Signaling of triangle merge mode indexes in video coding

A method of encoding video data, the method comprising:

• determining a maximum number of triangle merging candidates;
• signaling a first triangle merging index syntax element in the bitstream, the first triangle merging index syntax element specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• determining whether the maximum number of triangle merging candidates is greater than 2;
• based on the maximum number of triangle merging candidates not being greater than 2, omitting from the bitstream a second triangle merging index syntax element that specifies a second triangle merging candidate index indicating a second triangle merging candidate of the triangle shaped-based motion compensation candidate list, the second triangle merging candidate being different from the first triangle merging candidate;
• generating a prediction block for a coding unit (CU), wherein generating the prediction block for the CU comprises:
• inter-predicting a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• inter-predicting a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• generating residual data for the CU based on the prediction block for the CU and samples of the CU.

A device for decoding video data, the device comprising:

• a memory to store the video data;
• and
• one or more processors implemented in circuitry, the one or more processors configured to:
• determine, based on a first syntax element signaled in a bitstream that includes an encoded representation of the video data, a maximum number of triangle merging candidates;
• obtain a first triangle merging index syntax element from the bitstream, the first triangle merging index specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• determine whether the maximum number of triangle merging candidates is greater than 2;
• based on the maximum number of triangle merging candidates not being greater than 2, infer that a second triangle merging candidate index indicates a second triangle merging candidate of the triangular shape-based motion compensation candidate list without obtaining any syntax element specifying the second triangle merging candidate index from the bitstream, the second triangle merging candidate being different from the first triangle merging candidate;
• generate a prediction block for a coding unit (CU), wherein the one or more processors are configured such that, as part of generating the prediction block for the CU, the one or more processors:
• inter-predict a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• inter-predict a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• reconstruct the CU based on the prediction block for the CU and residual data for the CU.

A device for encoding video data, the device comprising:

• a memory to store the video data;
• and
• one or more processors implemented in circuitry, the one or more processors configured to:
• determine a maximum number of triangle merging candidates;
• signal a first triangle merging index syntax element in the bitstream, the first triangle merging index syntax element specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• determine whether the maximum number of triangle merging candidates is greater than 2;
• based on the maximum number of triangle merging candidates not being greater than 2, omit from the bitstream a second triangle merging index syntax element that specifies a second triangle merging candidate index indicating a second triangle merging candidate of the triangle shaped-based motion compensation candidate list, the second triangle merging candidate being different from the first triangle merging candidate;
• generate a prediction block for a coding unit (CU), wherein the one or more processors are configured such that, as part of generating the prediction block for the CU, the one or more processors:
• inter-predict a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• inter-predict a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• generate residual data for the CU based on the prediction block for the CU and samples of the CU.

A device for decoding video data, the device comprising:

• means for determining, based on a first syntax element signaled in a bitstream that includes an encoded representation of the video data, a maximum number of triangle merging candidates;
• means for obtaining a first triangle merging index syntax element from the bitstream, the first triangle merging index syntax element specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• means for determining whether the maximum number of triangle merging candidates is greater than 2;
• means for inferring, based on the maximum number of triangle merging candidates not being greater than 2, that a second triangle merging candidate index indicates a second triangle merging candidate of the triangular shape-based motion compensation candidate list without obtaining any syntax element specifying the second triangle merging candidate index from the bitstream, the second triangle merging candidate being different from the first triangle merging candidate;
• means for generating a prediction block for a coding unit (CU), wherein the means for generating the prediction block for the CU comprises:
• means for inter-predicting a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• means for inter-predicting a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• means for reconstructing the CU based on the prediction block for the CU and residual data for the CU.

A device for encoding video data, the device comprising:

• means for determining a maximum number of triangle merging candidates;
• means for signaling a first triangle merging index syntax element in the bitstream, the first triangle merging index syntax element specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• means for determining whether the maximum number of triangle merging candidates is greater than 2;
• means for omitting, based on the maximum number of triangle merging candidates not being greater than 2, from the bitstream a second triangle merging index syntax element that specifies a second triangle merging candidate index indicating a second triangle merging candidate of the triangle shaped-based motion compensation candidate list, the second triangle merging candidate being different from the first triangle merging candidate;
• means for generating a prediction block for a coding unit (CU), wherein the means for generating the prediction block for the CU comprises:
• means for inter-predicting a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• means for inter-predicting a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• means for generating residual data for the CU based on the prediction block for the CU and samples of the CU.

A computer-readable data storage medium having instructions stored thereon that, when executed, cause one or more processors to:

• determine, based on a first syntax element signaled in a bitstream that includes an encoded representation of video data, a maximum number of triangle merging candidates;
• obtain a first triangle merging index syntax element from the bitstream, the first triangle merging index syntax element specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• determine whether the maximum number of triangle merging candidates is greater than 2;
• based on the maximum number of triangle merging candidates not being greater than 2, infer that a second triangle merging candidate index indicates a second triangle merging candidate of the triangular shape-based motion compensation candidate list without obtaining any syntax element specifying the second triangle merging candidate index from the bitstream, the second triangle merging candidate being different from the first triangle merging candidate;
• generate a prediction block for a coding unit (CU), wherein generating the prediction block for the CU comprises:
• inter-predicting a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• inter-predicting a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• reconstruct the CU based on the prediction block for the CU and residual data for the CU.

A computer-readable data storage medium having instructions stored thereon that, when executed, cause one or more processors to:

• determine a maximum number of triangle merging candidates;
• signal a first triangle merging index syntax element in the bitstream, the first triangle merging index specifying a first triangle merging candidate index, the first triangle merging candidate index indicating a first triangle merging candidate of a triangular shape-based motion compensation candidate list;
• determine whether the maximum number of triangle merging candidates is greater than 2;
• based on the maximum number of triangle merging candidates not being greater than 2, omit from the bitstream a second triangle merging index syntax element that specifies a second triangle merging candidate index indicating a second triangle merging candidate of the triangle shaped-based motion compensation candidate list, the second triangle merging candidate being different from the first triangle merging candidate;
• generate a prediction block for a coding unit (CU), wherein generating the prediction block for the CU comprises:
• inter-predicting a first triangle partition of the CU using motion information of the first triangle merging candidate;
• and
• inter-predicting a second triangle partition of the CU using motion information of the second triangle merging candidate;
• and
• generate residual data for the CU based on the prediction block for the CU and samples of the CU.