Signalling for merge mode with motion vector differences in video coding

A device for decoding video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors implemented in circuitry and configured to:
• generate a first merge candidate list for a first block;
• determine that the first block is coded in a merge mode with motion vector differences;
• in response to determining that a maximum number of entries for the first merge candidate list is equal to 1, infer a value of a first instance of a flag to be equal to a first value, wherein the first value for the flag indicates that the first block is to be decoded using a first entry in the first merge candidate list;
• receive first motion vector difference information;
• determine first motion information for predicting the first block based on candidate motion information included in the first entry of the first merge candidate list and the first motion vector difference information;
• and
• decode the first block using the first motion information.

An apparatus for decoding video data, the apparatus comprising:

• means for generating a first merge candidate list for a first block;
• means for determining that the first block is coded in a merge mode with motion vector differences;
• means for inferring a value of a first instance of a flag to be equal to a first value in response to determining that a maximum number of entries for the first merge candidate list is equal to 1, wherein the first value for the flag indicates that the first block is to be decoded using a first entry in the first merge candidate list;
• means for receiving first motion vector difference information;
• means for determining first motion information for predicting the first block based on candidate motion information included in the first entry of the first merge candidate list and the first motion vector difference information;
• and
• means for decoding the first block using the first motion information.

A device for encoding video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors implemented in circuitry and configured to:
• generate a first merge candidate list for a first block;
• determine that the first block is coded in a merge mode with motion vector differences;
• determine first motion information for predicting the first block;
• determine first motion vector difference information, wherein the first motion vector difference information represents a difference between the first motion information for predicting the first block and candidate motion information included in a first entry of the first merge candidate list;
• in response to determining that a maximum number of entries for the first merge candidate list is equal to 1, refrain from including, in a bitstream of encoded video data, a flag, wherein a first value for the flag indicates that the first block is to be decoded using a first entry in the first merge candidate list and a second value for the flag indicates that the first block is to be decoded using a second entry in the first merge candidate list;
• generate, for inclusion in the bitstream of encoded video data, the first motion vector difference information;
• and
• output the bitstream of encoded video data.

A computer-readable storage medium storing instructions that when executed by one or more processors cause the one or more processors to:

• generate a first merge candidate list for a first block;
• determine that the first block is coded in a merge mode with motion vector differences;
• in response to determining that a maximum number of entries for the first merge candidate list is equal to 1, infer a value of a first instance of a flag to be equal to a first value, wherein the first value for the flag indicates that the first block is to be decoded using a first entry in the first merge candidate list;
• receive first motion vector difference information;
• determine first motion information for predicting the first block based on candidate motion information included in the first entry of the first merge candidate list and the first motion vector difference information;
• and
• decode the first block using the first motion information.