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.

Particular embodiments may remove a condition check in the semantics for checking a high-precision data flag. This simplifies the semantics used in the encoding and decoding process. In this case, even if the high-precision data flag is not set, the value of the weighted prediction syntax element is set by the BitDepth variable. However, even if the BitDepth is not considered high-precision data, such as 8 bits, the range for the weighted prediction syntax element is still the same as the fixed value. For example, the syntax elements luma_offset_l0[i], luma_offset_l1[i], delta_chroma_offset_l0[i][j], and delta_chroma_offset_l1[i][j] use the variable BitDepth as described above whether the flag extended_precision_processing_flag is enabled and not enabled to indicate whether the bit depth is above a threshold.

Particular embodiments may remove a condition check in the semantics for checking a high-precision data flag. This simplifies the semantics used in the encoding and decoding process. In this case, even if the high-precision data flag is not set, the value of the weighted prediction syntax element is set by the BitDepth variable. However, even if the BitDepth is not considered high-precision data, such as 8 bits, the range for the weighted prediction syntax element is still the same as the fixed value. For example, the syntax elements luma_offset_l0[i], luma_offset_l1[i], delta_chroma_offset_l0[i][j], and delta_chroma_offset_l1[i][j] use the variable BitDepth as described above whether the flag extended_precision_processing_flag is enabled and not enabled to indicate whether the bit depth is above a threshold.

For each prediction candidate of a set of one or more prediction candidates of the current block, a video coder computes a matching cost between a set of reference pixels of the prediction candidate in a reference picture and a set of neighboring pixels of a current block in a current picture. The video coder identifies a subset of the reference pictures as major reference pictures based on a distribution of the prediction candidates among the reference pictures of the current picture. A bounding block is defined for each major reference picture, the bounding block encompassing at least portions of multiple sets of reference pixels for multiple prediction candidates. The video coder assigns an index to each prediction candidate based on the computed matching cost of the set of prediction candidates. A selection of a prediction candidate is signaled by using the assigned index of the selected prediction candidate.

A system for decoding a video bitstream includes receiving a reference picture set associated with a frame including a set of reference picture identifiers. The reference picture set identifies one or more reference pictures to be used for inter-prediction of the frame based upon its associated least significant bits of a picture order count based upon the reference picture identifiers. The one or more reference pictures is a second or greater previous frame to the frame having the matching reference picture identifier.

A system for decoding a video bitstream includes receiving a reference picture set associated with a frame including a set of reference picture identifiers. The reference picture set identifies one or more reference pictures to be used for inter-prediction of the frame based upon its associated least significant bits of a picture order count based upon the reference picture identifiers. The one or more reference pictures is a second or greater previous frame to the frame having the matching reference picture identifier.

A decoder comprises circuitry and memory. The circuitry, using the memory, in operation, determines a number of first pixels and a number of second pixels used in a deblocking filter process, wherein the first pixels are located at an upper side of a block boundary and the second pixels are located at a lower side of the block boundary, and performs the deblocking filter process on the block boundary. The number of the first pixels and the number of the second pixels are selected from among candidates, wherein the candidates include at least 4 and M larger than 4. Response to a location of the block boundary being a predetermined location, the number of the first pixels used in the deblocking filter process is limited to be 4.

A method, computer program, and computer system is provided for video encoding and decoding. Video data including one or more frames is received. One or more quantization parameters associated with the received video data are determined for frame generation or enhancement of a target frame from among the one or more frames. The video data is decoded based on the determined quantization parameters.

The present disclosure provides video decoding method. An exemplary method includes: decoding a first parameter for a coding unit from a bitstream, and determining a candidate for the coding unit based on the first parameter; determining a value of a second parameter associated with the coding unit based on a value of a second parameter associated with the candidate, wherein the second parameter indicates whether a bi-directional prediction correction is enabled; and in response to the value of the second parameter associated with the coding unit indicating the bi-directional prediction correction being enabled, performing the bi-directional prediction correction on the coding unit.

In a method and a device for encoding or decoding an image according to the present invention, motion information for bidirectional prediction of a current block may be derived on the basis of an inter mode previously defined in the device for encoding or decoding an image, and inter prediction may be performed on the current block on the basis of the motion information, wherein the motion information for bidirectional prediction is adjusted to be motion information for unidirectional prediction according to the predefined inter mode.