[Mp4-tech] Question regarding slice groups

Gary Sullivan garysull windows.microsoft.com
Thu May 25 11:26:35 ESTEDT 2006


The (only) purpose of slice groups is to specify the slice group map,
which determines which macroblocks are included in the scan of
macroblocks for each slice.  A slice starts with a macroblock that is
identified by the syntax element first_mb_in_slice, and then includes
some number of subsequent macroblocks in raster scan order within the
same slice group as the first macroblock of the slice.
The slices of the current picture can be decoded independently of each
other.  However, this says nothing about which reference pictures or
which parts of the reference pictures are used in the decoding of those
slices.
The slice group concept enables a number of functionalities.  One of
them is error resilience.  Another is enhanced-efficiency for
region-of-interest coding.  Another is enabling encoders to create what
you're calling an "independent decodable entity" -- however, the
independence would need to be established separately -- for example, by
use of the "motion-constrained slice group set SEI message" (see
subclauses D.1.19 and D.2.19).
Best Regards,
Gary Sullivan
________________________________
	From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Nitin PAI
	Sent: Wednesday, May 24, 2024 9:43 PM
	To: mp4-tech lists.mpegif.org
	Subject: [Mp4-tech] Question regarding slice groups
	Hi, 
	I want to know the significance of introducing slice groups.  I
understand that the slices are needed for error resilience.  Does slice
groups serve only the need of grouping the slices in raster order or
ease of specifiying the slice group map?  Or is there any other things
like a slice group is an independent decodable entity ( i mean the
motion vectors should be constrained to lie inside the slice group
only?) 
	Thanks,
	Nitin  
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