Method and apparatus for processing video signal

1. A method of decoding a video, the method comprising:

deriving merge candidates of a current block, the merge candidates comprising a spatial merge candidate derived from a neighboring block adjacent to the current block;

generating a first candidate list including the merge candidates of the current block,

wherein when a number of the merge candidates included in the first candidate list is less than a predetermined value, a motion information candidate included in a second candidate list is added to the first candidate list;

decoding index information for specifying one of a plurality of merge candidates included in the first candidate list; and

deriving motion information of the current block from a merge candidate specified by the index information,

wherein the motion information candidate included in the second candidate list is derived from a spatial block that is decoded prior to decoding the current block and included in a current picture including the current block, and

wherein after deriving the motion information of the current block, the second candidate list is updated with the motion information of the current block wherein the motion information of the current block is added to the second candidate list as a new motion information candidate with a highest or lowest index; wherein at least one of a plurality of motion information candidates in the second candidate list is added to the first candidate list in a descending order of an index assigned to each of the plurality of motion information candidates.

2. The method of claim 1 , the spatial block from which the motion information candidate is derived is located at a position different from at least one neighboring block of the current block, and

wherein the at least one neighboring block comprises at least one of a top neighboring block and a left neighboring block.

3. The method of claim 1 , wherein if a first motion information candidate identical to the motion information of the current block is already present in the second candidate list, the first motion information candidate is deleted from the second candidate list and the motion information of the current block is added to the second candidate list as the new motion information.

4. The method of claim 3 , wherein the second candidate list is initialized per a pre-defined unit.

5. The method of claim 4 , wherein the pre-defined unit is a slice, a tile, a coding tree unit or a coding tree unit row.

6. The method of claim 1 , wherein, for one of the plurality of motion information candidates in the second candidate list, redundant check is performed with at least one merge candidate included in the first candidate list,

wherein if the at least one merge candidate in the first candidate list identical to the one of the plurality of motion information candidates is not found by the redundant check, the one of the plurality of motion information candidates is added to the first candidate list,

wherein if the at least one merge candidate in the first candidate list identical to the one of the plurality of motion information candidates is found by the redundant check, another of the plurality of motion information candidates is added to the first candidate list instead of the one of the plurality of motion information candidates, and

wherein the another of the plurality of motion information candidates has an index less than the one of the plurality of motion information candidates by 1.

7. The method of claim 6 , wherein, after adding the at least one of the plurality of motion information candidates in the second candidate list to the first candidate list, if a number of merge candidates included in the first candidate list is still less than a threshold value, an average merge candidate generated by using two merge candidates already included in the first candidate list is added to the first candidate list.

8. A method of encoding a video, the method comprising:

deriving merge candidates of a current block, the merge candidates comprising a spatial merge candidate derived from a neighboring block adjacent to the current block;

generating a first candidate list including the merge candidates of the current block,

wherein when a number of the merge candidates included in the first candidate list is less than a predetermined value, a motion information candidate included in a second candidate list is added to the first candidate list;

determining motion information of the current block based on the first candidate list; and

encoding index information specifying a merge candidate identical to the motion information of the current block among a plurality of merge candidates included in the first candidate list,

wherein the motion information candidate included in the second candidate list is derived from a spatial block that is encoded prior to encoding the current block and included in a current picture including the current block, and

wherein after determining the motion information of the current block, the second candidate list is updated with the motion information of the current block.

9. A non-transitory computer readable medium having stored thereon a compressed video data, the compressed video data comprising:

index information specifying one of a plurality of merge candidates included in a first candidate list,

wherein motion information of a current block being derived from a merge candidate specified by the index information,

wherein the first candidate list is generated by adding merge candidates derived for the current block,

wherein when a number of the merge candidates included in the first candidate list is less than a predetermined value, a motion information candidate included in a second candidate list is added to the first candidate list,

wherein the motion information candidate included in the second candidate list is derived from a spatial block that is decoded prior to decoding the current block and included in a current picture including the current block, and

wherein after deriving the motion information of the current block, the second candidate list is updated with the motion information of the current block wherein the motion information of the current block is added to the second candidate list as a new motion information candidate with a highest or lowest index; wherein at least one of a plurality of motion information candidates in the second candidate list is added to the first candidate list in a descending order of an index assigned to each of the plurality of motion information candidates.