Methods and apparatuses for video coding with triangle prediction

1. A method for video coding with geometric prediction, comprising:

partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU;

constructing a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both;

receiving a signaled first index value to indicate a first candidate that is chosen from the first merge list;

receiving a signaled second index value to indicate a second candidate that is chosen from the first merge list;

receiving a signaled first binary flag that is coded using a first context-adaptive binary arithmetic coding (CABAC) context modeling method to indicate whether a List 0 motion vector of the first candidate or a List 1 motion vector of the first candidate is selected for a first PU of the geometric prediction; and

receiving a signaled second binary flag that is coded using a second CABAC context modeling method to indicate whether a List 0 motion vector of the second candidate or a List 1 motion vector of the second candidate is selected for a second PU of the geometric prediction,

wherein the first CABAC context modeling method and the second CABAC context modeling method comprise:

signaling each binary flag as a CABAC context bin, and a CABAC probability under each context model is initialized differently in response to whether a current picture uses a backward prediction.

2. The method for video coding with geometric prediction of claim 1 , wherein at least two context models are available to decode the signaled second binary flag, with a context model selected based on a value of the signaled first binary flag.

3. The method for video coding with geometric prediction of claim 1 , wherein the CABAC probability under each context model is initialized differently further comprises: using a higher CABAC initial probability for each binary flag to indicate selecting a List 0 motion vector in case the current picture does not use the backward prediction than in case the current picture uses the backward prediction.

4. The method for video coding with geometric prediction of claim 1 , further comprising: decoding the first binary flag as a CABAC bypass bin, and decoding the second binary flag as a CABAC context coded bin.

5. An apparatus for video coding with geometric prediction, comprising:

one or more processors; and

a memory configured to store instructions executable by the one or more processors;

wherein the one or more processors, upon execution of the instructions, are configured to:

partition video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU;

construct a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both;

receive a signaled first index value to indicate a first candidate that is chosen from the first merge list;

receive a signaled second index value to indicate a second candidate that is chosen from the first merge list;

receive a signaled first binary flag that is coded using a first context-adaptive binary arithmetic coding (CABAC) context modeling method to indicate whether a List 0 motion vector of the first candidate or a List 1 motion vector of the first candidate is selected for a first PU of the geometric prediction; and

receive a signaled second binary flag that is coded using a second CABAC context modeling method to indicate whether a List 0 motion vector of the second candidate or a List 1 motion vector of the second candidate is selected for a second PU of the geometric prediction,

wherein the first CABAC context modeling method and the second CABAC context modeling method comprise:

signaling each binary flag as a CABAC context bin, and a CABAC probability under each context model is initialized differently in response to whether a current picture uses a backward prediction.

6. The apparatus for video coding with geometric prediction of claim 5 , wherein at least two context models are available to decode the signaled second binary flag, with a context model selected based on a value of the signaled first binary flag.

7. The apparatus for video coding with geometric prediction of claim 5 , wherein the one or more processors are further configured to: use a higher CABAC initial probability for each binary flag to indicate selecting a List 0 motion vector in case the current picture does not use the backward prediction than in case the current picture uses the backward prediction.

8. The apparatus for video coding with geometric prediction of claim 5 , wherein the one or more processors are further configured to: decode the first binary flag as a CABAC bypass bin, and decode the second binary flag as a CABAC context coded bin.

9. A non-transitory computer-readable storage medium for video coding with geometric prediction storing computer-executable instructions that, when executed by one or more processors, cause the one or more processors to perform acts comprising:

partitioning video pictures into a plurality of coding units (CUs), at least one of which is further partitioned into two prediction units (PUs) including at least one geometric shaped PU;

constructing a first merge list comprising a plurality of candidates, based on a merge list construction process for regular merge prediction, wherein each one of the plurality of candidates is a motion vector comprising a List 0 motion vector, or a List 1 motion vector, or both;

receiving a signaled first index value to indicate a first candidate that is chosen from the first merge list;

receiving a signaled second index value to indicate a second candidate that is chosen from the first merge list;

receiving a signaled first binary flag that is coded using a first context-adaptive binary arithmetic coding (CABAC) context modeling method to indicate whether a List 0 motion vector of the first candidate or a List 1 motion vector of the first candidate is selected for a first PU of the geometric prediction; and

receiving a signaled second binary flag that is coded using a second CABAC context modeling method to indicate whether a List 0 motion vector of the second candidate or a List 1 motion vector of the second candidate is selected for a second PU of the geometric prediction

wherein the first CABAC context modeling method and the second CABAC context modeling method comprise:

signaling each binary flag as a CABAC context bin, and a CABAC probability under each context model is initialized differently in response to whether a current picture uses a backward prediction.

10. The non-transitory computer-readable storage medium for video coding with geometric prediction of claim 9 , wherein at least two context models are available to decode the signaled second binary flag, with a context model selected based on a value of the signaled first binary flag.

11. The non-transitory computer-readable storage medium for video coding with geometric prediction of claim 9 , wherein the computer-executable instructions cause the one or more processors to further perform: using a higher CABAC initial probability for each binary flag to indicate selecting a List 0 motion vector in case the current picture does not use the backward prediction than in case the current picture uses the backward prediction.

12. The non-transitory computer-readable storage medium for video coding with geometric prediction of claim 9 , wherein the computer-executable instructions cause the one or more processors to further perform: decoding the first binary flag as a CABAC bypass bin, and decoding the second binary flag as a CABAC context coded bin.