TECHNICAL FIELD

This patent document relates to video coding techniques, decoding techniques, devices, and systems.

BACKGROUND

Motion compensation (MC) is a technique in video processing to predict a frame in a video, given the previous and/or future frames by accounting for motion of the camera and/or objects in the video. Motion compensation can be used in the encoding of video data for video compression.

SUMMARY

This document discloses methods, systems, and devices related to the use of affine motion compensation in video coding and decoding. In one representative aspect, a video processing method is disclosed. The method includes generating, for a reconstruction of a current video unit, a list of affine motion vector prediction candidates in which each candidate in the list is calculated without using a clipping operation, wherein the clipping operation limits a magnitude of the candidate motion vectors to a range; and performing the reconstruction of the current video unit using the list of affine motion vector prediction candidates.

In yet another aspect, another video processing method is disclosed. The method includes constructing, during generation of a video unit from a coded representation thereof, a list of affine motion vector predictors using a precision that is same as a precision used for encoding motion vector differences in an affine video coding mode in the coded representation and performing the generation of the video unit using the list of affine motion vector prediction candidates.

In yet another aspect, another video processing method is disclosed. The method includes determining, for a conversion between a coded representation of a video block and the video block that is affine coded, that usage of multiple motion vector differences (MVDs) with different precisions is enabled for the conversion; and performing the conversion based on the determining.

In yet another aspect, a video processing method is disclosed. The method includes applying a motion-based subblock coding tool to a current video unit, wherein the tool is at least based on deriving a first motion information for motion compensation at a first block size and a second motion information at a second block size different from the first block size; and storing the second motion information for motion prediction of a future video unit.

In yet another aspect, a video processing method is disclosed. The method includes reconstructing a video unit using a coded representation thereof, wherein the coded representation includes rounding a motion vector difference information for the video unit using:

((∑i=0n-1⁢d⁢M⁢VCi⁡[1]*w+o⁡(w))⪢k⁡(w),⁢(-∑i=0n-1⁢-d⁢M⁢VCi⁡[3]*w+o⁡(w))⪢k⁡(w))
wherein dMVic[1], dMVic[3] denote horizontal and vertical motion vector difference of a top-right control point used in a 4-parameter affine model derived in an ith iteration, wherein >> is bit shift operation, w is a width of the video unit, k(w) is a non-negative integer, and o(w) is an offset.

In yet another aspect, a video processing method is disclosed. The method includes using a coded representation of a video unit associated with an affine video coding mode that includes use of multiple motion vector differences (MVDs) coded with different precisions such that a first MVD has a first precision and a second MVD has a second precision different from the first MVD; and constructing the video unit using the coded representation.

In yet another representative aspect, the various techniques described herein may be embodied as a computer program product stored on a non-transitory computer readable media. The computer program product includes program code for carrying out the methods described herein.

In yet another representative aspect, a video encoder apparatus may implement a method as described herein.

In yet another representative aspect, a video decoder apparatus may implement a method as described herein.

The details of one or more implementations are set forth in the accompanying attachments, the drawings, and the description below. Other features will be apparent from the description and drawings, and from the claims.

