding unit can be determined by inheriting the filter index from the block that derives the current motion or by selecting the default filter, which is filter F0 in this example.

[0161] Continuing with the example, filter inheritance can be used when deriving the current motion from a spatial merge candidate, a combined merge candidate when two candidates being merged use the same filter, and an affine merge candidate. In each of these cases, the contents of the inherited block can influence the choice of filter. Also in this example, when deriving the current motion vector from a frame rate up-conversion merge candidate or a temporal merge candidate (e.g., TMVP, AMVP, STMVP, and zero motion vector) candidate, a default filter F0 is selected. In each of these cases, a filter with a high cutoff frequency may be needed to conserve detail within the block.

[0162] Continuing with the example, explicit signaling for filter indexing is enabled for AMVP mode. In JEM 3.0, two additional rate-distortion optimizations are included in the encoder, which can be used to select the best filter from three instance filter candidates. The additional optimization process can be simplified by reusing integer motion vectors; or by skipping the additional process by reusing the filter selected in a specific configuration. As an example, for the illumination compensation (IC) tool, when illumination compensation is on, the filter selected when illumination compensation is off can be reused. This reduces encoding time.

[0163] Continuing with the example, when explicitly signaling the filter index is enabled, `interpolation_filter_index` can be binary-coded using "0" for F0, "10" for F1, and "11" for F2. Two flags, FLAG0 and FLAG1, can be used to decode `interpolation_filter_index` as follows:

[0164] FLAG0

[0165] if(FLAG0)

[0166] FLAG1

[0167] Continuing with the above example, two contexts can be provided for each flag: (FLAG0_ctx0, FLAG0_ctx1) for FLAG0 and (FLAG1_ctx0, FLAG1_ctx1) for FLAG1. As an example, when using one-way prediction to decode the current block, FLAG0_ctx0 can be used to decode FLAG0, and FLAG1_ctx0 can be used to decode FLAG1. As another example, when using two-way prediction to decode the current block, FLAG0_ctx1 can be used to decode FLAG0, and FLAG1_ctx1 can be used to decode FLAG1.

[0168] In another instance of encoding two interpolation candidates F0 and F2, the `interpolation_filter_index` can be binary-coded as "0" for F0 and "1" for F1. In this instance, a flag can be used to decode the `interpolation_filter_index`. Each flag can have associated contexts `FLAG0_ctx0` and `FLAG0_ctx1`. When the current block size is less than (for the purposes of this instance) 256, `FLAG0_ctx0` can be used to decode `FLAG0`. Otherwise, when the size is greater than or equal to 256, `FLAG0_ctx1` can be used to decode `FLAG0`. The size of the current block is calculated as w × h, where w and h represent the width and height of the current block, respectively, in pixels.

[0169] Figure 7 An example of process 700 for switching interpolation filters during the encoding process is illustrated. At 702, process 700 includes acquiring video data. Video data may be acquired, for example, from a video capture device such as a camera. Alternatively or additionally, video data may be read from a storage location.

[0170] At 704, the process includes an encoding / decoding unit, wherein the encoding process includes selecting interpolation filters for motion estimation and motion compensation for the decoding unit, wherein the interpolation filters are selected from a set of interpolation filters. In some embodiments, the interpolation filters are selected from a subset of interpolation filters. In some embodiments, the subset of interpolation filters is determined based on the decoding level of the decoding unit. In some embodiments, the subset is determined based on the prediction mode of the decoding unit. In some embodiments, the subset is determined based on the results of motion estimation. In some embodiments, the subset is determined based on the decoding tools used to decode the decoding unit.

[0171] In some implementations, the interpolation filter is selected from previously decoded blocks. In some implementations, the interpolation filter is selected from adjacent blocks.

[0172] In some implementations, the interpolation filter is combined with another interpolation filter, and the resulting combined interpolation filter is used for motion estimation.

[0173] In some embodiments, the interpolation filter is coupled to a second interpolation filter. In these embodiments, the interpolation filter can be used for integer pixel locations, and the second interpolation filter can be used for fractional pixel locations. In some embodiments, the interpolation filter and the second interpolation filter may have different cutoff frequencies.

[0174] At 706, process 700 includes generating an encoded video bitstream, wherein the video bitstream includes encoded decoding units. In some embodiments, the encoded video bitstream may contain explicit values ​​identifying selected interpolation filters, such as filter indices. In some embodiments, the values ​​of the interpolation filters may be implied from the encoded video bitstream.

[0175] Figure 8 This is an example of a process 800 used to switch interpolation filters during decoding. At 802, process 800 includes obtaining the encoded video bitstream. The bitstream may be obtained, for example, from a storage location and / or via a network.

[0176] At 804, process 800 includes determining a reference frame from the encoded video bitstream for the decoding unit in the current frame. The reference frame may be temporally before or after the current frame. The reference frame may be the same frame as the current frame.

[0177] At 806, process 800 includes determining interpolation filters from the set of interpolation filters. In some embodiments, the interpolation filters may be selected from a subset of interpolation filters from the set of interpolation filters. In some embodiments, the subset of interpolation filters may be determined based on the decoding level of the decoding unit. In some embodiments, the subset may be determined based on the prediction mode used for the decoding unit. In some embodiments, the subset may be determined based on the results of motion estimation. In some embodiments, the subset may be determined based on the decoding tools used to decode the decoding unit.

[0178] In some implementations, the interpolation filter may be selected from a previously decoded block. In some implementations, the interpolation filter may be selected from an adjacent block.

[0179] In some implementations, the interpolation filter can be combined with a second interpolation filter, and the resulting combined interpolation filter can be used for motion estimation.

[0180] In some embodiments, the interpolation filter may be coupled to a second interpolation filter. In these embodiments, the interpolation filter can be used for integer pixel locations, and the second interpolation filter can be used for fractional pixel locations. In some embodiments, the interpolation filter and the second interpolation filter may have different cutoff frequencies.

[0181] In some implementations, the encoded video bitstream contains explicit values ​​that identify the selected interpolation filters, such as filter indices. In some implementations, the process includes using data from the bitstream to derive the identifier of the interpolation filters.

[0182] At 808, process 800 includes using the reference frame determined at 804 and the interpolation filter determined at 806 to reconstruct the decoding unit.

[0183] The decoding techniques discussed herein can be implemented in example video encoding and decoding systems (such as System 100). In some instances, the system includes a source device that provides encoded video data that will later be decoded by a destination device. Specifically, the source device provides video data to the destination device via computer-readable media. The source and destination devices can include any of a wide range of devices, including desktop computers, laptop computers, tablet computers, set-top boxes, mobile phones such as so-called "smart" phones, so-called "smart" tablets, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, and so on. In some cases, the source and destination devices may be equipped for wireless communication.

[0184] A destination device may receive encoded video data to be decoded via a computer-readable medium. The computer-readable medium may include any type of media or device capable of moving encoded video data from a source device to a destination device. In one example, the computer-readable medium may include communication media enabling the source device to transmit encoded video data directly to the destination device in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to the destination device. The communication medium may include any wireless or wired communication media, such as radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other devices that can be used to facilitate communication from the source device to the destination device.

[0185] In some instances, encoded data can be output from an output interface to a storage device. Similarly, encoded data can be accessed from a storage device via an input interface. The storage device can comprise any of a variety of distributed or locally accessible data storage media, such as hard disk drives, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. In other instances, the storage device can correspond to a file server or another intermediate storage device capable of storing encoded video generated by a source device. The destination device can access the stored video data from the storage device via streaming or downloading. The file server can be any type of server capable of storing encoded video data and transferring the encoded video data to the destination device. Example file servers include web servers (e.g., for websites), FTP servers, network attached storage (NAS) devices, or local disk drives. The destination device can access the encoded video data via any standard data connection including an internet connection. This connection may include a wireless channel (e.g., Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both, suitable for accessing encoded video data stored on a file server. The transfer of encoded video data from the storage device may be streaming, downloading, or a combination thereof.

[0186] The technology of this invention is not necessarily limited to wireless applications or settings. It can be applied to video decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, internet streaming video transmission such as HTTP Dynamic Adaptive Streaming (DASH), digital video encoded to data storage media, decoding digital video stored on data storage media, or other applications. In some instances, the system can be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and / or video telephony.

[0187] In one example, the source device includes a video source, a video encoder, and an output interface. The destination device may include an input interface, a video decoder, and a display device. The video encoder of the source device may be configured to apply the techniques disclosed herein. In other examples, the source and destination devices may include other components or arrangements. For instance, the source device may receive video data from an external video source, such as an external camera. Similarly, the destination device may interface with an external display device, rather than including an integrated display device.

[0188] The above example system is merely one instance. The techniques for parallel processing of video data can be performed by any digital video encoding and / or decoding device. Although the techniques of this invention are typically performed by video encoding devices, they can also be performed by video encoders / decoders, commonly referred to as "codecs." Furthermore, the techniques of this invention can also be performed by video preprocessors. The source and destination devices are merely examples of such decoding devices that generate decoded video data for transmission to the destination device. In some instances, the source and destination devices may operate in a substantially symmetrical manner, such that each of the devices includes video encoding and decoding components. Therefore, the example system can support one-way or two-way video transmission between video devices, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0189] A video source may include a video capture device, such as a video camera, a video archive containing previously captured video, and / or a video feed interface for receiving video from a video content provider. Alternatively, the video source may generate computer-graphics-based data as source video, or a combination of live video, archived video, and computer-generated video. In some cases, if the video source is a video camera, the source and destination devices may form a so-called camera phone or video phone. However, as mentioned above, the techniques described in this invention are generally applicable to video decoding and can be applied to wireless and / or wired applications. In each case, captured, pre-captured, or computer-generated video can be encoded by a video encoder. The encoded video information can then be output to a computer-readable medium via an output interface.

[0190] As mentioned, computer-readable media can include: transient media, such as wireless broadcasting or wired network transmissions; or storage media (i.e., non-transitory storage media), such as hard disks, flash drives, compact optical discs, digital video optical discs, Blu-ray discs, or other computer-readable media. In some instances, a network server (not shown) can receive encoded video data from a source device and provide the encoded video data to a destination device, for example, via a network transmission. Similarly, a computing device in a media production facility, such as an optical disc stamping facility, can receive encoded video data from a source device and produce an optical disc containing the encoded video data. Therefore, in various instances, computer-readable media can be understood to include one or more computer-readable media of various forms.

[0191] The input interface of the destination device receives information from a computer-readable medium. The information in the computer-readable medium may include grammatical information defined by a video encoder and also used by a video decoder. This grammatical information includes descriptive blocks and other characteristics and / or processed grammatical elements of a decoding unit (e.g., a group of pictures (GOP)). The display device displays the decoded video data to the user and may include any of a variety of display devices, such as a cathode ray tube (CRT), liquid crystal display (LCD), plasma display, organic light-emitting diode (OLED) display, or another type of display device. Various embodiments of the invention have been described.

[0192] Figure 9 and Figure 10 The image shows specific details of the encoding device 104 and the decoding device 112 respectively. Figure 9 This is a block diagram illustrating an example encoding apparatus 104 that may implement one or more of the techniques described herein. Encoding apparatus 104 may, for example, generate the syntax structures described herein (e.g., syntax structures of VPS, SPS, PPS, or other syntax elements). Encoding apparatus 104 may perform intra-frame prediction and inter-frame prediction decoding of video blocks within a video slice. As previously described, intra-frame decoding relies at least in part on spatial prediction to reduce or remove spatial redundancy within a given video frame or picture. Inter-frame decoding relies at least in part on temporal prediction to reduce or remove temporal redundancy within neighboring or surrounding frames of a video sequence. Intra-frame mode (I-mode) may refer to any of several spatially based compression modes. For example, inter-frame modes with unidirectional prediction (P-mode) or bidirectional prediction (B-mode) may refer to any of several temporally based compression modes.

[0193] The encoding device 104 includes a segmentation unit 35, a prediction processing unit 41, a filter unit 63, an image memory 64, a summer 50, a transform processing unit 52, a quantization unit 54, and an entropy coding unit 56. The prediction processing unit 41 includes a motion estimation unit 42, a motion compensation unit 44, and an intra-frame prediction processing unit 46. For video block reconstruction, the encoding device 104 also includes an inverse quantization unit 58, an inverse transform processing unit 60, and a summer 62. The filter unit 63 is intended to represent one or more loop filters, such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although the filter unit 63... Figure 9 The filter unit 63 is shown as an in-loop filter, but in other configurations, it may be implemented as a post-loop filter. The post-processing unit 57 may perform additional processing on the encoded video data generated by the encoding unit 104. In some cases, the techniques of the present invention may be implemented by the encoding unit 104. However, in other cases, one or more of the techniques of the present invention may be implemented by the post-processing unit 57.

[0194] like Figure 9 As shown, encoding device 104 receives video data, and segmentation unit 35 segments the data into video blocks. Segmentation may also include segmentation into slices, segments, picture blocks, or other larger units, as well as video block segmentation, for example, according to a quadtree structure of LCUs and CUs. Encoding device 104 is generally illustrated as the components for encoding video blocks within a video slice to be encoded. The slice can be divided into multiple video blocks (and possibly into a set of video blocks referred to as picture blocks). Prediction processing unit 41 can select one of multiple possible decoding modes for the current video block based on error results (e.g., decoding rate and distortion level, etc.), such as one of multiple intra-frame prediction decoding modes or one of multiple inter-frame prediction decoding modes. Prediction processing unit 41 can provide the resulting intra-frame or inter-frame decoded blocks to summer 50 to produce residual block data, and provide the resulting intra-frame or inter-frame decoded blocks to summer 62 to reconstruct the encoded blocks for use as reference pictures.

[0195] The intra-prediction processing unit 46 within the prediction processing unit 41 can perform intra-prediction decoding of the current video block relative to one or more adjacent blocks in the same frame or slice as the current block to be decoded, to provide spatial compression. The motion estimation unit 42 and motion compensation unit 44 within the prediction processing unit 41 perform inter-prediction decoding of the current video block relative to one or more predictive blocks in one or more reference pictures, to provide temporal compression.

[0196] Motion estimation unit 42 can be configured to determine an inter-frame prediction mode for video slices based on a predetermined pattern for the video sequence. The predetermined pattern can designate video slices in the sequence as P-slices, B-slices, or GPB-slices. Motion estimation unit 42 and motion compensation unit 44 can be highly integrated, but are shown separately for conceptual purposes. Motion estimation performed by motion estimation unit 42 is the process of generating motion vectors to estimate the motion of video blocks. For example, the motion vector can indicate the displacement of the prediction unit (PU) of a video block within the current video frame or picture relative to a predictive block within a reference picture.

[0197] A predictive block is a block found to be a close match of the PU (Power Unit) to the video block to be decoded in terms of pixel differences, which can be determined by the sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics. In some instances, the encoding device 104 can calculate the values ​​of the second-integer pixel positions of a reference image stored in the image memory 64. For example, the encoding device 104 can interpolate the values ​​of the quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference image. Therefore, the motion estimation unit 42 can perform motion search with respect to full-pixel positions and fractional pixel positions and output a motion vector with fractional pixel accuracy.

[0198] The motion estimation unit 42 calculates the motion vector of the PU for a video block in the inter-frame decoded slice by comparing the position of the PU with the position of a predictive block in a reference image. The reference image can be selected from a first reference image list (list 0) or a second reference image list (list 1), each of which identifies one or more reference images stored in the reference memory 64. The motion estimation unit 42 sends the calculated motion vector to the entropy coding unit 56 and the motion compensation unit 44.

[0199] Motion compensation performed by motion compensation unit 44 may involve extracting or generating predictive blocks based on motion vectors determined by motion estimation, possibly performing subpixel-accuracy interpolation. Upon receiving the motion vector of the PU for the current video block, motion compensation unit 44 can locate the predictive block pointed to by the motion vector in a list of reference images. Encoding device 104 forms a residual video block by subtracting the pixel values ​​of the predictive block from the pixel values ​​of the current video block being decoded, resulting in a pixel difference. The pixel difference forms residual data for the block and may include both luminance and chrominance difference components. Summer 50 represents the component or components performing this subtraction operation. Motion compensation unit 44 may also generate syntax elements associated with video blocks and video slices for decoding device 112 to use as video blocks in the video slices.

[0200] As an alternative to the inter-frame prediction performed by the motion estimation unit 42 and motion compensation unit 44 as described above, the intra-frame prediction processing unit 46 can intra-predict the current block. Specifically, the intra-frame prediction processing unit 46 can determine an intra-frame prediction mode for encoding the current block. In some instances, the intra-frame prediction processing unit 46 can use various intra-frame prediction modes to encode the current block, for example, during individual encoding passes, and the intra-frame prediction processing unit 46 can select an appropriate intra-frame prediction mode from tested modes for use. For example, the intra-frame prediction processing unit 46 can use rate-distortion analysis for various tested intra-frame prediction modes to calculate rate-distortion values, and can select the intra-frame prediction mode with the best rate-distortion characteristics from the tested modes. Rate-distortion analysis generally determines the amount of distortion (or error) between the coded block and the original uncoded block encoded to produce the coded block, as well as the bit rate (i.e., the number of bits) used to generate the coded block. Intra-prediction processing unit 46 can calculate the ratio from the distortion and rate of various coded blocks to determine which intra-prediction mode displays the optimal rate-distortion value for the block.

[0201] In any situation, after selecting an intra-prediction mode for a block, the intra-prediction processing unit 46 may provide information indicating the selected intra-prediction mode for the block to the entropy coding unit 56. The entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. The coding device 104 may include in the transmitted bitstream configuration data the definition of the context encoded for various blocks, as well as the most likely intra-prediction mode to be used for each context, an intra-prediction mode index table, and an indication of the modified intra-prediction mode index table. The bitstream configuration data may include multiple intra-prediction mode index tables and multiple modified intra-prediction mode index tables (also called codeword mapping tables).

[0202] After the prediction processing unit 41 generates a predictive block for the current video block via inter-frame prediction or intra-frame prediction, the encoding device 104 forms a residual video block by subtracting the predictive block from the current video block. The residual video data in the residual block may be contained in one or more TUs and applied to the transform processing unit 52. The transform processing unit 52 transforms the residual video data into residual transform coefficients using, for example, a discrete cosine transform (DCT) or a conceptually similar transform. The transform processing unit 52 can transform the residual video data from the pixel domain to the transform domain, such as the frequency domain.

[0203] The transform processing unit 52 can send the resulting transform coefficients to the quantization unit 54. The quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process can reduce the bit depth associated with some or all of the coefficients. The degree of quantization can be modified by adjusting the quantization parameters. In some instances, the quantization unit 54 can then perform a scan of a matrix containing the quantized transform coefficients. Alternatively, the entropy coding unit 56 can perform the scan.

[0204] After quantization, entropy coding unit 56 entropy codes the quantized transform coefficients. For example, entropy coding unit 56 can perform context-adaptive variable-length decoding (CAVLC), context-adaptive binary arithmetic decoding (CABAC), syntax-based context-adaptive binary arithmetic decoding (SBAC), probabilistic interval partitioned entropy (PIPE) decoding, or another entropy coding technique. After entropy coding by entropy coding unit 56, the encoded bitstream can be transmitted to decoding device 112 or archived for later transmission or retrieval by decoding device 112. Entropy coding unit 56 can also entropy code the motion vectors and other syntax elements used for the current video slice being decoded.

[0205] The inverse quantization unit 58 and the inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel domain for later use as a reference block for reference images. The motion compensation unit 44 calculates the reference block by adding the residual block to a predictive block of one of the reference images in the reference image list. The motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values ​​for motion estimation. The summer 62 adds the reconstructed residual block to the motion-compensated predictive block generated by the motion compensation unit 44 to generate the reference block for storage in the image memory 64. The reference block can be used by the motion estimation unit 42 and the motion compensation unit 44 as a reference block for inter-frame prediction of blocks in subsequent video frames or images.

[0206] In this way, Figure 9 The encoding device 104 represents an instance of a video encoder configured to generate a syntax for the encoded video bitstream. The encoding device 104 may, for example, generate VPS, SPS, and PPS parameter sets as described above. The encoding device 104 may perform any of the techniques described herein, including the processes described above. The techniques of the present invention have been described substantially with respect to the encoding device 104, but as mentioned above, some of the techniques of the present invention may also be implemented by the post-processing device 57.

[0207] Figure 10 A block diagram illustrating an example decoding device 112 is provided. Decoding device 112 includes an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, a summer 90, a filter unit 91, and an image memory 92. The prediction processing unit 81 includes a motion compensation unit 82 and an intra-frame prediction processing unit 84. In some instances, decoding device 112 can perform operations related to... Figure 10 The encoding pass described by the encoding device 104 is generally the inverse of the decoding pass.

[0208] During the decoding process, decoding device 112 receives a encoded video bitstream representing video blocks of encoded video slices and associated syntax elements sent by encoding device 104. In some embodiments, decoding device 112 may receive the encoded video bitstream from encoding device 104. In some embodiments, decoding device 112 may receive the encoded video bitstream from a network entity 79, such as a server, a media-aware network element (MANE), a video editor / cutter, or other such devices configured to implement one or more of the techniques described above. Network entity 79 may or may not include encoding device 104. Some of the techniques described in this invention may be implemented by network entity 79 before it transmits the encoded video bitstream to decoding device 112. In some video decoding systems, network entity 79 and decoding device 112 may be part of a single device, while in other cases, the functionality described with respect to network entity 79 may be performed by the same device including decoding device 112.

[0209] The entropy decoding unit 80 of the decoding device 112 entropy decodes the bitstream to generate quantized coefficients, motion vectors, and other syntax elements. The entropy decoding unit 80 forwards the motion vectors and other syntax elements to the prediction processing unit 81. The decoding device 112 can receive syntax elements at the video slice level and / or video block level. The entropy decoding unit 80 can process and parse both fixed-length and variable-length syntax elements from one or more parameter sets, such as VPS, SPS, and PPS.

[0210] When a video slice is decoded into an intra-frame decoded (I) slice, the intra-frame prediction processing unit 84 of the prediction processing unit 81 can generate prediction data for the video block of the current video slice based on the intra-frame prediction mode transmitted via the signal and data from the previously decoded block of the current frame or picture. When a video frame is decoded into an inter-frame decoded (i.e., B, P, or GPB) slice, the motion compensation unit 82 of the prediction processing unit 81 generates a predictive block for the video block of the current video slice based on the motion vector and other syntax elements received from the entropy decoding unit 80. Predictive blocks can be generated from one of the reference pictures in the reference picture list. The decoding device 112 can construct the reference frame list: list 0 and list 1, based on the reference pictures stored in the picture memory 92 using a default construction technique.

[0211] Motion compensation unit 82 determines prediction information for video blocks used in the current video slice by analyzing motion vectors and other syntax elements, and uses the prediction information to generate predictive blocks for the current video slice being decoded. For example, motion compensation unit 82 may use one or more syntax elements in the parameter set to determine the prediction mode (e.g., intra-frame prediction or inter-frame prediction) of the video blocks used to decode the video slice, the inter-frame prediction slice type (e.g., B-slice, P-slice, or GPB-slice), the construction information of one or more reference picture lists for the slice, the motion vectors of each inter-frame coded video block for the slice, the inter-frame prediction state of each inter-frame decoded video block for the slice, and other information used to decode video blocks in the current video slice.

[0212] The motion compensation unit 82 can also perform interpolation based on an interpolation filter. The motion compensation unit 82 can use an interpolation filter, such as that used by the encoding device 104 during the encoding of a video block, to calculate the interpolated values ​​of the second-integer pixels of the reference block. In this case, the motion compensation unit 82 can determine the interpolation filter used by the encoding device 104 from the received syntax elements, and can use the interpolation filter to generate predictive blocks.

[0213] The dequantization unit 86 dequantizes or dequantizes the quantized transform coefficients provided in the bitstream and decoded by the entropy decoding unit 80. The dequantization process may include using quantization parameters calculated by the encoding device 104 for each video block in the video slice to determine the degree of quantization to be applied and similarly determine the degree of dequantization to be applied. The inverse transform processing unit 88 applies an inverse transform (e.g., inverse DCT or other suitable inverse transform), an inverse integer transform, or a conceptually similar inverse transform process to the transform coefficients to produce a residual block in the pixel domain.

[0214] After the motion compensation unit 82 generates a predictive block for the current video block based on motion vectors and other syntax elements, the decoding device 112 forms a decoded video block by summing the residual block from the inverse transform processing unit 88 with the corresponding predictive block generated by the motion compensation unit 82. The summer 90 represents one or more components capable of performing this summation operation. If necessary, loop filters (in or after the decoding loop) can also be used to smooth pixel transitions or otherwise improve video quality. The filter unit 91 is intended to represent one or more loop filters, such as a deblocking filter, an adaptive loop filter (ALF), and a sample adaptive offset (SAO) filter. Although the filter unit 91 is in Figure 10The filter unit 91 is shown as an in-loop filter, but in other configurations, it can be implemented as a post-loop filter. The decoded video block in a given frame or image is then stored in image memory 92, which stores reference images for subsequent motion compensation. Image memory 92 also stores the decoded video for later presentation, for example... Figure 1 The video destination device 122 is displayed on the display device.

[0215] In the foregoing description, aspects of this application have been described with reference to specific embodiments thereof; however, those skilled in the art will recognize that the invention is not limited thereto. Therefore, while illustrative embodiments of this application have been described in detail herein, it should be understood that the inventive concepts may be embodied and used differently in other ways, and the appended claims are intended to be considered as encompassing such variations, except as limited by the prior art. Various features and aspects of the invention may be used individually or in combination. Furthermore, embodiments may be used in any number of environments and applications other than those described herein without departing from the broader spirit and scope of this specification. Therefore, this specification and the accompanying drawings are to be regarded as illustrative rather than limiting. For illustrative purposes, the methods are described in a particular order. It should be understood that in alternative embodiments, the methods may be performed in a different order than that described.

[0216] When a component is described as being "configured to" perform certain operations, such configuration may be achieved, for example, by designing electronic circuits or other hardware to perform the operations, by programming programmable electronic circuits (e.g., microprocessors or other suitable electronic circuits) to perform the operations, or any combination thereof.

[0217] The various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented as electronic hardware, computer software, firmware, or a combination thereof. To clearly illustrate this interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the system as a whole. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the invention.

[0218] The techniques described herein can also be implemented in electronic hardware, computer software, firmware, or any combination thereof. Such techniques can be implemented in any of a variety of devices, such as general-purpose computers, wireless communication mobile phones, or integrated circuit devices with multiple uses, including applications in wireless communication mobile phones and other devices. Any feature that can be described as a module or component can be implemented together in an integrated logic device or separately as a discrete but interoperable logic device. If implemented in software, the techniques can be implemented at least in part by a computer-readable data storage medium comprising program code containing instructions that, when executed, perform one or more of the methods described above. The computer-readable data storage medium can form part of a computer program product, which can include encapsulation material. The computer-readable medium can include memory or data storage media, such as random access memory (RAM), such as synchronous dynamic random access memory (SDRAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), flash memory, magnetic or optical data storage media, etc. Alternatively or concurrently, the technology may be implemented at least in part by a computer-readable communication medium that carries or conveys program code in the form of instructions or data structures that can be accessed, read and / or executed by a computer, for example, via propagated signals or waves.

[0219] The program code can be executed by a processor, which may include one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), or other equivalent integrated or discrete logic circuit systems. Such processors can be configured to perform any of the techniques described herein. A general-purpose processor may be a microprocessor; however, in alternative embodiments, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors incorporating a DSP core, or any other such configuration. Therefore, as used herein, the term "processor" may refer to any of the foregoing structures, any combination of the foregoing structures, or any other structure or device suitable for implementing the techniques described herein. Additionally, in some aspects, the functionality described herein may be provided within dedicated software or hardware modules configured for encoding and decoding, or incorporated into a combined video encoder-decoder (codec).

Claims

1. A method for encoding video data, comprising: Obtain the video data; Encoding syntax elements, the syntax elements being indicated for a subset of interpolation filters in an interpolation filter set for a decoding unit, including: determining a context model for encoding the syntax elements based on a reference frame to be used to encode the decoding unit; Encoding the decoding unit, wherein encoding the decoding unit includes: selecting an interpolation filter for motion estimation and motion compensation for the decoding unit, wherein the interpolation filter is selected from a subset of interpolation filters; and An encoded video bitstream is generated, wherein the encoded video bitstream includes the encoded decoding unit.

2. The method according to claim 1, wherein, The context model is determined based on the interpolation filters of adjacent blocks of the decoding unit.

3. The method according to claim 1, wherein, The context model is still determined based on the prediction direction of the decoding unit.

4. The method according to claim 1, wherein, The context model is determined based on whether the reference frame is contained in either the first reference list or the second reference list.

5. An apparatus for encoding video data, comprising: A memory configured to store the video data; as well as A processor configured to perform the following operations: Obtain the video data; Encoding syntax elements, the syntax elements being directed to a subset of interpolation filters in an interpolation filter set for the decoding unit, wherein, in order to encode the syntax elements, the processor is further configured to perform the following operation: determine a context model based on a reference frame to be used to encode the decoding unit; Encoding the decoding unit, wherein encoding the decoding unit includes: selecting an interpolation filter for motion estimation and motion compensation, wherein the interpolation filter is selected from a subset of the interpolation filters; and An encoded video bitstream is generated, wherein the encoded video bitstream includes the encoded decoding unit.

6. The device according to claim 5, wherein, The device includes a mobile unit having a camera for capturing images.

7. The device according to claim 5, wherein, The processor is also configured to determine the context model based on interpolation filters of adjacent blocks of the decoding unit.

8. The device according to claim 5, wherein, The processor is also configured to determine the context model based on the prediction direction of the decoding unit.

9. The device according to claim 5, wherein, The processor is also configured to determine the context model based on whether the reference frame is contained in either the first reference list or the second reference list.

10. An apparatus for encoding video data, comprising: Units used to acquire video data; Units for encoding syntax elements, the syntax elements indicating a subset of interpolation filters in an interpolation filter set for the decoding unit, include: units for determining a context model for encoding the syntax elements based on a reference frame to be used for encoding the decoding unit; The unit for encoding the decoding unit includes: selecting an interpolation filter for motion estimation and motion compensation, wherein the interpolation filter is selected from the set of interpolation filters; and Units for generating encoded video bitstreams, wherein the encoded video bitstreams include the encoded decoding units.

11. A method for decoding video data, comprising: Obtain the encoded video bitstream; The reference frame for the decoding unit in the current frame is determined from the encoded video bitstream; Decoding a syntax element, the syntax element indicating a subset of interpolation filters in an interpolation filter set, the decoding comprising: determining a context model for decoding the syntax element based on the reference frame; The subset of interpolation filters is determined from the set of interpolation filters based on the syntax elements; Determine interpolation filters from the subset of interpolation filters; and The decoding unit is reconstructed using the reference frame and the interpolation filter.

12. The method according to claim 11, wherein, The interpolation filter is associated with a second interpolation filter, wherein the interpolation filter is used for integer pixel positions, and wherein the second interpolation filter is used for fractional pixel positions.

13. The method according to claim 11, wherein, The context model is determined based on the interpolation filters of adjacent blocks of the decoding unit.

14. The method according to claim 11, wherein, The context model is still determined based on the prediction direction of the decoding unit.

15. The method according to claim 11, wherein, The context model is determined based on whether the reference frame is contained in either the first reference list or the second reference list.

16. An apparatus for decoding video data, comprising: A memory configured to store encoded video data; as well as A processor configured to perform the following operations: Obtain the encoded video bitstream; The reference frame for the decoding unit in the current frame is determined from the encoded video bitstream; Decoding a syntax element, the syntax element indicating a subset of interpolation filters in an interpolation filter set, the decoding comprising: determining a context model for decoding the syntax element based on the reference frame; The subset of interpolation filters is determined from the set of interpolation filters based on the syntax elements; Determine interpolation filters from the subset of interpolation filters; and The decoding unit is reconstructed using the reference frame and the interpolation filter.

17. The device according to claim 16, further comprising: A display for showing the video data.

18. The device according to claim 16, wherein, The device includes a mobile unit having a camera for capturing images.

19. The device according to claim 16, wherein, The processor is also configured to determine the context model based on interpolation filters of adjacent blocks of the decoding unit.

20. The device according to claim 16, wherein, The processor is also configured to determine the context model based on the prediction direction of the decoding unit.

21. The device according to claim 16, wherein, The processor is also configured to determine the context model based on whether the reference frame is contained in either the first reference list or the second reference list.

22. An apparatus for decoding video data, comprising: Units used to obtain encoded video bitstreams; A unit for determining a reference frame from the encoded video bitstream for a decoding unit in the current frame; A unit for decoding a syntax element, the syntax element indicating a subset of interpolation filters in an interpolation filter set, the decoding comprising: determining a context model for decoding the syntax element based on the reference frame; Units for determining the subset of interpolation filters from the set of interpolation filters based on the syntax elements; Units for determining interpolation filters from the subset of interpolation filters; and A unit for reconstructing the decoding unit using the reference frame and the interpolation filter.

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