Fusion improvement and sub-pel precision mode for template matching related tools for video coding

A device for coding video data, the device comprising:

• memory to store the video data;
• and
• one or more processors implemented in circuitry, the one or more processors configured to:
• apply a sub-pel precision mode to generate a prediction block for a current block of the video data, wherein a syntax element is signaled to indicate that the sub-pel precision mode is applied to the current block and the one or more processors are configured to, applying the sub-pel precision mode:
• apply an interpolation filter to samples of a reference region to generate an array of samples at full-pel and sub-pel precision;
• and
• identify, within the array, a reference template of the prediction block, wherein the reference template of the prediction block is a best match for a template of the current block within the array, wherein a template pattern defines a shape of the reference template of the prediction block and the template of the current block;
• generate a plurality of template matching (TM) candidates, wherein each of the TM candidates is associated with a respective prediction block and a respective motion vector predictor, and the one or more processors are configured to, as part of generating the plurality of TM candidates, for each of the TM candidates:
• apply the interpolation filter to samples of a reference region indicated by the motion vector predictor associated with the TM candidate to generate a respective array of samples at full-pel and sub-pel precision;
• and
• identify, within the respective array, a respective reference template of the respective prediction block, wherein the respective reference template of the respective prediction block is a best match for the template of the current block within the respective array;
• generate the prediction block for the current block as a linear combination of corresponding samples in the prediction blocks associated with two or more TM candidates of the plurality of TM candidates, wherein to generate the prediction block for the current block as the linear combination of the corresponding samples the processors are configured to:
• for each of the two or more TM candidates, calculate a template cost for the TM candidate, and
• generate the prediction block for the current block as a weighted average of the corresponding samples in the two or more TM candidates, wherein the processors are configured to determine the weights used in the weighted average based on the template cost for the TM candidate;
• and
• encode or decode the current block using the prediction block for the current block.