Bi-directional optical flow for video coding

A method of encoding video data, the method comprising:

• decoding a first reference picture and a second reference picture, the second reference picture being different than the first reference picture, wherein the first reference picture and the second reference picture are either both to be displayed before a current picture or both to be displayed after the current picture;
• determining a first motion vector (MV0) from a current block of the current picture to a first reference block of the first reference picture;
• determining a second motion vector (MV1) from the current block to a second reference block of the second reference picture;
• determining a first temporal distance (TD0) from the current picture to the first reference picture;
• determining a second temporal distance (TD1) from the current picture to the second reference picture;
• and
• encoding the current block according to bi-directional optical flow (BIO) using MV0, MV1, TD0, and TD1, wherein encoding the current block according to BIO comprises encoding the current block according to BIO when MV0 and MV1 are in proportion to TD0 and TD1, wherein MV0 includes an x-component (MV0x) and a y-component (MV0y), wherein MV1 includes an x-component (MV1x) and a y-component (MV1y), further comprising determining that MV0 and MV1 are in proportion to TD0 and TD1 when (|MV0x*TD1−MV1x*TD0|==0 &&|MV0y*TD1−MV1y*TD0|==0).

A device for decoding video data, the device comprising:

• a memory configured to store video data;
• and
• one or more processors configured to:
• decode a first reference picture and a second reference picture of the video data, the second reference picture being different than the first reference picture, wherein the first reference picture and the second reference picture are either both to be displayed before a current picture or both to be displayed after the current picture;
• determine a first motion vector (MV0) from a current block of the current picture to a first reference block of the first reference picture;
• determine a second motion vector (MV1) from the current block to a second reference block of the second reference picture;
• determine a first temporal distance (TD0) from the current picture to the first reference picture;
• determine a second temporal distance (TD1) from the current picture to the second reference picture;
• and
• decode the current block according to bi-directional optical flow (BIO) using MV0, MV1, TD0, and TD1, wherein to decode the current block according to BIO, the one or more processors are configured to decode the current block according to BIO when MV0 and MV1 are in proportion to TD0 and TD1, wherein MV0 includes an x-component (MV0x) and a y-component (MV0y), wherein MV1 includes an x-component (MV1x) and a y-component (MV1y), and wherein the one or more processors are configured to determine that MV0 and MV1 are in proportion to TD0 and TD1 when (|MV0x*TD1−MV1x*TD0|==0&&|MV0y*TD1−MV1y*TD0|==0).

A device for decoding a picture of video data, the device comprising:

• means for decoding a first reference picture and a second reference picture, the second reference picture being different than the first reference picture, wherein the first reference picture and the second reference picture are either both to be displayed before a current picture or both to be displayed after the current picture;
• means for determining a first motion vector (MV0) from a current block of the current picture to a first reference block of the first reference picture;
• means for determining a second motion vector (MV1) from the current block to a second reference block of the second reference picture;
• means for determining a first temporal distance (TD0) from the current picture to the first reference picture;
• means for determining a second temporal distance (TD1) from the current picture to the second reference picture;
• and
• means for decoding the current block according to bi-directional optical flow (BIO) using MV0, MV1, TD0, and TD1, wherein the means for decoding the current block according to BIO comprises means for decoding the current block according to BIO when MV0 and MV1 are in proportion to TD0 and TD1, wherein MV0 includes an x-component (MV0x) and a y-component (MV0y), wherein MV1 includes an x-component (MV1x) and a y-component (MV1y), further comprising means for determining that MV0 and MV1 are in proportion to TD0 and TD1 when (|MV0x*TD1−MV1x*TD0|==0&&|MV0y*TD1−MV1y*TD0|==0).

A non-transitory computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for decoding video data to:

• decode a first reference picture and a second reference picture, the second reference picture being different than the first reference picture, wherein the first reference picture and the second reference picture are either both to be displayed before a current picture or both to be displayed after the current picture;
• determine a first motion vector (MV0) from a current block of the current picture to a first reference block of the first reference picture;
• determine a second motion vector (MV1) from the current block to a second reference block of the second reference picture;
• determine a first temporal distance (TD0) from the current picture to the first reference picture;
• determine a second temporal distance (TD1) from the current picture to the second reference picture;
• and
• decode the current block according to bi-directional optical flow (BIO) using MV0, MV1, TD0, and TD1, wherein the instructions that cause the processor to decode the current block according to BIO comprise instructions that cause the processor to decode the current block according to BIO when MV0 and MV1 are in proportion to TD0 and TD1, wherein MV0 includes an x-component (MV0x) and a y-component (MV0y), wherein MV1 includes an x-component (MV1x) and a y-component (MV1y), further comprising instructions that cause the processor to determine that MV0 and MV1 are in proportion to TD0 and TD1 when (|MV0x*TD1MV1x* TD0|==0&&|MV0y*TD1−MV1y*TD0|==0).