WO2022101018A1

WO2022101018A1 - A method and an apparatus for encoding or decoding a video

Info

Publication number: WO2022101018A1
Application number: PCT/EP2021/079888
Authority: WO
Inventors: Antoine Robert; Philippe Bordes; Franck Galpin; Karam NASER
Original assignee: Interdigital Vc Holdings France, Sas
Priority date: 2020-11-13
Filing date: 2021-10-27
Publication date: 2022-05-19

Abstract

A method and an apparatus for video encoding or decoding are provided wherein a resolution for motion information is obtained for at least one block of a video, and a motion vector is derived based on the obtained resolution, and wherein the motion vector is used for reconstructing the block.

Description

A METHOD AND AN APPARATUS FOR ENCODING OR DECODING A VIDEO

TECHNICAL FIELD

[1] The present embodiments generally relate to a method and an apparatus for motion information derivation in video encoding or decoding.

BACKGROUND

[2] To achieve high compression efficiency, image and video coding schemes usually employ prediction and transform to leverage spatial and temporal redundancy in the video content. Generally, intra or inter prediction is used to exploit the intra or inter picture correlation, then the differences between the original block and the predicted block, often denoted as prediction errors or prediction residuals, are transformed, quantized, and entropy coded. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy coding, quantization, transform, and prediction.

SUMMARY

[3] According to an embodiment, a method for encoding a video is provided, wherein the method comprises obtaining a resolution for motion information for at least one block of a video, deriving a motion vector based on the obtained resolution, wherein the motion vector is used for reconstructing the block without signaling an information representative of said motion vector to a decoder and encoding the at least one block.

[4] According to an embodiment, a method for decoding a video is provided, wherein the method comprises

- obtaining a resolution for motion information for at least one block of the video,

- obtaining a motion vector predictor for the at least one block based on motion estimation,

- refining the motion vector predictor, based on the obtained resolution.

[5] According to another embodiment, an apparatus for video encoding is provided, comprising one or more processors, wherein said one or more processors are configured to:

- obtain a resolution for motion information for a block of the video,

- refining the motion vector predictor, based on the obtained resolution, wherein the motion vector is used for reconstructing the block without signaling an information representative of said motion vector to a decoder.

[6] According to another embodiment, an apparatus for video decoding is provided, comprising one or more processors, wherein said one or more processors are configured to:

- refining the motion vector predictor, based on the obtained resolution.

[7] According to another embodiment, an apparatus of video encoding is provided, comprising means for:

- obtaining a resolution for motion information for a block of the video,

[8] According to another embodiment, an apparatus of video decoding is provided, comprising means for obtaining a resolution for motion information for at least one block of the video, obtaining a motion vector predictor for the at least one block based on motion estimation, refining the motion vector predictor, based on the obtained resolution.

[9] One or more embodiments also provide a computer program comprising instructions which when executed by one or more processors cause the one or more processors to perform the encoding method or decoding method according to any one of the embodiments described above. One or more of the present embodiments also provide a computer readable storage medium having stored thereon instructions for encoding or decoding video data according to the methods described above. One or more embodiments also provide a computer readable storage medium having stored thereon a bitstream generated according to the methods described above. One or more embodiments also provide a method and apparatus for transmitting or receiving the bitstream generated according to the methods described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[10] FIG. 1 illustrates a block diagram of a system within which aspects of the present embodiments may be implemented.

[11] FIG. 2 illustrates a block diagram of an embodiment of a video encoder.

[12] FIG. 3 illustrates a block diagram of an embodiment of a video decoder.

[13] FIG. 4 illustrates an example of a coding tree unit and coding tree division for representing a block in a compressed HEVC picture.

[14] FIG. 5A illustrates an example of a division of a coding tree unit into coding units, prediction units and transform units according to the HEVC standard.

[15] FIG. 5B illustrates an example of a locations of spatial motion vector candidates for an AMVP coding mode, according to the HEVC standard.

[16] FIG. 6 illustrates an example of a bilateral matching cost function for deriving a motion vector, according to an embodiment.

[17] FIG. 7 illustrates an example of a template matching cost function for deriving a motion vector, according to an embodiment.

[18] FIG. 8 illustrates examples of search pattern for motion vector refinement according to an embodiment.

[19] FIG. 9 illustrates an example of a method for deriving a motion vector that is not explicitly signaled to a decoder, according to an embodiment.

[20] FIG. 10 illustrates an example of a method for obtaining a motion vector taking into account a motion resolution, wherein the motion vector is not explicitly signaled to a decoder, according to an embodiment.

[21] FIG. 11 illustrates an example of a method for deriving a motion vector based on a motion resolution, according to an embodiment.

[22] FIG. 12 illustrates an example of a method for deriving a motion vector based on a motion resolution, according to another embodiment.

[23] FIG. 13 illustrates an example of a method for deriving a motion vector based on a motion resolution, according to another embodiment.

[24] FIG. 14 shows two remote devices communicating over a communication network in accordance with an example of present principles.

[25] FIG. 15 shows the syntax of a signal in accordance with an example of present principles.

[26] DETAILED DESCRIPTION

[27] FIG. 1 illustrates a block diagram of an example of a system in which various aspects and embodiments can be implemented. System 100 may be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this application. Examples of such devices, include, but are not limited to, various electronic devices such as personal computers, laptop computers, smartphones, tablet computers, digital multimedia set top boxes, digital television receivers, personal video recording systems, connected home appliances, and servers. Elements of system 100, singly or in combination, may be embodied in a single integrated circuit, multiple ICs, and/or discrete components. For example, in at least one embodiment, the processing and encoder/decoder elements of system 100 are distributed across multiple ICs and/or discrete components. In various embodiments, the system 100 is communicatively coupled to other systems, or to other electronic devices, via, for example, a communications bus or through dedicated input and/or output ports. In various embodiments, the system 100 is configured to implement one or more of the aspects described in this application.

[28] The system 100 includes at least one processor 1 10 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this application. Processor 110 may include embedded memory, input output interface, and various other circuitries as known in the art. The system 100 includes at least one memory 120 (e.g., a volatile memory device, and/or a non-volatile memory device). System 100 includes a storage device 140, which may include non-volatile memory and/or volatile memory, including, but not limited to, EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic disk drive, and/or optical disk drive. The storage device 140 may include an internal storage device, an attached storage device, and/or a network accessible storage device, as non-limiting examples.

[29] System 100 includes an encoder/decoder module 130 configured, for example, to process data to provide an encoded video or decoded video, and the encoder/decoder module 130 may include its own processor and memory. The encoder/decoder module 130 represents module(s) that may be included in a device to perform the encoding and/or decoding functions. As is known, a device may include one or both of the encoding and decoding modules. Additionally, encoder/decoder module 130 may be implemented as a separate element of system 100 or may be incorporated within processor 1 10 as a combination of hardware and software as known to those skilled in the art.

[30] Program code to be loaded onto processor 110 or encoder/decoder 130 to perform the various aspects described in this application may be stored in storage device 140 and subsequently loaded onto memory 120 for execution by processor 110. In accordance with various embodiments, one or more of processor 1 10, memory 120, storage device 140, and encoder/decoder module 130 may store one or more of various items during the performance of the processes described in this application. Such stored items may include, but are not limited to, the input video, the decoded video or portions of the decoded video, the bitstream, matrices, variables, and intermediate or final results from the processing of equations, formulas, operations, and operational logic.

[31] In several embodiments, memory inside of the processor 1 10 and/or the encoder/decoder module 130 is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. In other embodiments, however, a memory external to the processing device (for example, the processing device may be either the processor 1 10 or the encoder/decoder module 130) is used for one or more of these functions. The external memory may be the memory 120 and/or the storage device 140, for example, a dynamic volatile memory and/or a non-volatile flash memory. In several embodiments, an external non-volatile flash memory is used to store the operating system of a television. In at least one embodiment, a fast external dynamic volatile memory such as a RAM is used as working memory for video coding and decoding operations, such as for MPEG-2, HEVC, or VVC.

[32] The input to the elements of system 100 may be provided through various input devices as indicated in block 105. Such input devices include, but are not limited to, (i) an RF portion that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a Composite input terminal, (iii) a USB input terminal, and/or (iv) an HDMI input terminal.

[33] In various embodiments, the input devices of block 105 have associated respective input processing elements as known in the art. For example, the RF portion may be associated with elements suitable for (i) selecting a desired frequency (also referred to as selecting a signal, or band-limiting a signal to a band of frequencies), (ii) down converting the selected signal, (iii) band-limiting again to a narrower band of frequencies to select (for example) a signal frequency band which may be referred to as a channel in certain embodiments, (iv) demodulating the down converted and band-limited signal, (v) performing error correction, and (vi) demultiplexing to select the desired stream of data packets. The RF portion of various embodiments includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters, demodulators, error correctors, and demultiplexers. The RF portion may include a tuner that performs various of these functions, including, for example, down converting the received signal to a lower frequency (for example, an intermediate frequency or a near-baseband frequency) or to baseband. In one set-top box embodiment, the RF portion and its associated input processing element receives an RF signal transmitted over a wired (for example, cable) medium, and performs frequency selection by filtering, down converting, and filtering again to a desired frequency band. Various embodiments rearrange the order of the above-described (and other) elements, remove some of these elements, and/or add other elements performing similar or different functions. Adding elements may include inserting elements in between existing elements, for example, inserting amplifiers and an analog-to-digital converter. In various embodiments, the RF portion includes an antenna.

[34] Additionally, the USB and/or HDMI terminals may include respective interface processors for connecting system 100 to other electronic devices across USB and/or HDMI connections. It is to be understood that various aspects of input processing, for example, Reed-Solomon error correction, may be implemented, for example, within a separate input processing IC or within processor 110 as necessary. Similarly, aspects of USB or HDMI interface processing may be implemented within separate interface ICs or within processor 1 10 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 110, and encoder/decoder 130 operating in combination with the memory and storage elements to process the data stream as necessary for presentation on an output device.

[35] Various elements of system 100 may be provided within an integrated housing, Within the integrated housing, the various elements may be interconnected and transmit data therebetween using suitable connection arrangement 115, for example, an internal bus as known in the art, including the I2C bus, wiring, and printed circuit boards.

[36] The system 100 includes communication interface 150 that enables communication with other devices via communication channel 190. The communication interface 150 may include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 190. The communication interface 150 may include, but is not limited to, a modem or network card and the communication channel 190 may be implemented, for example, within a wired and/or a wireless medium.

[37] Data is streamed to the system 100, in various embodiments, using a Wi-Fi network such as IEEE 802.1 1. The Wi-Fi signal of these embodiments is received over the communications channel 190 and the communications interface 150 which are adapted for Wi-Fi communications. The communications channel 190 of these embodiments is typically connected to an access point or router that provides access to outside networks including the Internet for allowing streaming applications and other over-the-top communications. Other embodiments provide streamed data to the system 100 using a set-top box that delivers the data over the HDMI connection of the input block 105. Still other embodiments provide streamed data to the system 100 using the RF connection of the input block 105.

[38] The system 100 may provide an output signal to various output devices, including a display 165, speakers 175, and other peripheral devices 185. The other peripheral devices 185 include, in various examples of embodiments, one or more of a stand-alone DVR, a disk player, a stereo system, a lighting system, and other devices that provide a function based on the output of the system 100. In various embodiments, control signals are communicated between the system 100 and the display 165, speakers 175, or other peripheral devices 185 using signaling such as AV. Link, CEC, or other communications protocols that enable device- to-device control with or without user intervention. The output devices may be communicatively coupled to system 100 via dedicated connections through respective interfaces 160, 170, and 180. Alternatively, the output devices may be connected to system 100 using the communications channel 190 via the communications interface 150. The display 165 and speakers 175 may be integrated in a single unit with the other components of system 100 in an electronic device, for example, a television. In various embodiments, the display interface 160 includes a display driver, for example, a timing controller (T Con) chip.

[39] The display 165 and speaker 175 may alternatively be separate from one or more of the other components, for example, if the RF portion of input 105 is part of a separate set-top box. In various embodiments in which the display 165 and speakers 175 are external components, the output signal may be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs.

[40] FIG. 2 illustrates an example video encoder 200, such as a High Efficiency Video Coding (HEVC) encoder. FIG. 2 may also illustrate an encoder in which improvements are made to the HEVC standard or an encoder employing technologies similar to HEVC, such as a VVC (Versatile Video Coding) encoder under development by JVET (Joint Video Exploration Team), or any video encoder.

[41] In the present application, the terms “reconstructed” and “decoded” may be used interchangeably, the terms “encoded” or “coded” may be used interchangeably, the terms “pixel” or “sample” may be used interchangeably, and the terms “image,” “picture” and “frame” may be used interchangeably. Usually, but not necessarily, the term “reconstructed” is used at the encoder side while “decoded” is used at the decoder side.

[42] Before being encoded, the video sequence may go through pre-encoding processing (201 ), for example, applying a color transform to the input color picture (e.g., conversion from RGB 4:4:4 to YCbCr 4:2:0), or performing a remapping of the input picture components in order to get a signal distribution more resilient to compression (for instance using a histogram equalization of one of the color components). Metadata can be associated with the preprocessing, and attached to the bitstream.

[43] In the encoder 200, a picture is encoded by the encoder elements as described below. The picture to be encoded is partitioned (202) and processed in units of, for example, CUs. Each unit is encoded using, for example, either an intra or inter mode. When a unit is encoded in an intra mode, it performs intra prediction (260). In an inter mode, motion estimation (275) and compensation (270) are performed. The encoder decides (205) which one of the intra mode or inter mode to use for encoding the unit, and indicates the intra/inter decision by, for example, a prediction mode flag. The encoder may also blend (263) intra prediction result and inter prediction result, or blend results from different intra/inter prediction methods.

[44] Prediction residuals are calculated, for example, by subtracting (210) the predicted block from the original image block. The motion refinement module (272) uses already available reference picture in order to refine the motion field of a block without reference to the original block. A motion field for a region can be considered as a collection of motion vectors for all pixels with the region. If the motion vectors are sub-block-based, the motion field can also be represented as the collection of all sub-block motion vectors in the region (all pixels within a sub-block has the same motion vector, and the motion vectors may vary from sub-block to sub-block). If a single motion vector is used for the region, the motion field for the region can also be represented by the single motion vector (same motion vectors for all pixels in the region).

[45] The prediction residuals are then transformed (225) and quantized (230). The quantized transform coefficients, as well as motion vectors and other syntax elements, are entropy coded (245) to output a bitstream. The encoder can skip the transform and apply quantization directly to the non-transformed residual signal. The encoder can bypass both transform and quantization, i.e., the residual is coded directly without the application of the transform or quantization processes.

[46] The encoder decodes an encoded block to provide a reference for further predictions. The quantized transform coefficients are de-quantized (240) and inverse transformed (250) to decode prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. In-loop filters (265) are applied to the reconstructed picture to perform, for example, deblocking/SAO (Sample Adaptive Offset) filtering to reduce encoding artifacts. The filtered image is stored at a reference picture buffer (280).

[47] FIG. 3 illustrates a block diagram of an example video decoder 300. In the decoder 300, a bitstream is decoded by the decoder elements as described below. Video decoder 300 generally performs a decoding pass reciprocal to the encoding pass as described in FIG. 2. The encoder 200 also generally performs video decoding as part of encoding video data.

[48] In particular, the input of the decoder includes a video bitstream, which can be generated by video encoder 200. The bitstream is first entropy decoded (330) to obtain transform coefficients, motion vectors, and other coded information. The picture partition information indicates how the picture is partitioned. The decoder may therefore divide (335) the picture according to the decoded picture partitioning information. The transform coefficients are de-quantized (340) and inverse transformed (350) to decode the prediction residuals. Combining (355) the decoded prediction residuals and the predicted block, an image block is reconstructed.

[49] The predicted block can be obtained (370) from intra prediction (360) or motion- compensated prediction (i.e., inter prediction) (375). The decoder may blend (373) the intra prediction result and inter prediction result, or blend results from multiple intra/inter prediction methods. Before motion compensation, the motion field may be refined (372) by using already available reference pictures. In-loop filters (365) are applied to the reconstructed image. The filtered image is stored at a reference picture buffer (380).

[50] The decoded picture can further go through post-decoding processing (385), for example, an inverse color transform (e.g. conversion from YCbCr 4:2:0 to RGB 4:4:4) or an inverse remapping performing the inverse of the remapping process performed in the preencoding processing (201 ). The post-decoding processing can use metadata derived in the pre-encoding processing and signaled in the bitstream.

[51] In the HEVC video compression standard (ITU-T H.265 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2014), SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS, Infrastructure of audiovisual services - Coding of moving video, High efficiency video coding, Recommendation ITU-T H.265), motion compensated temporal prediction is employed to exploit the redundancy that exists between successive pictures of a video. For example, a motion vector is associated with each prediction unit (PU). The picture is partitioned into Coding Tree Units (CTU), each CTU being represented by a Coding Tree in the compressed domain. The Coding Tree is a quad-tree division of the CTU, where each leaf is called a Coding Unit (CU), as illustrated in FIG. 4 showing an example of a coding tree unit and coding tree division.

[52] Each CU is then given some Intra or Inter prediction parameters (Prediction Info). To do so, it is spatially partitioned into one or more Prediction Units (PUs), each PU being assigned some prediction information. The Intra or Inter coding mode is assigned on the CU level. FIG. 5 illustrates an example of a division of a coding tree unit into coding units, prediction units and transform units according to the HEVC standard. Exactly one Motion Vector is assigned to each PU in HEVC. This motion vector is used for motion compensated temporal prediction of the considered PU.

In the Joint Exploration Model (JEM, “Algorithm Description of Joint Exploration Test Model 7”, Document JVET-G1001_v1, Joint Video Exploration Team of ISO/IEC JTC1/SC29/WG11 , 7^th meeting, 13 - 21 July 2017, Torino, IT.) and the Versatile Video Codec (VVC, “Versatile Video Coding (Draft 10)”, Document JVET-S2001_vB, Joint Video Exploration Team of ISO/IEC JTC1/SC29/WG11, 19^th meeting, Teleconference) developed by the JVET (Joint Video Exploration Team) group, a CU is no more divided into PU or TU, and some motion data is directly assigned to each CU. In this codec design, a CU can be divided into sub-CU with a motion vector computed for each sub-CU. In the following, a CU may be referred to blocks, and sub-CU to subblocks.

[53] A FRUC (Frame Rate Up Conversion) tool was introduced in the JEM. The FRUC tool allows deriving motion information of a CU on the decoder side without signaling from the encoder. The FRUC mode may be signaled at the CU level with a FRUC flag and an additional FRUC mode flag indicating which matching cost function (bilateral or template) shall be used to derive motion information for the CU at the decoder.

[54] On the encoder side, the decision on whether using a FRUC mode for coding a CU is based on a RD (Rate/Distortion) cost selection. The two matching modes (bilateral and template) can be both checked for the CU to be coded. The matching mode leading to the minimal RD cost is further compared to other coding modes. If the FRUC mode is the most efficient one, the FRUC flag is set to true for the CU and the related matching mode is used.

[55] The motion predictor derivation process for a FRUC mode can be performed in two steps. A CU-level motion search can be first performed followed by a sub-CU level motion refinement on a 4x4 basis. At the CU level, an initial motion vector predictor is selected from a list of candidate motion vector predictors for the whole CU based on a bilateral or template matching cost function. The candidate motion vector predictor leading to a minimum matching cost is selected as a starting point for a further motion vector refinement at the CU level. Then, a local search based on bilateral or template matching around this starting point is performed and the motion vector predictor (MVP) resulting in a minimum matching cost is taken as the MVP for the whole CU. Subsequently, the motion information can be further refined at the sub- CU level in a same way from a list of candidate motion vector predictors containing the refined CU motion vector predictor.

[56] As shown in FIG. 6, a bilateral matching cost function is used to derive motion information of a current CU ( Cur block) by finding the closest match between two blocks along the motion trajectory of the current CU in two different reference pictures (RefO, Ref 1 ). Under the assumption of continuous motion trajectory, the motion vectors MV0 and MV1 pointing to the two reference blocks shall be proportional to the temporal distances (TD0 and TD1 ) between the current picture (Cur Pic) and the two reference pictures (RefO and Ref1 ).

[57] As shown in FIG. 7, a template matching cost function is used to derive motion information of the current CU (Cur block) by finding the closest match between a template comprising top and/or left neighboring blocks of the current CU, in the current picture (Cur Pic) and an area having a same size and shape as the template, in a reference picture (RefO).

[58] According to an embodiment, the motion derivation process from the FRUC mode can also be applied to the AMVP (Advanced Motion Vector Predictor) coding mode of the HEVC standard. In this case, the template matching cost function is used for deriving a candidate motion vector predictor that is added to the list of motion vector predictor of the AMVP coding mode. For example, in the HEVC coding standard, the AMVP coding mode allows two candidates. One candidate can be derived using the FRUC tool with the template matching cost function. If this FRUC candidate is different from the first existing AMVP candidates, it is inserted at the very beginning of the AMVP candidate list and then the list size is set to two (meaning the second existing AMVP candidate is removed). When applied to the AMVP mode, only CU level search may be applied.

[59] FIG. 9 illustrates an example of a method 90 for deriving a motion vector according to the FRUC mode, according to an embodiment. This derived motion vector is not explicitly signaled to the decoder. In order to properly decode the bitstream, the decoder performs the same process of motion vector derivation has to be performed at the encoder and the decoder.

[60] At 91 , input motion vector predictor candidates are collected, for example, from: Regular AMVP candidates,

Regular merge candidates referring to a particular reference frame of a specific list, “Uni-lateral” candidates referring to a particular reference frame of a specific list, Motion vectors from top and left neighboring blocks, if these motion vectors use the same reference frame.

[61] For instance, regular AMVP candidates and regular merge candidates are obtained in a same way as for AMVP and merge coding modes of the HEVC standard respectively. “Unilateral” candidates refer to motion vectors obtained from interpolated motion field generated for a previous coded frame based on unilateral motion estimation.

[62] At 92, the template match costs of each of these candidates are computed, and at 93, the candidate having the minimum cost is selected as the best candidate. If, at this stage, several candidates have the same minimum cost, then the first encountered one in the list is selected as the best candidate, all others being ignored.

[63] At 94, the selected candidate is refined in several steps. One step stands for trying to add some small delta values to the selected candidate, i.e. with a diamond pattern, +2 or -2 in x or y, or +1 or -1 in x and y (as shown in FIG. 8(a)), and with a cross pattern, +1 or -1 in x or y (as shown in FIG. 8(b)). Each delta is added to the candidate and its new cost is calculated as the sum of the motion vector cost (a multiple M of the sum of absolute differences in x and y between the initial best candidate and the current tested candidate) and of its template matching cost. If one of the tested new candidates have a cost lower than the best one, it is defined as the new best candidate with its new best cost, the entry point of the next step.

[64] At step 94, the candidate selected at 93 is refined at a 1/4-pel accuracy recursively using the diamond pattern until no new best candidate can be found, i.e. no new lower cost is reached. Then one single step is also performed at a 1/4-pel accuracy but using the cross pattern.

[65] At step 95, a last single step using also the cross pattern is done at a 1/8-pel accuracy for further refining the selected candidate. In FIG. 9, indices of the diamond and cross searches stand for the accuracy (1/4 or 1/8), and the value for the number of possible loops (infinite sign indicating that the search is performed until no new lower cost is reached, 1 indicating one single step of refinement on the deltas of pattern search).

[66] The AMVR (Adaptive Motion Vector Resolution) coding tool introduced in the VVC standard allows signaling a motion vector difference (MVd) between a CU motion vector and its motion vector predictor at various accuracy. In the following, the terms “precision” or “resolution” could be also be used interchangeably with the term “accuracy”.

[67] According to the AMVR tool, some CU-level information may be signaled to indicate the resolution of the CLI’s MVd information. The AMVR tool can be applied to CUs coded in regular AMVP or affine AMVP modes. In regular AMVP mode, the supported MVd resolution levels can be quarter-luma-sample, half-luma-sample, integer-luma-sample or four-luma- sample. The signaling of the AMVR information at the CU level involves one flag that indicates whether quarter-luma-sample accuracy is used for the MVd information. If quarterluma-sample precision is not used, then an index indicates the use of half-luma-sample, integer-luma-sample or 4-luma-sample accuracy level. Finally, motion vector predictors are rounded to the same AMVR precision as that of the MVd to ensure the reconstructed motion vector has the desired precision level. The regular AMVP list is then constructed as follows:

- One spatial candidate from left positions (AO, A1 ) rounded to the AMVR precision as illustrated in FIG. 5B,

- One spatial candidate from top positions (BO, B1 , B2) rounded to the AMVR precision, as illustrated in FIG. 5B,

If both spatial candidates are identical, one is removed,

If temporal motion vector prediction is admissible, and the list is not full, i.e. the list does not comprise the maximum number of allowed candidates, one temporal candidate rounded to the AMVR precision is added,

If the list is not full, HMVP (History-based motion vector predictor) candidates rounded to the AMVR precision are added,

If the list is not full, the null motion vector is added, If the list comprises more candidates than the maximum list’s size, useless candidates are removed from the list. [68] In the case of the VVC standard, the list of regular AMVP candidates comprises at most 2 candidates. However, the present embodiments are not limited to this number and the regular AMVP list may comprise more or less motion vector candidates.

[69] The present application provides various embodiments for deriving a motion information for a block wherein the motion information is not explicitly signaled at a decoder, taking into account a motion information resolution associated to the block.

[70] FIG. 10 illustrates an example of a method 100 for obtaining a motion vector taking into account a motion resolution, wherein the motion vector is not explicitly signaled to a decoder, according to an embodiment. At 101 , a resolution is obtained for motion information for at least one block of a video to encode or decode.

[71] According to an embodiment, the resolution is obtained by decoding at least one information representative of the resolution. For instance, the at least one information representative of the resolution corresponds to the MVD resolution level encoded for a block or a group of blocks.

[72] At 102, a motion vector is derived based on the obtained resolution, wherein the motion vector is used for reconstructing the block without signaling an information representative of said motion vector to a decoder. For instance, the motion vector is derived using the FRUC tool explained above.

[73] Method 100 can be implemented in an encoding method for encoding a video or a decoding method for decoding a video. The derived motion information for the block can thus be used for coding or reconstructing the block in an encoding or decoding method. In a variant, the derived motion vector can be used for coding/reconstructing the block as a motion vector used for motion compensation of a reference frame. According to another variant, the derived motion vector can be used as a motion vector predictor candidate for predicting a motion vector determined for the block in an inter coding mode.

[74] According to the present principles, the same AMVR precision decided for a block can be reflected in the motion vector derivation process, such as the FRUC tool.

[75] According to different embodiments, the same AMVR precision can be used in the FRUC refinement process, and/or the FRUC refinement steps can be limited to the AMVR precision and/or input FRUC candidates can be rounded to the AMVR precision.

[76] FIG. 1 1 illustrates an example of a method 110 for deriving a motion vector based on a motion resolution, according to an embodiment. According to an embodiment, the motion vector derived according to the FRUC refinement process is derived at the same precision as the AMVR resolution.

[77] As explained in reference with FIG.9, the FRUC refinement has been designed for a precision at 1/4-pel precision. It first refines at 1/4-pel accuracy recursively using the diamond pattern until no new best candidate can be found (i.e. no new lower cost is reached). Then one single step is performed at 1/4-pel accuracy by using the cross pattern. And finally, a last single step using also the cross pattern is done at 1/8-pel accuracy.

[78] According to an embodiment, in order to adapt the FRUC refinement process to the AMVR precision, the recursive diamond and first single cross searches (step 1 14) are performed at the AMVR precision (AMVR_prec) and the final single cross step (1 15) at a finer precision (AMVRp_rec-1 ). The refinement process then consists in refining at AMVR accuracy recursively using the diamond pattern until no new best candidate can be found. Then one single step is performed at AMVR accuracy by using the cross pattern. And finally, a last single step using also the cross pattern is done at AMVR minus 1 accuracy as presented in FIG. 1 1 .

[79] For example, at AMVR integer-luma-sample precision, the recursive diamond and first single cross steps are performed at 1 -pel precision, and the last single cross step at 1/2-pel precision as presented in Table 1 below:

Table 1

[80] Table 1 illustrates an example of correspondence of AMVR precision, i.e. a motion information resolution associated to a block, and precision of refinement steps for deriving motion information at the decoder, such as for the FRUC tool. Such an adaptive precision motion vector refinement process allows limiting the number of refinement loops and thus decreases the overall complexity of deriving motion information at the decoder when motion information is not signaled at the decoder.

[81] FIG. 12 illustrates an example of a method 120 for deriving a motion vector based on a motion resolution, according to another embodiment. In addition to the previous embodiment, the adaptive precision motion information refinement process can also be limited to the AMVR precision.

[82] Since the last refinement step (1 15 in FIG. 1 1) is performed at a finer precision than the AMVR one, according to the variant illustrated in FIG. 12, this last step of motion information refinement is avoided.

[83] FIG. 13 illustrates an example of a method 130 for deriving a motion vector based on a motion resolution, according to another embodiment. As illustrated in FIG. 13, the precision of all refinement steps can be increased so that the refined motion vector obtained at the last refinement step is obtained at the AMVR precision. Thus, according to this embodiment, the recursive diamond and first single cross searches (step 134) are performed at a coarser precision than the AMVR precision (AMVRp_rec+1 ) and the final single cross step (135) at the AMVR precision (AMVR_prec). In that case, the correspondence between the motion information precision associated to a block (AMVR precision) and the refinement process search precision can be designed as illustrated in Table 2 below:

Table 2

[84] According to another embodiment, at least one candidate motion vector predictor is rounded based on the obtained resolution. At step 91 of FIG 11 -13, when determining the motion vector predictor candidates, the determined motion vector predictor candidates are rounded to the AMVR precision. For example, the FRUC input candidate list becomes:

Regular AMVP candidates rounded to the AMVR precision,

Regular merge candidates referring to a particular reference frame of a specific list, and rounded to the AMVR precision,

“Uni-lateral” candidates referring to a particular reference frame of a specific list, and rounded to the AMVR precision,

Top and left neighboring motion vectors if using the same reference frame and rounded to the AMVR precision.

[85] According to a variant, the above explained embodiments are used in the method for encoding or decoding a video which is described in reference to FIG. 2 or 3.

[86] According to an embodiment, the refined motion vector obtained from any one of the embodiments described in reference with FIG. 9-13 is used as a motion vector predictor for a block coding mode wherein motion information is signaled to the decoder, such as an AMVP or a merge coding mode for instance.

[87] According to this embodiment, the encoding method and respectively the decoding method comprises adding the motion vector derived from any one of the embodiments of FIG. 9-13 to a list of candidate motion vector predictors used by a coding mode for coding or decoding the block. This coding mode can be any coding mode using a motion vector information such as a coding mode wherein coding or decoding the block according to said coding mode comprises coding or decoding the motion vector difference between a motion vector determined for the block and a candidate motion vector predictor selecting from the list of candidate motion vector predictors.

[88] According to a variant, the derived motion vector is added in a first position of the list.

[89] According to another embodiment, the refined motion vector obtained from any one of the embodiments described in reference with FIG. 10-13 is used for coding the block for which the refined motion vector has been obtained. According to this embodiment, the encoding method comprises respectively coding the block using the derived motion vector. The decoding method comprises respectively reconstructing the block using the derived motion vector.

[90] According to an example of the present principles, illustrated in FIG. 14, in a transmission context between two remote devices A and B over a communication network NET, the device A comprises a processor in relation with memory RAM and ROM which are configured to implement a method for encoding a video as illustrated in FIG. 1 -13 and the device B comprises a processor in relation with memory RAM and ROM which are configured to implement a method for decoding a video as described in relation with FIGs 1 -13.

[91] In accordance with an example, the network is a broadcast network, adapted to broadcast/transmit encoded data representative of a video from device A to decoding devices including the device B.

[92] A signal, intended to be transmitted by the device A, carries at least one bitstream comprising coded data representative of a video. The bitstream may comprise syntax as described above.

[93] FIG. 15 shows an example of the syntax of such a signal transmitted over a packetbased transmission protocol. Each transmitted packet P comprises a header H and a payload PAYLOAD. According to embodiments, the payload PAYLOAD may comprise coded video data and at least at least one information representative of a resolution of motion information for at least one block of the video and at least one information representative of an activation of a derivation of a motion vector for the at least one block based on the obtained resolution, the motion vector being used for reconstructing the block without signaling an information representative of said motion vector in the signal.

[94] Various methods are described herein, and each of the methods comprises one or more steps or actions for achieving the described method. Unless a specific order of steps or actions is required for proper operation of the method, the order and/or use of specific steps and/or actions may be modified or combined. Additionally, terms such as “first”, “second”, etc. may be used in various embodiments to modify an element, component, step, operation, etc., for example, a “first decoding” and a “second decoding”. Use of such terms does not imply an ordering to the modified operations unless specifically required. So, in this example, the first decoding need not be performed before the second decoding, and may occur, for example, before, during, or in an overlapping time period with the second decoding.

[95] Various methods and other aspects described in this application can be used to modify modules, for example, the motion compensation, motion estimation, motion refinement modules (270, 272, 275,375, 372), of a video encoder 200 and decoder 300 as shown in FIG. 2 and FIG. 3. Moreover, the present aspects are not limited to VVC or HEVC, and can be applied, for example, to other standards and recommendations, and extensions of any such standards and recommendations. Unless indicated otherwise, or technically precluded, the aspects described in this application can be used individually or in combination.

[96] Various numeric values are used in the present application. The specific values are for example purposes and the aspects described are not limited to these specific values.

[97] Various implementations involve decoding. “Decoding,” as used in this application, may encompass all or part of the processes performed, for example, on a received encoded sequence in order to produce a final output suitable for display. In various embodiments, such processes include one or more of the processes typically performed by a decoder, for example, entropy decoding, inverse quantization, inverse transformation, and differential decoding. Whether the phrase “decoding process” is intended to refer specifically to a subset of operations or generally to the broader decoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art.

[98] Various implementations involve encoding. In an analogous way to the above discussion about “decoding”, “encoding” as used in this application may encompass all or part of the processes performed, for example, on an input video sequence in order to produce an encoded bitstream.

[99] The implementations and aspects described herein may be implemented in, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method), the implementation of features discussed may also be implemented in other forms (for example, an apparatus or program). An apparatus may be implemented in, for example, appropriate hardware, software, and firmware. The methods may be implemented in, for example, an apparatus, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. Processors also include communication devices, for example, computers, cell phones, portable/personal digital assistants (“PDAs”), and other devices that facilitate communication of information between end-users.

[100] Reference to “one embodiment” or “an embodiment” or “one implementation” or “an implementation”, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” or “in one implementation” or “in an implementation”, as well any other variations, appearing in various places throughout this application are not necessarily all referring to the same embodiment.

[101] Additionally, this application may refer to “determining” various pieces of information. Determining the information may include one or more of, for example, estimating the information, calculating the information, predicting the information, or retrieving the information from memory.

[102] Further, this application may refer to “accessing” various pieces of information. Accessing the information may include one or more of, for example, receiving the information, retrieving the information (for example, from memory), storing the information, moving the information, copying the information, calculating the information, determining the information, predicting the information, or estimating the information.

[103] Additionally, this application may refer to “receiving” various pieces of information. Receiving is, as with “accessing”, intended to be a broad term. Receiving the information may include one or more of, for example, accessing the information, or retrieving the information (for example, from memory). Further, “receiving” is typically involved, in one way or another, during operations, for example, storing the information, processing the information, transmitting the information, moving the information, copying the information, erasing the information, calculating the information, determining the information, predicting the information, or estimating the information.

[104] It is to be appreciated that the use of any of the following

“and/or”, and “at least one of’, for example, in the cases of “A/B”, “A and/or B” and “at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and/or C” and “at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This may be extended, as is clear to one of ordinary skill in this and related arts, for as many items as are listed.

[105] Also, as used herein, the word “signal” refers to, among other things, indicating something to a corresponding decoder. For example, in certain embodiments the encoder signals a quantization matrix for de-quantization. In this way, in an embodiment the same parameter is used at both the encoder side and the decoder side. Thus, for example, an encoder can transmit (explicit signaling) a particular parameter to the decoder so that the decoder can use the same particular parameter. Conversely, if the decoder already has the particular parameter as well as others, then signaling can be used without transmitting (implicit signaling) to simply allow the decoder to know and select the particular parameter. By avoiding transmission of any actual functions, a bit savings is realized in various embodiments. It is to be appreciated that signaling can be accomplished in a variety of ways. For example, one or more syntax elements, flags, and so forth are used to signal information to a corresponding decoder in various embodiments. While the preceding relates to the verb form of the word “signal”, the word “signal” can also be used herein as a noun.

[106] As will be evident to one of ordinary skill in the art, implementations may produce a variety of signals formatted to carry information that may be, for example, stored or transmitted. The information may include, for example, instructions for performing a method, or data produced by one of the described implementations. For example, a signal may be formatted to carry the bitstream of a described embodiment. Such a signal may be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information that the signal carries may be, for example, analog or digital information. The signal may be transmitted over a variety of different wired or wireless links, as is known. The signal may be stored on a processor-readable medium.

Claims

1 . A method, comprising encoding a video which comprises:

2. An apparatus for encoding a video, comprising one or more processors, wherein said one or more processors are configured to:

- obtain a resolution for motion information for a block of the video,

3. A method, comprising decoding a video which comprises:

- refining the motion vector predictor, based on the obtained resolution.

4. An apparatus for decoding a video, comprising one or more processors, wherein said one or more processors are configured to:

- refining the motion vector predictor, based on the obtained resolution.

5. The method of claim 1 or 3 or the apparatus of claim 2 or 4, wherein refining the motion vector predictor comprises performing a first step of motion refinement at the obtained resolution.

6. The method of claim 1 or 3 or the apparatus of claim 2 or 4, wherein refining the motion vector predictor comprises performing a first step of motion refinement at a coarser resolution than the obtained resolution, and a second step of motion refinement at the obtained resolution.

7. The method or the apparatus of any one of claims 5 to 6, wherein the first step of motion refinement comprises at least one of a diamond motion vector search and a cross motion search.

8. The method or the apparatus of claim 6, wherein the second step of motion refinement comprises at least a cross motion search.

9. The method any one of claims 1 , 3 or 5 to 8 or the apparatus of any one of claims 2 or 4 to 8, wherein deriving the motion vector comprises determining the motion vector predictor from a list comprising at least one candidate motion vector predictor based on a matching cost function.

10. The method or the apparatus of claim 9, wherein said at least one candidate motion vector predictor is rounded based on the obtained resolution.

1 1. The method or the apparatus of claim 9, wherein the matching cost function is signaled to the decoder.

12. The method of any one of claims 1 , 3 or 5 to 1 1 or the apparatus of any one of claims 2 or 4-1 1 , wherein obtaining a resolution for motion information for a block of a video comprises decoding at least one information representative of said resolution.

13. The method or the apparatus of claim 12, wherein the motion information is a motion vector difference used for reconstructing a motion vector for reconstructing the block.

14. The method or the apparatus of claim 13, further comprising adding the derived motion vector to a list of candidate motion vector predictors used by a coding mode for coding or decoding the block, wherein coding or decoding the block according to said coding mode comprises coding or decoding the motion vector difference between a motion vector determined for the block and a candidate motion vector predictor selecting from the list of candidate motion vector predictors.

15. The method of any one of claims 1 , 3 or 5 to 13 or the apparatus of any one of claims 2 or 4 to 13, further comprising coding the block using the derived motion vector.

16. The method of any one of claims 1 , 3 or 5 to 13 or the apparatus of any one of claims 2 or 4 to 13, further comprising reconstructing the block using the derived motion vector.

17. A signal comprising coded video data comprising at least one information representative of a resolution of motion information for at least one block of the video and at least one information representative of an activation of a derivation of a motion vector for the at least one block based on the obtained resolution, the motion vector being used for reconstructing the block without signaling an information representative of said motion vector in the signal.

18. A computer readable storage medium comprising a signal of claim 17.

19. A computer readable storage medium having stored thereon instructions for causing one or more processors to perform the method of any one of claims 1 , 3 or 5 to 16.

20. A computer program product including instructions which, when the program is executed by one or more processors, causes the one or more processors to carry out the method of any one of claims 1 , 3 or 5 to 16.

21 . A device comprising:

- an apparatus according to any one of claims 2 or 4 to 16; and

- at least one of (i) an antenna configured to receive a signal according to claim 17, (ii) a band limiter configured to limit the received signal to a band of frequencies, or (iii) a display configured to display the video.

22. A device according to claim 21 , comprising a TV, a cell phone, a tablet or a Set Top Box.

23. An apparatus comprising: o An accessing unit configured to access data comprising a signal according to claim 17, o A transmitter configured to transmit the accessed data.

24. A method comprising accessing data comprising a signal according to claim 17, and transmitting the accessed data.