Sub-prediction unit based advanced temporal motion vector prediction

1. A method of coding video data, the method comprising:

forming, for a current block of video data, a merge candidate list including a plurality of merge candidates, the plurality of merge candidates including four spatial neighboring candidates from four neighboring blocks to the current block and, immediately following the four spatial neighboring candidates, an advanced temporal motion vector prediction (ATMVP) candidate, wherein the ATMVP candidate indicates that the current block is to be predicted using a block identified by the ATMVP candidate that is split into a plurality of sub-blocks, each of the plurality of sub-blocks having a respective set of motion information;

coding an index into the merge candidate list that identifies the ATMVP candidate of the plurality of merge candidates in the merge candidate list; and

based on the index identifying the ATMVP candidate, coding the current block of video data, wherein coding the current block comprises coding sub-blocks of the current block using the respective motion information of the sub-blocks of the block identified by the ATMVP candidate.

2. The method of claim 1 , wherein forming the merge candidate list comprises:

determining, for the current block, a corresponding block in a reference picture;

determining whether motion information is available for the corresponding block; and

forming the merge candidate list to include the ATMVP candidate after determining that motion information is available for the corresponding block.

3. The method of claim 2 , wherein determining whether motion information is available for the corresponding block comprises determining whether a portion of the corresponding block is intra-predicted.

4. A device for coding video data, the device comprising:

a memory configured to store video data; and

a video coder configured to:

form, for a current block of the video data, a merge candidate list including a plurality of merge candidates, the plurality of merge candidates including four spatial neighboring candidates from four neighboring blocks to the current block and, immediately following the four spatial neighboring candidates, an advanced temporal motion vector prediction (ATMVP) candidate, wherein the ATMVP candidate indicates that the current block is to be predicted using a block identified by the ATMVP candidate that is split into a plurality of sub-blocks, each of the plurality of sub-blocks having a respective set of motion information;

code an index into the merge candidate list that identifies the ATMVP candidate of the plurality of merge candidates in the merge candidate list; and

based on the index identifying the ATMVP candidate, code the current block of video data, wherein to code the current block of video data, the video coder is configured to code sub-blocks of the current block using the respective motion information of the sub-blocks of the block identified by the ATMVP candidate.

5. The device of claim 4 , wherein to form the merge candidate list, the video coder is configured to:

determine, for the current block, a corresponding block in a reference picture;

determine whether motion information is available for the corresponding block; and

form the merge candidate list to include the ATMVP candidate after determining that motion information is available for the corresponding block.

6. The device of claim 5 , wherein to determine whether motion information is available for the corresponding block, the video coder is configured to determine whether a portion of the corresponding block is intra-predicted.

7. A device for coding video data, the device comprising:

means for forming, for a current block of video data, a merge candidate list including a plurality of merge candidates, the plurality of merge candidates including four spatial neighboring candidates from four neighboring blocks to the current block and, immediately following the four spatial neighboring candidates, an advanced temporal motion vector prediction (ATMVP) candidate, wherein the ATMVP candidate indicates that the current block is to be predicted using a block identified by the ATMVP candidate that is split into a plurality of sub-blocks, each of the plurality of sub-blocks having a respective set of motion information;

means for coding an index into the merge candidate list that identifies the ATMVP candidate of the plurality of merge candidates in the merge candidate list; and

means for coding the current block of video data, wherein the means for coding the current block of video data comprises means for coding sub-blocks of the current block using the respective motion information of the sub-blocks of the block identified by the ATMVP candidate based on the index identifying the ATMVP candidate.

8. The device of claim 7 , wherein forming the merge candidate list comprises:

means for determining, for the current block, a corresponding block in a reference picture;

means for determining whether motion information is available for the corresponding block; and

means for forming the merge candidate list to include the ATMVP candidate after determining that motion information is available for the corresponding block.

9. The device of claim 8 , wherein the means for determining whether motion information is available for the corresponding block comprises means for determining whether a portion of the corresponding block is intra-predicted.

10. A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause a processor to:

form, for a current block of video data, a merge candidate list including a plurality of merge candidates, the plurality of merge candidates including four spatial neighboring candidates from four neighboring blocks to the current block and, immediately following the four spatial neighboring candidates, an advanced temporal motion vector prediction (ATMVP) candidate, wherein the ATMVP candidate indicates that the current block is to be predicted using a block identified by the ATMVP candidate that is split into a plurality of sub-blocks, each of the plurality of sub-blocks having a respective set of motion information;

code an index into the merge candidate list that identifies the ATMVP candidate of the plurality of merge candidates in the merge candidate list; and

based on the index identifying the ATMVP candidate, code the current block of video data, wherein the instructions that cause the processor to code the current block comprise instructions that cause the processor to code sub-blocks of the current block using the respective motion information of the sub-blocks of the block identified by the ATMVP candidate.

11. The non-transitory computer-readable storage medium of claim 10 , wherein the instructions that cause the processor to form the merge candidate list comprise instructions that cause the processor to:

determine, for the current block, a corresponding block in a reference picture;

determine whether motion information is available for the corresponding block; and

form the merge candidate list to include the ATMVP candidate after determining that motion information is available for the corresponding block.

12. The non-transitory computer-readable storage medium of claim 11 , wherein the instructions that cause the processor to determine whether motion information is available for the corresponding block comprise instructions that cause the processor to determining whether a portion of the corresponding block is intra-predicted.