[Mp4-tech][H.264]questions on search range

[Gary Sullivan]

Yes, there is a restriction something like that in Annex A of the
standard. 
A conforming bitstream must meet the following requirements:
k)	Vertical motion vector component range luma motion vectors does
not exceed MaxVmvR in units of luma frame samples, where MaxVmvR is
specified in Table A-1
	NOTE - When chroma_format_idc is equal to 1 and the current
macroblock is a field macroblock, the motion vector component range for
chroma motion vectors may exceed MaxVmvR in units of luma frame samples,
due to the method of deriving chroma motion vectors as specified in
subclause 8.4.1.4.
l)	Horizontal motion vector range does not exceed the range of
-2048 to 2047.75, inclusive, in units of luma samples.
For levels 1 and 1b, the vertical range is [ 64,+63.75].  For levels 1.1
through 2, it is [ 128,+127.75].  For levels 2.1 to 3, it is [
256,+255.75].  For levels above level 3, it is [ 512,+511.75].
I'm not that familiar with the reference software.  I believe it has at
least one control parameter that controls the size of the search region
RELATIVE TO THE PREDICTION of the motion vector.  That is a different
kind of thing than a control over the magnitude of the resulting motion
vector.  I don't know whether the reference software offers control over
that or not at this time.
Best Regards,
Gary Sullivan
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org 
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Xu Ke
+> Sent: Friday, April 08, 2024 12:14 AM
+> To: mp4-tech
+> Subject: [Mp4-tech][H.264]questions on search range 
+> 
+> Dear experts,
+> In H.264 standard,is there any restriction on search range? 
+> And in JM reference software,is the "SearchRange" parameter 
+> specifies the search range in pixel unit or in motion vector 
+> unit? e.g,if SearchRange=16,this means search around 16 
+> pixels or 16/4=4 pixels of quater-pixel inter-prediction?
+> 
+> Many thanks in advance!
+> 
+> Best regards,
+> XU Ke
+> 
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