A method of video decoding performed in a video decoder includes receiving a coded video bitstream including a current block that is divided into a plurality of sub-blocks. The method includes performing sub-block based affine motion compensation on the current block to generate a sub-block prediction for each pixel in each sub-block of the current block. The method further includes determining one or more spatial gradients for each sub-block prediction. The method includes performing, for each sub-block prediction, prediction refinement with an optical flow process using the respective determined one or more spatial gradients and at least one constraint included in the coded video bitstream. The method further includes adding, for each sub-block prediction, an output of the respective prediction refinement to the respective sub-block prediction to generate a final prediction for each pixel in each sub-block of the current block.

The present disclosure provides systems and methods for constructing a merge candidate list used for video processing. One exemplary method includes: inserting a set of spatial merge candidates to a merge candidate list of a coding block, wherein the set of spatial merge candidates are inserted according to an order of: top neighboring block, left neighboring block, top neighboring block, left neighboring block and above-left neighboring block. The method can further include adding to the merge candidate list at least one of: a temporal merge candidate from collocated coding units, a history-based motion vector predictor (HMVP) from a First-In, First-Out (FIFO) table, a pairwise average candidate, or a zero motion vector.

A motion vector decoding unit derives a motion vector of a prediction block subject to decoding on the basis of a motion vector of a candidate block included in candidate blocks selected from neighboring blocks. The motion compensation prediction unit performs motion compensation prediction using the derived motion vector. In case a motion vector number of a first block and a motion vector number of a second block are identical with each other, the motion vector decoding unit determines whether or not to set the second block as a candidate block in accordance with whether or not a reference index indicating a reference picture that the motion vector of the first block refers to and a reference index indicating a reference picture that the motion vector of the second block refers to are identical with each other.

There is provided a method for estimating weighted prediction parameters intended to be used for predicting an image block.

A video decoding apparatus predicts a target block in a current picture to be decoded. The apparatus comprises a predictor configured to: determine first and second reference pictures and first and second motion vectors for bi-prediction by decoding a bitstream; generate a first reference block from the first reference picture referenced by the first motion vector and generate a second reference block from the second reference picture referenced by the second motion vector; and generate a prediction block of the target block using the first and second reference blocks. The predictor includes a first coding tool configured to generate the prediction block of the target block by performing a bi-directional optical flow process using the first and second reference blocks.

A video decoding apparatus predicts a target block in a current picture to be decoded. The apparatus comprises a predictor configured to: determine first and second reference pictures and first and second motion vectors for bi-prediction by decoding a bitstream; generate a first reference block from the first reference picture referenced by the first motion vector and generate a second reference block from the second reference picture referenced by the second motion vector; and generate a prediction block of the target block using the first and second reference blocks. The predictor includes a first coding tool configured to generate the prediction block of the target block by performing a bi-directional optical flow process using the first and second reference blocks.

A video decoding method performed by a video decoding apparatus, according to the present document, comprises the steps of: parsing a flag for weighted prediction from a bitstream; parsing a prediction weighted table syntax from the bitstream on the basis of the flag; generating prediction samples by performing weighted prediction on a current block within a current picture on the basis of the prediction weighted table syntax; and generating reconstructed samples for the current block on the basis of the prediction samples, wherein the prediction weighted table syntax may be parsed from a picture header or slice header of the bitstream on the basis of a value of the flag.

A frame processor may generate a mask based on one or more static regions of a first set of frames of a plurality of previous frame and adjust the mask to at least one of determine alpha data or conceal distorted content associated with the one or more static regions of the first set of frames. The distorted content may be caused by extrapolation of a frame from a second set of frames of the plurality of previous frames. The frame processor may generate a composite frame based on application of at least one of the mask or the alpha data to a previous frame of the plurality of frames, and application of the previous frame based on the at least one of the mask or the alpha data to the frame extrapolated from the second set of frames of the plurality of previous frames.

An encoding apparatus, includes a memory; and a processor coupled to the memory and configured to: perform intra-screen prediction encoding on an image of a region of a still image cut out from a first decoded image corresponding to a screen image before a predetermined region is switched from a video to a still image, generate a second decoded image obtained by decoding information for which the intra-screen prediction is performed, and when a first screen image after the predetermined region is switched from a video to a still image is received, perform inter-screen prediction encoding on an image of a region of a still image cut out from the first screen image after switching to a still image, by referring to the generated second decoded image.

An encoding apparatus, includes a memory; and a processor coupled to the memory and configured to: perform intra-screen prediction encoding on an image of a region of a still image cut out from a first decoded image corresponding to a screen image before a predetermined region is switched from a video to a still image, generate a second decoded image obtained by decoding information for which the intra-screen prediction is performed, and when a first screen image after the predetermined region is switched from a video to a still image is received, perform inter-screen prediction encoding on an image of a region of a still image cut out from the first screen image after switching to a still image, by referring to the generated second decoded image.