Bi-prediction for video coding
Systems, methods, and instrumentalities may be provided for determining whether to bypass bi-directional optical flow (BDOF) if BDOF is used in combination with bi-prediction with coding unit (CU) weights (e.g., generalized bi-prediction (GBi)). A coding system may combine coding modes, coding techniques, and/or coding tools. The coding system may include a wireless transmit/receive unit (WTRU). For example, the coding system may combine BDOF and bi-prediction with CU weights (BCW). BDOF may include refining a motion vector associated with a current CU based at least in part on gradients associated with a location in the current CU. The coding system may determine that BDOF is enabled, and/or that bi-prediction with CU weights is enabled for the current CU. The coding system's determination that bi-prediction with CU weights is enabled and/or that BDOF is enabled may be based on one or more indications.
1 . A device for video decoding, comprising:
a processor configured to:
determine that bi-directional optical flow (BDOF) is enabled for a picture;
obtain an indication for a weighted prediction (WP) parameter;
based on a condition that the indication indicates the WP parameter is not to be applied to a reference picture list of the picture, obtain a weight index of bi-prediction with coding unit weights (BCW);
based on the weight index of BCW, obtain a first weight of BCW and a second weight of BCW;
determine to bypass BDOF for video block of the picture responsive to a condition that the first weight and the second weight are unequal;
apply the first weight to a first prediction sample of the video block and the second weight to a second prediction sample of the video block; and
decode the video block based on the first weighted prediction sample and based on the second weighted prediction sample.
2 . The device of claim 1 , wherein the first prediction sample is associated with a first reference picture of the video block and the second prediction sample is associated with a second reference picture of the video block.
3 . The device of claim 1 , wherein the weight index of BCW indicates that the first weight and the second weight are not equal.
4 . The device of claim 1 , wherein the video block is a first video block, and the processor is further configured to:
determine to perform BDOF for a second video block based at least in part on a second weight index associated with the second video block;
determine a plurality of gradients based on a sample location in the second video block;
determine a motion refinement based on the plurality of the gradients; and
obtain a sample value associated with the second video block based on the determined motion refinement.
5 . The device of claim 1 , wherein the video block is a first video block, the picture is a first picture, and the processor is further configured to:
determine that WP is enabled for a second video block of a second picture;
obtain, in video data, a plurality of WP parameters associated with the second picture, wherein the plurality of WP parameters comprises a weight and an offset associated with the second picture; and
obtain a sample value associated with the second video block using the weight and the offset associated with the second picture, wherein the second picture is decoded based on the sample value associated with the second video block.
6 . The device of claim 5 , wherein the plurality of WP parameters is associated with a global illuminance change of the second picture.
7 . A method for video decoding, comprising:
determining that bi-directional optical flow (BDOF) is enabled for a picture;
obtaining an indication for a weighted prediction (WP) parameter;
based on a condition that the indication indicates the WP parameter is not to be applied to a reference picture list of the picture, obtaining a weight index of bi-prediction with coding unit weights (BCW);
based on the weight index of BCW, obtaining a first weight of BCW and a second weight of BCW;
determining to bypass BDOF for a video block of the picture responsive to a condition that the first weight and the second weight are unequal;
applying the first weight to a first prediction sample of the video block and the second weight to a second prediction sample of the video block; and
decoding the video block based on the first weighted prediction sample and based on the second weighted prediction sample.
8 . The method of claim 7 , wherein the first prediction sample is associated with a first reference picture of the video block and the second prediction sample is associated with a second reference picture of the video block.
9 . A device for video encoding, comprising:
a processor configured to:
determine that bi-directional optical flow (BDOF) is enabled for a picture;
obtain an indication for a weighted prediction (WP) parameter;
based on a condition that the indication indicates the WP parameter is not to be applied to a reference picture list of the picture, obtain a weight index of bi-prediction with coding unit weights (BCW);
based on the weight index of BCW, obtain a first weight of BCW and a second weight of BCW;
determine to bypass BDOF for a video block of the picture responsive to a condition that the first weight and the second weight are unequal;
apply the first weight to first prediction sample of the video block and the second weight to a second prediction sample of the video block; and
encode the video block based on the first weighted prediction sample and based on the second weighted prediction sample.
10 . The device of claim 9 , wherein the first prediction sample is associated with a first reference picture of the video block and the second prediction sample is associated with a second reference picture of the video block.
11 . A method for video encoding, comprising:
determining that bi-directional optical flow (BDOF) is enabled for a picture;
obtaining an indication for a weighted prediction (WP) parameter;
based on a condition that the indication indicates the WP parameter is not to be applied to a reference picture list of the picture, obtaining a weight index of bi-prediction with coding unit weights (BCW);
based on the weight index of BCW, obtaining a first weight of BCW and a second weight of BCW;
determining to bypass BDOF for a video block of the picture responsive to a condition that the first weight and the second weight are unequal;
applying the first weight to a first prediction sample of the video block and the second weight to a second prediction sample of the video block; and
encoding the video block based on the first weighted prediction sample and based on the second weighted prediction sample.
12 . The method of claim 11 , wherein the first prediction sample is associated with a first reference picture of the video block and the second prediction sample is associated with a second reference picture of the video block.
13 . The method of claim 7 , wherein the weight index of BCW indicates that the first weight and the second weight are not equal.
14 . The device of claim 9 , wherein the weight index of BCW indicates that the first weight and the second weight are not equal.
15 . The method of claim 11 , wherein the weight index of BCW indicates that the first weight and the second weight are not equal.
16 . A non-transitory computer-readable medium including instructions, which, when executed by one or more processors, cause the one or more processors to perform the method of claim 7 .
17 . The device of claim 1 , wherein the indication of the WP parameter is signaled at a slice-level.
18 . The method of claim 7 , wherein the indication of the WP parameter is signaled at a slice-level.
19 . A non-transitory computer-readable medium including instructions, which, when executed by one or more processors, cause the one or more processors to perform the method of claim 11 .