Zero residual flag coding
This disclosure relates to improved video coding scheme for zero residual or zero coefficient flags. For example, a method for decoding a current block in a video stream is disclosed. The method may include determining a zero-skip flag of at least one neighboring block of the current block as a reference zero-skip flag; determining a prediction mode for the current block as being either an intra prediction mode or inter prediction mode; deriving at least one context for decoding the zero-skip flag of the current block based on the reference zero-skip flag and the current prediction mode; and decoding the zero-skip flag of the current block according to the at least one context.
1. A method of video decoding, the method comprising:
receiving a video bitstream comprising a plurality of blocks including a current block;
determining a value of a first reference zero-skip flag of a first neighboring block of the current block;
deriving at least one context for decoding a zero-skip flag of the current block based on the value of the first reference zero-skip flag;
decoding the zero-skip flag of the current block according to the at least one context;
deriving at least one second context for decoding a prediction mode (is-inter) flag of the current block based on the value of the zero-skip flag;
decoding the is-inter flag of the current block according to the at least one second context; and
decoding the current block according to the zero-skip flag and the is-inter flag.
2. The method of claim 1 , further comprising:
determining a value of a second reference zero-skip flag of a second neighboring block of the current block; and
wherein the at least one context for decoding the zero-skip flag of the current block is further based on the value of the second reference zero-skip flag.
3. The method of claim 2 , wherein deriving the at least one context based on the first reference zero-skip flag and the second reference zero-skip flag comprises deriving the at least one context based on a sum of the first reference zero-skip flag and the second reference zero-skip flag.
4. The method of claim 2 , wherein the first neighboring block and the second neighboring block comprise a top neighboring block and a left neighboring block of the current block, respectively.
5. The method of claim 1 , wherein the at least one second context for decoding the is-inter flag is further based on the first reference zero-skip flag of the first neighboring block.
6. The method of claim 5 , wherein the first neighboring block comprises a top neighboring block or a left neighboring block.
7. The method of claim 1 , wherein deriving the at least one second context for decoding the is-inter flag of the current block based on the value of the zero-skip flag comprises:
when the value of the zero-skip flag is equal to 0, selecting a first set of one or more contexts as the at least one second context; and
when the value of the zero-skip flag is not equal to 0, selecting a second set of one or more contexts as the at least one second context.
8. The method of claim 1 , wherein the zero-skip flag is signaled before the is-inter flag in the video bitstream.
9. A computing system, comprising:
control circuitry; and
memory storing one or more programs configured to be executed by the control circuitry, the one or more programs comprising instructions for:
receiving video data corresponding to a plurality of blocks including a current block;
determining a value of a first reference zero-skip flag of a first neighboring block of the current block;
deriving at least one context for encoding a zero-skip flag of the current block based on the value of the first reference zero-skip flag;
encoding the zero-skip flag of the current block according to the at least one context;
deriving at least one second context for encoding a prediction mode (is-inter) flag of the current block based on the value of the zero-skip flag;
encoding the is-inter flag of the current block according to the at least one second context; and
encoding the current block according to the zero-skip flag and the is-inter flag.
10. The computing system of claim 9 , wherein the one or more programs further comprise instructions for:
signaling the encoded zero-skip flag, the encoded is-inter flag, and the encoded current block in a video bitstream.
11. The computing system of claim 10 , wherein the encoded zero-skip flag is signaled before the encoded is-inter flag in the video bitstream.
12. The computing system of claim 9 , wherein the at least one context for encoding the zero-skip flag of the current block is further based on a value of a second reference zero-skip flag of a second neighboring block of the current block.
13. The computing system of claim 12 , wherein the at least one context for encoding the zero-skip flag of the current block is based on a sum of the first reference zero-skip flag and the second reference zero-skip flag.
14. The computing system of claim 12 , wherein the first neighboring block and the second neighboring block comprise a top neighboring block and a left neighboring block of the current block, respectively.
15. The computing system of claim 9 , wherein the at least one second context for encoding the is-inter flag is further based on the first reference zero-skip flag of the first neighboring block.
16. The computing system of claim 15 , wherein the first neighboring block comprises a top neighboring block or a left neighboring block.
17. The computing system of claim 9 , wherein deriving the at least one second context for encoding the is-inter flag of the current block based on the value of the zero-skip flag comprises:
when the value of the zero-skip flag is equal to 0, selecting a first set of one or more contexts as the at least one second context; and
when the value of the zero-skip flag is not equal to 0, selecting a second set of one or more contexts as the at least one second context.
18. A non-transitory computer-readable storage medium storing one or more programs for execution by control circuitry of a computing system, the one or more programs comprising instructions for:
obtaining a source video sequence; and
performing a conversion between the source video sequence and a video bitstream according to a format rule, wherein:
the video bitstream comprises:
a plurality of encoded blocks corresponding to the source video sequence, the plurality of encoded blocks comprising a current block;
an encoded zero-skip flag for the current block; and
an encoded prediction mode (is-inter) flag for the current block; and
the format rule specifies that:
at least one context for decoding the encoded zero-skip flag is based on a value of first reference zero-skip flag of a first neighboring block of the current block; and
at least one second context for decoding the encoded is-inter flag is based on the value of the encoded zero-skip flag.
19. The non-transitory computer-readable storage medium of claim 18 , wherein the format rule further specifies that the at least one context for decoding the encoded zero-skip flag is further based on a value of a second reference zero-skip flag of a second neighboring block of the current block.
20. The non-transitory computer-readable storage medium of claim 18 , wherein the format rule further specifies that the at least one second context for decoding the encoded is-inter flag is further based on the first reference zero-skip flag of the first neighboring block.