# US 2021/0243434 A1 · Searching based motion candidate derivation for sub-block motion vector prediction > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0243434 A1 - Document ID: US20210243434A1 - Status: Published application - Kind: A1 - Application number: 17/238,518 - Filed: 2021-04-23 - Published: 2021-08-05 - Earliest claimed: 2018-10-24 - Assignees: Beijing Bytedance Network Technology Co., Ltd.; Bytedance Inc. - Applicants: Beijing Bytedance Network Technology Co., Ltd.; Bytedance Inc. - Inventors: Li ZHANG; Kai ZHANG; Hongbin LIU; Yue WANG - Web page: https://patentgrep.com/patent/US20210243434A1 ## CPC - H04N 19/52: by predictive encoding - H04N 19/105: Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction - H04N 19/137: Motion inside a coding unit, e.g. average field, frame or block difference - H04N 19/159: Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction - H04N 19/176: the region being a block, e.g. a macroblock - H04N 19/184: the unit being bits, e.g. of the compressed video stream - H04N 19/30: using hierarchical techniques, e.g. scalability (H04N19/63 takes precedence) - H04N 19/513: Processing of motion vectors - H04N 19/54: using feature points or meshes - H04N 19/56: Motion estimation with initialisation of the vector search, e.g. estimating a good candidate to initiate a search - H04N 19/61: in combination with predictive coding - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract Devices, systems and methods for the simplification of sub-block motion candidate lists for video coding are described. In a representative aspect, a method for video processing includes determining, for a conversion between a current block of a video and a bitstream representation of the video, one or more temporal motion vector prediction candidates for the current block and performing the conversion based on the one or more temporal motion vector prediction candidates. The one or more temporal motion vector prediction candidates are determined by identifying a first temporal adjacent block of the current block based on an initial motion vector, wherein the first temporal adjacent block includes invalid motion information, and examining additional temporal adjacent blocks of the current block to obtain the one or more temporal motion vector prediction candidates. ## Claims ### Claim 1 A method for processing video data, comprising: determining, for a conversion between a current video block of a video and a bitstream of the video, one or more temporal motion vector prediction candidates for the current block, wherein the one or more temporal motion vector prediction candidates comprise a default temporal motion vector prediction candidate; and performing the conversion based on the one or more temporal motion vector prediction candidates, wherein the default temporal motion vector prediction candidate is determined after identifying a first temporal adjacent block of the current video block based on an initial motion vector, wherein the first temporal adjacent block includes invalid motion information. ### Claim 2 (depends on 1) The method of claim 1, wherein the default temporal motion vector is inherited from a spatial neighboring block of the current video block, and wherein the default temporal motion vector is scaled. ### Claim 3 (depends on 1) The method of claim 1, wherein the default temporal motion vector prediction candidate is derived based a starting point motion vector, wherein the starting point motion vector is either associated with a spatial adjacent block of the current video block or a zero motion vector. ### Claim 4 (depends on 3) The method of claim 3, wherein the starting point motion vector is completely determined based on motion information associated with one or more spatial adjacent blocks of the current video block. ### Claim 5 (depends on 3) The method of claim 3, wherein the starting point motion vector is associated with a block whose corresponding reference picture is collocated with a reference picture of the current video block, and wherein the block includes a spatial adjacent block of the current video block, a spatial non-adjacent block of the current video block, or a temporal adjacent block of the current video block. ### Claim 6 (depends on 3) The method of claim 3, wherein, in case a first spatial adjacent block selected from spatial adjacent blocks of the current video block according to a sequential order is inter-coded and a first motion vector of the first spatial adjacent block is directed to a collocated picture of the current video block, the starting motion vector is determined to be the first motion vector, and wherein the starting motion vector is determined to be a zero motion vector otherwise. ### Claim 7 (depends on 3) The method of claim 3, wherein the starting point motion vector is determined to be motion information of a represented block in case motion information of the represented block that is identified by the starting point motion vector and a center position of the block is unavailable, wherein the represented block is a block that covers a point corresponding to the starting point motion vector in a collocated picture, and wherein the starting point motion vector is used to derive sub-block motion. ### Claim 8 (depends on 1) The method of claim 1, wherein the default temporal motion vector is a uni-prediction candidate derived by scaling a motion vector to a reference picture index within a reference picture list X, X being 0 or 1. ### Claim 9 (depends on 8) The method of claim 8, wherein the reference picture index is 0, or the reference picture index is a smallest reference picture index that corresponds to a short-term reference picture. ### Claim 10 (depends on 8) The method of claim 8, wherein X is determined based on a slice or a picture associated with the current block. ### Claim 11 (depends on 1) The method of claim 1, wherein the default temporal motion vector is a bi-prediction candidate derived by scaling a motion vector to a reference picture index within a reference picture list, and wherein, for each reference picture in the reference picture list, the reference picture index is same as a target reference picture index of a temporal motion vector prediction candidate. ### Claim 12 (depends on 8) The method of claim 8, wherein whether the default temporal motion vector is uni-prediction candidate or a bi-prediction candidate is determined based on a picture type of a slice type associated with the current video block or a size of the current video block. ### Claim 13 (depends on 1) The method of claim 1, wherein the conversion comprises encoding the current video block to generate the bitstream. ### Claim 14 (depends on 1) The method of claim 1, wherein the conversion comprises decoding the bitstream to generate the current video block. ### Claim 15 (depends on 1) The method of claim 1, wherein the one or more temporal motion vector prediction candidates are further determined by: identifying a first temporal adjacent block of the current video block based on an initial motion vector, wherein the first temporal adjacent block includes invalid motion information, and examining additional temporal adjacent blocks of the current video block to obtain the one or more temporal motion vector prediction candidates; performing the conversion based on the one or more temporal motion vector prediction candidates. ### Claim 16 (depends on 15) The method of claim 15, wherein the one or more temporal motion vector prediction candidates include an Alternative Temporal Motion Vector Prediction (ATMVP) candidate, the first temporal adjacent block is intra-coded, the additional temporal adjacent blocks comprise a second temporal adjacent block that includes a starting point positioned adjacent to a bottom-right corner of a starting point of the first adjacent temporal block, and the additional temporal adjacent blocks are identified based on a sequential multi-step search of blocks associated with the first temporal adjacent block. ### Claim 17 (depends on 16) The method of claim 16, wherein the sequential multi-step search comprises: examining spatial adjacent blocks of the first temporal adjacent block in an order of left, above, right, and bottom; and wherein the sequential multi-step search further comprises: examining spatial non-adjacent blocks that are one step away from the first temporal adjacent block in an order of left, above, right, and bottom. ### Claim 18 The method of 15, wherein the additional temporal adjacent blocks are positioned within a region associated with the first temporal adjacent block, the region includes a Coding Tree Unit (CTU) associated with the first temporal adjacent block and the region includes a single row of the CTU associated with the first temporal adjacent block. ### Claim 19 An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to: determine, for a conversion between a current video block of a video and a bitstream of the video, one or more temporal motion vector prediction candidates for the current block, wherein the one or more temporal motion vector prediction candidates comprise a default temporal motion vector prediction candidate; and perform the conversion based on the one or more temporal motion vector prediction candidates, wherein the default temporal motion vector prediction candidate is determined after identifying a first temporal adjacent block of the current video block based on an initial motion vector, wherein the first temporal adjacent block includes invalid motion information. ### Claim 20 A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises: determining one or more temporal motion vector prediction candidates for the current block, wherein the one or more temporal motion vector prediction candidates comprise a default temporal motion vector prediction candidate; and generating the bitstream based on the one or more temporal motion vector prediction candidates, wherein the default temporal motion vector prediction candidate is determined after identifying a first temporal adjacent block of the current video block based on an initial motion vector, wherein the first temporal adjacent block includes invalid motion information.