Coding motion prediction direction in video coding
This disclosure relates to techniques for reducing a cost of coding prediction information in video coding. Video blocks in a generalized P/B (GPB) frame are encoded using up to two motion vectors calculated from reference pictures in two separate reference picture lists that are identical. When one of the reference picture lists is preferred over the other reference picture list, the preferred reference picture list may be used for unidirectional prediction, by default. When a GPB frame is enabled such that the first and second reference picture lists are identical, either of the first and second reference picture lists may be used for unidirectional prediction. The techniques include coding one or more syntax elements indicating that a video block is coded using one of the unidirectional prediction mode with respect to a reference picture in a reference picture list and the bidirectional prediction mode using less than two bits.
1. A method of coding video data comprising:
storing a first reference picture list that includes at least one identifier for a decoded reference picture stored in a memory;
storing a second reference picture list that includes at least one identifier for a decoded reference picture stored in the memory, wherein the second reference picture list is stored separate from the first reference picture list;
coding a video block of a video frame using one of a unidirectional motion prediction mode with respect to a particular reference picture identified in the first reference picture list or a bidirectional motion prediction mode with respect to a first reference picture identified in the first reference picture list and a second reference picture identified in the second reference picture list, wherein only the first reference picture list is used for the unidirectional motion prediction mode;
coding the video frame as a generalized P/B (GPB) frame in response to the first and second reference picture lists including identifiers for identical decoded reference pictures; and
coding a single bit syntax element having bit-depth of a single bit indicating a motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode, without indicating which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
2. The method of claim 1 ,
wherein coding the single bit syntax element comprises decoding the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode at a video decoder; and
wherein coding the video block comprises decoding the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
3. The method of claim 1 , wherein coding the single bit syntax element comprises:
coding a first bit of a syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode without coding a second bit of the syntax element defined to indicate which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
4. The method of claim 1 , further comprising:
comparing the first reference picture list and the second reference picture list at a video decoder; and
based on the comparison, determining that the first reference picture list and the second reference picture list include identifiers for identical decoded reference pictures.
5. The method of claim 1 , further comprising coding a flag indicating that the GPB frame is enabled at one of a video frame level or a video sequence level.
6. The method of claim 1 , wherein the first reference picture list used for the unidirectional motion prediction mode is a preferred one of the first and second reference picture lists.
7. The method of claim 6 ,
wherein coding the single bit syntax element comprises decoding the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode at a video decoder; and
wherein coding the video block comprises decoding the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the preferred first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
8. A video coding device comprising:
a memory configured to store decoded reference pictures, store a first reference picture list that includes at least one identifier for one of the decoded reference pictures stored in the memory, and store a second reference picture list that includes at least one identifier for one of the decoded reference pictures stored in the memory, wherein the second reference picture list is stored separate from the first reference picture list; and
a processor configured to:
code a video block of a video frame using one of a unidirectional motion prediction mode with respect to a particular reference picture identified in the first reference picture list or a bidirectional motion prediction mode with respect to a first reference picture identified in the first reference picture list and a second reference picture identified in the second reference picture list, wherein only the first reference picture list is used for the unidirectional motion prediction mode,
code the video frame as a generalized PB (GPB) frame in response to the first and second reference picture lists including identifiers for identical decoded reference pictures, and
code a single bit syntax element having bit-depth of a single bit indicating a motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode, without indicating which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
9. The video coding device of claim 8 , wherein the video coding device comprises a video decoding device, wherein the processor is configured to:
decode the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode; and
decode the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
10. The video coding device of claim 8 , wherein the processor is configured to code a first bit of a syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode, without coding a second bit of the syntax element defined to indicate which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
11. The video coding device of claim 8 , wherein the processor is configured to compare the first reference picture list and the second reference picture list, and based on the comparison, determine that the first reference picture list and the second reference picture list include identifiers for identical decoded reference pictures.
12. The video coding device of claim 8 , wherein the processor is configured to code a flag indicating that the GPB frame is enabled at one of a video frame level or a video sequence level.
13. The video coding device of claim 8 ,
wherein the first reference picture list used for the unidirectional motion prediction mode is a preferred one of the first and second reference picture lists.
14. The video coding device of claim 13 , wherein the video coding device comprises a video decoding device, wherein the processor is configured to:
decode the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode; and
decode the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the preferred first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
15. The video coding device of claim 8 , wherein the video coding device comprises at least one of:
an integrated circuit;
a microprocessor; or
a wireless communication device.
16. The video coding device of claim 8 , further comprising a display configured to display the video frame and one or more of the decoded reference pictures.
17. The video coding device of claim 8 , further comprising a camera configured to capture the video frame and one or more of the reference pictures.
18. A video coding device comprising:
means for storing a first reference picture list that includes at least one identifier for a decoded reference picture stored in a memory;
means for storing a second reference picture list that includes at least one identifier for a decoded reference picture stored in the memory, wherein the second reference picture list is stored separate from the first reference picture list;
means for coding a video block of a video frame using one of a unidirectional motion prediction mode with respect to a particular reference picture identified in the first reference picture list or a bidirectional motion prediction mode with respect to a first reference picture identified in the first reference picture list and a second reference picture identified in the second reference picture list, wherein only the first reference picture list is used for the unidirectional motion prediction mode;
means for coding the video frame as a generalized PB (GPB) frame in response to the first and second reference picture lists including identifiers for identical decoded reference pictures; and
means for coding a single bit syntax element having bit-depth of a single bit indicating a motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode, without indicating which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
19. The video coding device of claim 18 , wherein the video coding device comprises a video decoding device, further comprising:
means for decoding the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode; and
means for decoding the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
20. The video coding device of claim 18 , further comprising:
means for coding a first bit of a syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode without coding a second bit of the syntax element defined to indicate which one of the first or second reference picture list is used for the unidirectional motion prediction mode.
21. The video coding device of claim 18 , wherein the video coding device comprises a video decoding device, further comprising:
means for decoding the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode; and
means for decoding the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the preferred first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
22. The video coding device of claim 18 , further comprising:
means for comparing the first reference picture list and the second reference picture list at a video decoder; and
means for, based on the comparison, determining that the first reference picture list and the second reference picture list include identifiers for identical decoded reference pictures.
23. A non-transitory computer-readable storage medium comprising instructions for coding video data that, upon execution in a processor, cause the processor to:
store a first reference picture list that includes at least one identifier for a decoded reference picture stored in a memory;
store a second reference picture list that includes at least one identifier for a decoded reference picture stored in the memory, wherein the second reference picture list is stored separate from the first reference picture list;
code a video block of a video frame using one of a unidirectional motion prediction mode with respect to a particular reference picture identified in the first reference picture list or a bidirectional motion prediction mode with respect to a first reference picture identified in the first reference picture list and a second reference picture identified in the second reference picture list, wherein only the first reference picture list is used for the unidirectional motion prediction mode;
code the video frame as a generalized PB (GPB) frame in response to the first and second reference picture lists including identifiers for identical decoded reference pictures; and
code a single bit syntax element having bit-depth of a single bit indicating a motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode without indicating which of the first or second reference picture list is used for the unidirectional motion prediction mode.
24. The non-transitory computer-readable storage medium of claim 23 , wherein the instructions cause the processor to:
decode the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode at a video decoder; and
decode the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
25. The non-transitory computer-readable storage medium of claim 23 , wherein the instructions cause the processor to:
code a first bit of a syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode, without coding a second bit of the syntax element defined to indicate which of the first or second reference picture list is used for the unidirectional motion prediction mode.
26. The non-transitory computer-readable storage medium of claim 23 , wherein the instructions cause the processor to:
decode the single bit syntax element indicating the motion prediction direction for the video block as the one of the unidirectional motion prediction mode or the bidirectional motion prediction mode at a video decoder; and
decode the video block using the one of the unidirectional motion prediction mode with respect to the particular reference picture identified in the preferred first reference picture list or the bidirectional motion prediction mode with respect to the first reference picture identified in the first reference picture list and the second reference picture identified in the second reference picture list.
27. The non-transitory computer-readable storage medium of claim 23 , wherein the instructions cause the processor to:
compare the first reference picture list and the second reference picture list at a video decoder; and
based on the comparison, determine that the first reference picture list and the second reference picture list include identifiers for identical decoded reference pictures.