Simplified history based motion vector prediction
A video coding or decoding method includes using history-based motion vector prediction (HMVP) for conversion between multiple video blocks including a current block of video and a bitstream representation of the multiple video blocks such that for a uni-predicted block that for which a single reference picture is used for motion compensation, refraining from updating a look-up table for HMVP candidates for the uni-predicted block. The video coding or decoding method further includes performing the conversion using look-up tables for the multiple video blocks.
1. A method of video processing, comprising:
determining, after a conversion between a video block of a video comprising multiple blocks and a bitstream representation of the video, whether a rule of updating one or more history based motion vector predictor (HMVP) tables with HMVP candidates is satisfied, wherein the rule of updating is based on a prediction direction used for the conversion; and
selectively updating the one or more HMVP tables based on the determining,
wherein the rule of updating specifies to skip updating the one or more HMVP tables due to the prediction direction being a uni-direction, or specifies to update the one or more HMVP tables due to the prediction direction being a bi-prediction.
2. The method of claim 1 , wherein the rule of updating specifies to update the one or more HMVP tables due to the prediction direction being a uni-direction and due to use of multiple reference pictures during the conversion.
3. The method of claim 2 , wherein the selectively updating comprises updating the one or more HMVP tables using multi-hypothesis motion information of the video block.
4. The method of claim 1 , wherein the rule of updating the one or more HMVP tables with HMVP candidates is further based on motion information associated with the multiple blocks of the video, wherein the HMVP candidates are stored using a first precision of motion information lower than a second precision of motion information used by motion candidates not stored in the one or more HMVP tables.
5. The method of claim 4 , wherein the first precision of motion information is 8, 10, 12 or 14, and the second precision of motion information is 16.
6. The method of claim 4 , wherein the determining whether the rule of updating is satisfied comprises:
selecting a HMVP candidate from the HMVP candidates; and
performing a comparison of the HMVP candidate with a motion candidate stored in a motion candidate list in accordance with the second precision of motion information.
7. The method of claim 6 , wherein the comparison includes applying a bit shift operation.
8. The method of claim 7 , wherein the bit shift operation is expressed as (1<<(K−L)), wherein K denotes the second precision of motion information and L denotes the first precision of motion information.
9. The method of claim 6 , wherein the selectively updating comprises:
upon determining that the HMVP candidate is different from the motion candidate, adding the HMVP candidate to the motion candidate list.
10. The method of claim 1 , wherein the rule of updating the one or more HMVP tables with HMVP candidates is further based on motion information associated with multiple blocks of the video, wherein the HMVP candidates in the one or more HMVP tables are stored in accordance with a rule based at least on a condition of reference pictures to which the HMVP candidates refer to.
11. The method of claim 10 , wherein only HMVP candidates referring to certain reference pictures are stored in the one or more HMVP tables, thereby avoiding having to store reference picture index information in the one or more HMVP tables, wherein the certain reference pictures are pre-defined or signaled in the bitstream representation of the video.
12. The method of claim 11 , wherein the selectively updating comprises:
upon determining that a motion information of the video block fails to refer to the certain reference pictures, scaling the motion information of the video block to at least one of the certain reference pictures prior to storing the motion information of the video block in the one or more HMVP tables.
13. The method of claim 1 , wherein the rule of updating the one or more HMVP tables with HMVP candidates is further based on motion information associated with the multiple blocks of the video, wherein the selectively updating comprises:
selecting an HMVP candidate from the HMVP candidates in the one or more HMVP tables; and
updating the one or more HMVP tables using a hash-table based pruning applied to the HMVP candidate and a motion information of the video block of the video.
14. The method of claim 13 , wherein the hash-table based pruning includes performing a comparison of a hash value of the HMVP candidate and a hash value of the motion information of the video block of the video.
15. The method of claim 14 , wherein the selectively updating further comprises:
upon determining that the hash value of the HMVP candidate is identical to that of the hash value of the motion information of the current block of the video, removing the HMVP candidate from the one or more HMVP tables.
16. The method of claim 1 , further comprising:
performing the conversion between the video block of the video and the bitstream representation of the video, wherein the one or more HMVP tables are used during the conversion.
17. An apparatus for video processing, comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:
determine, after a conversion between a video block of a video comprising multiple blocks and a bitstream representation of the video, whether a rule of updating of one or more history based motion vector predictor (HMVP) tables with HMVP candidates is satisfied, wherein the rule of updating is based on a prediction direction used for the conversion; and
selectively update the one or more HMVP tables based on the determining,
wherein the rule of updating specifies to skip updating the one or more HMVP tables due to the prediction direction being a uni-direction, or specifies to update the one or more HMVP tables due to the prediction direction being a bi-prediction.
18. A non-transitory computer-readable medium having code stored thereupon, the code including instructions causing a processor to implement a method of video processing, wherein the method comprises:
determining, after a conversion between a video block of a video comprising multiple blocks and a bitstream representation of the video, whether a rule of updating of one or more history based motion vector predictor (HMVP) tables with HMVP candidates is satisfied, wherein the rule of updating is based on a prediction direction used for the conversion; and
selectively updating the one or more HMVP tables based on the determining,
wherein the rule of updating specifies to skip updating the one or more HMVP tables due to the prediction direction being a uni-direction, or specifies to update the one or more HMVP tables due to the prediction direction being a bi-prediction.
19. The apparatus of claim 17 , wherein the rule of updating specifies to update the one or more HMVP tables due to the prediction direction being a uni-direction and due to use of multiple reference pictures during the conversion.
20. The apparatus of claim 19 , wherein the selectively updating comprises updating the one or more HMVP tables using multi-hypothesis motion information of the video block.