Searching based motion candidate derivation for sub-block motion vector prediction

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.

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.