Use and signaling of refining video coding tools

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• perform a conversion between a video picture of a video and a bitstream of the video,
• wherein the bitstream conforms to a format rule,
• wherein the format rule specifies that applicability of a decoder-side motion vector refinement coding tool and a bi-directional optical flow coding tool for the video picture are indicated separately in the bitstream;
• wherein a first two syntax elements specifying whether the decoder-side motion vector refinement coding tool is enabled and whether the bi-directional optical flow coding tool is enabled respectively are included in a sequence parameter set in the bitstream, and
• wherein a second two syntax elements specifying whether the decoder-side motion vector refinement coding tool is disabled and whether the bi-directional optical flow coding tool is disabled respectively are conditionally included in a picture header in the bitstream;
• wherein a syntax element specifying whether the bi-directional optical flow coding tool is disabled is conditionally included in the picture header based on a syntax element which is conditionally included in the sequence parameter set based on at least one of the first two syntax elements;
• and
• wherein a third syntax element specifying whether a prediction refinement with optical flow coding tool is disabled is conditionally included in the picture header in the bitstream based on a prediction refinement with optical flow enabling flag included in the sequence parameter set in the bitstream, and wherein the third syntax element is different from the second two syntax elements.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• perform a conversion between a video picture of a video and a bitstream of the video,
• wherein the bitstream conforms to a format rule,
• wherein the format rule specifies that applicability of a decoder-side motion vector refinement coding tool and a bi-directional optical flow coding tool for the video picture are indicated separately in the bitstream;
• wherein a first two syntax elements specifying whether the decoder-side motion vector refinement coding tool is enabled and whether the bi-directional optical flow coding tool is enabled respectively are included in a sequence parameter set in the bitstream, and
• wherein a second two syntax elements specifying whether the decoder-side motion vector refinement coding tool is disabled and whether the bi-directional optical flow coding tool is disabled respectively are conditionally included in a picture header in the bitstream;
• wherein a syntax element specifying whether the bi-directional optical flow coding tool is disabled is conditionally included in the picture header based on a syntax element which is conditionally included in the sequence parameter set based on at least one of the first two syntax elements;
• and
• wherein a third syntax element specifying whether a prediction refinement with optical flow coding tool is disabled is conditionally included in the picture header in the bitstream based on a prediction refinement with optical flow enabling flag included in the sequence parameter set in the bitstream, and wherein the third syntax element is different from the second two syntax elements.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• generating the bitstream of the video;
• wherein the bitstream conforms to a format rule,
• wherein the format rule specifies that applicability of a decoder-side motion vector refinement coding tool and a bi-directional optical flow coding tool for a video picture of the video are indicated separately in the bitstream;
• wherein a first two syntax elements specifying whether the decoder-side motion vector refinement coding tool is enabled and whether the bi-directional optical flow coding tool is enabled respectively are included in a sequence parameter set in the bitstream, and
• wherein a second two syntax elements specifying whether the decoder-side motion vector refinement coding tool is disabled and whether the bi-directional optical flow coding tool is disabled respectively are conditionally included in a picture header in the bitstream;
• wherein a syntax element specifying whether the bi-directional optical flow coding tool is disabled is conditionally included in the picture header based on a syntax element which is conditionally included in the sequence parameter set based on at least one of the first two syntax elements;
• and
• wherein a third syntax element specifying whether a prediction refinement with optical flow coding tool is disabled is conditionally included in the picture header in the bitstream based on a prediction refinement with optical flow enabling flag included in the sequence parameter set in the bitstream, and wherein the third syntax element is different from the second two syntax elements.