Inter-prediction method and apparatus for same

1. A method for decoding a video signal based on temporal motion prediction, the method comprising:

obtaining, from an input bitstream, a collocated picture index;

determining a slice type of a current slice including a current block;

determining, based on the determined slice type, a reference picture list including a collocated picture among a plurality of reference picture lists;

determining the collocated picture based on the collocated picture index and the determined reference picture list including the collocated picture;

determining a collocated block for deriving temporal motion information of the current block, the collocated block belonging to the collocated picture;

deriving the temporal motion information of the current block from motion information of the determined collocated block;

constructing a merge candidate list for the current block by using the temporal motion information;

deriving motion information of the current block based on the merge candidate list;

generating a prediction block for the current block based on the derived motion information;

generating a reconstruction block for the current block using the prediction block; and

applying an in-loop filter on the reconstruction block,

wherein the in-loop filter includes a deblocking filter and a SAO (Sample Adaptive Offset) filter,

wherein the derived motion information includes prediction direction information and both of L0 motion information and L1 motion information,

wherein when the prediction direction information of the current block indicates a bi-prediction and a size of the current block is smaller than a pre-determined size, the prediction direction information indicating the bi-prediction is changed to indicate a uni-prediction and the prediction block of the current block is generated by performing a motion compensation based on only the L0 motion information among the L0 motion information and the L1 motion information,

wherein when the prediction direction information indicates the bi-prediction and the size of the current block is equal to or greater than the pre-determined size, the prediction direction information indicating the bi-prediction is not changed to indicate the uni-prediction and the prediction block of the current block is generated by performing the motion compensation based on both the L0 motion information and the L1 motion information,

wherein the pre-determined size is representative of one of 8×8, 16×16 or 32×32,

wherein the collocated picture index is used for selecting a collocated picture among a plurality of reference pictures in the reference picture list, and

wherein the collocated picture index is variable.

2. The method of claim 1 , wherein the reference picture lists include an L0 reference picture list and an L1 reference picture list.

3. A method for encoding a video signal, the method comprising:

determining a slice type of a current slice including a current block;

determining, based on the determined slice type, a reference picture list among a plurality of reference picture lists;

determining a collocated picture based on the determined reference picture list;

determining a collocated block for deriving temporal motion information of the current block, the collocated block belonging to the collocated picture;

deriving the temporal motion information of the current block from motion information of the determined collocated block;

constructing a merge candidate list for the current block by using the temporal motion information;

deriving motion information of the current block based on the merge candidate list;

generating a prediction block for the current block based on the derived motion information;

generating a reconstruction block for the current block using the prediction block;

applying an in-loop filter on the reconstruction block; and

encoding a collocated picture index,

wherein the derived motion information includes prediction direction information and both of L0 motion information and L1 motion information,

wherein, when the prediction direction information of the current block indicates a bi-prediction and a size of the current block is smaller than a pre-determined size, the prediction direction information indicating the bi-prediction is changed to indicate a uni-prediction and the prediction block of the current block is generated by performing motion compensation based on only the L0 motion information among the L0 motion information and the L1 motion information,

wherein, when the prediction direction information indicates the bi-prediction and the size of the current block is equal to or greater than the pre-determined size, the prediction direction information indicating the bi-prediction is not changed to indicate the uni-prediction and the prediction block of the current block is generated by performing the motion compensation based on both the L0 motion information and the L1 motion information,

wherein the pre-determined size is representative of one of 8×8, 16×16, or 32×32,

wherein the in-loop filter includes a deblocking filter and a SAO (Sample Adaptive Offset) filter, and

wherein the collocated picture index is used for selecting a collocated picture among a plurality of reference pictures in the reference picture list.

4. A non-transitory computer-readable recoding-medium storing a bitstream used for a video encoding method,

the method comprising:

determining a slice type of a current slice including a current block;

determining, based on the determined slice type, a reference picture list among a plurality of reference picture lists;

determining a collocated picture based on the determined reference picture list;

determining a collocated block for deriving temporal motion information of the current block, the collocated block belonging to the collocated picture;

deriving the temporal motion information of the current block from motion information of the determined collocated block;

constructing a merge candidate list for the current block by using the temporal motion information;

deriving motion information of the current block based on the merge candidate list;

generating a prediction block for the current block based on the derived motion information;

generating a reconstruction block for the current block using the prediction block;

applying in-loop filter on the reconstruction block; and

encoding a collocated picture index,

wherein the derived motion information includes prediction direction information and both of L0 motion information and L1 motion information,

wherein, when the prediction direction information of the current block indicates a bi-prediction and a size of the current block is smaller than a pre-determined size, the prediction direction information indicating the bi-prediction is changed to indicate a uni-prediction and the prediction block of the current block is generated by performing motion compensation based on only the L0 motion information among the L0 motion information and the L1 motion information,

wherein, when the prediction direction information indicates the bi-prediction and the size of the current block is equal to or greater than the pre-determined size, the prediction direction information indicating the bi-prediction is not changed to indicate the uni-prediction and the prediction block of the current block is generated by performing the motion compensation based on both the L0 motion information and the L1 motion information,

wherein the pre-determined size is representative of one of 8×8, 16×16, or 32×32,

wherein the in-loop filter includes a deblocking filter and a SAO (Sample Adaptive Offset) filter, and

wherein the collocated picture index is used for selecting a collocated picture among a plurality of reference pictures in the reference picture list.