Systems and methods are described for reducing the complexity of using bi-directional optical flow (BIO) in video coding. In some embodiments, bit-width reduction steps are introduced in the BIO motion refinement process to reduce the maximum bit-width used for BIO calculations. In some embodiments, simplified interpolation filters are used to generate predicted samples in an extended region around a current coding unit. In some embodiments, different interpolation filters are used for vertical versus horizontal interpolation. In some embodiments, BIO is disabled for coding units with small heights and/or for coding units that are predicted using a sub-block level inter prediction technique, such as advanced temporal motion vector prediction (ATMVP) or affine prediction.

A video processing method includes determining, for a conversion between a current video block of a video including multiple video blocks and a coded representation of the video, and from types of reference pictures used for the conversion, applicability of a coding tool to the current video block and performing the conversion based on the determining. The method may be performed by a video decoder or a video encoder or a video transcoder.

Devices, systems and methods for digital video coding, which includes inter prediction with refinement, are described. An exemplary method of video processing includes determining to use, for a conversion between a current block of a video and a bitstream representation of the video, a first linear optimization model for the conversion using a first coding mode, the first linear optimization model being derived from a second linear optimization model that is used for the conversion using a second coding mode, and performing, based on the determining, the conversion. Another exemplary method of video processing includes determining to use, for a conversion between a current block of a video and a bitstream representation of the video, a gradient value computation algorithm for a bi-directional optical flow tool, and performing, based on the determining, the conversion.

A method for decoding or encoding includes obtaining views parameters for a set of views comprising at least one reference view and a current view of a multi-views video content wherein each view comprises a texture layer and a depth layer. For at least one couple of a reference view and the current view of the set of views, an intermediate prediction image applying a forward projection method to pixels of the reference view is generated to project these pixels from a camera coordinates system of the reference view to a camera coordinates system of the current view, the prediction image comprising information allowing reconstructing image data. At least one final prediction image obtained from at least one intermediate prediction image is stored in a buffer of reconstructed images of the current view. A current image of the current view from the images stored in said buffer is reconstructed, said buffer comprising said at least one final prediction image.

A method for decoding or encoding includes obtaining views parameters for a set of views comprising at least one reference view and a current view of a multi-views video content wherein each view comprises a texture layer and a depth layer. For at least one couple of a reference view and the current view of the set of views, an intermediate prediction image applying a forward projection method to pixels of the reference view is generated to project these pixels from a camera coordinates system of the reference view to a camera coordinates system of the current view, the prediction image comprising information allowing reconstructing image data. At least one final prediction image obtained from at least one intermediate prediction image is stored in a buffer of reconstructed images of the current view. A current image of the current view from the images stored in said buffer is reconstructed, said buffer comprising said at least one final prediction image.

A method of video processing includes determining, for a conversion between a current block of a video and a coded representation of the video, that a resolution of a current picture containing the current block and a reference picture used for the conversion are different, and performing the conversion based on the determining such that predicted values of a group of samples of the current block are generated using a horizontal or a vertical interpolation filter.

A method for decoding a 360-degree image includes: receiving a bitstream obtained by encoding a 360-degree image; generating a prediction image by making reference to syntax information obtained from the received bitstream; combining the generated prediction image with a residual image obtained by dequantizing and inverse-transforming the bitstream, so as to obtain a decoded image; and reconstructing the decoded image into a 360-degree image according to a projection format. Here, generating the prediction image includes: checking, from the syntax information, prediction mode accuracy for a current block to be decoded; determining whether the checked prediction mode accuracy corresponds to most probable mode (MPM) information obtained from the syntax information; and when the checked prediction mode accuracy does not correspond to the MPM information, reconfiguring the MPM information according to the prediction mode accuracy for the current block.

A system for storing and providing video pixel data for video encoding is disclosed. The system comprises a memory storage and a cache storage. The system further comprises a controller. The controller is configured to receive a request that causes transferring of a reference pixel block of a video, wherein the video is being encoded using the reference pixel block. The controller is configured to determine whether the reference pixel block has at least a portion that is outside a frame of the video. In response to the determination of the reference pixel block having at least a portion outside the frame of the video, the controller is configured to cause a portion of the reference pixel block of the video inside the frame of the video to be fetched from a memory storage and stored in a cache storage, pad a remaining missing portion of the reference pixel block of the video outside the frame of the video with padding pixel data to form the reference pixel block, and transfer the reference pixel block in response to the request.

A video processing method includes determining, for a conversion between a current video block of a video including multiple video blocks and a coded representation of the video, and from types of reference pictures used for the conversion, applicability of a coding tool to the current video block and performing the conversion based on the determining. The method may be performed by a video decoder or a video encoder or a video transcoder.

A video coder is configured to determine a reference block of a reference picture for prediction of a current block of a current picture using motion information and to generate a set of reference samples for the current block of the current picture. To generate the set of reference samples, the video coder is configured to perform reference sample clipping on the reference block of the reference picture based on a size of the reference picture. The video coder is further configured to generate a prediction block for the current block of the current picture based on the set of reference samples.