Schemes for adjusting adaptive resolution for motion vector difference

A method of video encoding, the method comprising:

• receiving video data that includes a current frame composed of a plurality of video blocks, the plurality of video blocks including a current video block;
• determining that the current video block is to be inter-coded using a prediction block and a motion vector (MV), wherein the MV is to be derived from a reference motion vector (RMV) and a motion vector difference (MVD) for the current video block;
• and
• when the MVD is coded with an adaptive MVD pixel resolution:
• determining a nominal MVD pixel precision for the current frame;
• identifying a maximum allowed MVD pixel precision for the current video block, wherein the maximum allowed MVD pixel precision is less than the nominal MVD pixel precision;
• determining a set of allowable MVD levels for the current video block by restricting the nominal MVD pixel precision according to the maximum allowed MVD pixel precision;
• and
• deriving the MVD having a first precision according to at least one MVD parameter for the current video block and the set of allowable MVD levels, wherein the first precision is selected from the set of allowable MVD levels.

A method of processing visual media data, the method comprising:

• obtaining a source video sequence;
• performing a conversion between the source video sequence and a bitstream of visual media data according to a format rule,
• wherein the bitstream comprises:
• a plurality of encoded data blocks, including a current video block corresponding to a current frame;
• a first indicator indicating a nominal motion vector difference (MVD) pixel precision for the current frame;
• and
• a second indicator indicating a maximum allowed MVD pixel precision for the current video block;
• and
• wherein the format rule specifies that, when the MVD is coded with an adaptive MVD pixel resolution:
• a nominal MVD pixel precision is to be determined for the current frame;
• a maximum allowed MVD pixel precision is to be identified for the current video block, wherein the maximum allowed MVD pixel precision is less than the nominal MVD pixel precision;
• a set of allowable MVD levels are to be determined for the current video block by restricting the nominal MVD pixel precision according to the maximum allowed MVD pixel precision;
• and
• the MVD having a first precision is derived according to the first and second indicators, wherein the first precision is selected from the set of allowable MVD levels.